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LSS Alimentary System > oesophagus and stomach > Flashcards

oesophagus and stomach Flashcards

gastric gland: recall the structure and function of a typical gastric gland and its constituent cells (including mucous cells, parietal cells, chief cells, enteroendocrine cells and epithelial stem cells)

1
Q

function of gastric pits

A

lead to multiple gastric glands which house functional secretory cells of stomach

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2
Q

what is present in gastric pits

A

mixture of cells responsible for secreting gastric juice

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3
Q

what is present in gastric juice

A

cocktail of HCl, enzymes, enzyme zymogens

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4
Q

3 other things cells in glands secrete

A

mucous, paracrine signalling molecules, hormones

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5
Q

fuction of mucous cells

A

secrete bicarbonate-rich mucosa to protect stomach lining

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6
Q

additional function of mucus lining

A

protect stomach lining from active lipase and protease (may interfere with bilayer and transmembrane proteins)

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7
Q

function of parietal cells

A

secrete HCl into stomach

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8
Q

normal state of parietal cells

A

quiescent (sleeping) state until activated; cytoplasmic tubulovesicles which contain H+/K+ ATPase; internal canaliculi which extend to apical surface (appear like empty reservoirs)

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9
Q

what happens when parietal cells are activated

A

tubovesicles in cytoplasm fuse with small invaginations on apical surface, making complicated canalicular surface, which has a high SA for HCl secretion

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10
Q

what is present in high abundance in parietal cells

A

mitochondria for membrane transport

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11
Q

3 functions of HCl

A

kill ingested pathogens, activate protease zymogens, alter protein structure to help digestion

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12
Q

what is intrinsic factor

A

glycoprotein essential for absorption of vitamin B12, secreted by parietal cells

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13
Q

what does intrinsic factor deficiency lead to

A

pernicious anaemia

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14
Q

function and structure of chief cells

A

produce protease zymogen (pepsinogen) and a lipase (gastric lipase); abundant rough ER; Golgi packaging and modifying for export

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15
Q

what activates pepsinogen to pepsin

A

HCl in gastric lumen

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16
Q

why is pepsinogen secreted as a precursor

A

prevent it auto digesting chief cells

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17
Q

function of pepsin

A

break dietary proteins into smaller peptide chains, autocatalysis back into pepsinogen

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18
Q

function of gastric lipase

A

digest fat by removing fattu acid from triglyceride molecule

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19
Q

what type of cells are G cells, and where in gastric pits are they located

A

enteroendocrine cells, bottom of gastric pits

20
Q

function of G cells

A

release gastrin hormone into bloodstream

21
Q

3 stimuli for secretion of gastrin hormone

A

vagus nerve stimulation, presence of peptides in stomach, stomach distension

22
Q

function of gastrin in stomach

A

stimulates gastric secretion and motility, leading to stronger contractions and the opening of pyloric sphincter to move food into duodenum

23
Q

function of gastrin in pancreas and gallbladder

A

increases secretion of pancreatic juice and bile

24
Q

what type of cell are enterochromaffin-like cells (ECL), and where are they located in the gastric glands

A

neuroendocrine cell deep in gastric gland, in vicinity of parietal cells

25
Q

function of enterochromaffin-like cells (ECL)

A

secrete histamine from chromaffin cells (lamina propia), stimulating secretion of acid from parietal cells

26
Q

what type of cell are D-cells

A

enteroendocrine cells

27
Q

function of D-cells

A

secrete somatostatin, having an inhibitory effect on gastrointestinal function

28
Q

function of D-cells in gastric gland

A

inhibits ECL production of histamine and parietal cell activity, inhibiting HCl secretion

29
Q

function of gastric stem cells

A

pluripotent so capable of differentiating into all cells of stomach under influence of different factors

30
Q

2 exocrine cells of stomach

A

parietal, chief

31
Q

production of HCl in parietal cells

A

CO2 diffuses in down gradient → combined with water in presence of carbonic anyhdrase → forms carbonic acid → dissociates into bicarbonate and H+ → exchange of bicarbonate for Cl- interstitial space → Cl- move down gradient into stomach lumen via Cl- channels → Na+/K+ exchanger in basolateral membrane and Cl- channels in apical membrane allow H+ to be pumped into lumen → K+ pumped into cell in exchange for H+ → K+ re-enters lumen → secreted H+ combines with Cl- to form HCl

32
Q

what do chief cells store pepsinogen in

A

masses of apical secretion granules until stimulated to exocytose

33
Q

three phases of stomach activity

A

cephalic (stimulatory), gastric (stimulatory), intestinal (inhibitory)

34
Q

afferents of cephalic phase

A

sight, smell, taste, thought of food

35
Q

efferents of cephalic phase

A

vagus nerve produces acetylcholine which stimulates histamine, switching on HCl production (stimulate secretion from mucous, chief, parietal and G-cells via submucosal plexus)

36
Q

effects of cephalic phase

A

small secretion for a few minutes

37
Q

afferents of gastric phase

A

distension of stomach and chemoreception of nutrients and reduced pH which stimulate local nerves

38
Q

efferents of gastric phase

A

vagus nerve stimulate secretion from mucous, chief, parietal and G-cells via submucosal plexus and increase motility via myenteric plexus, releasing more mucus, acid and pepsin

39
Q

effect of gastric phase

A

3-4 hours gastric activity (secretion of acid, enzymes and hormones) and mechanical digestion

40
Q

afferents of intestinal phase

A

duodenal stretch and chemodetection of reduced pH, duodenal distension and chemical constituents

41
Q

efferents of intestinal phase

A

enterogastrine reflex: I-cells secrete cholecystokinin (CCK) and S-cells secrete secretin into blood, decreasing parietal cells secretion and inhibiting gastric motility and emptying; stretch receptors input into enteric nervous system, reducing stomach activation; gastric inhibitory peptide also released

42
Q

effect of intestinal phase

A

gastric emptying slows fown allowing downstream organs to deal with current contents

43
Q

how does reduced intrinsic factor lead to pernicious anaemia

A

unable to absorb adequate vitamin B12, which limits erythropoiesis

44
Q

intestinal phase (excitatory component)

A

dependent on protein concentration of duodenum - if protein concentration high, stomach hasn’t effectively broken down proteins, so gastrin secretion to stimulate acid secretion

45
Q

what to drugs interfere with to decrease acid secretion

A

acetylcholine, histamine, gastrin; target acid producing machinery in parietal cells (e.g. carbonic anhydrase)

46
Q

what does omeprazole inhibit

A

H+/K+ exchange

47
Q

how does ranitidine work

A

histamine antagonist

LSS Alimentary System (40 decks)

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