Flashcards in Lecture 9: The Colonic Phase Deck (27):
Sections of the Large Intestine
Function of the large intestine?
digestion and absorption that was not done in small intestine
What is the important sphincter between the small intestine and large? Is it normally closed or open?
What opens the ileocecal sphincter?
peristalsis but the electrical activity of the small intestine does NOT propagate thru the ileocecal valve
What regulates colonic function?
What two reflexes influence colonic function?
1) Local (activated by passage of bolus of fecal matter - stimulate short bursts of Cl- and fluid secretion)
2) Long reflex arcs
What are the 2 long reflex arcs?
1) Gastrocolic reflex (distention of stomach, increases colonic motility)
2) Orthocolic reflex (rising from bed)
What hormone does the colon (and terminal ileum) secrete?
Peptide YY (in response to lipid in lumen)
What effects does Peptide YY have on the GI tract?
1) decreases gastric emptying and overall intestinal motility
2) reduces Cl- and fluid secretion (to reduce propulsion of chyme)
What are haustrations and how are they formed?
segments of large intestine; formed by short duration contractions
Why are haustrations important?
optimize water absorption and mixing
What is responsible for producing long duration contractions in the colon?
Where is propulsion of bolus the most vigorous?
high amplitude propagating contractions occur in healthy individuals _____ times a day from cecum to rectum to clear colon
Which autonomic branch enhances motility in the large intestine?
parasymp --> vagus controls haustrations in cecum and colon
The major role of the colonic epithelium is to absorb and secrete ____________ and ______ (not nutrients)
electrolytes and water
What special nutrient can the colon alone absorb?
Short chain fatty acids (SCFA) which are produced by colonic bacteria
How are SCFAs absorbed in the colon?
in a Na dependent fashion by symporters (Sodium Monocarboxylate Transporters SMCTS)
What key Na concentration feature is key to absorb SCFAs?
low intracellular Na (established by Na/K-ATPase)
Where is Na absorbed in the colon and how?
distal colon via ENaC (epithelial Na channel)
What opens ENaC?
neurotransmitters or hormones (Na enters the cytosol and is transported across basolateral membrane by Na/K ATPase)
How is ENaC implicated in patients with IBS?
these patients have reduced ENaC so water is not absorbed with Na (since Na is not absorbed) leading to diarrheal symptoms
True or false: The rectum contains circular muscle?
What type of muscle makes up the anal canal?
smooth and skeletal
What type of muscle makes up the internal anal sphincter?
What type of muscle makes up the external anal sphincter?