Intestines

Question 1

Where does the final breakdown of disaccharides into monosaccharides occur?

Answer 1

brush boarder of duodenum and ileum

Question 2

What bond does amylase break?

Answer 2

1-4 glycosidic bonds (straight) in starch and glycogen

Question 3

What breaks the 1-6 glycosidic bonds which make branched chains?

Answer 3

Isomaltase

Question 4

What does alpha dextrins do?

Answer 4

break multiple close by 1-4 glycosidic bonds to create smaller clumps of amylopectin (short, branched glucose clumps)

Question 5

How is fructose absorbed?

Answer 5

through GLUT5 transporters down diffusion graidents

Question 6

How do oral rehydration tablets work?

Answer 6

Contains glucose, salt and water. Glucose stimulates increased Na+ reabsobtion via Na- Glucose co transport. More Na moving in= more water moving in with it.

Question 7

What activates pancreatic zymogens?

Answer 7

trypsin (this itself is activated in the duodenum lumen by enteropeptidase)

Question 8

What is the difference between enteropeptidases and exopeptidases?

Answer 8

Enteropeptidases= break peptide bonds in middle of chain (elastase, trypsin ect) Exopeptidases= break bonds at end of chains (carboxypeptidase A and B)

Question 9

How are amino acids/ di and tripeptides absorbed in the intestine?

Answer 9

amino acids co transported w/ sodium,di and tripeptides H+ co transport by peptide transporter 1 (and then cytosolic peptidases convert them into amino acids

Question 10

What is the difference between water absorbtion in the small intestine and the large intestine

Answer 10

Small= passive- moves with electrolytes Large= specific aldosterone induced Na+ channels (active)

Question 11

Describe the process of calcium absorbtion in the intestine when calcium stores are low/ PTH is high.

Answer 11

• Facilitated diffusion on apical side - It binds to calbidin so it can diffuse through the cell - PMCA removes it on basal side - Process requires Vit D for calbidin and PTH to stimulate it -When Ca2+ is normal/ high it just absorbes by passive, paracellular diffusion

Question 12

How is iron absorbed in the intestines?

Answer 12

Needs to be oxidised to Fe2+ (generally by HCl in stomach). The binds to DMT and enters the enterocyte If iron deficient it will bind to the transferrin channel on the basal membrane and be transported to areas in need (induced by low hepcidin) If high iron, it is complexed to ferritin and trapped in the enterocytes. It is lost when the enterocyte is replaced.

Question 13

Why can proton pump inhibitors lead to iron deficiency?

Answer 13

Stomach acid is needed to oxidise Fe3+ to Fe2+

Question 14

How are most vitamins absorbed?

Answer 14

Na+ cotransport

Question 15

Where are B12+ IF complexes absorbed?

Answer 15

terminal ileum

Question 16

What are coeliacs intolerant to?

Answer 16

Gliadin (part of gluten). This is found in wheat, rye and barley.

Question 17

What is the pathophysiology of coeliac disease?

Answer 17

An immune response is triggered, which leads to mucosa damage; loss of villi, lengthening of crypts and lymphocytes infiltrating the epithelium.

Question 18

Why do coeliacs get loos stools, bloating and flatulence?

Answer 18

Loose stools because less sugar is absorbed, meaning more osmotic stuff is left in the colon lumen so less water absorbed and more water is in the stool. This sugar is fermented by bacteria in the colon, converting it into gas, which causes the bloating and flatulence.

Question 19

What investigations would be done on someone with coeliac disease?

Answer 19

Upper GI endoscopy, colonoscopy, serology, anaemia, electrolyte imbalences

Question 20

Describe 2 macroscopic differences between large and small bowel?

Answer 20

• Large intestine has no villi, only crypts - Large intestine has no plicae circularis, but it does have sacculations called haustra

Question 21

Describe the musculature of the large intestine

Answer 21

• 3 londitudional bands (collectively called teniae coli) - intermittant circular bands come off of the teniae coli, contractions of these form the haustra

Question 22

How is water absorbed in the colon and where does it predominate?

Answer 22

By ENaC, induced by aldosterone. Mostly in the ascending and traversing colon

Question 23

Which areas are affected by crohns and UC?

Answer 23

Crohns: anywhere in GI tract but mainly terminal ileum UC: tends to start in rectum and spreads upwards, almost exclusively affects large bowel

Question 24

What is the difference in depth of legions between UC and Crohns?

Answer 24

In crohns the legions are deep and go through all the wall. In UC it tends to be superficial inflammation

Question 25

Which, of crohns and UC, has skip legions, and which has a continuous distribution?

Answer 25

Crohns has skip legions, UC is continious

Question 26

Describe some extra intestinal manifestations of inflammatory bowel disease

Answer 26

50% have arthiritis/ MSK problems 30% have skin problems (psoriasis, erythema nodosum) Some have liver and billary tree problems 5% get eye problems

Question 27

List factors implicated in triggering inflammatory bowel disease

Answer 27

Smoking Antibiotics infections Diet

Question 28

Describe the common presentation of crohns (Age, presenting complaint, bloody/ non bloody stool, any pain/ fever/ anaemia?

Answer 28

Young- peak incidence 15-30 and again at 60 PC= many (\>4) loose, non bloody stools, weight loss RLQ pain Low grade fever MIild anaemia

Question 29

Would perianal disease be seen in crohns, UC or both?

Answer 29

very rare in UC, usually crohns

Question 30

Describe the gross pathological features of crohns (eg seen on colonoscopy)

Answer 30

- Bowel looks red, raw an inflamed - Mucosal odema - Cobblestone appearance - Superfical and deep ulcers - Narrowing of lumen/ wall thickening - Fistulas

Question 31

What microscopic finding is characteristic of crohns?

Answer 31

Granulomas

Question 32

Describe the common presentation of UC (Age, presenting complaint, bloody/ non bloody stool, any pain/ fever/ anaemia?

Answer 32

Generally affects young adults PC= \>4 loose, often bloody stools p/d Weight loss Mild lower abdo pain and cramping No fever

Question 33

What microscopic finding is quite characteristic of UC?

Answer 33

crypt abcesses

Question 34

What is the name for this finding following a barium enema? What IBD does it indicate?

Answer 34

Lead pipe colon Found in chronic UC

Question 35

Other than lead pipe colon, state 4 gross pathological changes seen in UC?

Answer 35

- Chronic inflammation of lamina propria - Crypt abcesses/ ulcers/ distrosion - Pseudopolyps - loss of haustra - Flat, red and blood appearance to epithelium - Dilation of lumen/ narrowing of wall

Question 36

How can inflammatory bowel diseases be treated?

Answer 36

Aminosalicylates (for flares and maintain remission) Corticosteroids (for flares only) Immunomodulators (for fistulas and maintain remission, only used when first two dont work) Surgery

Question 37

Describe the surgical options for crohns and UC and when theyre implicated

Answer 37

For UC- colectomy will cure but only done when inflammation not settling and start to see precancerous changes. For crohns- you can remove small bits of affected bowel but this is not usually done because it just appears somewhere else