Physio - Vallano - Peeing and Pooping - 2/24

Question 1

Contraction of what major muscle is critical to micturition?

Answer 1

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.

Question 2

What part of the brain controls the detrusor muscle?

Answer 2

Pontine micturition center, controls detrusor muscles and urinary sphincters.

Suprapontine centers exert tonic inhibition (PNS) over the pontine micturition center providing voluntary control.

Question 3

_____ fibers inhibit contraction of the detrusor (beta-adrenergic response) and stimulate contraction of the internal sphincter muscles (alpha-adrenergic)

Answer 3

SNS

Question 4

Why does LMN damage lead to neurogenic bladder where you cannot empty?

Answer 4

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.

Question 5

In what part of the colon is the dwell time the longest for chyme?

Answer 5

Transverse colon, can be up to 24 hrs.

Question 6

What is the result of poor motility through the colon?

Answer 6

Hard poops bc too much absorption occurs

Question 7

What are the two forms of diarrhea?

Answer 7

1. Osmotic - results from nonabsorbable solutes in the lumen, ie lactose intolerace
2. Secretory - excessive secretion by crypt cells due to bacterial overgrowth or cholera, ie.

Question 8

When is the gastroilieal reflex activated?

Answer 8

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.

Question 9

What is the common cause of appendicitis?

Answer 9

Obstruction of the appendix lumen by calcified fecal matter

Question 10

What does the colon contain in lieu of villi? Peyer’s Patches?

Answer 10

Crypts instead of villi

Solitary lymph nodes scattered but no Peyer’s Patches

Question 11

T/F: The colon absorbs Na+, HCO3- and H2O, and secretes K+ and Cl-.

Answer 11

FALSE. The colon absorbs Na+, Cl- and H2O, and secretes K+ and HCO3-.

Question 12

Severe hypokalemia, for example due to prolonged diarrhea, can lead to:

Answer 12

Cardiac arrhythmia

Question 13

What is the primary mechanism for interdigestive Na+ absorption?

Answer 13

“Electroneutral NaCl absorption”

Na-H exchanger and the Cl-HCO3 exchanger, which promote water re-absorption.

Question 14

How does aldosterone influence water reabsorption in the colon?

Answer 14

It increases the # of Na+ channels in the colon. Water and Cl- follow passively through tight junctions.

Question 15

T/F: The large intestine contains interstitial cells of Cajal.

Answer 15

True

Question 16

What are haustrations? In what disease are they absent?

Answer 16

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.

Question 17

Following a meal, the gastrocolic reflex results in:

Answer 17

increased incidence of “mass movements”

Question 18

T/F: Parasympathetic stimulation results in relaxation of the internal anal sphincter.

Answer 18

True

Question 19

What would happen if extrinsic autonomic nerves to the colon were removed?

Answer 19

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.

Question 20

Aganlionosis is also known as:

Answer 20

Hirschsprung’s disease, lack of ENS in the distal part of the GI tract, leads to early obstruction in infants.

Question 21

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

Answer 21

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.

Question 22

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

Answer 22

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.

Question 23

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

Answer 23

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.

Question 24

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

Answer 24

c) the gastrocolic reflex

The gastrocolic reflex may initiate a mass movement in the colon after a meal

Question 25

A healthy, 21-year-old woman eats a big meal and then takes a 3-hr ride on a bus that does not have a bathroom. Twenty minutes after eating. the woman feels a strong urge to defecate, but manages to hold it. Which of the following have occurred in this woman?
A) Relaxation of internal anal sphincter
B) Contractions of external anal sphincter
C) Contraction of rectum

Answer 25

A) Relaxation of internal anal sphincter –> YES
B) Contractions of external anal sphincter –> YES
C) Contraction of rectum –> YES

The defecation reflex (also called the rectosphincteric reflex) occurs when a mass movement forces feces into the rectum. When the rectum is stretched, the internal anal sphincter relaxes and the rectum contracts pushing the feces toward the anus. The external anal sphincter is controlled voluntarily and can be contracted when defecation is not possible. Therefore, when a person feels the urge to defecate, the internal anal sphincter is relaxed, the rectum is contracting, and the external anal sphincter is either contracted or relaxed depending on the circumstances.

