Stomach Secretions Flashcards
1
Q
why does the stomach have rugae?
A
permit large increases in volume (50–>1500mL)
2
Q
what does the stomach secrete
A
- mucus 2. HCl 3. pepsinogen 4. gastrin 5. histamine 6. ghrelin 7. intrinsic factor
3
Q
where are parietal cells?
A
in the body of the stomach
4
Q
what do parietal cells secrete?
A
HCl and intrinsic factor
5
Q
what do chief cells secrete?
A
pepsinogen
6
Q
where are chief cells?
A
in the body of the stomach
7
Q
which cells are found in the body of the stomach?
A
chief and parietal cells
8
Q
what cells are found in the antrum of the stomach
A
G cells and mucous cells
9
Q
what do G cells secrete
A
Gastrin
10
Q
what do mucous cells secrete
A
mucus and pepsinogen
11
Q
what substances are secreted in the lower esophageal sphincter and cardia?
A
mucus and HCO3
12
Q
what substances are secreted in the fundus and body of stomach?
A
H+ intrinsic factor mucus HCO3 pepsinogen lipase
13
Q
what substances are secreted in the antrum and pylorus
A
mucus and HCO3
14
Q
what do the glands in the cardia look like
A
shallow
15
Q
what do the glands in the body/fundus look like?
A
deep, deepest in the fundus
16
Q
what do the glands in the antrum/pylorus look like
A
intermediate with deep pits
17
Q
3 functional regions of the stomach
A
- cardia (overlaps LES) 2. fundus/body (secretory zone) 3. antrum (motility and mixing)
18
Q
what is the main function of the stomach?
A
as a reservoir. is not essential to digestion of a mixed meal, so can be resected. however, pt will not be able to tolerate large meals if resected bc reservoir function is lost
19
Q
what secretes Hcl and whats its function
A
parietal cell, for hydrolysis and sterilization
20
Q
what secretes intrinsic factor and what is its function
A
parietal cell, for vitamin B12 absorption
21
Q
what secretes pepsinogen and function
A
chief cells for protein digestion
22
Q
what secretes mucus and bicarb and funcitons?
A
surface mucus cells for gastroprotection
23
Q
what secretes trefoil factors and function?
A
surface mucus cells for gastroprotection
24
Q
what secretes histamine and function?
A
enterchromaffin like cells for HCl secretion – regulates gastric secretion
25
what secretes gastrin and function
G cells in antrum for regulation of gastric secretion (release H)
26
what secretes gastrin releasing peptide and function?
vagus nerve secretes bombesin for regulation of gastric secretion
27
what secretes Ach and function
nerves for regulation of gastric secretions
28
what secretes somatostatin and function
delta cells in pancreas, antrum and duodenum for regulation of gastric secretions (inhibit gastrin)
29
where are all the cells in the gastric glands?
mucous neck cell is at top
parietal cells in the middle kinda
ELC under parietal cells
chief cells under ELC
D cells under Chief cells
G cells under D cells
30
what is oxyntic?
parietal cells secrete HCl and intrinsic factor
acid secreting glands within openings (pits) to gastric mucosa
31
what transporters do parietal cells have
H/K ATPase
Cl leak
Na/K ATPase
HCO3/Cl antiport
32
describe how HCl is secreted from parietal cells
1. metabolic CO2 diffuses into gastric parietal cells where carbonic anhydrase hydrates (H2O) to form carbonic acid.
2. carbonic acid dissociates into HCO3 and H.
3. bicarb transported out of basolateral membrane into blood via Cl/HCO3 exchanger. outflow of bicarb into blood makes slight elevation of blood pH (alkaline tide)
4. Cl and K ions are transported into the lumen of the cannaliculus by conductance channels
5. H pumped out of cell in exhange for K via proton pump.
6. accumulation of H+ in cannaliculus generates osmotic gradient across membrane that results in outward diffusion of water.
33
what is the alkaline tide
the outflow of bicarb into blood out of parietal cells that increases blood pH slightly. maintains intracellular pH in parietal cell.
34
what is the gastric juice composed of after parietal cell transports?
155mM HCl
15mM KCl
small amount of NaCl
35
what triggers parietal cells to make HCl?
1. histamine (H2 receptors)
2. acetylcholine (M3 receptors)
3. gastrin (CCK2 receptors)
36
how do histamine receptors work?
increase intracellular cAMP
37
how do muscarinic rececptors work?
increase intracellular Ca levels
38
how do gastrin/CCK2 receptors work?
increase intracellular Ca levels
39
how does increasing cAMP and Ca levels impact acid?
act via protein kinases to increase the transport of acid into the stomach
40
what is cannaliculus and what does it do
deep infolding of the plasma membrane which serves to increase the surface area for secretion.
