QUESTION: 201

A 25-year-old male athlete has just completed a long distance bicycle race during a hot, humid day. At the conclusion of the race, he provides a urine sample for testing. Assuming that his fluid intake during the race was zero, in what portion of the nephron shown in below figure is the tubular fluid osmolality the lowest?

Answer(s): D

Explanation:

The bicycle racer is likely dehydrated from his exercise and ADH would be secreted by the posterior pituitary in response to increased extracellular osmolality. The area of the nephron with the lowest osmolality will be the early distal tubule (choice D), a nephrondiluting segment. The fluid in Bowman's capsule (choice A) will be at the same osmolality as the plasma entering the glomerular capillaries. The fluid at the end of the proximal tubule (choice B) is isoosmotic with the Bowman's capsule fluid while the fluid in the thin descending loop of Henle (choice C) is greatly concentrated due to water reabsorption into the hyperosmotic medullary interstitium. The fluid at the end of the collecting duct (choice E) can be very concentrated or very dilute, but since ADH greatly increases water reabsorption in this segment, the fluid becomes very concentrated.

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QUESTION: 202

A motor vehicle accident caused complete pituitary stalk transection. Secretion of all pituitary hormones is lost except for one, the blood level of which actually increases. Which one of the following pituitary hormones is distinctive in that its primary control is by inhibition rather than stimulation by the hypothalamus?

gonadotropin-releasing hormone
growth hormone
prolactin
proopiomelanocortin
thyroid-stimulating hormone

Answer(s): C

Explanation:

The primary control over prolactin secretion is inhibition by hypothalamic dopamine; all other anterior pituitary hormones are primarily controlled by hypothalamic hormone stimulation. Hence, with stalk transection, loss of connection of the hypothalamus to the pituitary is associated with decreased secretion of all pituitary hormones except prolactin, the secretion of which increases in the absence of dopamine.
Secretion of growth hormone (choice B), proopiomelanocortin (choice D), and thyroid- stimulating hormone (choice E) all decrease. Gonadotropinreleasing hormone (choice A) is a hypothalamic hormone, and is not made in the pituitary gland.

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QUESTION: 203

The parents bring a 5-month-old baby to the emergency room. It is their first child and they are insecure. The boy vomits frequently, seems to be constantly constipated, and has difficulties in defecation. A barium enema study reveals a region in the bowel that is collapsed and an enlarged colon above this area. Abiopsy from the part of the bowel 1 in above the anus is sent to the laboratory and histological analysis reveals the absence of ganglia in this tissue. What is the most likely diagnosis?

cholecystitis
gastroesophageal reflux disease
hirschsprung disease
polymyositis
temporary problem with no treatment required

Answer(s): C

Explanation:

Hirschsprung disease is a genetic disorder caused by the absence of enteric nerve cells in the wall of the sigmoid colon and/or rectum. The portion of the bowel wall without nerve ganglia (aganglionic) cannot relax in response to bowel content so that the stool builds up behind the obstruction. In some children the problems begin shortly after birth, other infants are not acutely ill, but develop chronic symptoms such as constipation or anemia. Cholecystitis (choice A), caused by inflammation of the gallbladder, gastroesophageal reflux disease GERD (choice B), and polymyositis (choice D), a disorder affecting esophageal skeletal muscle, do not affect the neuronal regulation of the large intestine. Hirschsprung disease is almost always treated by surgical removal of the affected bowel segment and then joining the healthy bowel segments (choice E). A GI motility disorder might improve on its own due to the ability of the enteric nervous system in healthy GI tract portions to learn new motility patterns. However, it takes a very long time and the success is not certain.

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QUESTION: 204

Exhibit: *missing*
A healthy 27-year-old male is given a treadmill stress test. His cardiovascular values at rest and during exercise were:

When compared to rest, what was the change in his arterial pulse pressure?

decreased from 140 to 65
increased from 30 to 75
increased from 68 to 140
increased from 115 to 140
remained unchanged since heart rate and systolic pressure both increased

Answer(s): B

Explanation:

By definition, arterial pulse pressure is the difference between peak systolic and minimum diastolic pressure. His resting pulse pressure was 105 - 75 = 30 and his exercise pulse pressure increased to 140
- 65 = 75.

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QUESTION: 201

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QUESTION: 202

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QUESTION: 203

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QUESTION: 204

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