The Digestive System Flashcards
(81 cards)
1
Q
What are the 6 main groups of the GI tract?
A
- oral cavity
- pharynx
- oesophagus
- stomach
- small intestine
- large intestine
2
Q
What 3 sub groups make up the oral cavity?
A
Teeth, tongue and palate
3
Q
What 3 subgroups make up the small intestine? What 2 other organs supports it?
A
- duodenum, jejunum, ileum
- secretion from liver and pancreas
4
Q
What 8 subgroups make up the large intestine?
A
- Iloilo-caecal junction
- caecum
- ascending colon
- transverse colon
- descending colon
- sigmoid colon
- rectum
- anus
5
Q
What is the tongue and how is it structured?
A
The tongue is important in mashing food against the teeth and hard palate and is divided into an anterior 2/3 and posterior 1/3
- the posterior 1/3 is the lingual tonsil
- the anterior 2/3 is covered in many taste buds
6
Q
What are the 4 different papillae controlling taste and what are the 5 main tastes?
A
The taste buds are found in relation to 4 different papillae on the dorsal surface of the tongue
- filiform papilla
- fungiform papilla
- circumvallete papilla
- foliate papilla
- sweet
- sour
- salty
- bitter
- umami
7
Q
What do the salivary glands do?
A
3 pairs of major salivary glands secrete serous (water) or mucous (thick) secretions into the oral cavity. These secretions are on demand.
8
Q
What are the parotid glands?
A
Secrete a serous fluid into the oral cavity via a very long duct
9
Q
What are the submandibular glands?
A
Secrete a seromucous fluid into the oral cavity via a long duct
10
Q
What are the sublingual glands?
A
Secrete a mucous fluid into the oral cavity via several short ducts
11
Q
What is ‘sialolithiasis’?
A
Salivary stones stuck in ducts, calcium deposits
12
Q
What is the pharynx? What are the 3 parts? What is its key function?
A
Sits posterior to the oral cavity and is divided into 3 parts -
- nasopharynx
- oropharynx
- laryngopharynx
Allows food from the oral cavity to reach oesaphagus
13
Q
What are the 3 muscles found in the pharynx?
A
The pharynx comprises a set of 3 constrictor muscles stacked on top of each other - when they squeeze, food moved inferiorly towards the oesophagus
- superior constrictor
-middle constrictor
- inferior constrictor
14
Q
What is the oral cavity? What is the structure of the oral mucosa?
A
- hard palate, soft palate, uvula
- gingivae (gums), palatine tonsil
- opening of submandibular duct
- stratified squamous epithelium
- squamous = flat, stratified = many layers
Oral mucosa
- basement membrane (oral epithelium)
- lamina propria
15
Q
What are the 3 basic region of the oral cavity (oral mucosa)?
A
- masticatory mucosa (gingivae and hard palate)
- stratified squamous epithelium (very strong)
- specialised mucosa (surface tongue)
- incorporates taste buds
- ordinary lining mucosa (everywhere else)
- stratified squamous non-keratinised epithelium (strong)
16
Q
What is the oesophagus?
A
A muscular tube which carriers masticated food from the pharynx to the stomach, passing through the diaphragm to enter the abdomen
17
Q
What are the 2 important transitions in the oesophagus?
A
1) Muscular skeletal (voluntary) muscle in superior portion smooth in inferior and mixed in the middle
2) Histological - epithelial transitions sharply from SSNK to simple columnar in stomach @ gastro-oesophageal junction
18
Q
What is Barrett’s Oesophagus?
A
A condition involving abnormal metaplastic changes in the distal oesophagus, with the normal stratified squamous epithelium being replaced with stomachs simple columnar epithelium.
This condition predisposes cancer.
19
Q
What are the key functions of the stomach?
A
- breakdown solid food into semi solid chyme (mechanical/chemical)
- deliver chyme to the duodenum
-digest protein (some) using pepsin - regulate rate of passage into the duodenum
- create intrinsic factor (required for B12)
20
Q
From the top, what are the key features of the stomach?
