Which term describes the maintenance of a stable internal environment?

Correct Answer: C

Rationale: Homeostasis is the maintenance of a stable internal environment to support optimal physiological functioning. It involves mechanisms that regulate variables within a narrow range. Negative feedback is a key mechanism in maintaining homeostasis by counteracting deviations from set points. Positive feedback amplifies changes and is not involved in maintaining stability. Metabolism refers to the chemical processes in the body and is not specifically related to the maintenance of internal stability. Therefore, the correct answer is C (homeostasis) because it directly relates to the concept of maintaining a stable internal environment through regulatory mechanisms.

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: A

Rationale: The correct answer is A: Parathyroid and thyroid. The parathyroid glands secrete parathyroid hormone, which increases blood calcium levels by promoting calcium release from bones and increasing calcium absorption in the intestines. The thyroid gland produces calcitonin, which lowers blood calcium levels by inhibiting bone breakdown and increasing calcium excretion by the kidneys. The adrenal medulla and pancreas do not play a direct role in regulating calcium levels. Testes are not involved in calcium regulation. The thymus is responsible for developing T-cells and does not have a role in calcium regulation.

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.