Case 4

Question 1

what are the functions of the colon?

Answer 1

1. Absorption of water and electrolytes from the chyme to form solid faeces.
2. Storage of faecal matter until it can be expelled.

Question 2

what is the proximal half of the colon primarily concerned with?

Answer 2

absorption

Question 3

what is the distal half of the colon primarily concerned with?

Answer 3

storage

Question 4

what are movements of the colon usually like? what is the function of these movements?

Answer 4

Intense colon wall movements aren’t required for the functions of the colon and so the movements of the colon are normally very sluggish.
• These movements still play similar roles as the movement in the small intestine:
 Mixing movements
 Propulsive movements

Question 5

mixing movement

• another word for this
• describe the movement
• what produces it
• where
• what happens

Answer 5

Mixing Movements (“Haustrations”) - Segmentation
•	In the same manner that segmentation movements occur in the small intestine, large circular constrictions occur in the large intestine. 
	At each of these constrictions, about 2.5cm of the circular muscle contracts, sometimes constricting the lumen of the colon almost to occlusion. 
•	At the same time, the longitudinal muscle of the colon, which is aggregated into three longitudinal strips called the teniae coli, contracts. 
•	These combined contractions of the circular and longitudinal strips of muscle cause the unstimulated portion of the large intestine to bulge outward into bag-like sacs called haustrations. 
	Each haustration usually reaches peak intensity in about 30 seconds and then disappears during the next 60 seconds.
•	They also at times move slowly toward the anus during contraction, especially in the cecum and ascending colon, and thereby provide a minor amount of forward propulsion of the colonic contents. 
•	After another few minutes, new haustral contractions occur in other areas nearby. 
•	Therefore, the faecal material in the large intestine is slowly dug into and rolled over.
•	In this way, all the faecal material is gradually exposed to the mucosal surface of the large intestine, and fluid and dissolved substances are progressively absorbed.

Question 6

how much faeces expelled each day?

Answer 6

Between 80-200ml

Question 7

propulsive movements

• what produces this
• how long does it take
• what can take over the propulsive role
• when does this occur

Answer 7

• Propulsion in the cecum and ascending colon results from the slow but persistent haustral contractions, requiring as many as 8 to 15 hours to move the chyme from the ileocecal valve through the colon.
• From the cecum to the sigmoid, mass movements can, for many minutes at a time, take over the propulsive role.
• These movements usually occur only one to three times each day, in many people especially for about 15 minutes during the first hour after eating breakfast.

Question 8

mass movement

• what is it
• what happens

Answer 8

• A mass movement is a modified type of peristalsis characterized by the following sequence of events:
1. First, a constrictive ring occurs in response to a distended or irritated point in the colon, usually in the transverse colon.
2. Then, rapidly, the 20 or more centimetres of colon distal to the constrictive ring lose their haustrations and instead contract as a unit, propelling the faecal material in this segment en masse further down the colon.
3. The contraction develops progressively more force for about 30 seconds, and relaxation occurs during the next 2 to 3 minutes.
4. Then, another mass movement occurs, this time perhaps farther along the colon.
 A series of mass movements usually persists for 10 to 30 minutes.
 Then they cease but return perhaps a half day later.
5. When they have forced a mass of faeces into the rectum, the desire for defecation is felt.

Question 9

what are the small intestinal reflexes?

Answer 9

• Ileogastric reflexes: distention of ileum leased to decreased gastric motility.
• Gastro-ileal reflexes: increased gastric distention leads to increased ileal motility and ileocaecal valve relaxes.
• The ileocaecal valve is normally closed. It opens (gastroileal reflex) when a peristaltic wave reaches it.

Question 10

how are peristaltic contractions regulated? explain this

Answer 10

• “Slow waves” determine the frequency of contraction. There is a basic electrical rhythm (B.E.R).
• The slow waves have a resting potential of -40 to -60 mV.
• The slow waves are superimposed on the resting potential.
• The size of the slow wave is modulated by nervous and hormonal inputs.
• Contraction of the smooth and striated muscles in the intestinal wall will only occur if the potential of a slow wave exceeds the threshold potential.
• Vm positive of threshold  voltage-gated Ca2+ channels   [Ca2+]i =contraction.

Question 11

what are the pacemaker cells of the GI tract? what do they do?

Answer 11

• Interstitial cells of Cajal

- These create slow wave potentials that leads to the contraction of the smooth muscle.

Question 12

how are ‘slow waves’ modulated?

Answer 12

 Food stimulates nerve and hormonal activity:
Increase or decrease size of the maximum depolarisation.
 Nerves (intrinsic & extrinsic):
 ACh, Substance P  depolarisation (=  contraction)
 NO, VIP, opioids  hyperpolarisation (= ↓ contraction)
 Noradrenaline  hyperpolarisation (= ↓ contraction)
 Hormones:
 Motilin  depolarisation (=  contraction)
 Secretin, G.I.P.  hyperpolarisation (= ↓ contraction)
 Adrenaline  hyperpolarisation (= ↓ contraction)

Question 13

what is the difference between long reflexes and short reflexes?

Answer 13

long = extrinsic nerves

• PNS interacts with ENS
• sympathetic and parasympathetic

short = ENS

• afferet, inter and efferent neurones all in ENS
• e.g. local distention -> motility (muscle contraction)

Question 14

enterochromaffin cells

• what are they
• what percentage of enteroendocrine cells are these
• what does stimulation cause
• what stimulates
• what ends signal
• side effect of SSRIs
• what is linked to IBS

Answer 14

 These are the main mechano- and chemo-sensory cells in the GI tract.
- 90% of enteroendocrine cells are enterochromaffin cells
 Stimulation of ECL cells causes release of serotonin (5-HT) intracellularly.
 5-HT stimulates sensory nerves via 5-HT3 receptors.
 Different stimuli produce varied (stimulatory or inhibitory) responses via 5-HT signalling to the parasympathetic NS.

Stimulation -> release of serotonin (5-HT)

• Cell can be stimulated by strong forces such as distention or gentle stroking of microvilli
• Stimulation causes release of vesicles containing 5-HT into the interstitial fluid of the epithelial layer
• Released 5-HT stimulates afferent neurones via 5-HT3 receptors
• Action potential sent through enteric nervous system and then to extrinsic nerves
• SERT removes 5-HT to terminate signal
• SSRIs: side-effect = diarrhoea
• SERT mutations also linked to IBS
• 5-HT3 antagonist & 5-HT4 agonists in trial for IBS

Question 15

the rectum empty most of the time, what is this due to?

Answer 15

 A weak functional sphincter which exists between the sigmoid colon and the rectum, therefore preventing the entry of food into the rectum.
 The sharp angulation at the junction between the sigmoid colon and the rectum that contributes additional resistance to filling of the rectum.

Question 16

when does the desire for defecation occur? what else happens along with this?

Answer 16

• When a mass movement forces faeces into the rectum, the desire for defecation occurs immediately, including reflex contraction of the rectum and relaxation of the anal sphincters.

Question 17

what prevents the continual dribble of faecal matter through the anus?

Answer 17

Tonic constriction of:

1. An internal anal sphincter, a several-centimetres-long thickening of the circular smooth muscle that lies immediately inside the anus
2. An external anal sphincter, composed of striated voluntary muscle that both surrounds the internal sphincter and extends distal to it.

Question 18

what controls the external anal sphincter?

Answer 18

• Nerve fibres in the pudendal nerve
• Which is part of the somatic nervous system and therefore is under voluntary, conscious or at least subconscious control; subconsciously, the external sphincter is usually kept continuously constricted unless conscious signals inhibit the constriction.

Question 19

defecation is initiated by defecation reflexes - what are these two reflexes?

Answer 19

• intrinsic myenteric defecation reflex

- parasympathetic defecation reflex

Question 20

describe the intrinsic reflex of defecation

• what mediated by
• what happens
• how strong

Answer 20

mediated by the local enteric nervous system in the rectal wall.
 When faeces enter the rectum, distention of the rectal wall initiates afferent signals that spread through the myenteric plexus to initiate peristaltic waves in the descending colon, sigmoid, and rectum, forcing faeces toward the anus.
 As the peristaltic wave approaches the anus, the internal anal sphincter is relaxed by inhibitory signals from the myenteric plexus; if the external anal sphincter is also consciously, voluntarily relaxed at the same time, defecation occurs.

 The intrinsic myenteric defecation reflex functioning by itself normally is relatively weak.
• To be effective in causing defecation, it usually must be fortified by another type of defecation reflex, a parasympathetic defecation reflex

Question 21

describe the parasympathetic defecation reflex

• what does it involve
• what other effects do defecation signals entering the spinal cord initiate

Answer 21

involves the sacral segments of the spinal cord.
 When the nerve endings in the rectum are stimulated, signals are transmitted first into the spinal cord and then reflexly back to the descending colon, sigmoid, rectum, and anus by way of parasympathetic nerve fibres in the pelvic nerves.
 These parasympathetic signals greatly intensify the peristaltic waves as well as relax the internal anal sphincter, thus converting the intrinsic myenteric defecation reflex from a weak effort into a powerful process of defecation that is sometimes effective in emptying the large bowel all the way from the splenic flexure of the colon to the anus.
 Defecation signals entering the spinal cord initiate other effects:
 Taking a deep breath
 Closure of the glottis
 Contraction of the abdominal wall muscles to force the faecal contents of the colon downward and at the same time the pelvic floor is relaxed downward and pull outward on the anal ring to evaginate the faeces

Question 22

how can defecation reflexes be purposely activated?

Answer 22

• The defecation reflexes can purposely be activated by taking a deep breath to move the diaphragm downward and then contracting the abdominal muscles to increase the pressure in the abdomen, thus forcing faecal contents into the rectum to cause new reflexes.
• Reflexes initiated in this way are almost never as effective as those that arise naturally, for which reason people who too often inhibit their natural reflexes are likely to become severely constipated.

Question 23

describe the mucosa of the large intestine

• what does it contain
• what doesn’t it

Answer 23

 Crypts of Lieberkühn
 No villi
 Epithelial cells contain almost no enzymes. They consist mostly of mucous cells that secrete only mucus.

Question 24

what does the large intestine mostly secrete?

Answer 24

mucus

Question 25

what does mucus contain?

Answer 25

moderate amounts of bicarbonate ions

Question 26

what regulates the rate of secretion of mucus in the large intestine? what else can effect it?

Answer 26

• The rate of secretion of mucus is regulated principally by direct, tactile stimulation of the epithelial cells lining the large intestine and by local nervous reflexes to the mucous cells in the crypts of Lieberkühn. • Stimulation of the pelvic nerves from the spinal cord, which carry parasympathetic innervation to the distal one half to two thirds of the large intestine, also can cause marked increase in mucus secretion.  This occurs along with increase in peristaltic motility of the colon. • During extreme parasympathetic stimulation, often caused by emotional disturbances, so much mucus can occasionally be secreted into the large intestine that the person has a bowel movement of ropy mucus as often as every 30 minutes; this mucus often contains little or no fecal material.

Question 27

what is the function of mucus in the large intestine?

Answer 27

 Protects the intestinal wall against excoriation.  Provides an adherent medium for holding faecal matter together.  Protects the intestinal wall from the great amount of bacterial activity that takes place inside the faeces.  Plus the alkalinity of the secretion (pH of 8.0 caused by large amounts of sodium bicarbonate) provides a barrier to keep acids formed in the faeces from attacking the intestinal wall.

Question 28

what causes diarrhoea? what happens in diarrhoea?

Answer 28

Diarrhea Caused by Excess Secretion of Water and Electrolytes in Response to Irritation • Whenever a segment of the large intestine becomes intensely irritated, as occurs when bacterial infection becomes rampant during enteritis, the mucosa secretes extra large quantities of water and electrolytes in addition to the normal viscid alkaline mucus. • This acts to dilute the irritating factors and to cause rapid movement of the faeces toward the anus. • The result is diarrhoea, with loss of large quantities of water and electrolytes. • But the diarrhoea also washes away irritant factors, which promotes earlier recovery from the disease than might otherwise occur.

Question 29

where does electrogenic Cl- secretion occur? what stimulated by? what is Cl- secretion a major component of?

Answer 29

* Electrogenic Cl- secretion occurs in crypts of both the small and the large intestine. * Cl- secretion is markedly stimulated by secretagogues such as ACh and other neurotransmitters. * Cl- secretion is the major component of the ion transport events that occur during most diarrhoeal disorders.

Question 30

describe the cellular model of Cl- secretion

Answer 30

• The cellular model of Cl- secretion includes three transport pathways on the basolateral membrane: 1. Na-K pump (sodium out, potassium in) 2. Na/K/Cl cotransporter (all three in) 3. Two types of K+ channels (IK1 and BK1) (potassium out) • In addition, a Cl- channel (cystic fibrosis transmembrane regulator (CFTR)) is present on the apical membrane. * This complex Cl− secretory system is energized by the Na-K pump, which generates a low [Na+]i and provides the driving force for Cl− entry across the basolateral membrane through Na/K/Cl cotransport. * As a result, [Cl−]i is raised sufficiently that the Cl− electrochemical gradient favors the passive efflux of Cl− across the apical membrane.

Question 31

what is one of the consequences of Cl- release into lumen?

Answer 31

* One consequence of these many transport processes is that the transepithelial voltage becomes more lumen negative, thereby promoting voltage-dependent Na+ secretion. * This Na+ secretion that accompanies active Cl− secretion presumably occurs through the tight junctions (paracellular pathway). * Thus, the net result is stimulation of NaCl and fluid secretion.

Question 32

how much Cl- is normally released into lumen? what does secretion require?

