Lecture 11: Stomach (Sanchez) Flashcards
Why is it normal to have backflow into the stomach from the duodenum in horses?
They have a loose pylorus
Where do most gastric mucosa secretions occur?
fundic part of stomach
What is secreted from cardiac part of stomach?
mucuous, bicarb.
What is secreted from fundic part of stomach?
pepsin, lipase, somatostatin, histamine, HCl
What is secreted from pyloric part of stomach?
pepsin, lipase, somatostatin, gastrin
gastric glands can be comprised of many types of cells including:
mucus surface cells, mucus neck cells, enterochromaffin-like cells, parietal cells, chief cell, D cells
D cells produce:
somatostatin
ECL cells produce:
histamine
parietal cells produce:
HCl
chief cells produce:
pepsinogen, gastric lipase
G cells produce:
gastrin
Parietal cells have receptors for:
- Ach
- gastrin
- histamine (most important)
ECL cells have receptors for:
Ach, gastrin
Major mech. of secretion for parietal cells
via H/K ATPase. On the basolateral surface of the cell, Na/K, Na/H, and HCO3/Cl exchangers get K and Cl into the cell so K can be exchanged for H by H/K ATPase, ultimately allowing the free H and Cl to combine and form HCl.
What stimulates G cells?
Ach, amino acids in gastric lumen, gastric distension
What inhibits G cells?
somatostatin
What stimulates D cells?
acidic lumen (lower than pH 4)
T or F: horses are continuous acid secreters
T
Do ECL secretions (histamine) have a paracrine or endocrine effect?
paracrine
Do G cell secretions (gastrin) have a paracrine or endocrine effect?
endocrine
What stimulates ECL cells?
Ach, gastrin
What inhibits ECL cells?
somatostatin
Main stimulators of acid secretion
1) amino acids
2) protein
3) gastric distension
4) Helicobacter pylori bacteria
Main inhibitors of acid secretion
1) luminal acid
2) lower than pH 4 gastric pH
Where and under what conditions is pepsinogen converted to pepsin?
within gastric lumen if pH is lower than 4
What secretes pepsinogen?
chief cells
Is gastric lipase secreted in active or inactive form? What secretes it? What does it do?
active via chief cells. Hydrolyzes long chain fats, but is NOT essential to digestion/absorption of fats
Why is high bloodflow to the stomach important?
Digestion + High rate of turnover of gastric cells
prostaglandin upregulates:
bicarb/mucus secretion, mucosal blood flow
prostaglandin downregulates:
acid secretion
functional properties of mucins
- lubricate epithelial surfaces
- diffusion barrier
- bind bad things (i.e. bacteria)
- interact w/immune surveillance system
mucus/bicarbonate secretion stimulators
prostaglandin, CGRP, nitric oxide, bradykinin
mucus/bicarb. secretion inhibitors
NSAIDs, tachykinins
2 basic components of gastric smooth muscle activity
1) the slow wave
2) the action potential (spike) - causes actual contraction when combined with slow wave
what is the slow wave of gastric smooth m. activity?
recurring oscillation of the resting memb. potential (underlying electrical current of the muscle) that does not cause muscle contraction
fx of interstitial cells of Cajal (ICC)
located within network of pacemaker region and throughout entire GI tract to help control rate and coordination of movement of ingest through GI tract. They propagate the slow wave
Where do slow waves usually start?
the fundus of the stomach. Their amplitude and rate increases aborally (towards pylorus)
What is a terminal antral contraction?
a mixing contraction in the distal stomach against a closed pylorus. Aids in particle size breakdown
which empties out of stomach faster: liquids or solids?
liquids. They empty almost instantaneously
What is gastric receptive relaxation?
Relaxation of the stomach in preparation for consumption of a meal. As a bolus of food moves down the esophagus, lower esophageal sphincter and gastric fundus relax
What is gastric accomodation?
great ability of stomach to distend in response to a meal
What is gastric compliance?
ability of stomach to contract back down as a meal empties into the duodenum
Feedback inhibition of gastric motility is effected by 3 things
osmolality, caloric density (higher fat meals stay in stomach longer), and CCK
Compare and contrast the contents, density, and pH of the top vs. bottom of an equine stomach
top: fiber solids, low density, high pH
bottom: liquids, high density, low pH
Products of equine intragastric fermentation
lactate (from soluble CHO in low pH regions) and VFA (from insoluble CHO in high pH regions)
What part of equine GI tract is lactate at the highest lvl?
stomach, due to intragastric fermentation
