All of the following statements regarding cardiac glycosides are true EXCEPT:

Correct Answer: C

Rationale: The correct answer is C because digoxin actually has a shorter half-life than digitoxin. Digoxin has a half-life of approximately 36 hours, while digitoxin has a longer half-life of around 7 days. A: Digoxin is a mild inotrope, which means it increases myocardial contractility. B: Digoxin increases vagal tone, leading to a decrease in heart rate. D: Digoxin acts by inhibiting the Na+/K+ ATPase pump, resulting in increased intracellular calcium levels and improved contractility. Therefore, choices A, B, and D are true statements regarding cardiac glycosides.

Correct Answer: C

Rationale: To increase blood pressure in low cardiac output, positive inotropic drugs (Choice C) are used to improve the heart's contractility and increase cardiac output. Ganglioblockers (Choice A) block sympathetic activity, potentially worsening low cardiac output. Vasoconstrictors (Choice B) can increase blood pressure but may not address the underlying cause of low cardiac output. Diuretics (Choice D) reduce blood volume and may further decrease cardiac output. Therefore, Choice C is the correct option to address low cardiac output by improving heart function and increasing blood pressure.

Correct Answer: C

Rationale: The correct answer is C because the secretion of thyrotropin (TSH) is regulated by a negative feedback loop. When the concentration of thyroid hormones in the blood decreases, the hypothalamus signals the pituitary gland to release more TSH to stimulate the thyroid gland to produce more thyroid hormones. Conversely, when the thyroid hormone levels are high, TSH secretion is inhibited. Choices A and B are incorrect because the amount of iodine and thyroid hormones in the thyroid gland itself does not directly regulate TSH secretion. Choice D is incorrect as catecholamines do not directly influence TSH secretion.

Correct Answer: A

Rationale: Estrogens have immunomodulatory properties by enhancing immune responses, while progestins have immunosuppressive effects by inhibiting immune responses. Therefore, the statement is TRUE. Choice B is incorrect because the statement is not false. Choice C is incorrect as it does not provide a clear answer. Choice D is incorrect as it does not apply in this scenario.

Correct Answer: B

Rationale: The correct answer is B because adaptive immunity is characterized by antigen-specific defense mechanisms that target and eliminate specific pathogens. This type of immunity takes time to develop, usually several days, and involves the activation of lymphocytes such as T and B cells that can recognize and respond to specific antigens. This process leads to the formation of memory cells that provide long-lasting protection against future encounters with the same antigen. Choices A, C, and D are incorrect: A: This describes innate (natural) immunity, which is present at birth and provides immediate, nonspecific defense mechanisms against pathogens. C: Interferons are signaling proteins produced in response to viral infections and are part of the innate immune response, not adaptive immunity. D: Immunosuppressive agents are drugs that suppress the immune system and are used to prevent rejection of transplanted organs or treat autoimmune diseases. They do not enhance adaptive immunity.