GI IX: Integrated Response to a Meal - Colonic Phase Flashcards
How is colonic function primarily regulated?
primarily through neural pathways, although not exclusively in this way
What are the different reflexes involved with colonic function?
- local reflexes: activated by passage of a bolus of fecal material, stimulates short bursts of Cl- and fluid secretion
- long reflex arcs: gastrocolic reflexes (distension of stomach incr. colonic motility and mass movement of fecal material) and orthocolic reflex (activated on rising from bed, stimulates morning urge of defecation)
Occur in healthy individuals 10 times/day from cecum to rectum to clear the colon and produce mass movement of feces:
high-amplitude propagating contractions
The major role of colonic epithelium is to absorb/secrete __________ rather than _______.
electrolytes and water; nutrients
In addition to absorbing electrolytes and water, colonic epithelium also absorb __________.
short-chain fatty acids (SCFAs) salvaged from non-absorbed carbs by colonic bacteria
Where does the colon terminate?
in the rectum at the rectosigmoid junction
Does the rectum contain circular muscle?
no, it is a reservoir for the storage of waste
What are the 2 important sphincters in the rectum?
1) internal anal sphincter: contains thick circular muscle under involuntary control
2) external anal sphincter: contains striated muscle wrapped around canal and innervated by pudendal nerves, under voluntary control
What is the purpose of the goblet cells present in the colon?
they release a lot of mucous and lubricate the tract so that feces can be smooth
How does bowel inflammation affect the transporters in the colon?
It can reduce ENaC expression, causing Na+ to be retained in the GI lumen. Water follows sodium into the lumen, causing diarrheal symptoms.
What is the function of peptide YY?
It functions as an “ileal break” by decreasing gastric emptying and overall intestinal motility, and by reducing Cl- and fluid secretion by intestinal cells (which inhibits motility).
Which cells secrete peptide YY?
enteroendocrine cells in the terminal ileum and colon
Which part of the colon do the pelvic nerves control?
descending and sigmoid colons, rectum, and anus
How are short-chain fatty acids absorbed in the colonic epithelium?
they are absorbed in the luminal side in a Na+-dependent mechanism by symporters known as sodium-monocarboxylate transporters (SMCTs)
What is the purpose of SCFAs?
they are used by colonocytes for intracellular metabolism
