Colon and Urinary Excretion - RS Flashcards
What does the pontine micturition center control? What about the suprapontine centers?
It controls the detrusor muscle and urinary sphincters. The suprapontine centers control the pontine micturition center providing voluntary control.
What is destroyed if there is an atonic bladder?
The afferents are destroyed
What is destroyed if there is an uninhibited neurogenic bladder?
The sacral nerves are destroyed. It is caused by lack of inhibitory signals from the brain
What is the order of sphincter relaxation during micturition (when you piss)?
Voiding begins with voluntary relaxation of the external urinary sphincter, followed by the internal sphincter.
What happens when a small amount of urine reaches the proximal urethra?
The micturition reflex continues as pontine centers no longer inhibit the parasympathetic preganglionic neurons that innervate the detrusor muscle. As a result the bladder contracts.
What do SNS fibers do in the micturition process?
They inhibit contraction of the detrusor (B-adrenergic response) and stimulate contraction of the internal sphincter muscles (a-adrenergic).
What is automatic bladder caused by?
Spinal cord damage above the sacral region.
What does the gastroileal reflex do?
It intensifies peristalsis in the ileum and emptying of the ileal contents into the cecum.
What does the ascending colon do?
Extracts water and electrolytes
What does the transverse colon do?
Removes electrolytes and water
What does the descending colon do?
It stores feces
Do meals mix in the large intestine?
Yes they do because of the long duration it takes feces to move through the colon
What causes constipation?
Poor motility which leads to greater absorption of liquids and hard feces.
What causes diarrhea? What about osmotic diarrhea? How about secretory diarrhea?
The rapid movement of fecal matter through the large intestine. Osmotic results from non-absorbable solutes in the lumen (e.g. lactase deficiency). Secretory results from excessive secretion of fluids by crypt cells due to bacterial overgrowth (e.g. cholera toxin)
What are common causes of diarrhea?
bacterial infections, viral infections, food intolerances, parasites, intestinal diseases, reactions to meds, functional bowel disorders, psychogenic factors, long distance running
What is the function of the ileocecal sphincter?
It prevents backflow from colon to ileum; emptying is regulated by stretch, composition & fluidity of chyme
How is the colon epithelium distinct from that in the small intestine?
The colon performs both absorptive and secretory functions. The colon lacks the numerous villi and folds that characterize the small intestine it contains numerous crypts of invaginations of the epithelium. It contains solitary lymphatic nodules but few or no Peyer’s patches. It has mucus secreting goblet cells and columnar absorptive cells.
What does the colon absorb? What does it secrete?
Absorbs Na+, Cl- and H20.
Secretes K+ and HCO3-
Major exchanges occur in the ascending and transverse colon
Are tight junctions “tighter” in the large intestine?
Yes! They offer a greater resistance to fluid flow through the paracellular pathway than the small intestine. This prevents back-diffusion of ions and allows more complete absorption of Na+
How is Na+ actively absorbed by the large intestine?
Na-H and Cl-HCO3 exchange is coupled by a change in intracellular pH that results in “electroneutral NaCl absorption” which is the primary mechanism for interdigestive Na+ absorption
What causes mass movement in the large intestine?
The gastrocolic reflex.
How is motility characterized in the large intestine?
Slow segmental propulsion, segmental mixing, and mass movements (motility is sluggish compared to the small intestine)
What is Hirschsprung’s disease?
Also called megacolon it is present at birth. It results from a lack of ENS in the distal part of the GI tract. The aganglionic segment is tonically contracted due to lack of inhibitory motor neuron function. Surgery removes the agonglionic portion and often results in normal fecal excretion. (t is analogous to the aganglionosis in the esophagus. Acholasia in the esophagus.)
What composes flatus?
Swallowed air, bacterial action, and diffusion from blood