A
- oesophagus
- cardia sphincter
- fundus (air bubble)
- lesser curvature
- body (muscularis externa)
- greater curvature
- ruggae on surface
- pylorus sphincter
21
Q
What is found at the 2 ends of the stomach?
A
- the proximal end is guarded by the lower oesophageal (or cardiac) sphincter
- continuation to the duodenum is regulated at the distal end by the pyloric sphincter
22
Q
What are the key features of the hollow tube structure?
A
- adventitia/serosa
- mucosa (epithelium, lamina propria, muscularis mucosae)
- sub mucosa
- muscularis externa
- extrinsic gland (eg pancreas, liver)
- mucosal gland (eg gastric gland)
- sub mucosal gland (eg brunners)
23
Q
Describe the structures and functions of the gastric pit
A
Mucus layer - large amounts of mucus needed to protect gastric epithelium from low pH
Surface mucus cells - these are called secretory sheet
Parietal cells - produce HCl+ intrinsic factor
Mucus neck cells
Endocrine cells - includes G cells producing gastric (protein), D cells producing somatostatin
Chief cells - produce pepsin
24
Q
What 2 plexi forms the enteric nervous system?
A
- Meissners Plexus is associated with the muscularis mucosae of the mucosal layer and regulated fluid absorption as well as blood flow
- Averbachs plexus is associated with the muscularis externa and regulates motility in the GI tract
25
What is Zollinger-Ellison syndrome?
Examples of stomach (peptic ulcers) as a result of damage by stomach acids
Eg Zollinger-Ellison syndrome where an neuroendocrine tumour causing excessive gastric secretion drives overproduction of HCl, eroding the mucosa to cause gastric ulcers
26
What are the 3 components of the small intestine? What are they responsible for?
The small intestine has 3 components -
In order from proximal to distal:
1) duodenum (-25cm long)
2) Jejunum (-1m long)
3) Ileum (-2m)
The small intestines are very tightly folded in the abdomen and the 3 components are structurally all quite similar
- the small intestines are principally responsible for the absorption of products of digestion into the blood lymph
27
What is the duodenum and what does it do?
- receives chyme from the stomach
- forms a characteristic c-shape, wrapping around the head of the pancreas
- protected from acid by lots of mucus glands
28
Name the structures of the duodenum and the structures found immediately around it.
- pyloric sphincter
- superior part
- descending part
- horizontal part
- ascending part
- gall bladder located behind
- pancreas located in the middle
- main pancreatic duct
- hepatopancreatic ampulla of vater duct behind
29
What enters the GI tract at the duodenum? Where is this originally formed?
Secretions from liver and pancreas enter the GI tract at the duodenum
- bile produced in the liver and stored in the gall bladder
- pancreatic juice and digestive enzymes produced by the pancreas
30
What is bile? Where is it produced and stored? What does it do?
Bile is produced in the liver and stored in the gall bladder
- bile acts as a surfactant and aids emulsification of fats within the chyme
- secreted continuously
31
What type of digestive enzymes are produced by the pancreas?
Pancreatic juice and digestive enzymes produced by the pancreas
- includes digestive enzymes (eg trypsin, chymotrypsin, amylase, lipase) plus bicarbonate ions to neutralise stomach acid
- secreted intermittently
32
Where does bile and pancreatic juice enter the duodenum?
Both bile and pancreatic juice reach the duodenum through a shared duct emerging from the second (descending part) of the duodenum
33
What happens when chyme enters the duodenum?
- the sphincter guarding the ampulla relaxes
- the gall bladder contract
- bile and pancreatic juice exit into the duodenum and mix with the chyme
34
What are gallstones?
Example of gall stones - cholelithiasis - made of calcium and can block up entire gall bladder
35
What are the 3 folds found on the surface of the intestines?
