Question 1

A newborn boy does not pass meconium in the first 24 hours. His abdomen is distended, and he begins vomiting. Hirschsprung's disease is suspected. Which of the following is virtually absent from the constricted segment of the colon in this patient?

Accepted Answer

Hirschsprung's disease is a congenital disorder in which there is an absence of ganglion cells in the submucosal and myenteric plexuses of the distal colon, resulting in an inability to pass feces. The constricted segment of the colon lacks ganglion cells, which are responsible for coordinating normal contractions and relaxation of the intestine. The absence of ganglion cells also leads to a lack of peristalsis in the affected area, which contributes to the accumulation of stool and the development of abdominal distension. Blood flow, circular smooth muscle, mucosa, and serosa are all present in the affected segment of the colon.

Question 2

Receptive relaxation of the fundus is mediated by which substance?

Accepted Answer

Receptive relaxation of the fundus is mediated by vasoactive intestinal peptide (VIP). VIP is a neurotransmitter released from enteric nerves in the stomach and acts on smooth muscle cells to induce relaxation.

Question 3

An 87-year-old man has a stroke that eliminates vagal nerve input to the gastrointestinal tract and severely curtails function of the glossopharyngeal nerve. Which of the following is operational in this man?

Accepted Answer

Secondary peristalsis of the esophagus is a reflex that is initiated by the distension of the esophagus itself, rather than by neural input from the vagus or glossopharyngeal nerves. This means it can still function in the absence of input from these nerves, helping to clear the esophagus of remaining food.

Question 4

Which of the following reflexes results in the urge to defecate when the duodenum is distended?

Accepted Answer

The duodenocolic reflex is a reflex that results in the urge to defecate when the duodenum is distended. This reflex is activated when sensory nerve fibers in the duodenal wall are stimulated by distension or irritation, and send signals to the spinal cord. From there, efferent nerve fibers are activated, leading to a contraction of the colon and the urge to defecate. The other choices are not associated with the defecation reflex triggered by duodenal distension.

Question 5

Which one of the pressure tracings given below illustrates normal function of the lower esophageal sphincter before and after swallowing (arrow)? The dashed line represents a pressure of 0 mm Hg.

Accepted Answer

The answer of Which one of the pressure tracings given...

Question 6

A person sustaining a stroke can have trouble swallowing because a stroke can cause damage to the swallowing center.

Accepted Answer

The statement is correct as a person with a stroke can have difficulty swallowing due to damage to the swallowing center in the brain. The reason is also correct as it explains why a person with a stroke may have trouble swallowing. The two are related as they both address the same issue.

Question 7

Conditions that tend to increase gastric emptying include which of the following?

Accepted Answer

Increased tone of the orad (upper) part of the stomach helps in propelling the contents towards the pylorus and into the duodenum, thus increasing gastric emptying.

Question 8

A 52-year-old man eats a healthy meal. Approximately 20 minutes later, the man has the urge to defecate. Which of the following reflexes results in the urge to defecate when the stomach is stretched?

Accepted Answer

The gastrocolic reflex is the reflex responsible for the urge to defecate when the stomach is stretched. The stretching of the stomach triggers a reflex that increases the motility of the colon, resulting in the urge to defecate. The duodenocolic reflex and the ileocecal reflex are not involved in the urge to defecate. The enterogastric reflex is involved in regulating gastric motility and secretion, not the urge to defecate. The intestine-intestinal reflex is involved in the coordination of motility and secretion between different segments of the intestine, not the urge to defecate.

Question 9

Ileocecal sphincter tone decreases after distention of which of the following?

Accepted Answer

The ileocecal sphincter tone decreases after distention of the ileum. This is part of the gastroileal reflex, which increases the force of segmentation in the ileum and relaxes the ileocecal valve, allowing contents from the ileum to pass into the large intestine more easily.

Question 10

A 43-year-old medical student suffers severe damage to the conus medullaris in an accident. He initiates defecation by inserting a balloon-tipped Foley catheter into his rectum and inflating the balloon with a 50 mL syringe. Which reflex is stimulated by the balloon in this patient?

Accepted Answer

The use of a catheter and balloon to initiate defecation suggests that the patient is using the Intrinsic Defecation Reflex. This reflex involves distention of the rectum by feces or a balloon, leading to activation of mechanoreceptors and the spinal reflex pathway, resulting in contraction of the rectum and relaxation of the internal anal sphincter. This allows for fecal expulsion. The other reflexes listed are not involved in this particular scenario.

Question 11

A 19-year-old man is admitted to the emergency department after an automobile accident. A CT scan shows that the spinal cord is severed at T5. Balloon distension of the rectum is most likely to cause which of the following in this patient? $\begin{array}{lll}
&External&&Internal\
&\text { Ana1 Sphincter } & \text { Rectum } &\text { Anal Sphincter }\\hline
A.&\text { Contraction } & \text { Contraction } & \text { Contraction } \
B.&\text { Contraction } & \text { No effect } & \text { Contraction } \
C.&\text { Relaxation } & \text { Relaxation } & \text { Contraction } \
D.&\text { No effect } & \text { Contraction } & \text { No effect } \
E.&\text { Relaxation } & \text { No effect } & \text { No effect } \
F.&\text { No effect } & \text { Contraction } & \text { Relaxation } \
G.&\text { No effect } & \text { Relaxation } & \text { Relaxation } \
H.& \text { Relaxation } & \text { Relaxation } & \text { Relaxation }
\end{array}$

Accepted Answer

The answer of A 19-year-old man is admitted to the...

Question 12

The diagram shows manometric recordings from a patient before and after pelvic floor training. A balloon placed in the rectum was inflated (arrows) and deflated repeatedly. Tracing Z is a manometric recording obtained from the external anal sphincter before and after pelvic floor training. Which of the following best describe the origin of tracing X?

Accepted Answer

Tracing X likely represents the pressure exerted by the internal anal sphincter. This is because the balloon was placed in the rectum, and tracing Z represents the external anal sphincter, which is closer to the opening of the anus. Tracing X being closer to the balloon inflation/deflation points suggests that it is measuring pressures within the rectum itself, which are likely originating from the internal anal sphincter.

Question 13

Parasympathetic stimulation can increase intestinal motility because parasympathetic stimulation increases slow wave frequency.

Accepted Answer

Parasympathetic stimulation does increase intestinal motility, but it does not do so by increasing slow wave frequency. Instead, it enhances the amplitude of contractions and the activity of the enteric nervous system.

Quiz 64: Propulsion and Mixing of Food in the Alimentary Tract