Sometimes prolonged excessive exposure to high hormone concentrations causes a phenomenon known as ________.

Correct Answer: C

Rationale: The correct answer is C: down-regulation. Prolonged exposure to high hormone concentrations can lead to down-regulation, where cells decrease their responsiveness to the hormone by reducing the number of hormone receptors. This is a regulatory mechanism to prevent overstimulation. A: Diabetes mellitus is a chronic condition characterized by high blood sugar levels, usually caused by insulin deficiency or insulin resistance, not directly related to prolonged exposure to high hormone concentrations. B: Cellular inhibition is a broad term that may refer to various cellular processes being inhibited, but it is not a specific phenomenon resulting from prolonged exposure to high hormone concentrations. D: Metabolism of protein kinases is a cellular process involved in signal transduction, but it is not a direct consequence of prolonged exposure to high hormone concentrations.

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 peptide hormones typically bind to receptor proteins on the plasma membrane. This is because peptide hormones are not able to pass through the cell membrane due to their size and polarity. Once the hormone binds to the receptor on the plasma membrane, it activates a second messenger system within the cell, leading to various cellular responses. Choice A is incorrect because peptide hormones do not bind directly to intracellular components like second messengers inside the cell. Choice B is incorrect because peptide hormones do not directly activate particular genes within the cell. Choice D is incorrect because peptide hormones do not bind directly to genes on the plasma membrane.

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.