Physiology of Absorption in the Stomach and Intestines Flashcards
(38 cards)
What is splanchnic circulation and what arteries supply it?
-receives 25–30% of cardiac output
- It is supplied by the celiac, superior mesenteric, and inferior mesenteric arteries
How is oxygen distributed in the liver through splanchnic circulation?
Blood from hepatic portal vein (75%) and hepatic artery (25%) creates an oxygen gradient: higher PO2 near triads, lower near central vein
**chylomicrons bypass the hepatic portal circulation
How does splanchnic blood flow change with activity?
- decreases between meals
- increases during digestion (postprandial hyperemia)
- decreases during trauma or exercise
What determines the pattern of vasodilation during digestion?
Vasodilation follows the sequence of food through the GI tract, starting with the stomach (alkaline tide)
How does exercise or hemorrhage affect splanchnic blood flow after a meal?
- triggers sympathetic activation (alpha-1 receptors), reducing blood flow to 25% of baseline
- Blood flow is compromised as the GI tract and skeletal muscles are both competing
for the blood flow
What are the effects of prolonged splanchnic vasoconstriction after severe hemorrhage?
Can cause villus tip death —> endotoxemia, multi-organ failure, and irreversible cardiovascular collapse
What is Succus Entericus and where do small bowel secretions come from?
small bowel isotonic secretions from three sources
- Brunner’s glands: alkaline mucus
- duodenal bicarbonate
- fluid from Crypts of Lieberkuhn: enzyme rich
What enzymes are released by crypt cells at the brush border?
- Peptidases, sucrase, maltase, lactase
- lipase
- DNAase, RNAase
- ***enterokinase converts trypsinogen to trypsin
Where does protein digestion begin and which enzymes are involved?
Begins in the stomach with pepsin (not essential)
- Enzymes include endopeptidases and exopeptidases.
How are amino acids and peptides absorbed in the small intestine?
Amino acids use Na⁺ gradients; di/tripeptides use H⁺-driven symport. ***Cystinuria is a genetic disorder that affects amino acid transport.
How is starch and disaccharide digestion accomplished?
- Amylase breaks starch to oligosaccharides
- Disaccharidases convert disaccharides to glucose, fructose, galactose.
How are carbohydrates absorbed in the small intestine?
- SGLT1 absorbs glucose/galactose (Na⁺-linked)
- GLUT5 for fructose (facilitated)
- GLUT2 exports all to blood.
How are lipids digested in the GI tract?
Lipases and bile salts emulsify fats
- Enzymes include pancreatic lipase, co-lipase, cholesterol hydrolase, phospholipase A2
How are lipids absorbed and transported?
- packaged into chylomicrons with ApoB and transported via lymphatics
- MTTP mutation causes abetalipoproteinemia —> fat malabsorption
Where and how is water and NaCl absorbed in the intestine?
Mostly in small intestine via villi tips
- 97.8% of fluid is reabsorbed; only 0.2L is lost
What is the main site of water and electrolyte reabsorption?
- Jejunum
- Fluid is absorbed isosmotically through paracellular pathways to maintain osmolarity
How much fluid do different parts of the bowel absorb?
Jejunum/duodenum absorb 5.5L, ileum 2L, colon 1.3L daily
- Total capacity can increase with need.
How is sodium absorbed in the intestine?
- Na⁺/glucose co-transport
- Na⁺/H⁺ exchanger
- electroneutral NaCl
- electrogenic Na⁺ transport
- paracellular drag.
What is absorbed in the ileum?
absorbs bile acids, vitamin B12, and short-chain fatty acids
What types of motility occur in the small intestine?
- fasting state uses MMCs
- fed state uses segmentation and peristalsis to move chyme caudad
How does motility change in the fed small intestine?
Increased activity helps mixing/absorption and fat slows transit rate
Three types: segmentation, peristalsis, villus movement.
What is the difference between segmentation and peristalsis?
- Segmentation mixes contents in both directions
- Peristalsis propels contents caudally using muscle coordination
How do propulsive (peristaltic) movements work?
Require ENS, triggered by stretch, and move contents toward caudad.
What causes movement of the villi?
Triggered by chyme presence, acids, fats, and vagal stimulation; increases absorption rate