1) Pilicae circularis (circular folds) - a feature of a the sub mucosa
2) villi - a feature of the mucosal layer
3) Microvilli - forming a brush border - a feature of the apical plasma membrane
36
What happens in the jejunum and ileum? What mechanism propels food along? What is the key feature of them both?
- principle site of nutrient absorption in the GI tract
- peristalsis propels digested food along the track with movements under the control of Aubachs plexus
- absorption is most important here to several specialisations to the epithelium of the jejunum and ileum - all of these work collectively to increase surface area
37
What is the environment like on the lining of the small intestine? What is needed because of this?
The lining of the small intestine is a very harsh and hostile environment, enterocytes only live a few days
- a pool of stem cells to replace cells being sloughed off is required
- these are found in the crypts of lieberkuhn, invaginaions between villi
38
What is the epithelium of the small intestine like? What is the key cell type here?
The epithelium itself is simple cuboidal and compresses enterocytes - intestinal absorptive cells specialised for breakdown and transport of small molecules derived from lipids, proteins and carbohydrates as well as water electrolytes and vitamins
39
What is the Ilio-caecal junction and the appendix?
The junction between the ileum and the caecum is the transition from the small intestine to the large intestine
- the caecum is the first part of the large intestine and food arrives at this point 3-4hrs after swallowing. Entrance to the caecum is guarded by the ileo-caecal valve
- the true function of the appendix is unknown. it is a blind-ended tube projecting from the caecum which has a highly variable position and length
40
What do parietal cells in the stomach produce? What binds to this? What can lack of this substance lead to?
- parietal cells in stomach produce intrinsic factor IF
- in the small intestine, vit B12 binds to IF
- B12-IF complex absorbed by enterocytes in the terminal ileum
- B12 is required for erythrocyte proliferation and differentiation
- as a consequence, vit b12 cannot be as easily absorbed in the terminal ileum and defection enterocytes form, leading to anaemia
- in pernicious anaemia there is often autoimmune attack on parietal cells leading to to reduced production of IF
41
What is the large intestine? What does the longitudinal muscle form?
- the large intestine spans from caecum to anal canal with a total length of 1.6m
- the longitudinal muscle layer forms 3 ribbons of muscle the contracted intestine then forms bulges known as haestra
- ileum
- ilea-caecal valve
- caecum
- appendix
- ascending colon
- transverse colon
- descending colon
- sigmoid colon
- rectum
42
What is the physiology of the large intestine?
- most nutrient absorption is completed by the small intestine so the major function of the large intestine is the absorption of ions and water
- peristalsis continues, mixing and advancing contents, aided by strong waves 3-4 times a day
- around 12 hours after eating, material reaches the end of the large intestine
- around 24 hrs post-eating, contents move into the rectum, stimulating the need to defecate
43
What is a key difference between the LI and SI?
- less absorption in LI so no need for 3 layers, but there are crypts of lierbukn present
- abundant goblet cells
- no villi or plicae on surface epithelium
44
How can bowel cancer form?
Examples of bowel (colorectal) cancer with polyps (growth of tumour) separating from the epithelium into the lumen of the GI tract
45
What is the anal canal and what is the 3 step process that occurs in it? What is the histological transition present?
- the rectum remains empty until it receives faeces from the sigmoid colon. When the rectal walls distend, defection is triggered, involving a 3 step process -
1) contraction of the colon
2) relaxation of he involuntary anal sphincter
3) relaxation of the voluntary anal sphincter
transition from simple columnar epithelium of the intestines back to the stratified squamous non-keratinised (SSNK) epithelium
46
Describe the structure of the anal canal.
- mucus membrane
- internal sphincter (involuntary)
- external sphincter (voluntary)
- anus
47
What is the role of the stomach? What are the 3 phases of secretion?
Regulation of gastric secretion and motility
- regulated by combination of nervous and hormonal factors
3 phases of secretion
1) cephalic
2) gastric
3) intestinal
48
What is the cause and effect of the cephalic phase?