Answer 32

• Normally (i.e., in the unstimulated state), the crypts secrete little Cl− because the apical membrane Cl− channels are either closed or not present. • Cl− secretion requires activation by cyclic nucleotides or [Ca2+], which are increased by any of several secretagogues: 1. Bacterial exotoxins (i.e. enterotoxins) 2. Hormones and neurotransmitters 3. Products of cells of the immune system (e.g. histamine) 4. Laxatives

Question 33

what is the primary mechanism for net colonic secretion?

Answer 33

passive K+ secretion

Question 34

where is active K+ secretion present? what is it induced by?

Answer 34

present throughout the large intestine and is induced both by aldosterone and by cAMP.

Question 35

is K+ secretion active or passive?

Answer 35

• K+ ions can be both passively and actively secreted.

Question 36

where does active transport (secretion and absorption) of K+ take place?

Answer 36

• Active transport of K+ ions is subject to considerable segmental variation in the colon.  Whereas active K+ secretion occurs throughout the colon, active K+ absorption is present only in the distal segments of the large intestine.  Thus, in the recto-sigmoid colon, active K+ absorption and active K+ secretion are both operative and appear to contribute to total body homeostasis.

Question 37

what is the model of active K+ secretion?

Answer 37

 Uptake of K+ across the basolateral membrane is a result of both the Na-K pump and the Na/K/Cl cotransporter (NKCC1), which is energized by the low [Na+]i that is created by the Na-K pump.  Once K+ enters the cell across the basolateral membrane, it may exit either across the apical membrane (K+ secretion) or across the basolateral membrane (K+ recycling).

Question 38

what controls how much secretion occurs of K+ ions? what normally happens to K+ ions?

Answer 38

 The cell controls the extent to which secretion occurs, in part by K+ channels present in both the apical and the basolateral membranes.  When apical K+ channel activity is less than basolateral channel activity, K+ recycling dominates.  Indeed, in the basal state, the rate of active K+ secretion is low because the apical K+ channel activity is minimal in comparison with the K+ channel activity in the basolateral membrane.

Question 39

what stimulates active K+ secretion where? how do they work?

Answer 39

• Aldosterone stimulates active K+ secretion in surface epithelial cells of the large intestine, whereas cAMP enhances active K+ secretion in crypt cells.  In both cases, the rate-limiting step is the apical BK K+ channel, and both secretagogues act by increasing K+ channel activity.

Question 40

how does aldosterone affect overall net K+ secretion? how?

Answer 40

• This mineralocorticoid enhances overall net K+ secretion by two mechanisms: 1. First, it increases passive K+ secretion by increasing Na-K pump activity and thus increasing electrogenic Na+ absorption.  The net effects are to increase the lumen-negative VTE and to enhance passive K+ secretion. 2. Second, aldosterone stimulates active K+ secretion by increasing the activity of both apical K+ channels and basolateral Na-K pumps.

Question 41

how do cAMP and Ca2+ affect K+ secretion? how? what affects cAMP and Ca2+?

Answer 41

* VIP and cholera enterotoxin both increase [cAMP]i and thus stimulate K+ secretion. * Increases in [Ca2+]I also stimulate active K+ secretion. * Increases [cAMP]I and [Ca2+]I increase the activity of both the apical and the basolateral K+ channels. * Because the stimulation of K+ channels is greater at the apical than at the basolateral membrane, the result is an increase in K+ secretion from the epithelial cell across the apical membrane. * Stimulation of K+ secretion by cAMP and Ca2+, both of which also induce active Cl− secretion, contributes to the significant faecal K+ losses that occur in many diarrheal diseases.

Question 42

passive secretion of K+ ions?

Answer 42

- Na+/K+ pump ?? | - through intercellular junctions

Question 43

K+ absorption - passive and active?

Answer 43

passive: - through intercellular junctions with water - then taken up by Na+/K+ pump active: - K+/H+ pump in apical? - ? channel out of basolateral - Na+/K+ pump in basolateral

Question 44

how much water and electrolytes absorbed in colon? what left over?

Answer 44

* Most of the water and electrolytes in the chyme are absorbed in the colon, usually leaving less than 100ml of fluid to be excreted in the faeces. * Nearly all the ions are absorbed, leaving only 1-5mEq each of sodium and chloride ions to be lost in the faeces.

Question 45

where does active absorption of sodium ions take place? what does this absorption cause?

Answer 45

* Active absorption (electroneutral absorption) of sodium ions takes place in the ileum and throughout the large intestine, with the exception of the most distal segment. * This creates and electrical potential gradient which causes chloride absorption as well.

Question 46

what are the tight junctions between the epithelial cells of the large intestine like compared to that of the small intestine? what does this cause?

Answer 46

much tighter than those of the small intestine. • This prevents significant amounts of back-diffusion of ions through these junctions, thus allowing the large intestinal mucosa to absorb sodium ions far more completely—that is, against a much higher concentration gradient—than can occur in the small intestine.  This is especially true when large quantities of aldosterone are available because aldosterone greatly enhances sodium transport capability.

Question 47

the overall electroneutral NaCl absorption process is regulated by what? what is this relevant to?

Answer 47

* The overall electroneutral NaCl absorptive process is regulated by both cAMP and cGMP, as well as by intracellular Ca2+. * Increases in each of these three intracellular messengers reduce NaCl absorption. * Decreases in [Ca2+]I increase NaCl absorption. * Decreased NaCl absorption is important in the pathogenesis of most diarrheal disorders.

Question 48

what is the primary mechanism of electrogenic Na+ absorption in the distal part of the colon?

Answer 48

epithelial Na+ channels

Question 49

how specific are epithelial Na+ channels? what are these blocked by?

Answer 49

* In electrogenic Na+ absorption, Na+ entry across the apical membrane occurs through epithelial Na+ channels (ENaCs) that are highly specific for Na+. * These ENaCs are blocked by the diuretic amiloride (a potassium sparing diuretic).

Question 50

how efficient is Na+ absorption in the distal colon? why?

Answer 50

* Na+ absorption in the distal part of the colon is highly efficient. * Because this segment of the colon is capable of absorbing Na+ against large concentration gradients, it plays an important role in Na+ conservation.

Question 51

how is Na+ absorption enhanced?

Answer 51

* Na+ movement through electrogenic Na+ absorption is markedly enhanced by mineralocorticoids (e.g aldosterone). * Aldosterone increases electrogenic Na+ absorption by increasing Na+ entry through the apical Na+ channel and by stimulating activity of the Na-K pump.

Question 52

what are the three modes of Cl- absorption in the intestine? where does each occur?

Answer 52

1. Voltage-dependent Cl- absorption: o Cl− may passively diffuse from lumen to blood across the tight junctions, driven by the lumen-negative transepithelial voltage (paracellular route). o Alternatively, Cl− may diffuse through apical and basolateral Cl− channels. o This usually occurs in the jejunum, ileum and the distal colon. 2. Electroneutral Cl-HCO3 exchange: o In the absence of a parallel Na-H exchanger, electroneutral Cl-HCO3 exchange at the apical membrane results in Cl− absorption and HCO3 secretion. o This occurs in the ileum, proximal colon and the distal colon. 3. Parallel Na-H and Cl-HCO3 exchange: o Electroneutral NaCl absorption can mediate Cl− absorption in the interdigestive period. - Na+ in and H+ out (due to Na+/K+ pump basolateral) - H2O and CO2 -> HCO3- -> leaves apical membrane and Cl- comes in

Question 53

what does absorption of sodium and chloride ions create?

Answer 53

creates an osmotic gradient across the large intestinal mucosa, which in turn causes absorption of water.

Question 54

what is the maximum absorption capacity of the large intestine?

Answer 54

5-8 litres of fluid and electrolytes each day.

Question 55

where is bacteria present in the colon? which in particular? what are they capable of doing?

Answer 55

• Numerous bacteria, especially colon bacilli, are present even normally in the absorbing colon. • They are capable of digesting small amounts of cellulose, in this way providing a few calories of extra nutrition for the body.  This source of energy is of little importance in human beings.

Question 56

what are other substances formed as a result of bacterial activity?

Answer 56

- vitamin K - vitamin B12 - thiamine - riboflavin - various gases that contribute to flatus in the colon, especially carbon dioxide, hydrogen gas, and methane.

Question 57

which of these substances produced by bacterial activity is particuarly important and why?

Answer 57

The bacteria-formed vitamin K is especially important because the amount of this vitamin in the daily ingested foods is normally insufficient to maintain adequate blood coagulation.

Question 58

what is the composition of faeces?

Answer 58

```  ¾ water  ¼ solid matter  30% dead bacteria  10-20% fat  10-20% inorganic matter  2-3% protein  30% undigested roughage from the food and dried constituents of digestive juices, such as bile pigment and sloughed epithelial cells ```

Question 59

what causes the brown colour of faeces?

Answer 59

stercobilin, a derivative of bilirubin.

Question 60

what causes the odour of faeces?

Answer 60

products of bacterial action; these products vary from one person to another, depending on each person’s colonic bacterial flora and on the type of food eaten.  The actual odoriferous products include indole, skatole, mercaptans, and hydrogen sulfide.

Question 61

what is hypertrophy/atrophy?

Answer 61

Change in size of cells  Atrophy - cell shrinking  This may be achieved by apoptosis, reduced functional activity, loss of innervation, reduced blood supply, diminished nutrition, loss of hormonal or growth factor stimulation.  Hypertrophy - increase in size of existing cells  It is accompanied by an increase in functional capacity.  The number of cells doesn’t change, the cells just get bigger.

Question 62

what is hyperplasia/aplasia?

Answer 62

 Hyperplasia - increased number of cells caused by an increase in cell division.  Aplasia - decreased number of cells.

Question 63

what is metaplasia?

Answer 63

Change in differentiation  Specialised cell types change their pattern of differentiation to a new mature stable cell type.  This allows them to withstand stress better.

Question 64

what is metaplasia, dysplasia and anaplasia? how does this relate to cancer?

Answer 64

* Metaplasia - this is an adaptive response to environmental stimuli * Dysplasia - the enlargement of tissue by the proliferation of abnormal (metaplasia) cells, as a developmental disorder or an early stage in the development of cancer. * Anaplasia - loss of intracellular structural differentiation within a cell often with increased capacity for multiplication, as in a malignant tumour. * Cancer>>>>> metaplasia followed by dysplasia followed by anaplasia.

Question 65

describe interphase

Answer 65

• Interphase commences with G1 (G = Gap)  G1 – normal cell functions + cell growth, duplication of organelles. - This is the phase where the cell is sensitive to growth factors (thus entering cell cycle) and anti-proliferative factors (thus not entering cell cycle). - Once the cell has entered the cell cycle, there is no reversal – the point at which the cell enters the cell cycle and can no longer be affected by growth/anti-proliferative factors, is called the ‘restriction point'. (each chromosome represented by 1 chromatid)  G0 – Cells that stay in G1 for a long time, and possibly never divide again are said to be in G0  S phase (synthesis phase) – DNA replication  G2 – Chromosomes begin to condense in preparation for the next mitotic division (each chromosome represented by 2 chromatids)

Question 66

what are the stages of mitosis?

Answer 66

* Prophase – chromosome becomes visible, 2 pairs of centriole separate, and nucleus disintegrates. * Metaphase – chromatids move to a midline (equator) * Anaphase – Chromatids are pulled apart * Telophase – Chromosomes uncoil, two nuclei formed * Cytokinesis – Cytoplasmic division.

Question 67

what controls progression through the cell cycle?

Answer 67

cyclic dependent kinases - enzymes - provide checkpoint control

Question 68

what do cyclins do?

Answer 68

activate CDKs

Question 69

what do checkpoint controls do?

Answer 69

prevent DNA replication or mitosis of damaged cells and either stop the cell cycle to allow for DNA repair or eliminate irreversibly damaged cells by apoptosis.

Question 70

how do CDKs work?

Answer 70

by promoting DNA replication and various aspects of the mitotic process and are required for cell cycle progression.

Question 71

what are cyclin kinase inhibitors? what is example?

Answer 71

* Cyclin Kinase Inhibitors (CKIs) inhibit CDKs. | * One particular CKI is p21, which is a potent inhibitor of CDKs.

Question 72

which cyclins activate which CDKs? what order/stage in cell cycle?

Answer 72

- cyclinD/CDK4(/6) - G1 - before R - cyclinE/CDK2 - G1 - after R - cyclinA/CDK2 - S - cyclinA/CDK1 - (S/)G2 - cyclinB/CDK1 - G2/M

Question 73

cyclin B - when in cell cycle - what complex does it form - what does this complex to

Answer 73

• Cyclin B is a protein found in high quantities in the late G2 stage, peaking during mitosis. • It associates with cyclin-dependent kinase (CDK1) to activate it. • Cylin B/CDK1 complex phosphorylates proteins to cause mitosis. - phosphorylates MAP proteins, lamin and histones

Question 74

what are MAPs?

Answer 74

microtubule associated proteins – cause spindle formation.

Question 75

what is lamin?

Answer 75

usually makes a protein meshwork which the nuclear envelope sits on. Upon phosphorylation, this meshwork breaks down, leading to the breakdown of the nuclear envelope.

Question 76

what do histones do?

Answer 76

cause condensation of chromosomes

Question 77

what form is Ras normally in?

Answer 77

normally bound to GDP and is inactive

Question 78

what activates Ras? what happens once active? whta actually is Ras?

Answer 78

• Upon binding to GTP, it becomes active. • Once in the active form, Ras can initiate signalling cascades to cause:  Inhibition of apoptosis  Cell growth  Protein synthesis etc - A GTPase - It’s a switch – either on or off - When bound to GTP it’s on, it activates all sorts of downstream signalling pathways - Ras then hydrolyses the GTP to GDP, that switches the switch off - When mutated, Ras can’t do this conversion and when Ras binds to GTP, it’s activated, and it can never be switched off

Question 79

what is Ras? what does a mutation cause?

Answer 79

oncogene – its mutation causes it to remain in the active form, thus causing a significant increase in cell growth and proliferation.

Question 80

what must be mutated to cause colorectal cancer?

Answer 80

the Wnt signalling pathway (APC and B-catenin genes)

Question 81

what is Wnt? what is it associated with inside the cell?

Answer 81

 Ligand = Wnt - Wnt is a growth factor  Intracellular protein complex which comprises of:  GSK-3B  Adenomatous Polyposis Coli (APC) (a tumour suppressor gene)  B-catenin (an oncogene)

Question 82

what is B-catenin?

Answer 82

an oncogene

Question 83

what is the tumour supressor gene associated with Wnt? what does it do?

Answer 83

adenomatous polyposis coli (APC) | - degrades B-catenin

Question 84

what happens in the absence of Wnt?

Answer 84

* In the absence of Wnt (unstimulated state), GSK-3B is active, thus phosphorylating B-catenin. * This causes the proteolytic degradation of B-catenin.

Question 85

what happens when Wnt signals are present? what are the target genes?

Answer 85

* When Wnt signals are present, and they bind to the receptor, the intracellular protein complex becomes disrupted. * The GSK-3B is switched off (something moves away from it to membrane near where Wnt is), thus B-catenin is no longer phosphorylated. * This means that B-catenin is no longer targeted for proteolytic degradation. * B-catenin can now move to the nucleus, where it interacts with transcription factors, thus changing gene expression, and so increasing cell proliferation. - Target genes include Cyclin D & Myc (they drive the cell cycle) - When the Wnt receptor is in unstimulated state, a complex with B-catenin and APC assembles, and B-catenin get’s degraded - In the stimulated state, the Wnt binds to receptor, which inactivates the complex, B-catenin no longer gets degraded, its levels increase, it goes into nucleus where it activates gene expression, and drives the cell into proliferation

Question 86

what does a mutation in B-catenin gene cause?

Answer 86

causes it to remain unphosphorylated and stable, thus increasing cell proliferation. - When B-catenin gets mutation, it means there’s change in phosphorylation site, so it can never get phosphorylated and so can never get degraded, so will go into the nucleus even in the absence of Wnt signals

Question 87

what stimulates Ras? what happens when stimulated? what gene expression does it affect in particular? what does this lead to? what is this describing?

Answer 87

Cell Cycle Entry * Growth factors stimulate Ras, which binds to its receptors, thus activating transcription factors and affecting gene expression, especially Cyclin D1. * Wnt signals, via B-catenin, also activate transcription factors, and affect gene expression, especially Cyclin D1. * Cyclin D1 activates CDK4. * CDK4 phosphorylates Rb = pRb. * Normally Rb binds to the E2F family of transcription factors, it inhibits them. * When CDK4 phosphorylates Rb, pRb now causes the liberation of E2F transcription factors, thus allowing them to enter the nucleus and modulating gene expression, especially of Cyclin E. * Cyclin E can now bind to its CDK (CDK2), thus triggering the S phase of the cell cycle. Growth factors -> Ras -> fos/jun -> cyclin D1 (upregulation and expression of proliferative genes) Wnt signals -> B-Catenin -> Tcf/lef -> cyclin D1 - Cyclin D binds to CDK4/6 - pRb becomes phosphorylated and lets E2F go (which it was attached to) - which switches on expression of cyclin E - it binds to its CDK - this drives this cell into S phase

Question 88

what is Rb?

Answer 88

a tumour suppressor gene

Question 89

what must happen to Rb for it to cause problems? what happens then?

Answer 89

* If one copy of this gene is mutated, it has no effect on the liberation of E2F. * However, if both copies of Rb are mutated, then E2F is always liberated and the cell continuously enters the cell cycle and the S phase without the importance of the checkpoint control. - its job is to bind to E2F - if you lose both copies of Rb, E2F is now liberated, and can drive entry into S phase even when there are no growth factors around

Question 90

what is the principal cell type of the epithelium of the small intestine? where are these found? what is the environment here and what influenced by?

Answer 90

* The principle cell type of the epithelium of the small intestine are Paneth cells. * These are found below the stem cells in the crypts. * These belong to the ‘stem cell niche’. This is a microenvironment where stem cells are found, where they are influenced by growth (e.g. Wnt) and differentiating factors to regulate cell fate.

Question 91

S phase - how is this part of cycle controlled - is stability of genome maintained - what happens if this phase doesn't go as planned

Answer 91

* Here, all the control of the cell cycle happens internally, i.e. external factors don’t influence this phase of the cycle. * Here, the stability of the genome is maintained without any damage to the DNA. * If the S phase doesn’t go as planned, it results in the activation of p53, which will then aim to shut down the cell cycle (defense mechanism).

Question 92

what is p53?

Answer 92

a transcription factor which is degraded normally, but in response to stimuli it can become active and remains non-degraded.  Kinases and ubiquitin ligases which would normally break down p53 are inhibited. - it a tumour supressor gene/protein - Transcription factor - Normally degraded (so levels usually low) - ‘activated’ by stabilisation (in response to damage) - Kinases and ubiquitin ligases  p53 (guardian of the genome) - if genome encounters problems, you want to stop the cycle and fix the damage before it turns into mutation in both daughter cells - if can’t fix damage then cell goes into apoptosis - p53 crucial for all of this

Question 93

what can activation of p53 be a result of?

Answer 93

