Why can a single endocrine hormone produce a wider spread of responses in more of the body than a single nerve cell?

Correct Answer: B

Rationale: The correct answer is B because the bloodstream can carry hormones throughout the body simultaneously, reaching various target cells and organs. This enables a single endocrine hormone to produce responses in multiple parts of the body. In contrast, nerve cells can only target a limited number of cells through direct connections. Choice A is incorrect because endocrine hormones can also target multiple responses, not just one. Choice C is incorrect as the endocrine system and nervous system can interact. Choice D is incorrect as endocrine hormones can have broad effects on multiple target cells.

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: B

Rationale: The correct answer is B because the parathyroid glands target the bone and activate osteoclasts to release calcium into the bloodstream. This process helps maintain adequate blood calcium levels. By activating osteoclasts, calcium is released from the bone into the blood, ensuring a balance of calcium levels. A: Blocking the action of growth hormone is unrelated to the function of parathyroid glands in maintaining blood calcium levels. C: Antagonizing the synthesis of calcitonin is not the primary mechanism through which parathyroid glands regulate blood calcium levels. D: Slowing the activity of tissues that require calcium for activity would not help maintain adequate blood calcium levels as it does not address the direct release of calcium from bone by activating osteoclasts.

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.