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Physiology Unit 6 > Micturition and Colonic Function > Flashcards

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
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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
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3
Q

pontine micturition center

A
  • controls detrusor and urinary sphincters

- suprapontine centers control the pontine micturition center

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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
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5
Q

nervous control of micturition-empyting

A
  • detrusor contracted, caused by PNS muscarinic
  • internal relaxed-PNS
  • external relaxed voluntarily
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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
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7
Q

abnormalities of micturition

A
  1. atonic bladder and incontinence caused by destruction of sensory nerve fibers
  2. automatic bladder caused by spinal cord damage above the sacral region
  3. uninhibited neurogenic bladder caused by lack of inhibitory signals from the brain
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8
Q

primary functions of colon

A
  1. move material through the large intestine to the rectum
  2. eliminate fecal material through the anus
  3. 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
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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
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10
Q

constipation

A
  • poor motility
  • leads to greater absorption of liquids and hard feces
  • dietary fiber promotes normal colonic function
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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
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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

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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
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14
Q

colon absorbs

A
  • Na, Cl, water

- secretes K and HCO3

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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
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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

Physiology Unit 6 (12 decks)

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