Flashcards in Colonic Phase Deck (22)
How does chyme empty from the ileum into the cecum?
Regulation of the ileocecal valve- short range peristalsis (electrical activity does not propagate through the valve) briefly opens the sphincter and allows for squirting of chyme from the ileum to the cecum
What is the primary regulation of colonic function?
Neural pathways (although not 100%)
What is the gastrocolic reflex?
Long reflex arc: distention of the stomach increases colonic motility and mass movement of fecal material --> basically moving fecal matter down the colon to make room for the food you just ate
What is the orthocolic reflex?
Movement of feces activated on rising from the bed (such as needing to poop after sleeping)
Where is peptide YY secreted?
Peptide YY is secreted from enteroendocrine cells in the terminal ileum
What is the action of peptide YY?
Peptide YY is known as the "ileal brake"- released in response to lipid in the lumen. It decreases gastric emptying and overall intestinal motility
How does peptide YY decrease gastric emptying and intestinal motility?
Reducing Cl- secretion and therefore fluid secretion. Reducing fluidity of intestinal contents reduces propulsion of the chyme
Describe the two different types of contractions in the colon
1) Shorter segmental contractions: contents are moved back and forth between haustra, maximizing content time with the epithelium.
2) High-amplitude propagating contractions- occur 10 times per day as a mass movement of feces through the colon. Meant to clear the colon
In addition to innervation from the vagus, what other nerves innervate the colon?
Pelvic nerves from the sacral spine innervate the descending colon, sigmoid colon, rectum and anal canal
Why does the colon have so many goblet cells?
Goblet cells secrete mucus. The colon requires a ton of mucus to keep feces lubricated such that it can move along
The major role of colonic epithelium is to absorb/secrete what?
Electrolytes and water (rather than nutrients)
What nutrient is absorbed in the colon?
Short Chain Fatty Acids
How are short chain fatty acids transported into the cell?
They are transported in a sodium-dependent manner
SCFA's enter the cell through Na+/SCFA symporters called Sodium monocarboxylate transporters (SMCTs)
How is sodium absorbed in the colon?
Na+ is absorbed in the distal colon through ENaC channels
What regulates sodium absorption in the distal colon?
Neurotransmitter or hormones bind to the ENaC channels and Na+ can enter the cytosol.
How is water and Cl- absorbed in the colon?
Cl- and water flow passively via tight junctions following Na+ in order to maintain electrical neutrality
Why do patients with bowel inflammation have diarrhea?
They have reduced ENaC channels- therefore more water and NaCl remains in the stool
What is the role of the enteric bacterial ecosystem?
Bacteria contribute to maintain normal GI physiology through the production of important molecules that aid in normal digestive and reabsorptive processes.
Differentiate the internal vs external anal sphincter
Internal: thick circular muscle
External: Striated muscle
What is required for defecation to occur?
Voluntary relaxation of the external anal sphincter
Why are rates of cancer higher in the colon that other tissues?
Rapid turnover of the colonic epithelium and exposure to bacterially synthesized or environmental toxins