Cause - sensation and thoughts
Effect -
cerebral cortex/hypothalamus
parasympathetic - vagus (x cranial nerve)
49
What happens in the gastric phase? What is the role of gastrin?
neural negative feedback -
- stretch receptors and chemoreceptors rated via the submucosal plexus - peristalsis stimulated
Hormonal negative feedback mechanisms - emptying
- distension, partly digested proteins, caffeine, stimulate the 9 enteroendocrine cells
Gastrin secretion is:
- inhibited at pH<2
- stimulated when pH rises
Gastrin is transported in the blood to the gastric glands
- stimulates gastric secretions
- contraction of lower oesophageal (cardiac) sphincter
- increased motility
- relaxes pyloric sphincter
50
How is HCl secretion controlled by parietal cells?
- stimulation by 3 signal chemicals
- gastrin, acetylcholine, histamine
- all 3 needed for strong H+ secretion
51
What is the intestinal phase?
Enterogastric reflex (enterogastrone secretion)
- enteroendocrine cells in the small intestine release:
- cholecystokinin (CCK)
- gastric inhibitory peptide (GIP_
- secretin
They all inhibit gastric secretions
52
What is the mechanism behind secretion of juices from the pancreas?
1) parasympathetic impulses along vagus (x) nerves
2) stimulation secretion of pancreatic enzymes
3) Acidic chyme containing partially digested fats (fatty acids) and proteins (amino acids)
4) CCK and secretin
5) stimulates secretion of the pancreatic juice rich in bicarbonate ions
6) stimulates secretion of pancreatic juice rich in digestive enzymes
53
What is the mechanism behind secretion of bile in the liver?
1) Parasympathetic impulses along vagus (x) nerves stimulates bile production by liver
2) fatty acids and amino acids in chyme entering the duodenum simulate secretion of cholecystokin (CCK) into blood - acidic chyme entering duodenum stimulates secretion int blood
3) CCK causes contraction of gallbladder
4) secretin enhances flow of bile rich in HCO3- from liver
54
What are the 5 satiety signals to slow gastric emptying?
- cholecystokinin (CCK)
- glucagon-like peptide-1
- Peptide YY (PYY)
- lepton
- insulin + oestrogen
55
What is the role of cholecystokinin (CKK)?
- secreted in response to food
- reduces appetite and inhibits eating
- in hypothalamus neurotransmitter to inhibit eating
56
What is glucagon-like peptide 1?
From intestine in response to food
57
What is peptide YY (PYY)?
From intestine, in response to food
58
What is leptin?
From white adipose tissue
59
What are peripheral hunger signals mediated by?
Mediated by ghrelin
- only GIT hormone to increase food intake
- secreted by endocrine cells of gastric mucosa
- increases hunger, growth hormone secretion and fat stores (anorexegenic)
60
What is the melanocortin system?
- peptides adrenocorticotropin and melanocyte-stimulating (MSH) hormones
- anorexigenic
- occurs in arcute nucleus of hypothalamus, integrates long and short term signals
- activated by POMC and CART, inhibited by NPY and AgRP
61
What are the NPY/AgRP neurons?
- neurons are suppressed by insulin and leptin
- stimulation releases NPY and AgRP (removal of inhibition)
- neurotransmitters in hypothalamus
- NPY - activates its receptor which are GPCR, stimulates eating
- AgRP - binds to and inhibits MC4R, inhibits anorexigenic effects of alpha-MSH
62
What are the 2 hormones stimulated by leptin?
POMC - pro-opiomelanocortin
CART - cocaine-amphetamine regulated transcript
63
What are the 4 parts of ruminant anatomy?
- reticulum
- omasum
- abomasum
- rumen
64
What is the rumen?
10-20% live weight
- cows produce -150L of saliva/day
- contents are 85% -93% water
- ruminal papillae
- stratified squamous epithelium (keratinised)
- absorption still occurs here
- cows spend -8hrs a day grazing and 8 hrs ruminating
65
What is the process of rumination?
