Gastric Digestion and Disease Flashcards
Functions of the stomach
- food reservoir
- food digestion (antrum mixes/grinds)
- controls passage of food to SI (pylorus regulates size/timing)
- Gastric acid secretion (+ other secretions for protection against acid)
What is required to have normal function of gastric emptying
- intact atrum, pylorus and duodenum
- Normal vagal function to co-ord activity
- normal hormonal function
How does food move through the stomach?
1- Fundus (storage) relaxes when food is about to enter, (vagus nerve), causing reflex
2- body & antrum contract together allowing food to be moved to the distal stomach
3- Pylorus is contracted (stops spillage)
4- mixing of food in antrum (retropulsion)
Abnormal Gastric emptying
Rapid GE: common post-gastric surgery, when antrum/pylorus removed> “dumping Syndrome”
Delayed GE: eg) diabetic gastroparesis due to vagal nerve damage, usually due to ANS neuropathy
Role of Gatric Acid
main role is to sterilise food, make the stomach environment hostile to bacteria (par H.pylori)
Dumping syndrome is?
nausea vomiting cramping, poop as food moves too fast stomach > duodenum, food not completely digested.
-Hyperosmolar chyme = fluid shift = intestinal distention = pain =diarrhoea
Achlorhydria
absent or low gastric acid, often related to pernicious anaemia
How is acid secreted in the stomach?
Parietal cells. Located in the body, with proton pumps to secrete HCL. Secrete ~2L/day
how does the H/K ATPase pump in the Parietal cells work and what is it for
A proton pump that actively pumps H+ from cells into stomach
H20 + CO2»_space; H+ + HCO3
in exchange K enters cell, HCO3 transported out of cell into bloodstream exchanged with Cl-.
Requires ATP
H20 + CO2»_space; H+ + HCO3
is catalysed by what enzyme
carbonic anhydrase
Why does HCO3 swap for Cl- and H+ swap for K+
because pH and osmolarity need to stay in equilibrium.
How exactly does the parietal cells secrete acid?
Tubovesicles fuse with canaliculus, increased SA and proton pump numbers increase acid secretion into lumen and gut, against a 3 mill fold conc gradient
Protective factors of the gastric mucosa?
What happens if these protective factors results in?
Mucus layer
Bicarbonate secretion
Damage to these = ulceration
ECL cells are?
Enterochromaffin-like cells
-located body of stomach, secrete histamine (paracrine activity)
Stimulates acid secretion from adjacent parietal cells
G cells
antrum of stomach
secrete gastrin
endocrine activity
(enters blood circ. binds to ECL, > histamine release > HCL release)
D cells
antrum of stomach
secrete somatostatin
endocrine & paracrine
inhibits acid secretion by acting on adjacent G cells
ACh
neurotransmitter, released by vagus and enteric neurons
Stimulates parietal, ECL and gastrin cells
Abnormal Gastric Secretion
Increased : ‘Gastrinoma’, cancer with tumours that produce gastrin> ulcers and destruction of gastric mucosa
Decreased:
-‘Pernicious anaemia’ AB against parietal cells and/or IF
-gastric surgey, body or antrum removed
-vagotomy: loss of vagus nerve > less ACh
-drugs
What are other gastric secretions
- pepsinogen
- Intrinsic Factor
- Prostaglandins
Pepsinogen?
from Chief cells
cleaved to form pepsin
pepsin degrades protein
Intrinsic Factor?
Parietal cells
B12 absorbtion
Prostaglandins
Lipid molecules to repair mucosa due to acid damage
Celiac phase
think/see/smell food
brain stimulates vagus/enteric nerve
ACh release
Parietal, HCL and G cells released
Gastric phase
- when food starts to enter the stomach
- physical digestion + AA release (stimulate G cells)
- food causes distention, stimulates enteric nerves > ACh > parietal, ECL and G