```  Lack of nucleotides  UV radiation  Ionizing radiation  Oncogene signalling  Hypoxia  Blockage of transcription factors ```

Question 94

what does activation of p53 cause?

Answer 94

causes the following cascades:  Cell cycle arrest, leading to senescence or return to proliferation. - This occurs by the upregulation of p21 (CKI). (switched on by p53 – normally p21 has low levels as well) - This inhibits CDKs, thus arresting the cell cycle. (p21 then binds to the CDKs and inhibits them, blocking the cell cycle)  DNA repair  Block of angiogenesis  Apoptosis - P53 drives expression of genes such as Puma and Noxa. - These activate the BAX intrinsic apoptotic pathway, thus leading to programmed cell death. - Bcl-X is a pro-survival protein in colon cancer (oncogenic driver in colon cancer)

Question 95

what is p53 known as?

Answer 95

guardian of the genome

Question 96

apoptosis - what is it - what are the pathways

Answer 96

* Programmed cell death * This is a programmed sequence of intracellular events leading to the death of the cell without the release of products harmful to the surrounding cells. * Extrinsic/ Intrinsic Pathways

Question 97

what is the proteolytic cascade (apoptosis)?

Answer 97

1. Cell shrinks and condenses. 2. Digestion of the nuclear DNA into small DNA fragments. 3. Cell’s cytoskeleton disassembles. 4. Blebbing. 5. Cell surface membrane altered to allow phagocytosis.

Question 98

what is the extrinsic pathway for apoptosis?

Answer 98

* Ligand (TNFα or Fas) bind to a receptor on the cell surface membrane of the cell. * The activation of the receptor causes a DISC (death inducing signaling complex) to bind to the internal aspect of the receptor. * This causes the activation of enzymes known as caspases (known as paracaspases when inactivated). * Proteolytic cascade occurs.

Question 99

what is the intrinsic pathway?

Answer 99

* Cell recognises internal damage. * BAX (in the cytoplasm) binds to a receptor on the mitochondria. * Upon binding, BAX changes shape. * Proteins (cytochrome C) in the intramembranous space of the mitochondria leak out into the cytoplasm. * Cytochrome C activates the paracaspases into caspases, leading to apoptosis.

Question 100

what is necrosis? what due to?

Answer 100

• Cell death due to: 1. Trauma 2. Disease 3. Ischaemia as a result of lack of blood supply • Release of intracellular content into the surrounding tissue.

Question 101

familial cancers - what percentage - what is cause - what are most - what most due to - what need in somatic cells

Answer 101

 1% of all cancers.  Single gene mutations (Mendelian disorders)  Most are inherited as autosomal dominant traits.  Most due to inherited mutations of tumour suppressor genes.  Further genetic events are necessary if the mutation is in somatic cells. Even though the mutated gene is inherited, it isn’t sufficient for malignancy.  The inherited mutated gene increases cancer susceptibility.

Question 102

sporadic cancers - what percentage - what result of - what results in

Answer 102

 99% of all cancers.  Result of exposure to carcinogenic agents and unrepaired DNA replication errors.  Results in somatic activation/ inactivation of cancer genes.

Question 103

compare familial and sporadic cancers - onset - how many tumours - how many types of tumours - tumour cells - how many copies of inactivated TS gene - other cells - how many copies of inactivated TS gene?

Answer 103

Familial cancer: - Early onset - Multiple tumours of same type - Other types of tumours - Tumour cells: both copies of tumour suppressor gene inactivated - All other cells: one copy of tumour suppressor gene inactivated Sporadic cancer: - Late onset - Single tumour usually - No other tumours usually - Tumour cells: both copies of tumour suppressor genes inactivated - All other cells: normal

Question 104

what are the different types of cancer? what most common?

Answer 104

* Adenoma: cancer of the glands (glandular cells) * Carcinoma: epithelial cells (more than 90% of all cancers) * Lymphoma: lymphocytes or lymphatic system * Sarcoma: connective tissue * Blastoma: immature/ pre-cursor cells (dendrites – white blood cells) * Papilloma: surface epithelia (skin)

Question 105

what is neoplasia?

Answer 105

means new growth (tumour) and it is described as malignant.

Question 106

describe characteristics of benign tumour

Answer 106

- Capsule surrounds tumour - Well differentiated cells - Structure is similar to tissue organ - LOW MITOTIC ACTIVITY – slow rate of growth - NO INVASION of surrounding tissue - NO METASTASIS

Question 107

describe characteristics of malignant tumour

Answer 107

- No capsule - Lack of differentiation (anaplasia) - Structure is different to tissue organ - HIGH MITOTIC ACTIVITY – rapid rate of growth - INVASION of surrounding tissue - METASTASIS – cause multiple organ failure

Question 108

genomic instability - what is this - what are types

Answer 108

• Cancer genomes are unstable:  Either chromosomal instability (CIN) – result of many numerical and structural abnormalities.  Or microsatellite instability (MIN) – result of impaired DNA Mismatch Repair (MMR). - normal genomes are stable - cancer genomes are unstable - cancer cells are constantly shuffling around their chromosomes - chromosomal instability -> either whole chromosomes or parts of chromosomes are duplicated or deleted - genome stability – increased mutation rate

Question 109

what is telomerase?

Answer 109

an enzyme that prevents the shortening of the telomere, thus preventing senescence (specific number of cell divisions). telomere = a region of repetitive nucleotide sequences at each end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes. Overtime, telomeres get a bit shorter, until they get so short that it triggers a DNA damage response and it triggers the cells into senescence – they no longer proliferate Cancer cells find a way of bypassing this, which leads to telomere erosion, which leads to chromosome fusion - telomeres – T-loops, DSB (double strand breaks) & senescence

Question 110

what is senescence?

Answer 110

Senescence is the process by which cells irreversibly stop dividing and enter a state of permanent growth arrest without undergoing cell death. Senescence can be induced by unrepaired DNA damage or other cellular stresses.

Question 111

is telomerase normally switched on or off? what about in malignant cells? what does this lead to?

Answer 111

* In normal cells, telomerase is switched off. * In malignant cells, telomerase is switched on, thus inhibiting senescence. Telomere repeats maintained by telomerase: - OFF in normal cells - ON in tumour cells

Question 112

what does successful carcinogenesis require?

Answer 112

 Either mutations that increase the rate of cell proliferation, so as to provide an expanded target for further mutations (clonal evolution).  Or mutations that destabilise the genome, so as to increase the rate of further mutations.

Question 113

for a cancer cell to become malignant, it must what? (hallmarks of cancer)

Answer 113

1. Become independent of external growth signals (this means not responding to signals which tell it to grow. The cell should be able to grow independently). 2. Become insensitive to external anti-growth signals (this means not responding to signals which tell the cell to stop dividing. The cell should be able to divide independently). 3. Become able to avoid apoptosis. 4. Become capable of indefinite replication (cells have a finite number of times they divide before dying – senescence). 5. Become capable of sustained angiogenesis (must be able to cause blood vessels to enter the tumour to provide nutrition). 6. Become capable of tissue invasion and metastasis. - Self-sufficiency in growth signals - Insensitivity to anti-growth signals - Tissue invasion & metastasis - Limitless replicative potential - Sustained angiogenesis - Evading apoptosis - Genomic instability - Deregulated metabolism - Avoiding immune destruction - Tumour promoting inflammation

Question 114

what is cancer mediated by?