41
how are number of canaliculi impacted
they rise and fall according to secretory need
42
how is H/K ATPase pump activated?
via cAMP (histamine)
and
Ca (Ach and gastrin)
through the protein kinase pathway
43
what is unique about parietal cells
H/K ATPase is unique to parietal cells and transports H against a concentration gradient of 3mil:1
44
what is the steepest ion gradient formed in the human body?
H/K ATPase, 3 mil:1
45
where do PPI (proton pump inhibitors work)?
parietal cell H/K ATPase
inhibits H into lumen and K into cell
46
how does vagus nerve help secrete acid in stomach
vagus releases Ach (and gastrin releasing peptide) to act on M3 receptor. this increases IP3/Ca to increase action of K/H ATPase to increase HCl
47
how do G cells contribute to HCl secretion
G cells secrete gastrin. Gastrin binds to CCKb/2 receptor. increases IP3/Ca. IP3/Ca increases K/H ATPase proton pump. increase HCl
48
how do ECL cells contribute to HCl secretion
ECL cells release histamine. Histamine binds H2 receptors. H2 receptors increase cAMP to increase H/K ATPase activity. increases HCl.
49
how does somatostatin decrease HCl
D cells relase somatostatin which inhibits cAMP release. inhibits H/K ATPase. decreased HCl secretion.
50
how does atropine work?
blocks M3 receptor so vagus released ACh cannot bind.
51
how do cimetidine, ranitidine, famotidine and nizatidine work?
they are all H2 receptor blocker. prevent histamine from binding H2 to increase cAMP. decreases HCl production.
52
what are the PPIs
omeprazole prilosec
lansoprazole (prevacid)
pentoprazole (protonix)
53
what can cause pernicious anemia?
deficiency in intrinsic factor due to autoimmune attack against parietal cells
54
what does atrophic gastritis cause?
in the elderly, will cause inability to absorb B12
55
what does pepsin do
cleaves peptide bonds, breaks long polypeptide chains into shorter ones at the C terminal side of tyrosine, phenylalanine and tryptophan
56
what things promote G cells to produce gastrin?
1. peptides and HCl in stomach (just ate a meal)
2. stretch receptors stimulate vagus nerve to secrete ACh to bind M3 receptor
3. stretch receptors stimulate vagus nerve secrete gastrin releasing peptide
57
what things inhibit G cell release of gastrin
1. glucose and AA (are absorbable monomers, so that means digestion is good and ready to empty)
2. decreased pH stimulates somatostatin to inhibit gastrin and HCl release via decreasing cAMP
58
what activates pepsinogen to pepsin?
HCl
59
what causes peptic ulcers
over acidity of the stomach
60
what is the most potent at reducing gastric acid production?
PPI because that is the final common pathway of all stimulation of acid production
61
how can antacids be used for peptic ulcers?
can enhance the natural tolerance of gastric lining
62
what drugs can reduce acid secretion?1
1. antimuscarinic drugs to decrease IP3/Ca
2. antihistamines (H2) to decrease cAMP
3. PPI (most potent) to inactivate H/K ATPase proton pump
63
what occurs in pernicious anemia?
autoantibodies directed against parietal cells or intrinsic factor causes reduction in B12 absorption
64
how is pernicious anemia treated
injections of B12 (hydroxocobalamin or cyanocobalamin)
65
what is achlorhydria
autoimmune disease of parietal cells where damaged parietal cells are unable to produce the required amount of HCl (gastric acid). this results in increase of gastric pH, impaired digestion of food and increased risk of gastroenteritis
66
how does the stomach protect itself from digestion?
1. thick alkaline mucus
2. rapid mitosis to replace damaged cells
3. tight junctions between cells to prevent acid leakage
4. trefoil factors are cytoprotective
67
what fat soluble substances are absorbed in the stomach?
alcohol, aspirin, some drugs
68
what are trefoil factors?
TFF3 are small peptides found in the gut, respiratory tract and brain. function is largely unknown but TFF3 is cytoprotective!
69
what does TFF3 do?
1. protects mucosa from insults
2. stabilizes mucus layer
3. affects healing of the epithelium
70
what other factors protect stomach from self-autolysis?q
1. goblet cells (mucous surface cells) secrete mucus
2. mucous neck cells secrete mucus
3. bicarb released from parietal cells (in exchange for Cl) are trapped below mucus -- protective layer of alkaline mucus!
