Which hormone is involved in the regulation of calcium levels in the blood?

Correct Answer: A

Rationale: The correct answer is A: parathyroid hormone. Parathyroid hormone is responsible for regulating calcium levels in the blood by increasing calcium release from bones, enhancing calcium absorption in the intestines, and promoting calcium reabsorption in the kidneys. This hormone acts to elevate blood calcium levels when they are low. B: Aldosterone is a hormone that regulates sodium and potassium levels, not calcium. C: Calcitonin is involved in lowering blood calcium levels by inhibiting the breakdown of bone tissue, but it is not the primary hormone responsible for regulating calcium levels in the blood. D: Thyroid hormone plays a role in metabolism regulation, growth, and development, but it is not directly involved in the regulation of calcium levels in the blood.

Correct Answer: A

Rationale: The correct answer is A because aldosterone increases the transport of epithelial sodium channels (ENaCs) from the cytoplasm to the cell membrane. This process leads to enhanced sodium reabsorption in the kidneys, promoting water retention and increasing blood pressure. Choices B and C are incorrect as aldosterone does act on the cell membrane and binds to a receptor located in the cytoplasm, which then translocates to the nucleus. Choice D is incorrect as aldosterone does not directly activate heat shock proteins.

Correct Answer: B

Rationale: The correct answer is B: Follicle stimulating hormone. The pituitary gland produces luteinizing hormone and follicle stimulating hormone to regulate reproductive cells. Luteinizing hormone triggers ovulation and testosterone production, while follicle stimulating hormone stimulates egg development in females and sperm production in males. Choice A (Androgens) are male sex hormones produced by the testes, not by the pituitary gland. Choices C (Epinephrine) and D (Norepinephrine) are hormones produced by the adrenal glands and are not involved in regulating reproductive cells.

Correct Answer: C

Rationale: The correct answer is C: homeostasis. Homeostasis refers to the body's ability to maintain a stable internal environment despite external changes. It involves various physiological mechanisms to regulate temperature, pH, blood sugar levels, and more. Negative feedback (choice A) is a key component of homeostasis, where the body reverses a deviation from the set point to restore balance. Positive feedback (choice B) amplifies a response and does not contribute to maintaining stability. Metabolism (choice D) is the sum of all chemical processes in the body and is necessary for homeostasis but does not directly regulate the internal environment.

Correct Answer: D

Rationale: The correct answer is D: Somatomedins. Somatomedins, also known as insulin-like growth factors (IGFs), inhibit the secretion of growth hormone by negative feedback on the anterior pituitary. When somatomedins are present in sufficient levels, they signal to the pituitary gland to decrease the secretion of growth hormone. A: Sleep does not directly inhibit the secretion of growth hormone. In fact, growth hormone is predominantly secreted during sleep. B: Stress can stimulate the secretion of growth hormone, rather than inhibit it. C: Puberty is a stage of development where growth hormone secretion is typically increased, not inhibited.