Answer 114

```  Genes – oncogenes and TSGs  Telomeres – telomerase and senescene  Signalling Pathways – Wnt and Ras  Genome Instability – CIN/ MMR  P53 and Apoptosis  Cell Cycle Control – cyclin/ CDK/CKI(p21)/ ```

Question 115

what are the cancer genes?

Answer 115

1. (Proto-)Oncogenes • Gain of function • Dominant (only need one mutated allele to be activated) 2. Tumour Suppressor Genes • Loss of function • Recessive (need two mutated alleles to be inactivated)

Question 116

proto-oncogenes - what is it - what is the resultant protein called - what do these genes do

Answer 116

* A proto-oncogene is a normal gene that may be activated into an oncogene due to mutations or increased expression. * The resultant protein may be termed an oncoprotein. * Proto-oncogenes promote cell division, survival and growth.

Question 117

how can proto-oncogenes be activated?

Answer 117

1. Point mutations that increase protein function. 2. Gene amplification that causes overexpression. 3. Chromosomal translocation (e.g. MYC). 4. Viral stimulation that may lead to addition/deletion of genes when viral DNA is integrated with human DNA.

Question 118

what does the translocation of MYC cause? what is MYC?

Answer 118

MYC - This is a regulator gene that codes for a transcription factor. If translocated, MYC will be continually expressed, causing unregulated expression of many genes, some of which are involved in cell proliferation (e.g. cyclin D1) and results in the formation of cancer.

Question 119

oncogenes - what are they - what happens - what do they usually code for? and examples for each of these?

Answer 119

• An oncogene is a gene that has the potential to cause cancer (e.g. β-catenin and KRAS) • When one allele is mutated, there is a gain in protein function. • In tumour cells, they are often mutated or expressed in high levels. • Oncogenes usually code for: 1. Secreted growth factors (e.g. EGF/ Wnt/ Ras) 2. Cell surface receptors (e.g. HER) 3. Signal transduction system components (ABL) 4. Nuclear proteins, transcription factors (e.g. MYC) 5. Cyclins/ cyclin-dependent kinases (cyclin D1, CDK4)

Question 120

tumour suppressor genes - what are they - what happens - what does familial predisposition mean - examples

Answer 120

* Tumour suppressor genes are the body’s natural defence mechanism against malignancy. * When both alleles of this gene are mutated, there is a loss in protein function. * If there is a familial predisposition, then one allele has already been mutated, therefore, only a second hit is required for fatal effects (“two-hit hypothesis”). - If one copy already mutated, only 1 random hit required - Two random hits required - APC & p53 - Familial form of retinoblastoma – already have one form of the gene - Sporadic form of retinoblastoma – no mutations, have to get both throughout life to develop cancer

Question 121

what is inactivation of TSGs caused by?

Answer 121

1. Mutations 2. Chromosomal abnormalities 3. Methylation of promoters 4. Interaction with viral proteins - methylation -> reduced binding of transcription factors -> inactive gene -> decrease gene expression

Question 122

what is worse loss of TSG or activation of oncogenes?

Answer 122

loss of TSG

Question 123

what are the functions of tumour supressor genes? and examples

Answer 123

1. Inhibit progression through the cell cycle (CDKIs = p21) 2. Promote apoptosis (e.g. p53 gene and APC). 3. Inhibit cell growth (anti-proliferative). 4. DNA repair and genomic stability (mismatch DNA repair genes (replication error genes) and BRCA1 gene). 5. Cell adhesion to prevent metastasis.

Question 124

metastasis - what is it - what does it show - which cancers metastasise - how do cancers spread - where are common metastasis sites

Answer 124

• Metastasis is the development of secondary malignant growths at a distance to the primary site of cancer. • Metastasis marks a tumour as malignant because benign neoplasms do not metastasise. • All cancers metastasise, except: 1. Glial cells of the CNS (these usually form benign tumours) 2. Basal cell carcinomas of the skin • Cancer spreads by three pathways: 1. direct seeding of body cavities or surfaces (local invasion of surrounding tissue) 2. lymphatic spread 3. hematogenous spread (blood) • Common metastasis sites: lungs, liver, spine and bone

Question 125

colorectal cancer - what is it - what type of cancer - familial or sporadic - when genetic

Answer 125

* Colorectal cancer – this is the development of cancer in the colon or rectum (parts of the large intestine). * It is caused due to an abnormal growth of cells that have the ability to invade or spread to other parts of the body. * It is usually an adenocarcinoma that develops. * Majority of colorectal cancers are sporadic. * Severe rare familial diseases – FAP/ HNCC

Question 126

epidemiology of colorectal cancer - how common - age - survival

Answer 126

 Colorectal cancer is the 3rd most common cancer and 2nd most common cause of UK cancer deaths (16,000 deaths/ year).  56% of presentations are in those >70 years old. - about 10% of all cancer deaths - 57% survive 10 or more years - Much better than for pancreatic or ovarian cancer but still not great - Large intestine, not the small intestine - Regions of higher proliferation, which develop into polyps, which are relatively benign, but some cells within that polyp will become more mutated, which is now a cancerous polyp, with can now invade

Question 127

what are the different locations of colorectal cancer? how common is each?

Answer 127

```  15% caecum and ascending colon  10% transverse colon  5% descending colon  25% sigmoid colon  45% rectum ```

Question 128

what are risk factors for colorectal cancer?

Answer 128

 Diet - High in red meats and processed meats – red and processed meats contain high levels of N-nitros compounds (NOCs), which are carcinogenic. - Low-fibre diet: not using the muscles as much  Lack of physical activity and Obesity  Smoking and  Heavy use of alcohol  Age - >50  Family history: - Neoplastic adenomatous polyps - Colorectal cancer  Inherited diseases: - Familial Adenomatous Polyposis (FAP) - Hereditary Non-Polyposis Colon Cancer (HNCC)  History of inflammatory bowel disease (e.g. Chron’s disease/ Ulcerative Colitis) - tyoe 2 diabetes

Question 129

what is the presentation of left-sided cancer?

Answer 129

``` o Bleeding/ mucus (PR) o Altered bowel habit or obstruction (25%) o Tenesmus (continual feeling of needing to evacuate bowel) o Mass (PR) o Abdominal mass o Perforation o Haemorrhage o Fistula ```

Question 130

what is the presentation of right-sided cancer?

Answer 130

``` o Weight loss o Reduced haemoglobin o Abdominal pain o Obstruction less likely o Abdominal mass o Perforation o Haemorrhage o Fistula ```

Question 131

what are the tests of colorectal cancer?

Answer 131

 Blood Test  Full blood count – indicate low serum levels (microcytic anaemia)  Serum proteins –  Calcium – check for metastatic hypercalcemia (bone metastasis)  Liver Function Test  Bilirubin – colorectal cancer liver metastasis causes severe hyperbilirubinaemia  Alkaline phosphatase (ALP) – ALP levels elevated with liver metastasis of colorectal cancer  Kidney Function Test  Creatinine – creatinine levels elevated with kidney metastasis of colorectal cancer  Sigmoidoscopy/ Colonoscopy/ Barium enema (If the liver is not working properly, it may be unable to make bilirubin water-soluble. This may result in too much bilirubin building up in the liver.)

Question 132

how is colorectal cancer spread?

Answer 132

 Local  Lymphatic  By blood (liver [HPV], lung, bone)  Transcoelomic

Question 133

what are the NICE guidelines for colorectal cancer investigations?

Answer 133

• For patients without major comorbidity – offer colonoscopy to confirm diagnosis of colorectal cancer. • For patients with major comorbidity – offer flexible sigmoidoscopy then barium enema. If a lesion suspicious of cancer is detected, perform a biopsy to obtain histological proof of diagnosis, unless it is contraindicated (for example, patients with a blood clotting disorder).

Question 134

what does a lower GI endoscopy consist of?

Answer 134

1. Sigmoidoscopy – the endoscope only reaches to the top of the descending colon 2. Colonoscopy – the endoscope reaches the entire length of the colon to the ileocecal valve • Both these allow the doctor to view the mucosal lining of the lower GI.

Question 135

what are indications of lower GI endoscopy?

Answer 135

 Screening  Abdominal pain  Rectal bleeding  Change in bowel habits

Question 136

what can lower GI endoscopy detect?

