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)
what are "mass movements"?
1-3 times a day, usually after breakfast, peristaltic movements are created that force chyme/feces to rectum
-haustrations disappear and persist for 10-30 minutes
-signal urge to defecate
-increased incidence during gastrocolic reflex (after a meal)
what do factors that increase colon motility also cause?do?
diarrhea, by limiting haustra formation and increasing mass movements
what do people with ulcerative colitis have?
persistent mass movements due to irritation in colon
what do sympathetic VS parasympathetic stimulation increas?
symp: reduce motility and secretions
para: increase motility, secretions, and relaxation of internal anal sphincter
what happens if extrinsic autonomic nerves to colon removed
gastrocolic and duodenocolic reflexes (facilitate appearance of mass movement after a meal in response to distension of stomach and duodenum) are weak or absent
what is Hirschsprung's disease (megacolon)? what causes it? what are its symptoms?
congenital from lack of ENS in distal part of GIT (aganglionosis)
-aganglionic segment is tonically contracted due to inhibitory motor neuron function, so proximal segment is distended with unpassable fecal matter
-affected segment extends cranially from anus to encompass variable part of gut
-lack of propulsive movements causes early obstructive syndrome in infants (life-threatening) or severe constipation; if mild, not detected until later in life
how is Hirschprung's disease treated?
with surgery to remove affected part of colon
-after surgery, children pass stool normally
what is flatus?
derived from swallowed air, bacterial action, diffusion from blood
-each day 7-10 L enter colon
--0.6 L expelled thru anus and remainder is absorbed into blood, exhaled, or combined with fecal matter and excreted
-made of H2, N2, CO2, O2, and methane (varies with diet)
-colonic microflora is highly individual and impacts composition and net production of flatus
what does increased diet of baked beans do to flatus?
increases CO2 and methane
what is flatulence an important signal for?
-often documented by nursing staff following surgical or other procedures, showing returning to normal
what are symptoms of excessive flatulence?
IBS, lactose intolerance, celiac disease, or other organic diseases
what is feces makeup?
~100-150 g (70% water)
-has organic materials: mucus, desquamated cells, enzyme secretions, undigested food residues
-stercobilin is responsible for color
-electrolyte content extremely variable (higher in K+, lower in Na+ compared to chyme)
-bacteria make up 10% of dry weight
what is IBS?
-which people is this seen more in
-is there a cure?
common GI disease with crampy pain, bloating, gassiness, altered bowel habits (diarrhea-predominant, constipation-predominant, or alternating between both)
-no evidence of organic disorder, associated with stress, anxiety
-observed in 10-20% of population, more in females
-no cure, but not life-threatening b/c no increased risk of cancer or damage to intestine
what is fecal incontinence?
-related to trauma, injury to pelvic floor (childbirth, surgery, prolapsed rectum)
-rectophincteric reflex are typically normal, but pathology is with the external anal sphincter
-treatments include bulking agents, surgery, strengthening pelvic floor of sphincter muscles
how is the rectosphincteric reflex triggered and sensed?
distension of rectum by feces is sensed by mechanoreceptors that activate myenteric nerves
-impulses transduced to SC and back to relax internal anal sphincters
-spinal cord conveys signals to brain to stimulate defecation
-reflex actions cause voluntary contraction of external anal sphincter until defecation occurs
what happens during defecation?
EAS relaxes, person increases intra-abdominal pressure, and feces eliminated during rectum
since the intrinsic myenteric defecation reflex is weak, how does defecation work?
it needs to be fortified by another type of defecation reflex, a parasympathetic defecation reflex (sacral segments of spinal cord)