Question 26

Mass movements constitute an important intestinal event that lead to bowel movements. Mass movements cause which of the following?

a) Contraction of internal anal sphincter
b) Duodenal peristalsis
c) Gastric retropulsion
d) Hunger sensations
e) Rectal distension

Answer 26

e) Rectal distension

The rectum is empty of feces most of the time. When a mass movement forces feces into the rectum, the desire to defecate is initiated immediately. Reflex contraction of the rectum and relaxation of the internal anal sphincter follows. If a person is in a place where defecation is possible (like a bathroom), the external anal sphincter is consciously relaxed and the feces is expelled. It should be clear that mass movements do not cause duodenal peristalsis, gastric retropulsion, or hunger sensations.

Question 27

A newborn boy does not pass meconium in the first 24 hr. His abdomen is distended and he begins vomiting. Various tests lead to a diagnosis of Hirschsprung disease. An obstruction is most likely found in which portion of the gut?

a) Ascending colon
b) Ileocecal sphincter
c) Lower esophageal sphincter
d) Pylorus
e) Sigmoid colon

Answer 27

e) Sigmoid colon

Hirschsprung disease is characterized by a congenital absence of ganglion cells in the distal colon resulting in a functional obstruction. Most cases of Hirschsprung disease are diagnosed in the newborn period. Hirschsprung disease should be considered in any newborn who fails to pass meconium within 24 to 48 hr after birth. Although contrast enema is useful in establishing the diagnosis, rectal biopsy remains the criterion standard. Aganglionosis begins with the anus, which is nearly always involved, and continues proximally for a variable distance. Both the myenteric (Auerbach) and submucosal (Meissner) plexus are absent, resulting in reduced bowel peristalsis and function.The precise mechanism underlying the development of Hirschsprung disease is poorly understood.

Question 28

Which of the following statements is correct? In the colon

a) The amount of flatus produced will more than double if one switches from an average diet to one in which 25% of the caloric intake is pork and beans
b) Na+ and water are secreted into the chyme
c) The concentration of K+ and HCO3- in the chyme is decreased
d) Any glucose in the chyme are actively absorbed
e) any amino acids in the chyme are actively absorbed

Answer 28

a) The amount of flatus produced will more than double if one switches from an average diet to one in which 25% of the caloric intake is pork and beans

The colon does not actively absorb glucose or amino acids. The value of nutritive enemas is thought to be negligible. Staying on a diet high in beans for 2 weeks has been shown to increase the volume of flatus from 17 to 203 mL/h.

Question 29

Which of the following describes the external anal sphincter?

a) It is composed of striated muscle and is under voluntary control
b) It is composed of intestinal smooth muscle and is under involuntary control
c) It automatically relaxes when a peristaltic wave approaches the anus
d) It is innervated by sympathetic fibers

Answer 29

a) It is composed of striated muscle and is under voluntary control

The external anal sphincter is composed of voluntary, or at least semiconsciously, controlled striated muscle. In adults, it is usually kept continuously constricted unless conscious signals inhibit the constriction.

Question 30

Which of the following statements is correct?

a) More protein in the feces comes from the diet than from bacteria
b) An increase in the cellulose content in the diet tends to cause a decrease in the frequency of bowel movements
c) Constipation is associated with a restlessness, dull headache, loss of appetite, and occasionally nausea, all of which are attributable to the absorption of toxins from the feces
d) An individual who defecates fewer than three times a week should not necessarily be considered constipated or unhealthy
e) Ammonium ions are produced in the stomach

Answer 30

d) An individual who defecates fewer than three times a week should not necessarily be considered constipated or unhealthy

Apparently, the symptoms associated with constipation are attributable to distention of the rectum rather than toxins. What few toxins do enter the blood (NH4+, for example) pass via the portal circulation to the liver, where they are removed before they can enter the general circulation. An individual who defecates only once a week, if he does not have the symptoms listed above, should be considered healthy and not constipated. Unfortunately, many confuse what is healthy with what is average. Approximately 10% of the dry weight of the feces is bacteria. In a series of healthy men, it was shown that by changing the fiber content of the diet from 30 to 100 mg/kg/day, the interval between defecations changed from 30 hours to 17 hours. This is not to deny that one’s attitudes do not also affect the frequency of defecation. Stool water contains an average of 14 mEq of NH4+ per liter, NH4+ is produced in the colon by the oxidative deamination of amino acids and by the hydrolysis of urea.