Answer 136

```  Inflammation  Infections  Ulcerations  Diverticulosis  Intestinal narrowing  Colorectal polyps  Cancer ```

Question 137

what is the preparation before a colonscopy? does a sigmoidoscopy require this?

Answer 137

 IV pain medication and sedative  Blood pressure, pulse and oxygen monitored  Supplemental oxygen • A sigmoidoscopy doesn’t require this much preparation.

Question 138

what happens during a colonoscopy?

Answer 138

 Patient may be asked to change positions to allow for better manoeuvring of the endoscope.  A biopsy may be taken to:  Distinguish between benign and malignant tissue.  Identify the cause of bleeding, inflammation and diarrhoea.

Question 139

what is barium enema? what happens? what does colon cancer show?

Answer 139

* Barium enema – this is a test used to identify problems in the colon, such as polyps, inflammation (colitis), narrowing of the colon, tumours etc. * A thick liquid (containing barium) is placed in the lower gut via the rectum. * This coats the mucosal lining of the colon, thus highlighting the colon in an x-ray. * Characteristic findings are indicative of pathology. • Colon cancer leaves an “applecore” sign.

Question 140

analysing faeces - what is it - what help diagnose - what is stool checked for

Answer 140

* A stool analysis is a series of tests done on a stool (faeces) sample to help diagnose certain conditions affecting the digestive tract. * These conditions can include infection (parasites, viruses, orbacteria), poor nutrient absorption, or cancer. * For a stool analysis, a stool sample is collected in a clean container and then sent to the laboratory. Laboratory analysis includes microscopic examination, chemical tests, and microbiologic tests. * The stool will be checked for: ```  Colour  Consistency  Amount  Shape  Odour  Presence of mucus  Hidden blood  Fat  Meat fibers  Bile  White blood cells  Sugars  pH ``` • A stool culture is done to find out if bacteria may be causing an infection.

Question 141

surgery for colorectal cancer - what does it aim to do - what are the different types

Answer 141

• This aims to cure and increase survival times by up to 50%. • Laparoscopic surgery is a safe alternative to an open approach. • Right Hemicolectomy - for caecal, ascending or proximal transverse colon (2/3) tumours (midgut) • Left Hemicolectomy – for tumours in distal transverse colon (1/3) or descending colon (hindgut)  The reason they perform it with regards to ‘midgut’ and ‘hindgut’ is so that the area with the same blood supply is removed. • Anterior Resection – for low sigmoid or high rectal tumours. • Abdomin-perineal (A-P) Resection – for tumours in low rectum: permanent colostomy and removal of rectum. • Hartmann’s Procedure – in emergency bowel obstruction or palliation. Colectomy: - Surgery to remove all or part of the colon - Nearby lymph nodes are also removed - Hemicolectomy, partial colectomy, or segmental resection = only part of colon removed - Surgeon takes out part of the colon with cancer and a small segment of normal colon on either side - For a small early stage cancer, your surgeon might just remove the cancer from the bowel lining, along with a border of healthy tissue. This is called a local resection. - If your cancer is larger, your surgeon might remove the part of the bowel where the cancer is, and join the two ends back together. This is called a colectomy. They might also remove the lymph nodes near to the bowel in case the cancer has spread to the nodes. - To give the bowel time to heal, the surgeon might make a temporary ileostomy or colostomy. This is an opening from the bowel that leads to the surface of the abdomen and is called a stoma. Waste matter from the bowel collects into a special bag over the opening. You have another operation to repair the stoma after a few months (a stoma reversal). - The surgeon might have to make a permanent stoma if a lot of your bowel is removed. But most people don't need a permanent stoma. Colectomy: - Left hemi colectomy = left side of colon - Transverse colectomy - Right hemi colectomy - Sigmoid colectomy

Question 142

radiotherapy for colorectal cancer - when used - what associated with

Answer 142

* Radiotherapy may be used pre-op in rectal cancer to reduce the local recurrence and increase 5 year survival. * It may be associated with a higher rate of post-operative complication, e.g. DVT. * Pre-op radiotherapy is only used in patients with rectal tumours at high risk of local recurrence.

Question 143

chemotherapy for colorectal cancer - what agents - how effective

Answer 143

* Good evidence adjuvant fluorouracil (5-FU) and other agents (e.g. folinic acid, levamisole). * Chemotherapy reduces Duke’s C mortality by about 25%. Dukes' A means that the cancer is only in the innermost lining of the bowel or slightly growing into the muscle layer. Dukes' B means the cancer has grown through the muscle layer of the bowel. Dukes' C means the cancer has spread to at least one lymph node in the area close to the bowel.

Question 144

fluorouracil (5-FU) - what is it - what does it do

Answer 144

* Fluorouracil is a pyrimidine analog that is an antineoplastic antimetabolite. * An antimetabolite prevents purine/pyramidine (e.g. thymine) from incorporating into the DNA during the “S” phase, stopping normal development and division. * Fluorouracil blocks the enzyme which converts the cytosine nucleotide into the deoxy derivative. * Fluorouracil inhibits the incorporation of the thymidine (a pyrimidine) nucleotide into the DNA strand. - One of the most commonly used drugs to treat cancer - Treatment for many types of cancer - Part of group of chemotherapy drugs known as anti-metabolites – similar to normal body molecules but they have a slightly different structure - These differences means they stop cancer cells working properly – they stop the cells making and repairing DNA

Question 145

what is the mechanism of action of 5-FU?

Answer 145

 Fluorouracil is converted in cells to 5-fluoro-2’-5’-monophosphate (5-FdUMP) and 5-fluorouridine-5’-triphosphate (FUTP), its metabolites.  5-FdUMP incorporates into the DNA of fast growing cells in the body.  Here, it interferes with DNA synthesis by blocking thymidylate synthetase.  Normally, thymidylate synthetase converts uracil into thymidylate.  Blocking this enzyme inhibits the synthesis of thymidylate.  This means that thymidine (a pyrimidine) can no longer be incorporated into DNA.  Incorporation of FdUMP into DNA inhibits DNA synthesis function.  Incorporation of FUTP into RNA interferes with RNA processing and function.  Tumour cell resistance mechanisms include decreased activation of 5-FU, increased thymidylate synthase activity, and reduced drug sensitivity of this enzyme.

Question 146

what are the side effects of 5-FU?

Answer 146

 Diarrhoea  Nausea and vomiting  Stomatitis – inflamed or sore mouth

Question 147

folinic acid - how administered - what is it - when used - what form - indications

Answer 147

• This is generally administered as calcium or sodium folinate (or leucovorin calcium/sodium). • It is an adjuvant used in cancer chemotherapy involving the drug methotrexate. • It is also used in synergistic combination with chemotherapy agent 5-FU. • Folinic acid can be taken as a pill or injected into a vein (intravenously) or muscle. • Indications:  Used to diminish the toxicity and counteract the effects of impaired methotrexate elimination and of inadvertent overdosages of folic acid antagonists, and to treat megaloblastic anaemias due to folic acid deficiency.  Also used in combination with 5-fluorouracil to prolong survival in the palliative treatment of patients with advanced colorectal cancer. It enhances the effect of 5-FU by inhibiting thymidylate synthase. - A reduced folic acid - Used in combination with other chemotherapy drugs to either enhance effectiveness, or as a ‘chemoprotectant’ - Used in combination with fluorouracil to treat cancers such as; colon and rectal, head and neck, oesophageal, and other cancers of the GI tract - Used as an antidote to effects of certain chemotherapy drugs such as methotrexate - Used as treatment of megaloblastic anaemia when folic acid deficiency is present - When given in combination with fluorouracil the side effects of fluorouracil may be more severe - When given in combination with methotrexate, leucovorin is given to lessen the side effects of methotrexate

Question 148

what is mechanism of action of folinic acid?

Answer 148

 As leucovorin is a derivative of folic acid, it can be used to increase levels of folic acid under conditions favouring folic acid inhibition (following treatment of folic acid antagonists such as methotrexate).  Leucovorin enhances the activity of fluorouracil by stabilizing the bond of the active metabolite (5-FdUMP) to the enzyme thymidylate synthetase.  This is because 5-FU doesn’t stay long in the system and so folinic acid allows 5-FU to bind to this enzyme.

Question 149

describe the TMN staging of colon cancer

Answer 149

Tumour: Tis: Cancer is at its earliest stage (in situ), it is growing into the mucosa but no further T1: Tumour has grown into the submucosa metastasis T2: Tumour has grown into the muscle layer of the bowel wall but no further T3: Tumour has grown into the outer lining of the bowel wall (serosa) but no further T4: Tumour has grown through the outer wall of the bowel wall (serosa) and through the membrane covering the outside of the bowel wall (peritoneum) T4a: Tumour has grown into other nearby structures, such as parts of the bowel or other organs or body structures T4b: Tumour has caused a hole in the bowel wall (perforation) and cancer cells have spread outside the bowel Node: N0: no nodes involved N1: 3 nodes involved N2: 4+ nodes involved Metastasis: M0: no metastasis M1: distant metastasis

Question 150

what is Dukes' staging for colorectal cancer?

Answer 150

* This provides a 5 year prognosis. * Dukes’ A: 90% chance of survival over the next 5 years. * Dukes’ B: 66% chance of survival over the next 5 years. * Dukes’ C: 33% chance of survival over the next 5 years. * Dukes’ D: <5% chance of survival over the next 5 years due to widespread metastasis.

Question 151

what is the number staging for colorectal cancer?

Answer 151

Stage 0 • The cancer is at its earliest stage and is only in the mucosa (Tis N0 M0). Stage 1 • The cancer has grown into the submucosa or muscle but has not spread to the lymph nodes or elsewhere (T1 N0 M0 or T2 N0 M0). Stage 2 • The cancer has grown through the muscle wall or through the outer layer of the bowel, and may be growing into tissues nearby. The cancer has not spread to the lymph nodes or elsewhere (T3 N0 M0 or T4 N0 M0). Stage 3 • The tumour is any size and has spread to lymph nodes nearby, but has not spread anywhere else in the body (Any T N1 or N2 M0). Stage 4 • The tumour is any size. It may have spread to nearby lymph nodes. The cancer has spread to other parts of the body such as the liver or lungs (Any T Any N M1).

Question 152

grading of cancer - what does this refer to? - what is the grading?

Answer 152

• Grading refers to how closely the tumour cells resemble their tissue of origin; level of malignancy is based on cytological differentiation (dysplasia and anaplasia) of tumour cells and the number of mitoses within the tumour. Grade I = Tumour cells resemble normal (well differentiated) and aren’t growing rapidly. Grade II = Tumour cells don’t look normal and are growing faster than normal cells. Grade III = Tumour cells look abnormal (poorly differentiated) and are proliferating rapidly. * Cells that resemble ‘tissue’ tend to be well differentiated. * Cells that resemble ‘stem cells’ tend to be poorly differentiated. * Cancer cells are poorly differentiated which allows them to be more independent in their own growth.

Question 153

pathology of colon cancer - what are the sites of mutation in colon cancer - when is a mutation not so harmful - hwhen is it very harmful

Answer 153

* The mucosal lining of the colon contain crypts. * These are the sites of mutations in colon cancer. * If the mutation occurs in the differentiated villi/ epithelial cells, then the development of the tissue isn’t so harmful. * If the mutation occurs in the crypts (the site of colon stem cells), then the development of the tissue is very harmful (polyps).

Question 154

what is FAP?

Answer 154

familial adenomatous polyposis

Question 155

FAP - what is it - how related to colorectal cancer

Answer 155

• This is an inherited disease of the colon which predisposes the individual to developing colorectal cancer. • In this condition, hundreds of polyps line the luminal surface of the colon. • This condition has a low but predictable frequency of development into colorectal cancer. - Because there’s so many polyps, it’s only a matter of time before one will gain a mutation and go on to form cancer - Majority of CRC (colorectal cancer) sporadic (no known cause?) - Several rare familial diseases - Familial adenomatous polyposis (1%) - FAP – Wnt, APC, B-catenin

Question 156

what is APC?

Answer 156

adenomatous polyposis coli - forms part of the Wnt signalling pathway - formed part of the intracellular protein complex

Question 157

what is APC gene?

Answer 157

tumour supresssor gene

Question 158

what does the APC protein do?

Answer 158

* APC gene encodes a protein consisting of 2800 amino acids which binds to B-catenin, thus causing down regulation of it by initiating its proteolytic degradation (along with activated GSK-3B). * This stops the cell from over proliferating.

Question 159

what happens if there's a mutation in APC?

Answer 159

1. Prevents the degradation of B-catenin and so results in excessive proliferation of the cell. 2. Makes the genome unstable by affecting the spindling during mitosis. 3. Stimulates the migration of malignant stem cells out of the crypts (polyps).

Question 160

what is an obligate and early step in CRC?

Answer 160

Deregulation of APC/B-catenin

Question 161

what is mutated in what percentage of sporadic CRCs?

Answer 161

* APC IS MUTATED IN 80-90% OF SPORADIC COLORECTAL CANCERS! | * B-CATENIN IS MUTATED IN 10-20% OF SPORADIC COLORECTAL CANCERS!

Question 162

what is HNCC?

Answer 162

hereditary non-polyposis colon cancer

Question 163

HNCC - what is it - what does it cause - what also known as - what does it predispose to - what happens in this condition

Answer 163

* This is an inherited disease of the colon that causes about 2-3% of all colorectal cancers. * It is also known as ‘Lynch syndrome’. * HNCC not only predisposes the individual to colorectal cancer, it predisposes them to other cancers too (ovarian, small intestine, urinary tract, skin and brain). * In this condition, very few polyps form but the progression of development into colorectal cancer is fast (2-3 years instead of 8-10 ).

Question 164

what is the mutation rate of mismatch repair genes like?

Answer 164

higher mutation rate than other genes.

Question 165

what happens if mismatch genes are mutated?

Answer 165

* If mismatch genes are mutated then any errors in newly made DNA strands can’t be repaired. * This leads to an increase in mutations newly made DNA strands.

Question 166

what is an example of a mismatch repair gene? what is it associated with? what can a mutation lead to?

Answer 166

MLH1 gene is a mismatch repair gene, associated with microsatellite stability. A mutation of this can lead to microsatellite instability and HNCC.

Question 167

how can a MLH1 mutation cause cancer?

Answer 167

 The cells are constantly making mistakes when making new DNA strands that aren’t being repaired.  This means the mutation rate in these patients increases significantly. - This means that they can acquire more mutations more easily in specific regions of the genome such as oncogenes and TSGs. - An elevated mutation rate doesn’t cause cancer; mutations in specific areas of the genome give us cancer (i.e. in oncogenes/ TSGs).

Question 168

what is TGF-beta?

Answer 168

a growth inhibitory factor

Question 169

how does TGF-B normally work? where can mutations occur?

Answer 169

 TGF-B binds to its receptor, thus causing a signalling cascade to occur via Smad intracellular proteins.  This causes: - Activation of CKIs – thus inhibiting proliferation - Inhibition of MYC (a pro-proliferative molecule) – thus inhibiting proliferation • Mutations can occur in the Smad 4 pathway (25% of CRC), thus leading to an increase in proliferation.

Question 170

what do mismatch repair mutations cause? what does this cause in terms of TGF-B? how common is this?

Answer 170

 Mismatch repair mutations cause deletion of AA bases.  This causes a truncation of the TGF-B receptor gene, meaning that it is no longer synthesised.  As a result, the cell now becomes unresponsive to anti-proliferative signals (such as that from TGF-B).  TGF-B receptor gene mutation occurs in 90% of colorectal cancers with a mismatch repair gene defect. - TGF-B is growth inhibitory - Mutated in 90% of CRC with MSI - MSI = microsatellite instability (vs. MSS – microsatellite stability) – genomic instability at the nucleotide level

Question 171

what happens without the TGF-B pathway?

Answer 171

Without the TGF-B pathway (anti-proliferative effect), the colon becomes sensitised to inflammation and so can develop colorectal cancer.

Question 172

what happens in response to the inflammatory response?

Answer 172

the NF-kB pathway is upregulated, leading to an upregulation of gene expression, causing:  Proliferation (via Cyclin D1)  Anti-apoptosis (via Bcl-X = pro-survival protein)  Synthesis of Pro-inflammatory prostaglandins (via COX2) - NSAIDs can block this pathway. - Evidence suggests that long-term prophylactic use of NSAIDs can reduce the incidence rate of colorectal cancer.

Question 173

in this manner, what does chronic inflammation cause?

Answer 173

causes ulcerative colitis, which increases the risk of developing colorectal cancer.

Question 174

what does damage to vasculature (due to the invasive effects of the tumour) lead to? what does this result in? how treated?

Answer 174

an increase in vascular endothelial growth factor (VEGF). • This results in angiogenesis. • Angiogenesis can be treated by VEGF-inhibitors (eg. Avastin).

Question 175

what are veteran genes? what do they cause? | what is methylation like in malignant cells?

Answer 175

* In a differentiated cell, ‘veteran genes’ are turned on. This only causes certain genes to be expressed and thus only certain proteins are synthesised. * In normal cells, genes are turned off by methylation. * Malignant cells are hyper-methylated.

Question 176

what is the potential role of psychology in cancer? model

Answer 176

Illness onset: cancer - beliefs: seriousness, costs, benefits - behaviours: smoking, diet, screening - coping with diagnosis - illness representations - psychological consequences Progression: - behaviour change - coping with illness - life stressors outcome: - disease free interval - recovery - longevity - quality of life

Question 177

what are the psychosocial factors in the initiation and promotion of cancer?

Answer 177

1) Behavioural Factors Smith and Jacobson (1989) reported that  30% of cancers are related to tobacco use,  35% are related to diet,  7% are due to reproductive and sexual behaviour  3 % are due to alcohol. 2) Stress Laudenslager et al. (1983) • If this stressor could be controlled, there would be a decrease in the rate of tumour development. However, if the stressor was perceived as uncontrollable, this resulted in an increase in the development. Sklar and Anisman (1981) • An increase in stress increased the promotion of cancer, not its initiation 3) Life Events Jacobs and Charles (1980) • reported that in families who had a cancer victim there were  higher numbers who had moved house,  higher numbers who had changed some form of their behaviour,  higher numbers who had had a change in health status other than the cancer person,  higher numbers of divorces,  indicating that life events may well be a factor contributing to the onset of cancer 4) Control • Control over stressors and control over environmental factors may be related to an increase in the onset of cancer 5) Coping Styles • If an individual is subjected to stress, then the methods they use to cope with this stress may well be related to the onset of cancer. • For example, maladaptive, disengagement coping strategies, such as smoking and alcohol, may have a relationship with an increase in cancer 6) Depression • Chronic mild depression, but not clinical depression, may be related to cancer. 7) Personality Temoshok and Fox (1984) • Argued that individuals who develop cancer have a ‘type C personality’ (passive, appeasing, helpless, other focused and unexpressive of emotion) Eysenck (1990) • Described ‘a cancer-prone personality’, and suggests that this is characteristic of individuals who react to stress with helplessness and hopelessness, and individuals who repress emotional reactions to life events. • E.g. heavy smokers who develop lung cancer have a poorly developed outlet for their emotions, perhaps suggesting type C personality. • The type of individual who was more likely to develop cancer as having impaired self-awareness, being self-sacrificing and self-blaming, and not being emotionally expressive (16% greater risk). 8) Hardiness • Kobasa et al. (1982) described a coping style called ‘hardiness’, • has three components: control, commitment and challenge.  Low control suggests a tendency to show feelings of helplessness in the face of stress.  Commitment is defined as the opposite of alienation: individuals high in commitment find meaning in their work, values and personal relationships.  Individuals high in challenge regard potentially stressful events as a challenge to be met with expected success. • Hardiness may be protective in developing cancer.

Question 178

what are cognitive responses to cancer?

Answer 178

• A ‘fighting spirit’ is negatively correlated with anxiety and depression while ‘fatalism’, ‘helplessness’ and ‘anxious preoccupation’ are related to lowered mood • Taylor (1983) examined the cognitive adaptation of 78 women with breast cancer. She reported that these women responded to their cancer in three ways.  First, they made a search for meaning (understand why they developed cancer). Meanings that were reported included stress, hereditary factors, ingested carcinogens such as birth control pills, environmental carcinogens such as chemical waste, diet, and a blow to the breast.  Second, they also attempted to gain a sense of mastery by believing that they could control their cancer and any relapses. - Such attempts at control included meditation, positive thinking, and a belief that the original cause is no longer in effect.  Third, the women began a process of self-enhancement. - This involved social comparison, whereby the women tended to analyse their condition in terms of others they knew. • The women showed ‘downward comparison’, which involved comparing themselves to others worse off, thus improving their beliefs about their own situation. • According to Taylor’s theory of cognitive adaptation, the combination of meaning, mastery and self-enhancement creates illusions which are a central component of attempts to cope.

Question 179

classical and operant conditioning?

Answer 179

Classical conditioning (also known as Pavlovian or respondent conditioning) refers to a learning procedure in which a biologically potent stimulus (e.g. food) is paired with a previously neutral stimulus (e.g. a bell). Operant conditioning is a method of learning that occurs through rewards and punishments for behavior. Through operant conditioning, an individual makes an association between a particular behavior and a consequence (Skinner, 1938).

Question 180

what is adjuvant psychological therapy for cancer?

Answer 180

• In addition to physical interventions, patients with breast cancer should be offered adjuvant psychological therapy.  This involves encouraging cancer patients to examine the personal meaning of their cancer and what they can do to cope with it

Question 181

voluntary euthanasia | - what is this

Answer 181

* Euthanasia carried out by A at the request of B. * There is a close connection between voluntary euthanasia and assisted suicide, where one person will assist another to end her life - for example, when A obtains the drugs that will allow B to suicide. * Euthanasia can be voluntary even if the person is no longer competent to assert her wish to die when her life is ended. * You might wish to have your life ended should you ever find yourself in a situation where, whilst suffering from a distressing and incurable condition, illness or accident have robbed you of all your rational faculties, and you are no longer able to decide between life and death. * If, whilst still competent, you expressed the considered wish to die when in a situation such as this, then the person who ends your life in the appropriate circumstances acts upon your request and performs an act of voluntary euthanasia.

Question 182

what is non-voluntary euthanasia?

Answer 182

• When the person whose life is ended cannot choose between life and death for herself - for example, because she is a hopelessly ill or handicapped newborn infant, or because illness or accident have rendered a formerly competent person permanently incompetent, without that person having previously indicated whether she would or would not like euthanasia under certain circumstances.

Question 183

what is involuntary euthanasia?

Answer 183

* When it is performed on a person who would have been able to give or withhold consent to her own death, but has not given consent - either because she was not asked, or because she was asked but withheld consent, wanting to go on living. * Whilst clear cases of involuntary euthanasia would be relatively rare (for example, where A shoots B without B's consent, to save her from falling into the hands of a sadistic torturer), it has been argued that some widely-accepted medical practices (such as the administration of increasingly large doses of pain killing drugs that will eventually cause the patient's death, or the unconsented-to withholding of life-sustaining treatment) amount to involuntary euthanasia.

Question 184

how common is small intestine cancer?

Answer 184

- Small intestine cancer is rare | - Normally called small colon cancer

Question 185

what is a polyp?

Answer 185

an abnormal growth of tissue projecting from a mucous membrane

Question 186

describe the process of genes to tissues

Answer 186

Genome – (transcription)> transcriptome – (translation)> proteome – (biogenesis, metabolism)> cell function – (proliferation)> tissue architecture  Deregulated tissue homeostasis

Question 187

describe the process of tumorigenesis

Answer 187

MULTI-STEP TUMORIGENESIS - Normally many mutations - First clonal expansion of group of cells with one mutation, then all those clonal cells have mutation and may gain another mutation, this keeps happening -> increased mutation rate - Cancer arises from a single cell - Multi-step process - Clonal expansion - Mutation of multiple oncogenes and tumour suppressor genes - Darwinian evolution

Question 188

how can viruses caues cancer?

Answer 188

- Certain viruses can cause cancer - Viral genes that when introduced into cells had dominant, transformative effects - Cellular oncogenes – cancer DNA transfected into normal cells caused transformation, again in a dominant manner - A single ‘activating’ mutation is sufficient – B-catenin & KRAS - Only need one mutation

Question 189

what is a example pathways and how does it work?

Answer 189

