Gastric secretion Flashcards
What is the fundus of the stomach mainly used for?
storage
List some of the stomach bodies uses
storage
Produce mucus, HCL, pepsinogen and intrinsic factor
Why is mucus important in the stomach?
To protect from acid
What is pepsinogen a precursor for and why is it stored in this way?
pepsin - to prevent autodigestion
Where is gastrin synthesised?
the ANTRUM and duodenum
What is gastrin?
A hormone produced from g cells which initiates gastric acid secretion by acting on cells in the stomach
What is the gastric pit?
The top part of the gastric gland containing the surface mucousal cells
What do the mucousal neck cells produce? What is special about these cells?
mucus
can migrate upwards to become surface mucousal cells
What are the 3 parts of the gastric gland?
mucous neck cells, parietal cells and chief cells
What do the parietal cells produce?
HCL, intrinsic factor
What do the chief cells produce?
pepsinogens
Why is it very important for the tight junctions between the cells in gastric glands to be very tight?
to prevent acid getting in
What 3 substances turn on gastric acid secretion?
Gastrin, histamine and acetylcholine
What substance turns off gastric acid secretion?
prostaglandins
What cells does gastrin work on?
parietal cells
What is released to work on the protein kinase in terms of gastrin?
calcium
Explain the similarities and differences between prostaglandin and histamine action on gastric acid secretion
Histamine is stimulatory of adenylate cyclase to convert ATP to cAMP whereas prostaglandins inhibits this process to turn on the cyclic kinase
How is acetylcholine production innervated?
By parasympathetic nerves to act on muscarinic cholinergic receptors
What messenger is used in terms of acetylcholine and gastric acid secretion?
calcium
What are the 3 broad mechanisms of gastric acid secretion?
neurocrine
endocrine
paracrine
When does the cephalic phase of digestion begin? What does this innervate?
thought, smell, sight of food and whilst eating
vagus nerve
What does the vagus nerve stimulate in the cephalic phase?
acetylcholine release
Work on g cells to form gastrin
These both work on parietal cells
What other chemical do acetylcholine and gastrin act on in the cephalic phase?
ECL cells to release histamine which also works on the parietal cells
What is the gastric phase?
food has physically entered the stomach
What does the distension of the stomach do in the gastric phase?
vagal (long) and enteric (short) reflexes releasing acetylcholine to act on parietal cells
What stimulates the G cells to release gastrin in the gastric phase?
peptides in the lumen
What stimulates histamine release in the gastric phase?
Same as in the cephalic phase - gastrin and acetylcholine work on ECL cells to promote histamine release
What inhibits the cephalic phase of producing acid?
stopping eating as this reduces vagal activity
Why does the gastric phase cease to produce acid?
pH falls as the acid is produced and this works by negative feedback and reduces gastrin secretion
What 2 things does acid in the duodenum stimulate?
enterogastric reflex
secretin release
What does acid sensed in the duodenum ultimately lead to?
reduced gastrin secretion and decreased gastrin stimulation of parietal cells
What happens when fat is sensed in the duodenum?
GIP is released to decrease gastrin secretion and parietal HCL secretion
What are enterogastrones?
Hormones released from gland cells in the duodenal mucosa
What are the 3 enterogastrones?
secretin, CCK, GIP
What 4 situations are enterogastrones released in response to?
acid ALL IN DUODENUM
hypertonic solutions
fatty acids
monoglycerides
What do enterogastrones allow?
Prevention of acid buildup in the duodenum
What 2 ways do enterogastrones prevent acid buil up?
reduce gastric motility and gastric acid secretion
What is a zymogen?
An inactive precursor
Why is pepsin stored as an inactive precursor?
to prevent autodigestion
What cells secrete pepsinogen?
chief cells
Is the pepsinogen-pepsin loop positive or negative feedback?
positive
What pH is pepsin inactivated?
neutral
What cells in the gastric gland secrete mucus?
Epithelial surface cells and mucous neck cells
In what 2 ways does mucus protect?
From injury - lubrication
From acid - bicarbonate present
What is the only essential function of the stomach?
intrinsic factor
What cells produce intrinsic factor?
parietal cells
Why is intrinsic factor needed?
Vitamin B12 absorption - prevent pernicious anaemia
Where is the vit B12 - intrinsic factor absorbed?
ileum
