The receptor for a peptide hormone ___________.

Correct Answer: B

Rationale: The correct answer is B because peptide hormones are hydrophilic and cannot pass through the cell membrane. Therefore, their receptors must be located on the cell's outer membrane to bind and trigger intracellular signaling pathways. Option A is incorrect because hydrophobic hormones can directly pass through the cell membrane, so their receptors are typically inside the cell. Option C is incorrect because hydrophobic hormones do not require a receptor on the cell's outer membrane. Option D is incorrect because hydrophilic hormones, like peptide hormones, require receptors on the cell's outer membrane.

Correct Answer: C

Rationale: The correct answer is C: Gonadal glands. These glands differ between males and females in terms of the hormones they secrete. In males, the gonadal glands (testes) produce testosterone, while in females, the gonadal glands (ovaries) produce estrogen and progesterone. Adrenal glands (A) secrete hormones like cortisol and adrenaline, which are not gender-specific. Parathyroid glands (B) regulate calcium levels and are not gender-specific. Pancreas (D) secretes insulin and glucagon, which are also not gender-specific. Therefore, the key difference in secretions between males and females lies in the gonadal glands.

Correct Answer: D

Rationale: The correct answer is D. During pregnancy, high levels of estrogen and progesterone inhibit lactation by suppressing the release of prolactin, the hormone responsible for milk production. Estrogen and progesterone maintain the pregnancy and prevent premature labor, so the body prioritizes their functions over lactation. Choices A, B, and C are incorrect because low blood prolactin levels, human placental lactogen levels, and fetal adrenal gland's estriol production are not directly related to the suppression of lactation during pregnancy.

Correct Answer: A

Rationale: The correct answer is A because thyroid hormone is a lipid-soluble hormone that can diffuse across the cell membrane and bind to intracellular receptors within the nuclei. This binding activates gene transcription, leading to various metabolic effects. Choice B is incorrect because thyroid hormone actually has a significant impact on body metabolism. Choice C is incorrect as thyroid hormone does not directly affect blood vessel adrenergic receptors or blood pressure. Choice D is incorrect as thyroid hormone actually acts to increase basal metabolic rate, not decrease it.

Correct Answer: D

Rationale: The correct answer is D: humoral stimulation. This mechanism directly responds to changing blood levels of ions and nutrients. Humoral stimulation refers to the regulation of hormone secretion in response to changes in blood levels of various substances like ions and nutrients. It is a feedback mechanism that helps maintain homeostasis by adjusting hormone levels based on the body's needs. A: Rapid oxidation of carbohydrates is not related to endocrine control systems responding to changing blood levels of ions and nutrients. B: Catabolic inhibition does not directly respond to changing blood levels of ions and nutrients. C: Protein synthesis is not a mechanism that directly responds to changing blood levels of ions and nutrients.