``` - The EGF (epidermal growth factor) network, just one of many How they work: - Ligands (hormones, growth factors) -> - Receptors -> - Signalling cascade -> - Transcription factors -> - Gene expression ```

Question 190

what is important about G1?

Answer 190

G1 – part of G1 – period during which cells are responsive to mitogenic GFs and to TGF-B (signals that tell cell to divide or to not divide) – this is the commitment point R = restriction point – then you are committed

Question 191

how does concentration of CDKs change throughout cell cycle?

Answer 191

Concentration of CDKs constant throughout the cell cycle They’re regulated by binding to their regulators – the cyclins Concentration of cyclins oscillate with the cell cycle (hence the name cyclins)

Question 192

what is required for p53 to downregulate other genes (act as a tumour suppressor gene?)?

Answer 192

p21 p21 = p53 target - i think more this

Question 193

what causes continuous damge in the genome?

Answer 193

``` THE GENOME IS UNDER CONSTANT ATTACK Continuous damage: - Oxidation - Replication errors - UV - X-rays - Chemicals - Mitosis ```

Question 194

what causes continuous repair in the genome?

Answer 194

Continuous repair: - BER - NER - Proofreading - NHEJ - DSBR/HR - The SAC

Question 195

what is the genetic stability of colon cancers like? explain this

Answer 195

All colon cancers are genetically unstable - Mismatch repair and HNPCC - APC and chromosome instability

Question 196

what maintains genome integrity?

Answer 196

p53 and apoptosis

Question 197

colonic crypts - what are they - what is found in them - what is remarkable about them - why chemotherap works

Answer 197

- Straight tubular glands in the colonic mucosa - At the base of the crypts are the stem cells (Lgr5+ stem cells) – give rise to the whole of the intestine - The regenerative capacities of these tissues are quite remarkable - Chemotherapy will wipe out a lot of the dividing cells, but then they recover due to this regenerative capacity

Question 198

where have FAP locus genes been identified?

Answer 198

Identification of FAP locus genes from chromosome 5q21

Question 199

what gene is FAP associated with?

Answer 199

- Identification of FAP locus genes from chromosome 5q21 - They then discovered that adenomatous polyposis coli (APC) is mutated in 80-90% of sporadic CRC (studying rare familial disease given insight into sporadic disease) - People with FAP are born with one mutated APC gene, and then over time the other is lost so that they have no APC genes (tumour suppressor)

Question 200

describe APC and B-catenin in the crypt and the effect of mutation

Answer 200

- 80-90% CRCs have APC mutation - 10-20% have B-catenin mutations - Deregulation of APC/B-catenin is an obligate and early step in CRC - Wnt signalling - The cells surrounding the stem cells at the bottom of the crypt are the ones that secrete Wnt signal, which tells the stem cells to proliferate, when the cells move up/migrate up the cypt they are moving away from where the Wnt signal is being generated, so they no longer receive a Wnt signal, so signals no longer proliferate - However, if APC is mutated (lost both copies), of B-catenin is mutated such that it’s no longer degraded, cells that migrate up, still proliferate as B-catenin pathway is still on even though they no longer have the Wnt signals -> hyperproliferative zone -> polyp

Question 201

what is mismatch repair?

Answer 201

- DNA is constantly under attack - Errors in newly made strand – mismatches form - This doesn’t matter as proofreading proteins recognise this mismatch and bind to DNA and reset and repair it

Question 202

what herited condition is mismatch repair associated with ? how? what else discovered?

Answer 202

- Scientist studying DNA repair mechanisms in E. coli and yeast - MutSalpha (MSH6 & MSH2) - MutLalpha (MLH1 & PMS2) - Cloned the human version of MSH2, mapped it to chromosome 2 and linked it to HNPCC - Both teams also later discovered mutations in MLH1 – MLH1 promoter is silenced by methylation in about 15% of sporadic CRCs THEREFORE, studying rare familial cancers has given insight into sporadic disease

Question 203

what happens in familial and sporadic cases of the disease in terms of MSH2 and MLH1? and what are these genes?

Answer 203

In familial cases, MSH2 and MLH1 (mismatch repair genes) are mutated, in sporadic disease the promoter gets methylated, switching the gene off

Question 204

does a mutation in MSH2 or MLH1 cause cancer? what happens?

Answer 204

- Mutation in MSH2 or MLH1 is not what causes cancer, what it does is it elevates the mutation rate – remember, to become a cancerous cell it has to require many mutations - That’s what losing mismatch repair does - It means that you’re more likely to get mutations in the oncogenes and tumour suppressor genes, and that’s what gives you cancer

Question 205

what is the mutation rate of mismatch repair genes like compared to non-mismatch repair genes?

Answer 205

high -> leads to genomic instability

Question 206

chromosome instability

Answer 206

- Hypermutate tend to be diploid (i.e. chromosome number variation (CNV) low) - Non-hypermutated tend to exhibit CIN (chromosome instability) & are therefore aneuploid (i.e. CNV high)

Question 207

Wnt signalling pathway is mutated in virtually every colon cancer, what exactly is mutated?

Answer 207

either through APC or B-catenin mutation

Question 208

what do the mutations of B-catenin and ACP look like?

Answer 208

``` B-catenin - 29 cases - Deletions - Spanning exon 3 APC - 35 cases - Upstream of exon 9 - Slicing defect - Protein truncation ```

Question 209

why is it useful to know if a cancer is hypermutated or not?

Answer 209

- If you have hypermutated cancer you are a very good candidate for immunotherapy (revolutionising cancer treatment) - With hypermutated cancer, many different mutations, some of these mutant proteins end up getting expressed on the cell surface, which should be recognised by T-cells but isn’t, as tumour cells are very good at evading the immune system - This is because these abnormal antigens interact with T-cells, which would normally activate the T-cell to kill it, but the tumour cell also expresses things like PD-L1 which binds to PD-1 receptor on the T-cell and switches it off - However, antibodies can block PD-1 – PD-L1 interaction which switches the immune cells back on - Pembrolizumab – humanised monoclonal antibody with blocks PD-1 (licensed by FDA in 2017) – first drug to be licensed for any cancer type based on its molecular profile

Question 210

how does effect of primary tumour site affect outcome in colon cancer?

Answer 210

- Left sided tumours associated with better outcomes - Right sided tumours associated peritoneal & omental metastasis, whereas left associated with liver and lung metastasis (a lot of liver with left as well and some lung) - Right and left side of the colon

Question 211

what are frequent but later targets?

Answer 211

Ras and p53

Question 212

what are the three subtypes of colon cancer?

Answer 212

- POLE hyper mutated (<1%) - MSI – microsatellite instability (9%) - MSS – microsatellite stable (90%) – but high CNV (copy number variation) due to CIN

Question 213

which tumours are prioritised for immune checkpoint therapy?

Answer 213

MSI tumours In gastrointestinal cancers, one of the leading causes of hypermutation is a defect in DNA mismatch repair, which results in microsatellite instability (MSI).

Question 214

what is an obligate and early target?

Answer 214

Wnt pathway, either via APC or B-catenin

Question 215

what are liquid biopsies?

Answer 215

- Tumours shed cells and DNA into the blood - Minimally invasive and relatively inexpensive biopsy - Advanced in detection technology, e.g. NGS, Mass Spectrometry - Early detection - Predictive biomarkers – find out mutation profile – decide which treatment strategy - Monitor response to therapy - Able to detect colon cancer cells with about 90% sensitivity - Liquid biopsies – early diagnosis

Question 216

what are organoids?

Answer 216

Organoids = tiny, self-organised three-dimensional tissue cultures that are derived from stem cells - Build many organs in the lab - Single Lgr5+ stem cells build crypt-villus structures in vitro without a mesenchymal niche - ‘we perceive patient-derived organoids to be used to directly test drug sensitivity of the tumour in a personalised treatment approach’ - Organoids – tools for personalised drug profiling

Question 217

what is important about HNPCC? and FAP?

Answer 217

- rare familial cancers tell us a lot about sporadic disease - genome stability & mutator phenotype - MSI vs MSS - FAP – Wnt, PAC, B-catenin

Question 218

what is maximum absoprtion of nutrients achieved? what is and isn't controlled?

Answer 218

Achieved by: 1. Regulating motility 2. Controlling secretion of digestive juices (little control of absorption) = excellent ‘scavenger’, evolved when food was in short supply

Question 219

what receptors sense what in the contents of the lumen?

Answer 219

- Distention – mechanoreceptors - Osmolality – osmoreceptors - Acidity – chemoreceptors - Digestive products – chemoreceptors

Question 220

what does receptor activation cause?

Answer 220

1. Hormones 2. Nerves a. Short reflexes b. Long reflexes 3. Paracrine transmission N.B. this is not either a 1 or 2 or 3 response but more 1 and 2 and 3 all together

Question 221

describe enteroendocrine cells - what proportion of cells?

Answer 221

- Main sensory cells - about 1% of mucosal cells (about 2 m^2) - Granules in cell store hormones/transmitter - Microvilli – sense lumen contents or movement

Question 222

what are incretins? give examples

Answer 222

- they enhance insulin release by endocrine pancreas | - GIP and GLP-1

Question 223

what are the only enteroendocrine cells in the colon?

