The only amine hormone to act like a steroid is ________.

Correct Answer: A

Rationale: The correct answer is A: TH (Thyroid Hormone). TH is the only amine hormone that acts like a steroid because it is derived from an amino acid but functions similarly to steroid hormones by entering target cells and binding to intracellular receptors to regulate gene expression. ACTH, GH, and ADH are peptide hormones that do not act like steroids. ACTH stimulates the adrenal glands to produce cortisol, GH stimulates growth, and ADH regulates water balance in the body.

Correct Answer: C

Rationale: The correct answer is C because ADH (antidiuretic hormone) increases water reabsorption by the kidneys (increasing blood volume), causes vasoconstriction (narrowing of blood vessels), and ultimately leads to an increase in blood pressure. Choice A is incorrect because ADH does not decrease water reabsorption. Choice B is incorrect because ADH does not cause dilation of blood vessels, which would decrease blood pressure. Choice D is incorrect because ADH does not cause dilation of blood vessels, which would not lead to a decrease in blood pressure.

Correct Answer: A

Rationale: The correct answer is A: thyroid hormone. The thyroid hormone plays a crucial role in regulating metabolism by increasing the body's metabolic rate. It accomplishes this by stimulating the production of proteins that control the rate at which cells use energy. Calcitonin (B) is involved in regulating calcium levels in the blood, not metabolic rate. Aldosterone (C) is a hormone that regulates electrolyte balance and blood pressure. Parathyroid hormone (D) regulates calcium and phosphorus levels in the blood, not metabolic rate. Thus, the correct choice is thyroid hormone as it directly affects metabolic rate.

Correct Answer: A

Rationale: The correct answer is A: atrial natriuretic hormone (ANH). ANH opposes the actions of aldosterone by promoting salt and water excretion, thus reducing blood volume and blood pressure. ANH is released in response to high blood pressure or high blood volume. B: antidiuretic hormone (ADH) is not the antagonistic hormone to aldosterone; it acts on the kidneys to regulate water balance. C: cortisol is a stress hormone and is not directly involved in regulating sodium and water balance. D: glucagon is a hormone that increases blood sugar levels and is not related to the regulation of aldosterone.

Correct Answer: B

Rationale: Leptin is the correct answer because it is a hormone produced by adipose tissue that signals satiety to the brain, helping regulate energy balance and food intake. Melatonin is a hormone that regulates sleep-wake cycles, not hunger. Thymosins are involved in immune function. Glucagon is a hormone that increases blood sugar levels, not related to satiety.