Physio - Vallano - Peeing and Pooping - 2/24 Flashcards
Contraction of what major muscle is critical to micturition?
Detrusor muscle, smooth muscle in the bladder. (PNS activation when emptying, S activation when holding it)
Note that the trigone and internal sphincter are also smooth muscle, but relax during bladder emptying.
What part of the brain controls the detrusor muscle?
Pontine micturition center, controls detrusor muscles and urinary sphincters.
Suprapontine centers exert tonic inhibition (PNS) over the pontine micturition center providing voluntary control.
_____ fibers inhibit contraction of the detrusor (beta-adrenergic response) and stimulate contraction of the internal sphincter muscles (alpha-adrenergic)
SNS
Why does LMN damage lead to neurogenic bladder where you cannot empty?
PNS innervation, for voiding, comes through the splanchnic nerves at S2-S4, but the SNS controls holding it, and they come off at T11-T12, so if you get hurt in between there, neurogenic bladder can result in which you cannot void.
In what part of the colon is the dwell time the longest for chyme?
Transverse colon, can be up to 24 hrs.
What is the result of poor motility through the colon?
Hard poops bc too much absorption occurs
What are the two forms of diarrhea?
- Osmotic - results from nonabsorbable solutes in the lumen, ie lactose intolerace
- Secretory - excessive secretion by crypt cells due to bacterial overgrowth or cholera, ie.
When is the gastroilieal reflex activated?
When food enters the empty stomach
It intensifies peristalsis of the small intestine, relaxes theileocecal sphincter and promotes passage of the material from ileum to colon.
What is the common cause of appendicitis?
Obstruction of the appendix lumen by calcified fecal matter
What does the colon contain in lieu of villi? Peyer’s Patches?
Crypts instead of villi
Solitary lymph nodes scattered but no Peyer’s Patches
T/F: The colon absorbs Na+, HCO3- and H2O, and secretes K+ and Cl-.
FALSE. The colon absorbs Na+, Cl- and H2O, and secretes K+ and HCO3-.
Severe hypokalemia, for example due to prolonged diarrhea, can lead to:
Cardiac arrhythmia
What is the primary mechanism for interdigestive Na+ absorption?
“Electroneutral NaCl absorption”
Na-H exchanger and the Cl-HCO3 exchanger, which promote water re-absorption.
How does aldosterone influence water reabsorption in the colon?
It increases the # of Na+ channels in the colon. Water and Cl- follow passively through tight junctions.
T/F: The large intestine contains interstitial cells of Cajal.
True
What are haustrations? In what disease are they absent?
Haustrations are formed by large circular muscle contractions and constriction of 3 flat bands of taenia coli. They are specialized for slow segmental propulsion and mixing.
Haustrations are missing in ulcerative colitis, at least in the distal colon.
Following a meal, the gastrocolic reflex results in:
increased incidence of “mass movements”
T/F: Parasympathetic stimulation results in relaxation of the internal anal sphincter.
True
What would happen if extrinsic autonomic nerves to the colon were removed?
The gastrocolic and duodenocolic reflexes, which facilitate appearance of mass movements after a meal in response to distension of the stomach and duodenum, respectively, would be weak or absent.
Aganlionosis is also known as:
Hirschsprung’s disease, lack of ENS in the distal part of the GI tract, leads to early obstruction in infants.
A 17-year-old male presents with urethral burning following urination. He is asked to provide a urine sample and swabbed to test for a possible bacterial infection. Which of the following is responsible for initiating micturition when providing a urine sample?
a) Pontine micturition center
b) Uroepithelial mechanoreceptors
c) Spontaneous detrusor contractions
d) Rising intravesical pressure
e) Internal urethral sphincter relaxation
a) Pontine micturition center
Voiding is initiated and coordinated by the pontine micturition center, which relaxes the internal (involuntary) urethral sphincter and facilitates detrusor muscle contraction once voluntary relaxation of the external urethral sphincter has occurred. Although internal sphincter relaxation is required for urine flow, it does not initiate voiding. Uroepithelial mechanoreceptors trigger spontaneous detrusor contractions when intravesical pressure rises during bladder filling, but bladder emptying is suppressed by the pontine micturition center until voiding is convenient.
A 28-year-old woman recently gave birth to her second child by cesarean delivery. She is now experiencing both urinary and fecal incontinence during straining maneuvers. A pudendal nerve conduction test indicates that the pudendal nerve is the cause of the fecal incontinence. Which sphincter is most likely affected?
a) Pyloric
b) Ileocecal
c) Rectosigmoid
d) Internal anal
e) External anal
e) External anal
The pudendal nerve innervates the external anal sphincter, which is a skeletal muscle under voluntary, somatic motor control. The internal anal sphincter is composed of smooth muscle and is innervated by the pelvic nerves and under involuntary control. The pyloric sphincter regulates gastric emptying into the duodenum. The rectosigmoid is a junction rather than a sphincter. The ileocecal valve controls movement of waste materials between the small and large intestines but is not directly involved in defecation.
A 4-week-old boy was brought to the emergency department in a semiconscious state. He was severely dehydrated and an electrocardiogram showed abnormal waveforms. The boy’s parents reported that he had severe acute diarrhea that had worsened over the past 24 hours. No vomiting had occurred. They had tried to treat the child with fluids orally. Serum analysis revealed a potassium concentration of 1.9 mM. Which mechanism accounts for severe hypokalemia in this case?
a) Excess secretion of potassium in the small intestine
b) Excess secretion of potassium in the large intestine
c) Failure to absorb potassium in the small intestine
d) Failure to absorb potassium in the large intestine
b) Excess secretion of potassium in the large intestine
Potassium secretion in the distal large intestine occurs through tight junctions, and is driven by a lumen negative tranepithelial voltage. There is also active K+ secretion throughout the colon. The delivery of increased amounts of sodium and fluid to the large intestine in diarrhea drives excess K+ secretion because it drives more Na+ uptake, depolarizing the apical membrane and thus increasing the driving force for K+ secretion through tight junctions.
In infants, defecation often follows a meal. The cause of colonic contractions in this situation is:
a) histamine
b) increased circulating levels of CCK
c) the gastrocolic reflex
d) increased circulating levels of somatostatin
e) the enterogastric reflex
c) the gastrocolic reflex
The gastrocolic reflex may initiate a mass movement in the colon after a meal