Answer 223

GLP-producing cells

Question 224

where are the following secreted? - gastrin - CCK - secretin - GIP - motilin

Answer 224

- Gastrin – mainly produced in antrum of stomach, small amounts in duodenum and jejunum - CCK – duodenum & jejunum, smaller amount ileum - Secretin – duodenum & jejunum, smaller amounts ileum - GIP – duodenum & jejunum - GLP-1 – ileum & colon, smaller amounts duodenum & jejunum - Motilin – duodenum & jejunum (involved in inter-digestive motility = ‘migrating motor complex’)

Question 225

GI hormones - what are they - what are they secreted by - what do they target/affect

Answer 225

- All are short chain peptides - Secreted by enteroendocrine cells found in mucosa into the blood - Target various regions of GI and glands - Many have effects on nervous system e. g. CCK - Secreted: intestine - Affects: pancreas, gall bladder, stomach - CNS: satiety

Question 226

ENS - how many neurones - layers - what release (neurotransmitters) - excitatory - inhibitory

Answer 226

100 million neurons in the myenteric and submucosal plexus Layers outer to inner: - Myenteric plexus - Circular smooth muscle - Submucosal plexus - Epithelium ACh (also various peptides released - SP; GRP; NO; VIP) Excitatory: substance P; gastrin releasing peptide Inhibitory: nitric oxide; vasoactive intestinal peptide

Question 227

what are short reflexes?

Answer 227

Short reflex = all neurones involved are part of ENS | - E.g. local distention -> motility (muscle contraction)

Question 228

how are extrinsic nerves invovled?

Answer 228

Parasympathetic: preganglionic fibres synapse with ENS (which can release: ACh, SP; GRP; NO; VIP) - Involved in long reflexes, e.g. vago-vagal (vagus = both afferent and efferent – 80% vagal fibres are sensory) Sympathetic: post-ganglionic fibres -> noradrenaline = decrease motility and decrease blood flow - No major role in ‘day to day’ motility - Sympathetic (postganglionic) and parasympathetic (preganglionic) nerves synapse to myenteric plexus and submucosal plexus - Parasympathetic nerves synapse with ENS - No ‘true’ ganglia - Release of different transmitters – ACh; SP; GRP; NO; VIP – parasympathetic - Noradrenaline – sympathetic

Question 229

describe the signalling that takes place in terms of CCK and the gall bladder

Answer 229

- When have a meal the gall bladder contracts, squeezing its contents into the duodenum, through the sphincter of Oddi, which relaxes when the gall bladder contracts - Gall bladder mainly controlled by CCK – when food leaves the stomach, you get release of CCK - CCK can also act in a paracrine/neurocrine fashion – it stimulates nerves -> vagal afferent -> dorsal vagal complex -> vagal efferents  ACh -> gall bladder = vago-vagal (long) reflexes - other vagal efferents go to the sphincter of Oddi and release NO & VIP (inhibitory) – relaxes smooth muscle

Question 230

what percentage of body 5-HT is in the GI tract?

Answer 230

95% | - Release of 5-HT is a key signal in physiology and pathophysiology

Question 231

describe how luminal stimulu sleads to motility with serotonin

Answer 231

- Luminal stimulus - Enterochromaffin cell releases 5-HT - That 5-HT picked up by afferent fibres in the enteric nervous system (intrinsic primary afferent neurones) - Which can link short reflexes to excitatory motor neurones -> ACh, SP -> contraction - Inhibitory motor neurones also stimulated -> VIP, NO -> relaxation

Question 232

what is the link between serotonin and vomiting?

Answer 232

- Toxins (produced by bacteria) and cytotoxic drugs (such as chemotherapy and radiation) in the lumen, damage the epithelium of the gut - This causes inappropriate amounts of 5-HT to be released - So instead of getting local reflexes occurring, you stimulate vagal fibres which take information to the ‘vomiting centre’ (medulla), which stimulates vomiting - 5-HT3R on afferent vagal nerves - 5-HT3 antagonists are very useful anti-emetics (in chemotherapy)

Question 233

what are opiates used for in terms of gut problems? what are side effects?

Answer 233

Opiates = powerful analgesic for visceral pain in metastatic cancer Side-effects: - Vomiting in 30% of patients (central action on vomiting centre) - Dysphoria (agitation) - Constipation which needs to be managed as part of palliative care = real problem in palliative care – not nice for anyone involved Vomiting and dysphoria tend to wear off

Question 234

what is the mechanism of action for opioids? why does it cause constipation?

Answer 234

- u (mu), delta, K receptors expressed in GI tract - u-receptors of paramount importance in GI tract - receptor activation = G protein (G0) -> direct interactions with channel proteins - activates K+ channels - inhibits Ca2+ channels =decrease synaptic transmission =main mechanism for analgesia and for decreased GI motility  increase transit time in colon = increase H2O absorption = lack of motility and hardness of faecal matter -> constipation

Question 235

how do opioids affect motility?

Answer 235

- excitatory motor neurones are particularly affected - however, the inhibitor motor neurones are inhibited by opioids - so reduced release of NO and VIP -> reduced relaxation - therefore, opioids reduce forward propulsion and cause failure of sphincters to relax – part of intestine in front of the food being digested is contracted intestine behind can’t propel food

Question 236

what are endogenous opioids? what do they cause?

Answer 236

- discovered in 1970s (peptides of 4-8 amino acids) - enkephalins and endomorphins in GI tract = peptides that are the endogenous ligands for the opioid receptors - endogenous opioids -> decrease motility - experimental

Question 237

what can be used to increase motility and increase intestinal secretion?

Answer 237

- experimental 1. u-receptor knock-out mice -> increase motility (decrease transit time) 2. humans treated with naloxone (opioid receptor antagonist) -> increase motility & also increase intestinal secretion

Question 238

how do opioids affect secretion?

Answer 238

- PGE2 & secretin: GPCR -> Gs (stimulatory G protein) -> increase adenylate cyclase - Enkephalin (acts on u-receptor): GPCR -> Gi (inhibitory G protein) -> decrease adenylate cyclase

Question 239

opioids as anti-diarrhoeal drugs - how work - names/examples - often used - what are better than opioids particularly in children

Answer 239

- u-receptor agonists - loperamide (opioid receptor agonist) – Immodium - diphenoxylate (opioid) + atropine (muscarinic agonist) – Lomotil = decrease peristalsis, decrease gastric emptying - don’t normally use for diarrhoea, normally with diarrhoea the causal agent is removed, and it gets better into few days - enkephalinase inhibitors = enhance actions of endogenous enkephalins (children) - better because opioids are very addictive - Hidrasec (racecadotril): anti-secretory action with no great increase in transit time

Question 240

what are the elements of valid consent?

Answer 240

- Voluntary - Informed - Person must have capacity

Question 241

how is landscape changing with informed consent? what came from Sidaway case?

Answer 241

Four out of five Law Lords agreed on: a) Risk <1% not conventionally discussed b) Rejection of ‘transatlantic test’ i.e. what a reasonable patient would want to know as a marker for what a doctor should tell a patient c) Mrs Sidaway had not asked about risk

Question 242

what is the biopsychosocial model?

Answer 242

THE BIOPSYCHOSOCIAL MODEL Social: - Culture, social interactions, sick role Psycho : - Illness behaviour, beliefs, coping strategies, emotions, distress Bio: - Physiological dysfunction & neurophysiological changes

Question 243

what are the different models?

Answer 243

``` COM-B and PRIME SRM – self regulatory model Lazarus and Folkman Health beliefs GAS/biopsychosocial stress ```

Question 244

what is the COM-B framework?

Answer 244

``` Determinants of behaviour: - Capability -knowledge and skills - Motivation -reflective – weighing up -autonomic – habit and cueing - Opportunity -physical (time, resource), social (believing people want you do to that behaviour) behaviour ```

Question 245

what is prime theory?

Answer 245

- Plans - Responses - Impulses - Motives - Evaluations External environment (stimuli, information) Internal environment (precepts, drives, emotional states, arousal ideas, frame of mind)

Question 246

what is the health belief model?

Answer 246

``` Demographic variables -> - Susceptibility - Severity - Costs - Benefits - Cues to action - Health motivation - Perceived control  Likelihood of behaviour ```

Question 247

what is the self-regulation model?

Answer 247

``` Illness representation: - Identity - Timeline - Cause - Control/cure - Consequences Representation of emotional reaction: - E.g. fear, distress Coping behaviour: - For control of illness - For control of emotion Appraisal of coping: - Outcomes ```

Question 248

what is Lazarus and Folkman's model?

Answer 248

Transactional model of stress and coping - Environment - Person - Constraints - Stress appraisal process

Question 249

what affects surface area in small and large intestines? which bigger surface area?

Answer 249

The GI tract has an undulating surface which increases surface area for absorption and secretion - Crypt – in small and large intestine - Villi – in small intestine - Submucosa & muscle Large surface in both, but small intestine has a larger surface area

Question 250

what is the innate mechanism of defence? what lines majority of GI tract? what other protection?

Answer 250

- Pre-epithelial defence mechanisms – innate mechanisms - Simple columnar epithelium – lines majority of the GI tract - Sub-epithelial space – immune cells and primed and ready to respond to pathogens but not to self or commensal bacteria - Pre-epithelial – bacteria, mucus, IgA - Epithelial – epithelium - Sub-epithelial – innate & adaptive cellular responses if the mucus didn’t work at preventing pathogens getting through

Question 251

what cells secreted mucus?

Answer 251

goblet cells

Question 252

what is function of mucus?

Answer 252

- Lubricant - Prevents mechanical stress on epithelium - Thick layer provides stable microenvironment – huge amount of mucus - Prevents invasion - Essential environment for microflora

Question 253

how does mucus layer vary throughout gut?

Answer 253

- Colon – thickest part of loosely adherent mucus layer - this is where you have the biggest microbial burden - Ileum have fair amount of mucus

Question 254

what does Shiga toxin cause?

Answer 254

haemolytic uraemic syndrome (HUS) -rare

Question 255

how many layers of muscle? describe mucosal surface - why important?

Answer 255

- 3 layers of muscle that all work against each other to churn up the food - Mucosal surface - crypts - heterogenous layers of cells – some of which secrete mucus - Mucus is very important in the stomach because we’ve got a really low pH environment in which the pepsin works in, so the lumen pH is 1-2, but if you put this on you epithelium you will have a problem, there are cells in the epithelium that secrete carbonate, and because the mucus is dense, it means that you get a nice pH density/gradient from the epithelium to the lumen - Protection of gastric epithelium by mucus and secretion of neutralising bicarbonate by specialised epithelial cells - When this goes wrong -> problems with H. pylori

Question 256

what are the four mechanisms that allow bacteria to get to the epithelium?

Answer 256

1. it can swim – flagella 2. can make urease – neutralises the gastric acid and creates a neutral bubble around it 3. proliferates because it’s in a neutral environment 4. bacterial mucinases causes mucosal damage -> damage to epithelium

Question 257

what is it that actually causes the ulcer?

Answer 257

The bacteria don’t directly cause the ulcer, it’s the environment that it creates that creates the ulcer – so the acid can then cause the damage to the epithelium once the bacteria has damaged the mucus layer

Question 258

where in mucus and GI tract is there the most the bacteria?

Answer 258

- Upper layer of mucus is colonised by bacteria | - Lower part of the gastrointestinal tract has a much higher level of microbes/higher microbial burden

Question 259

what does the absence of gut bacteria affect?

Answer 259

- Behaviour - Gut homeostasis - Immune response under stress - Body weight - Brain development and gene expression

Question 260

who can 'healthy' bacteria be given to?

Answer 260

- Giving live bacteria to patients that have uncontrollable inflammation in their gut - ‘mutaflor’ - Ulcerative colitis - Gastroenteritis - IBS - Pouchitis - Crohn’s disease

Question 261

what is faecal transplant therapy? is it effective? why?

Answer 261

- If you take someone else’s microbiome and administer it to patients with chronic inflammation, you can reverse the inflammation - Instead of using antibiotics which reduce the microbiota - Healthy individual - Takes antibiotics - Reduced gut microbial species and diversity - Ingestion of C. difficile spores from the environment - C. difficile spores germinate – bloom of C. difficile - Development of CDI - Take antibiotics - C. difficile killed but spores can remain - Recurrent infection But if you give FMT (faecal microbiota transplant) then you get restoration of stable, healthy gut microbiota (instead of antibiotics to get rid of C. difficile because it doesn’t get rid of it completely and leaves you in a cycle) = VERY good results – 80-90% rate of cure compared with 20-30% with antibiotics

Question 262

C. difficile infection - what is it - how common - why survives - what causes - what can happen if not treated

Answer 262

CLOSTRIDIUM DIFFICILE INFECTION - The leading cause of health care-associated infectious diarrhoea (1,646 deaths in England and Wales 2012) - Caused by spore-forming gram-positive bacillus which is part of normal healthy flora in 4% of healthy individuals - Spores are resistant to stomach acid - Once in intestine, germinate and move into vegetative state ``` Pseudomembranous ulcerative colitis Asymptomatic -> - Severe diarrhoea - Severe abdominal pain - White blood cell count > 15000 cells/ul - Toxic megacolon - Organ failure - Mortality rate 35-80% If not treated ``` - can treat with faecal transplant therapy

Question 263

what is an example of natural antimicrobials? what secreted by? what does it create? what stimulates their production?

Answer 263

ANTIMICROBIAL PEPTIDES Alpha and beta defensins – natural antimicrobials - Secreted by Paneth cells - Creates a gradient of antimicrobials coming from the base of a crypt - There is good experimental evidence that gut bacteria actually stimulate secretion of antimicrobial peptides maintaining homeostasis

Question 264

what is the route of these natural antimicrobials? what effect do they have in each location?

Answer 264

Paneth cell = secrete natural antimicrobials -> goes into crypt lumen -> intestinal lumen -> remote locations - Crypt lumen – protect epithelial stem cells from microbial invasion and parasitation - Lumen – impact on resident microflora - Remote locations – chemoattraction or other signals for coordinated host defence

Question 265

what is an important antibody and why?

Answer 265

IgA is a GI specific antibody responsible for primary defence against bacteria - Main antibody released at mucosal surfaces

Question 266

how is IgA transported?

