Micturition and Colonic Function Flashcards
1
Q
micturition
A
- process by which the urinary bladder empties when full
- progressive filling until the tension in the wall rises above threshold
- triggering of a reflex that empties the bladder
- smooth muscles in the ureter walls contract regularly to draw urine into the bladder
- urethra passes through the urogenital diaphragm containing a layer of skeletal muscle under voluntary control (external)
- stretch signals from post urethra strong and trigger emptying until we learn control
2
Q
bladder
A
- smooth muscled chamber composed of the rough/folded body and the neck/posterior urethra
- trigone area lies on the posterior wall of the bladder between the orifices of the ureters
- body composed of detrusor muscle
- trigone and internal sphincter composed of smooth muscle that relaxes during emptying
3
Q
pontine micturition center
A
- controls detrusor and urinary sphincters
- suprapontine centers control the pontine micturition center
4
Q
nervous control of micturition-filling
A
- detrusor is relaxed, controlled by SNS beta2
- internal is contracted, controlled by SNS alpha1
- external is contracted, controlled voluntarily
5
Q
nervous control of micturition-empyting
A
- detrusor contracted, caused by PNS muscarinic
- internal relaxed-PNS
- external relaxed voluntarily
6
Q
afferent
A
- sensory fibers detect stretch in bladder wall, transmit signal to spinal cord, PNS mediates detrusor contraction and internal sphincter relaxation
- voluntary fibers control external sphincter via pudendal
7
Q
abnormalities of micturition
A
- atonic bladder and incontinence caused by destruction of sensory nerve fibers
- automatic bladder caused by spinal cord damage above the sacral region
- uninhibited neurogenic bladder caused by lack of inhibitory signals from the brain
8
Q
primary functions of colon
A
- move material through the large intestine to the rectum
- eliminate fecal material through the anus
- extract water, electrolytes and some nutrients
- colon doesn’t secrete digestive enzymes, but produces mucous to bind feces, aid its movement through the colon, and protect its lining
- ascending colon travels up right side of body and is involved in extraction of water and electrolytes
- transverse colon removes electrolytes and water
- descending colon stores stool
- sigmoid move stools between descending and rectum
- rectum is last 8 inches and stores stools
- anus is exterior opening and controlled by internal and external sphincters
9
Q
ileocecal valve
A
- separates the small and large intestine
- when open, liquid moves from SI to cecum (herbivores have large cecum)
- gastroileal reflex intensifies peristalsis in the ileum to push things into the cecum- vagus or intrinsic nerves or both
10
Q
constipation
A
- poor motility
- leads to greater absorption of liquids and hard feces
- dietary fiber promotes normal colonic function
11
Q
diarrhea
A
rapid movement of fecal matter through the large intestine
- can be fatal in infants
- osmotic- results from non-absorbable solutes in the lumen (draws water out)
- secretory- excessive secretion of fluids by crypt cells due to bacterial overgrowth
- bacterial/viral infections, food intolerances, parasites, intestinal diseases, reactions to meds, functional bowel disorders, psychogenic factors, long distance running
12
Q
ileocecal sphincter
A
-prevents backflow from colon to ileum
-emptying is regulated by stretch, composition, and fluidity of chyme
-pressure and chemical irritation relax sphincter and excite peristalsis, opens valve
-backpressure inhibits peristalsis and closes valve
2L chyme per day enter
13
Q
colon epithelium
A
- absorptive and secretory functions
- lacks numerous villi and folds that characterize the small intestine
- contains numerous crypts, solitary lymphatic nodules but few/no peyer’s patches
- surface epi is columnar with many goblet cells and columnar absorptive cells
- alkaline mucous is protection and adherent medium for binding feces
- colonic epithelial cells are polarized and contain various ion channels, carriers, and pumps, located on the luminal or basolateral membrane
- proteins regulate highly efficient transport of large amounts of electrolytes and water
14
Q
colon absorbs
A
- Na, Cl, water
- secretes K and HCO3
15
Q
exchangers for Na absorption and HCO3 secretion
A
- Na/H and Cl/HCO3 exchange is coupled by a change in intracellular pH that results in electoneutral NaCl absorption- primary mechanism for interdigestive Na absorption
- absorption of Na and Cl creates an osmotic gradient across mucosa, promoting water absorption
- colon is net secretor of K-passive secretion through tight junctions, DF is lumen neg trans epi voltage, active K secretion throughout colon (aldosterone and cAMP)
- cholera toxin increases K secretion-significant fecal loss in diarrhea
- tight junctions in the colon offer greater resistance to fluid flow through the paracellular pathway than the small intestine-prevents back diffusion of ions and allows more complete absorption of Na ions
- enhanced in presence of aldosterone
16
Q
motility in the colon
A
