Nokea
Somatostatin secreted by the pancreas is considered paracrine because it acts on __________.
- A. the cells that secrete it
- B. distant target organs
- C. cells other than those that secrete it
- D. the hypothalamus to inhibit or activate the secretion of other hormones
Correct Answer: C
Rationale: The correct answer is C because somatostatin acts on nearby cells other than those that secrete it, which is the definition of paracrine signaling. This type of signaling involves the release of signaling molecules that affect neighboring cells within the same tissue or organ. Choices A and B are incorrect because paracrine signaling does not target the cells that secrete the signaling molecule or distant target organs. Choice D is incorrect because the hypothalamus is not typically the target of somatostatin action in the pancreas.
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Intravenous administration of epinephrine to a patient results in a severe decrease in diastolic pressure and an increase in cardiac output. Which of the following drugs might the patient have previously taken that could account for this unexpected effect?
- A. Propranolol
- B. Atropine
- C. Phenylephrine
- D. Prazosin
Correct Answer: D
Rationale: The correct answer is D: Prazosin. Prazosin is an alpha-1 adrenergic receptor antagonist, which blocks the vasoconstrictor effect of catecholamines like epinephrine, leading to vasodilation and a decrease in diastolic pressure. The unexpected effect of a decrease in diastolic pressure and an increase in cardiac output after epinephrine administration suggests that the patient might have taken a drug that blocks alpha-1 receptors. Propranolol (A) is a beta-blocker, which would not cause this effect. Atropine (B) is a muscarinic receptor antagonist and would not explain the observed effects. Phenylephrine (C) is an alpha-1 agonist, so it would not result in the described response. Therefore, Prazosin (D) is the most likely drug the patient previously took to account for the unexpected effects of epinephrine administration.
Which of the following glands disappears during old age?
- A. Thymus
- B. Parathyroid
- C. Thyroid
- D. Pituitary
Correct Answer: A
Rationale: The thymus gland is the correct answer because it involutes or shrinks with age, leading to decreased immune function. The parathyroid, thyroid, and pituitary glands do not disappear with old age but may undergo changes in function. The parathyroid regulates calcium levels, the thyroid controls metabolism, and the pituitary gland secretes various hormones. Therefore, the thymus gland is the only gland that disappears during old age, making it the correct answer.
During surgery, we administer hexamethonium to an anesthetized patient. Which of the following effects should you expect in response to this drug?
- A. Bradycardia mediated by activation of the baroreceptor reflex
- B. Increased GI tract motility, possible spontaneous defecation
- C. Increased salivary secretions
- D. Vasodilation
Correct Answer: D
Rationale: The correct answer is D: Vasodilation. Hexamethonium is a ganglionic blocking agent that blocks nicotinic receptors in autonomic ganglia, leading to vasodilation due to inhibition of sympathetic vasoconstrictor tone. This causes a decrease in blood pressure.
A: Bradycardia is not a direct effect of hexamethonium.
B: Increased GI motility and defecation are not expected effects of hexamethonium.
C: Increased salivary secretions are not directly affected by hexamethonium.
In summary, the correct answer is D because hexamethonium causes vasodilation by blocking nicotinic receptors in autonomic ganglia, leading to a decrease in blood pressure.
Abrupt, sudden withdrawal of prednisone (cortisol) is most likely to cause:
- A. Cushing syndrome.
- B. hypocalcemic tetany.
- C. diabetes insipidus.
- D. acute adrenal insufficiency.
Correct Answer: D
Rationale: The correct answer is D: acute adrenal insufficiency. Abrupt withdrawal of prednisone can lead to adrenal insufficiency due to suppression of the adrenal glands' natural cortisol production. This can result in symptoms such as fatigue, weakness, abdominal pain, and low blood pressure. Cushing syndrome (choice A) is caused by excessive cortisol, hypocalcemic tetany (choice B) is due to low calcium levels, and diabetes insipidus (choice C) is a disorder of water balance regulation, not related to prednisone withdrawal.
A common second messenger used in signaling pathways of water-soluble hormones is
- A. tRNA.
- B. ATP.
- C. cAMP.
- D. PTH.
Correct Answer: C
Rationale: The correct answer is C: cAMP. Water-soluble hormones, such as adrenaline or glucagon, bind to cell surface receptors and activate a signaling cascade that often involves cAMP as a second messenger. Upon hormone binding, the receptor activates adenylyl cyclase, which converts ATP to cAMP. cAMP then activates protein kinase A, leading to phosphorylation of target proteins, ultimately affecting cellular responses.
Explanation for incorrect choices:
A: tRNA is involved in protein synthesis, not in signaling pathways of water-soluble hormones.
B: ATP is used as an energy source in various cellular processes, but it is not a second messenger in hormone signaling pathways.
D: PTH (parathyroid hormone) is a hormone involved in calcium regulation and does not act through cAMP signaling in the same manner as water-soluble hormones.