Answer 266

- Designed to cross the epithelium, over the mucosal layer and into the luminal space - Actively transported across the gut

Question 267

what is the single highest immune deficiency in Europeans? how common? what susceptible to? why?

Answer 267

S(secretory)IGA COATS COLITOGENIC BACTERIA WITH HIGH AFFINITY IN MICE - Lack of IgA is the single highest immune deficiency in Europeans - 1/700 people don’t make IgA - Now clear that people who don’t make IgA are susceptible to a wide range of mucosal infections - All the bacteria that IgA binds to are colitogenic (tends to produce colitis) – somehow IgA can pick out bacteria that is particularly pathogenic

Question 268

another signifinant finding in SIgA coating colitogenic bacteria?

Answer 268

SIGA COATS COLITOGENIC BACTERIA WITH HIGH AFFINITY IN CROHN’S AND UC PATIENTS Authors found: - Colitogenic bacteria were highly coated with IgA - Antigen specific IgA production - CD and UC patients each had unique bacterial populations coated with IgA - When isolated, these bacteria exacerbated colitis in mice - IgA response is insufficient to clear/neutralise bacteria - Can IgA coating be used to identify disease-promoting bacteria in individual patients?

Question 269

give a summary of the natural defences

Answer 269

- Mucus - Microbiome - Antibody But: The GI tract is also lined with a single layer of epithelial cells which delineate our host immune cells from the outside environment

Question 270

histology of the epithelium in the stomach, small and large intestine

Answer 270

all columnar epithelium

Question 271

what is found in the crypts? why important?

Answer 271

- Paneth cells which secrete the natural antimicrobials, form a nursey for stem cells (keep them healthy) at the bottom of every single crypt - Every crypt has 6 to 8 stem cells, which are there from birth, and these proliferate and then differentiate into a number of different cell types - All of which are important for maintaining homeostasis

Question 272

describe cell renewal and differentation in the epithelium. what is important to do? why useful?

Answer 272

- Stem cells - Proliferative zone - Differentiation zone Stem cells at bottom proliferate and differentiate as they move up, and once they get to the top of the crypt they sloth of Need to strike a balance between apoptosis and proliferation Damage resulting in denuding of epithelium -> restitution -> healing -> healing completed If epithelium denuded you lose all defences, so you want the stem cell proliferation rate to increase to replace the epithelium, to heal the crypt

Question 273

what is giardia intestinalis? what does it do? what is similar to it?

Answer 273

- Most common intestinal parasite found in the USA - 10-25 cysts can cause clinical disease - Pathology results from vilous atrophy (as differentiation speed can’t keep up with proliferative speed causing hyperplasia) and crypt hyperplasia (crypt gets longer) - Parasite increases enterocyte apoptosis – ultimately resulting in atrophy, malabsorption, and weight loss COELIAC DISEASE - Autoimmune response - Similar pathology to giardia intestinalis – why it’s important to maintain that balance between differentiation and proliferation

Question 274

what do macrophages and dendritic cells both do?

Answer 274

Macrophages and dendritic cells – present antigens, first cell type to mark up that there is non-self-antigens present

Question 275

compare dendritic cells and macrophages - migratory or non-migratory - what express - etc.

Answer 275

Dendritic cells: - Migratory - Excellent primers of T cells via antigen presentation - Discrete subsets with different functions - CD11b+/-CD103+/- - Derive from committed progenitor - Sample luminal bacteria? Macrophages: - Non-migratory - Express CD64, CD11b, CD11c, CX3CR1 - Replenished by blood monocytes - Phagocytes - Sample luminal bacteria?

Question 276

what do resident macrophages do?

Answer 276

- In mice, CX3CR1+ macrophages control translocation of luminal bacteria to the draining lymph node - Macrophages are defending the sub-epithelial space

Question 277

what other immune cells present in gut?lymph?

Answer 277

GUT ASSOCIATED LYMPHOID TISSUE (pop up lymph nodes) Apart from antigen-presenting cells, we also have adaptive T and B cells in the gut Have a draining lymph node, which in the gut is the mesenteric lymph node, but you also have pop up lymph nodes which are right below the epithelium – important for having a localised adaptive immune response

Question 278

describe lymphocytes in the lamina propria - what interactions - what produced - how get out of control / how controlled

Answer 278

- Antigen-presenting cell (usually a dendritic cell) interacts with a naïve CD4+ T cell - Then depending on what cytokine it gets (from the APC?), it can either become a Th1, Th2, Th17 or Treg cell - If the effector cytokines produced by the T cells are out of control and not moderated, they will cause pathology – so the Treg is really important on keeping a lid on inflammation, allowing it to happen but not too much

Question 279

what are innate lymphoid cells involved in? why are they innate? what do they have? what part of immunity are they part of?

Answer 279

INNATE LYMPHOID CELLS ARE INVOLVED IN HOMEOSTASIS AND INFLAMMATION - Don’t have T cell or B cell receptors therefore they are innate - But they have a lymphoid like progenitor - But they are very much part of the innate immune compartment and not the adaptive

Question 280

ILCs - what are derived from - what do they rely on - what does innate mean - what stimulated by - presnt as what in what numbers - how characterised

Answer 280

- Derived from common lymphoid progenitor - Rely on IL2R signalling (as do T cells) - INNATE lymphocytes i.e. no T cell receptor - Stimulated by cytokines or microbes (probably indirectly) - Present at very low numbers in steady state - Characterised as ILC1, 2 or 3 Innate lymphoid cells (ILCs) are a group of innate immune cellsthat are derived from common lymphoid progenitor (CLP) and belong to the lymphoid lineage. These cells are defined by absence of antigen specific B or T cell receptor because of the lack of recombination activating gene (RAG).

Question 281

ILC1 - what do they produce - what do they include - what do they include

Answer 281

- IFNy producers - Includes NK cells - Express T-bet

Question 282

ILC2 - what do they produce - what do they express - where seen - what do they respond do - what also called

Answer 282

- IL5/IL13 producers - Express RORalpha/GATA3 - Seen in allergy - Respond to IL25/IL33 - Also called nuocytes, natural helper cells

Question 283

ILC3 - what do they produce - what do they express - what do they respond do

Answer 283

- IL17A&F/IL22 (IFNy?) producers - Express RORy(gamma)t - Respond to IL23 - Important in fœtal lymphoid organogenesis - Important in GALT (gut-associated lymphoid tissue) formation - Important in mucosal homeostasis

Question 284

which is the really important ILC? what relevant to?

Answer 284

This is the really important one, this is what is lost as HIV patients progress to AIDS

Question 285

regulatory T cells - what essential for - where develop - what some develop in response to - what expression is critical for the suppressive function of what? - what do Tr1 T regs secrete in the absence of what? - what can T regs inhibit

Answer 285

Essential for control & homeostasis - Native T regs develop in thymus - Inducible Tregs develop in response to TGFbeta and trans retinoic acid in the periphery - Foxp3 expression critical for the suppressive function of foxp3+ T regs - Tr1 T regs secrete IL10 and TGFbeta in the absence of foxp3 T regs can inhibit both Th1 and Th2 immune responses

Question 286

Treg cells contribute significantly to homeostasis - what happens if you don't have IL10 and TGFbeta what do you end up with?

Answer 286

you end up with lots of IFNy and TNF

Question 287

why is IL10 important in mucosal deficiency? what shows this?

Answer 287

WHY IL10 IS IMPORTANT IN MUCOSAL HOMEOSTASIS: A DEFICIENCY IN IL10 RECEPTOR - Severe inflammatory bowel disease - Symptoms cured by bone marrow transplant – shows you how important IL10 receptor is it puts a break on inflammation

Question 288

what else puts a break on inflammation? examples?

Answer 288

- PD-1/PD-L1 - CTLA4/B71 OR 2 = receptors

Question 289

how do CTLA4/B7 do this?

Answer 289

CTLA4/B7 INTERACTION BETWEEN T CELLS AND ANTIGEN PRESENTING CELL STOPS T CELL ACTIVATION - When T cells and APC interact, it’s driven by interaction between CD28 (on T cell) and B7 (on APC) - CTLA4 inhibits that, allowing you to inhibit T cell responses

Question 290

how do PD-1/PD-L1 do this?

Answer 290

PD-1/PD-L1 INTERACTION REDUCES T CELL ACTIVATION PD-1 is an immune suppressive molecule to avoid over-activation - Expressed by infected cells – prevents efficient immunity to virally infected cells - Express on APCs and tissue – prevents immune recognition of self - Expressed on tumour cells – tumour evasion mechanism

Question 291

what happens when mucosal homeostass

Answer 291

- inflammatory bowel disease - Crohn's disease - tumorigenesis

Question 292

what is inflammatory bowel disease? what consist of?

Answer 292

- Ulcerative colitis (UC) - tends to present from the rectum, moving up the colon - Crohn’s Disease (CD) - can be patchy and anywhere in the GI tract

Question 293

what is Crohn's disease? what is cause?

Answer 293

``` Barrier defects: - Tight junction dysfunction - Defective neutrophil function - Reduced secretion of HD5 - Effector T cell/T reg imbalance Paneth cell defects: - NOD2 polymorphisms - Potentially affecting microbiome and response to commensal flora Dysregulation of host flora may cause disease ```

Question 294

what promotes tumorigenesis?

Answer 294

an inflammatory microenvironment

Question 295

colorectal cancer - how begin - development pace - chance of developping

Answer 295

- Colorectal cancer usually begins as a non-cancerous (or benign) polyp - A polyp - is a growth inside the colon or rectum that is not normal - can be several types - is not always cancerous - In most people, colorectal cancers develop slowly over a period of several years – 10 to 20 years - Chances of developing colorectal cancer sometime in your life: - a man has a 1 in 17 chance - a woman has a 1 in 18 chance

Question 296

how does IBD and diabetes increase your risk of having CRC?

Answer 296

Inflammatory bowel disease (IBD) includes: - Ulcerative colitis and - Crohn’s disease The overall increased risk of colorectal cancer for someone with IBD is estimated to be 4-20 times higher than normal Personal history of type 2 diabetes: - Increases your risk of having CRC and colorectal polyps by 50%

Question 297

what does an inflammatory microenvironment promote tumorigenesis?

Answer 297

- Loss of barrier function (so bacteria get in) - Pathobiotic bacteria-induced inflammation - Genotoxic bacteria-induced mutations - Dysbiosis and altered bacterial metabolites (soluble factors released by bacteria that can damage the epithelium) dysbiosis = Dysbiosis (also called dysbacteriosis) is a term for a microbial imbalance or maladaptation on or inside the body, such as an impaired microbiota

Question 298

what else affects chance of developping CRC? why?

Answer 298

``` Environment: - Radiation - Early life exposures Lifestyle: - Diet (red meat, fat) - Obesity - Physical activity - Cigarette smoking - Excessive alcohol - Metabolic syndrome Specific factors: - Age - Sex - Race - Colonic polyps = affect intestinal microbiota ```

Question 299

what promotes natural anti-tumour immunity?

Answer 299

checkpoint inhibitors - IL10 and TGFbeta – in a cancer situation you want them to try and protect your epithelium, but what you don’t want them to do is to stop fighting the cancer cells - IL10 and TGFbeta are both very important in maintaining barrier integrity - To make sure T cells are still active you can inhibit the inhibitors of T cell activation – antibody for CTLA-4 and antibody for PD-L1 – works in certain cancers

Question 300

however what can checkpoint inhibitors cause? what are examples of these inhibitors

Answer 300

significant gastrointestinal inflammation - Anti-CTLA-4 - Anti-PD-L1

Question 301

the cancer-inflammation paradigm - what is the intrinsic pathway to inflammation - what is the extrinsic pathway driven by chronic inflammation - what balance is needed?

Answer 301

Intrinsic pathway to inflammation (in tumour cells): - Normal tissue homeostasis disrupted - Sequential mutations - Epigenetic alterations - Oxidative stress (Bcl2, p53) - Proliferation/apoptosis dysregulation Extrinsic pathway driven by chronic inflammation (e.g. IBD, dysbiosis) - Inflammatory tumour microenvironment - Inflammatory cytokines (TNFalpha, IFNy, IL1, IL6) - Reduced regulatory cytokines (IL10, TGFB) - Disrupted homeostasis - Proliferation/apoptosis dysregulation  Tumour progression Need a balance so that have enough inflammation to fight things like cancer but not enough to damage epithelium??

Question 302

what is the first line of defence against pathogens?

Answer 302

- Mucus, the microbiome and antibody provide the first line of defence against pathogens - Epithelial cells play a major role in maintain the mucosal physical barrier - Immune cells maintain homeostasis via soluble and membrane bound interactions - Disruption of these factors can lead to chronic inflammation and ultimately tumorigenesis

Question 303

what is the earliest form of precancerous lesion recognisable in a biopsy? what can also be called?

Answer 303

- Dysplasia is the earliest form of precancerous lesion recognisable in a biopsy - High-grade dysplasia may also be referred to as carcinoma in situ The term carcinoma in situ is a term used to define and describe a cancer that is only present in the cells where it started and has not spread to any nearby tissues. Carcinoma in situ is the earliest stage of a cancer, and is, at this stage, considered "non-invasive." With regard to staging, carcinoma in situ is considered stage 0 cancer. Stage 1 to stage 4 are all considered "invasive" cancers, as they have spread beyond something called the "basement" membrane in tissues. When cancers are found at this stage, they should theoretically be 100 percent curable. That said, not all cancers have a CIN stage.

Question 304

what is oxaliplatin? what used for? how works? used with? how given?

Answer 304

- Used to treat colorectal cancer, oesophageal cancer, stomach cancer, and pancreatic cancer - Often used together with fluorouracil and folinic acid in advanced cancer - Given by injection into a vein - Oxaliplatin interferes with the development of DNA in a cell. This stops it from dividing into 2 new cells and kills it