- segmental mixing, propulsion, mass movements
- colon contains ICCs that provide spontaneous electrical activity and other factors influence the triggering of spike/APs at the peaks of slow waves
- no slow waves without ICCs
- haustrations specialized for slow segmental propulsion and mixing, allowing time for electrolyte and fluid absorption, solidifying chyme- formed by large circular muscle constrictions and also by constriction of taenia coli
- each haustration reaches peak intensity in 30 sec and disappears during the next minute
- 1-3 times a day, mass movements create peristaltic movements that force feces toward rectum. Haustrations disappear during mass movements, they last 10-30 min
- signal urge to defecate
- following meal, increased via gastrocolic reflex (pelvic splanchnic/ intrinsic or both)
- factors that increase motility of the colon can cause diarrhea by limiting haustrae formation and increasing mass movements
17
Q
autonomic innervation of colon
A
- SNS and PNS
- SNS from spinal cord lead to celiac, sup mesenteric, and inf mesenteric gang
- reduces motility and secretion
- PNS from vagus (to transverse) and pelvic (descending colon down) nerves
- increases motility and secretions and relaxation of internal anal sphincter
- when extrinsic autonomic nerves removed, gastrocolic and duodenocolic reflexes are weak/absent
- ulcerative colitis-persistent mass movements due to irritation in the colon
18
Q
Hirschsprungs
A
- congenital
- results from lack of ENS in the distal part of the GI tract (anus)
- aganglionic segment is tonically contracted due to lack of inhibitory motor neuron functions- proximal segment (colon) becomes distended with fecal matter that can’t be passed
- affected segment extends cranially from the anus and encompasses a variable portion of the gut
- lack of propulsive movements may lead to early obstructive syndrome or severe constipation
- may not be detected until later in mild cases
- treated with surgery to remove affected portion of the colon
19
Q
flatus
A
- derived from swallowed air, bacterial action, diffusion from blood
- each day ~7-10 L enters the colon, 0.6 L expelled through the anus and remainder is absorbed into blood and exhaled or combined with fecal matter and excreted
- composed of nitrogen, hydrogen, carbon dioxide, methane, oxygen
- composition of colonic microflora is highly individual and impacts the composition and net production of flatus
- flatulence is an important signal of bowel activity, often documented by nursing staff following surgical or other procedures
- sx of excessive flatulence can indicate IBS, lactose intolerance, celiac disease or other organic diseases
20
Q
feces
A
- average weight is 110-150 g (70%) water
- contains organic materials-mucous, desquamated cells, enzyme secretions, undigested food residues, stercobilin is responsible for color
- electrolyte content is extremely variable (Typically higher in K, lower in Na compared to chyme)
- bacteria comprise 10% of dry weight
21
Q
IBS
A
- common GI
- crampy pain, bloating, gassiness, altered bowel habits
- no evidence of an organic disorder
- observed in 10-20% of pop, more common in females (20-40 yrs)
- often associated with stress and/or high anxiety
- sx treated with opioids and serotonin receptor antagonists in diarrhea predominant cases
- selective serotonin receptor agonists and/or soluble fiber in constipation predominant cases
- cramping pain symptoms treated with tricyclic antidepressants or antispasmotics
- probiotics to alter intestinal microflora are under investigation
- no cure, but not life threatening
22
Q
reflexive defecation
A
- the rectum is usually empty due to weak functional sphincter 20 cm from anus at junction between sigmoid colon and rectum
- also sharp angulation that adds resistance
- tension in the wall of the rectum signals urge to defecate
- movement of stool from sigmoid colon to rectum causes increased pressure due to passive distention
- causes active contraction of rectal smooth muscles in conjunction with relaxation of the internal anal sphincter (pelvic splanchnic)
- also voluntary contraction of external through pudendal
23
Q
fecal incontinence
A
- involuntary defecation
- often related to trauma
- injury to pelvic floor during childbirth/ surgery, prolapsed rectum
- rectosphincteric reflex is typically normal, but external anal sphincter doesn’t work
- bulking agents, surgery, and kegels
24
Q
cerebral control over defecation
A
-connections to sc
-intrinsic reflex mediated by local ENS in rectal wall (myenteric)- stretch signals peristalsis and relaxation of internal sphincter by inhibitory neurons from myenteric-weak on its own
-fortified by PNS defecation reflex-sacral segments of spinal cord
^nerve endings stim, sign to sc and back to descending, sigmoid, rectum, anus-intensify peristalsis and relax internal sphincter
-converts myenteric to a powerful process- can empty all the way from the splenic flexure
-sc also initiates bearing down- relaxes pelvic floor too
-destruction of pathways-lose voluntary control
-destruction of nerves leading to ano rectal region causes fecal retention
