QUESTION: 193

A 35-year-old weight lifter, who has been injecting testosterone for muscle mass augmentation, is evaluated for sterility and found to have an extremely low sperm count. Which of the following is an effect of testosterone and contributes to the mentioned sterility?

activation of inhibin
feedback activation of leptin
feedback inhibition of GnRH
inhibition of seminal prostaglandins
lowered core temperature

Answer(s): C

Explanation:

Testosterone directly inhibits the secretion of GnRH from the hypothalamus, which affects secretion of LH and FSH and consequently secretion of testosterone. To initiate spermatogenesis, both FSH and testosterone are necessary. To maintain spermatogenesis after puberty, extremely high concentrations of testosterone seem to be required. Systemically administered testosterone does not raise the androgen level in the testes to as great a degree and it additionally inhibits LH secretion. Consequently, the net effect is generally a decrease in sperm count. There are two forms of inhibin (choice A) that are produced by Sertoli cells in males. They are activated by FSH, not testosterone, and inhibit FSH secretion by a direct action on the pituitary. Testosterone has been shown to have a suppressive, not activating (choice B) effect on leptin production. Prostaglandins (choice D) are produced by seminal vesicles and found in large quantities in semen. They are not known to play a role in spermatogenesis. They are believed to aid fertilization by reacting with female cervical mucus and to support smooth muscle movements in the uterus and fallopian tubes. Testosterone stimulates basic metabolic rate and can raise, not lower body core temperature (choice E). Excessive temperature of the testes can temporarily cause sterility.

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QUESTION: 194

Evaluating the cause for a coma can be challenging. As a first step, the causes can be divided into two broad categories, structural/ surgical and metabolic/medical reasons. Which of the following findings suggests a metabolic cause in a comatose patient?

failure to withdraw from painful stimuli
gross blood in the cerebrospinal fluid
impaired pupillary light responses
posturing of limbs
serum sodium of 115 meq/L

Answer(s): E

Explanation:

Hyponatremia of this magnitude for any reason is likely to cause seizures and coma, especially if the deviation from normal occurred rapidly (e.g., over 1 or 2 days). Withdrawal from painful stimuli (choice A) is a normal reaction. If intact, it would have provided information on the intactness of sensation and motor reflexes on the tested side. However, lack of withdrawal would be consistent with either a structural or a metabolic cause of coma, and therefore does not help. Blood in the cerebral spinal fluid (choice B) in a nontraumatic lumbar puncture suggests a structural rather than a metabolic cause of coma. Pupillary light responses (choice C) are typically preserved in metabolic encephalopathies. Posturing of limbs (choice D) is suggestive of a focal process involving the brainstem or midbrain rather than a metabolic encephalopathy.

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QUESTION: 195

Exogenous peripherally injected insulin differs from endogenously secreted insulin in a number of aspects, including which of the following?

achieves a higher concentration in the periphery than in the liver, contrary to endogenous insulin
contains C-peptide, which is missing from secreted endogenous insulin
is able to bypass insulin resistance observed with endogenous insulin
is always extracted from animal sources and, therefore, is less effective due to sequence differences and anti-insulin antibodies
is in the form of proinsulin, whereas endogenous insulin has had C-peptide removed

Answer(s): A

Explanation:

The concentration of exogenous insulin is higher at the site of injection in the periphery, compared to its concentration in the liver. On the other hand, endogenous insulin is higher concentrated in the liver than in the periphery. Insulin is normally secreted by the endocrine pancreas into the portal venous drainage.
Thus, it passes through the liver before being seen by the periphery. Acertain fraction of insulin is extracted by the liver; so that the concentration of insulin seen by the liver is normally higher than that seen by the periphery. This discrepancy between exogenous and endogenous insulin might contribute to the problems experienced by diabetics such as hypertension and cardiovascular disease. Injected insulin is missing C- peptide (choice B), while endogenous insulin is cosecreted with C- peptide, the physiologic functions of which remain unknown. Injected insulin is biologically active and not in the proinsulin form (choice E).
Exogenous insulin generally used today in the United States is recombinant human insulin, not from animal sources (choice D). The problem of developing anti- insulin antibodies is now rarer since the injected insulin is not from animals. Insulin resistance (choice C) is generally due to receptor downregulation or desensitization, or anti-insulin antibodies. Tissues become equally resistant to both the body's own (endogenous) and administered (exogenous) insulin.

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QUESTION: 196

A 23-year-old Caucasian male is admitted to the hospital following a motorcycle accident. On examination, no bones appear to be broken, but there is extensive muscle bruising resulting in tissue swelling from increased capillary permeability. His arterial blood pressure is 80/40. He is awake and able to walk with assistance. Based on this information, it is likely that which of the following will be decreased from normal?

circulating levels of catecholamines
left atrial pressure
plasma aldosterone concentration
plasma lactate concentration
plasma renin activity

Answer(s): D

Explanation:

The accident trauma produces extensive loss of fluid from the vasculature into the interstitial fluid space.
Hence venous return to the heart, and thus left atrial pressure will be reduced. The decrease in arterial pressure will trigger arterial baroreflexes which will activate the sympathetic nervous system and increase catecholamine release (choice A). Likewise the fall in pressure will cause increased renin/angiotensin/ aldosterone (choices C and E). Finally, the reduced perfusion of the tissues will generate increased lactate formation (choice D).

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QUESTION: 193

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QUESTION: 194

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QUESTION: 195

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QUESTION: 196

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