oesophagus and stomach

Question 1

function of gastric pits

Answer 1

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

Question 2

what is present in gastric pits

Answer 2

mixture of cells responsible for secreting gastric juice

Question 3

what is present in gastric juice

Answer 3

cocktail of HCl, enzymes, enzyme zymogens

Question 4

3 other things cells in glands secrete

Answer 4

mucous, paracrine signalling molecules, hormones

Question 5

fuction of mucous cells

Answer 5

secrete bicarbonate-rich mucosa to protect stomach lining

Question 6

additional function of mucus lining

Answer 6

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

Question 7

function of parietal cells

Answer 7

secrete HCl into stomach

Question 8

normal state of parietal cells

Answer 8

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

Question 9

what happens when parietal cells are activated

Answer 9

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

Question 10

what is present in high abundance in parietal cells

Answer 10

mitochondria for membrane transport

Question 11

3 functions of HCl

Answer 11

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

Question 12

what is intrinsic factor

Answer 12

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

Question 13

what does intrinsic factor deficiency lead to

Answer 13

pernicious anaemia

Question 14

function and structure of chief cells

Answer 14

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

Question 15

what activates pepsinogen to pepsin

Answer 15

HCl in gastric lumen

Question 16

why is pepsinogen secreted as a precursor

Answer 16

prevent it auto digesting chief cells

Question 17

function of pepsin

Answer 17

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

Question 18

function of gastric lipase

Answer 18

digest fat by removing fattu acid from triglyceride molecule

Question 19

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

Answer 19

enteroendocrine cells, bottom of gastric pits

Question 20

function of G cells

Answer 20

release gastrin hormone into bloodstream

Question 21

3 stimuli for secretion of gastrin hormone

Answer 21

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

Question 22

function of gastrin in stomach

Answer 22

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

Question 23

function of gastrin in pancreas and gallbladder

Answer 23

increases secretion of pancreatic juice and bile

Question 24

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

Answer 24

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

Question 25

function of enterochromaffin-like cells (ECL)

Answer 25

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

Question 26

what type of cell are D-cells

Answer 26

enteroendocrine cells

Question 27

function of D-cells

Answer 27

secrete somatostatin, having an inhibitory effect on gastrointestinal function

Question 28

function of D-cells in gastric gland

Answer 28

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

Question 29

function of gastric stem cells

Answer 29

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

Question 30

2 exocrine cells of stomach

Answer 30

parietal, chief

Question 31

production of HCl in parietal cells

Answer 31

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

Question 32

what do chief cells store pepsinogen in

Answer 32

masses of apical secretion granules until stimulated to exocytose

Question 33

three phases of stomach activity

Answer 33

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

Question 34

afferents of cephalic phase

Answer 34

sight, smell, taste, thought of food

Question 35

efferents of cephalic phase

Answer 35

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

Question 36

effects of cephalic phase

Answer 36

small secretion for a few minutes

Question 37

afferents of gastric phase

Answer 37

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

Question 38

efferents of gastric phase

Answer 38

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

Question 39

effect of gastric phase

Answer 39

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

Question 40

afferents of intestinal phase

Answer 40

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

Question 41

efferents of intestinal phase

Answer 41

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

Question 42

effect of intestinal phase

Answer 42

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

Question 43

how does reduced intrinsic factor lead to pernicious anaemia

Answer 43

unable to absorb adequate vitamin B12, which limits erythropoiesis

Question 44

intestinal phase (excitatory component)

Answer 44

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

Question 45

what to drugs interfere with to decrease acid secretion

Answer 45

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

Question 46

what does omeprazole inhibit

Answer 46

H+/K+ exchange

Question 47

how does ranitidine work

Answer 47

histamine antagonist