Flashcards in Unit 6 - Micturition and Colonic Function Deck (47)
what is micturition?
process by which urinary bladder empties when full
1. progressive filling until tension in walls rises above threshold
2. triggering reflex that empties bladder
structure of bladder
smooth muscle chamber composed of:
-rough/folded body (where urine collects)
-neck/posterior urethra (funnel-shaped extension of body that connects to urethra and includes the internal sphincter
-smooth trigone area on posterior wall of bladder between orifices of ureters
what is detrusor muscle?
smooth muscle that composes body of bladder
-contraction is major step in bladder emptying
what do the trigone and internal sphincter do?
relax during bladder emptying
-made of smooth muscle
what happens beyond the posterior urethra?
urethra passes thru urogenital diaphragm containing external sphincter
-stretch signals from posteiror urethra are strong and trigger bladder emptying reflexes, but usually inhibited and control is learned during childhood
what does the pontine micturition center do? the suprapontine centers?
control detrusor muscle and urinary sphincters
-in turn, suprapontine centers control pontine micturition center providing voluntary control
if bladder is being filled, what happens to...
DM: relaxed and controlled by sympathetic beta2
IS: contracted and controlled by sympathetic alpha1
ES: contracted and voluntarily controlled
if bladder is being emptied, what happens to...
DM: contracted and controlled by parasympathetic muscarinic
IS: relaxed and controlled by parasympathetic muscarinic
ES: relaxed and voluntarily controlled
what are some abnormalities of micturition?
1. atonic bladder and intontinence caused by destruction of sensory nerve fibers (crush injuries)
2. automatic bladder caused by spinal cord damage above sacral region
3. uninhibited neurogenic bladder caused by lack of inhibitory signals from brain
what does the colon secrete and not secrete?
doesn't secrete digestive enzymes, but produces mucus to bind feces and aid movement thru colon and protect its lining
what happens when ileocecal valve is open/relaxed?
liquid moves from SI into cecum, usually 2 L/day
-gastroileal reflex intensifies peristalsis in ileum to empty contents
what happens if there's a faulty gastroileal reflex?
reflux of bacteria into ileum, also in IBD
what are the different parts of the colon used for?
ascending: extraction of water and electrolytes, but dwell time of chyme is comparatively short
transverse: remove electrolytes and water, with long (24h) dwell time
descending: stores stool
sigmoid:move stool between descending and rectum
what are the different parts of the rectum/anus used for?
rectum: usually empty until mass movement
rectal sac: last 8 inches of colon, stores stool until eliminated thru anus
anal canal: last 2-3 inches of colon
anus: exterior opening to colon guarded by internal and external sphincters
what are the different "stages" of feces as they progress thru the colon?
what does constipation result from?
poor motility, so greater absorption of liquids, and harder feces
what does dietary fiber usually do?
promote normal colonic function
-increased colonic intraluminal bulk
-enhanced transit thru colon
what is osmotic VS secretory diarrhea?
osmotic: non-absorbable solutes in lumen (ex: lactase deficiency)
secretory: excessive secretion of fluids by crypt cells due to bacterial overgrowth
what does distension/pressure/irritation of cecum do?
inhibit ileal peristalsis and excite sphincter contraction to delay emptying
what is appendicities?
medical emergency acutely presenting as severe gastric pain followed by vomiting, then fever
-due to obstruction of appendix lumen by calcified fecal matter
-if untreated, causes ischemia, tissue necrosis, peritonitis, septicemia, and death
what is the surface epithelium of colon?
columnar with many mucus-secreting goblet cells and columnar absorptive cells, which comprise 95% of cells
-epithelial cells are polarized and have ion channels, carriers, and pumps on luminal or basolateral membrane to regulate transport of large amounts of electrolytes and water
what does the colon absorb and secrete? where do major changes occur?
absorbs: Na+, Cl-, H2O
secrete: K+, HCO3
mostly in ascending and transverse colon, removing 1.9 L/day so 0.1 L/day is left in feces
what is the main mechanism for Na+ absorption and HCO3 secretion?
parallel Na+/H+ and Cl-/HCO3- exchangers (electroneutral)
-creates osmotic gradient across intestinal mucosa for absorption of water
what is the driving force of K+ secretion in colon?
lumen-negative transepithelial voltage
-colon is net secretor of k+
-passive K+ secretion thru tight junctions that occurs throughout colon
-also active K+ secretion throughout colon intensified by aldosterone and cAMP
what is the importance of the tighter junctions in colon VS SI?
greater resistance to fluid flow ("tighter") throughout paracellular pathway than SI
-prevents back-diffusion of ions to allow more complete absorption of Na+ ions compared to SI
-enhanced by aldosterone
what happens if there are no ICCs in SI or colon?
no slow waves
how is motility in colon characterized?
slow segmental propulsion, segmental mixing, and mass movements
what are haustrations?
specialized for slow segmental propulsion and mixing to allow time for electrolyte and fluid absorption to solidify chyme
-formed by large circular muscle constrictions and constriction of taenia coli
how often do haustrations reach peak intensity?
in 30 seconds (disappearsi n next minute)