- material drawn back into the oesphagus and muscle contractions return to mouth
- liquid rapidly re-swallowed, coarse material chewed again before swallowing
- each bonus chewed 40-50 times
66
What are reticulo-rumen micro-organisms?
The rumen and reticulum provide a culture system for micro-organisms
- over 200 species identified so far
- mostly anaerobic bacteria and fungi
- symbiotic relationships
- heterotrophic and autotrophic (inc. methanogens)
- chemostat
- complex interrelationships
67
How do different/fungi breakdown different food sources? What does fermentation produce?
eg high carbohydrate feed increases the number of lactobascilli
Fermentation produces volatile fatty acids (VFAs) which are absorbed, gas and more microorganisms
- more than 30L/hr of gas
68
What are the structural changes of the ruminant system during development?
- at birth, the abomasum is the largest chamber
- at 18 months, reticulorumen occupies >90% of the stomach
69
What is the recticulum?
- keratinised stratified squamous epithelium
- particle sorting
- muscularis mucosa (around top of each compartment, aids seperation, mixing and breakdown)
- keratinised
70
What is the omasum?
- regulates entry of food into the abomasum
- many return food to the reticulo-rumen
- water and VFA absorption
71
What is the abomasum?
- true stomach - like the fundus, broadly the same as humans
- oesophageal groove, simple columnar, glandular (gastric pits), parietal
72
What is cellulose?
A chain of glucose units bound by beta 1-4 linkages
intramolecular H bonds
- decreased flexibility
- increased tensile strength
- decreased solubility in water or dilute acid
Intermolecular H bonds
- allows the development of a crystalline lattice
73
What is hemicellulose?
- a mixture of pentose, hexose, ironic acids bound to a beta-1,4 linked core composed primarily of xylose
- closely bound to lignin
74
What is lignin?
A poorly defined polymer of phenylpropane
- binds to hemicellulose only
- forms a matrix around cellulose
- increased strength under compression
Lignification
- significant factor in reducing digestibility
75
What are the 3 ways cellulose is digested?
90% of cellulose digestion is in the recticulum
Transport of bacteria to fibre -
- slow
- dependent on number of bacteria
Non-specific adhesion of bacteria to sites on substrate
- most commonly at cut or macerated areas
Specific adhesions of bacteria with digestible cellulose
- cellulosome: large, multenzyme complexes for adhesions and hydrolysis of cellulose
76
How is protein digested in ruminants?
- microorganisms in the reticulum
- most of the protein that reaches the abomasum will be of microbial origin
- there is an optimum level of ammonia in the reticulum
(Can add urea to the diet from which they can make amino acids)
77
What is starch?
- chief storage polysaccharide in plants
- 2 components
- amylose (glucose units bund by a-1,4 linkages)
- amylopectin (glucose units by a-1,4-linkages with a-1,6 branch points)
78
How is starch digested in ruminants?
Rumen: 47%-95% digested
- digested by alpha amylase to oligosaccharides
(70% associated with particulate-bound organisms)
Oligosaccharides are degraded to glucose -
- Protozoa uptake
- bacterial uptake
- may account for up to 50% of carbohydrate leaving rumen
79
What are the end products of microbial carbohydrate digestion in ruminants?
- VFA
- heat
- gas
- microbial mass
70% of glucose required comes from VFAs
20% from protein
Protein = propionate, acetate, butyrate
80
What are the advantages of rumination digestion?
- utilise feeds too fibrous for non-ruminants
- uses the most abundant carbohydrate
- produces high quality microbial protein from NPN
- produces vitB complexes (co-required)
81
What are the disadvantages of ruminant digestion?
- complex mechanism
- large quantities of alkaline saliva needed
- large amounts of gas produced
- needs powerful mechanical breakdown
- metabolic adaptions for VFA use
