____________ is a steroid hormone.

Correct Answer: A

Rationale: Vitamin D is the correct answer as it is a steroid hormone synthesized from cholesterol. Steroid hormones are derived from cholesterol and have a similar chemical structure. Epinephrine and Insulin are not steroid hormones. Epinephrine is a catecholamine produced by the adrenal glands, and Insulin is a peptide hormone produced by the pancreas. Choice D is incorrect as not all options listed are steroid hormones.

Correct Answer: A

Rationale: Step-by-step rationale: 1. The posterior pituitary gland stores oxytocin and antidiuretic hormone (ADH). 2. Oxytocin is responsible for uterine contractions and milk ejection. 3. ADH regulates water balance by controlling urine concentration. 4. These hormones are produced in the hypothalamus and released from the posterior pituitary. 5. Choice A is correct as it accurately identifies the hormones stored and secreted by the posterior pituitary. Summary: - Choice B is incorrect because human growth hormone and thyroid stimulating hormone are not stored or secreted by the posterior pituitary. - Choice C is incorrect because prolactin and follicle stimulating hormone are produced by the anterior pituitary. - Choice D is incorrect because glucocorticoids and androgens are not stored or secreted by the posterior pituitary.

Correct Answer: D

Rationale: The correct answer is D: hormones. Hormones are chemical substances secreted by cells into extracellular fluids to regulate metabolic functions in other cells. They act as messengers, traveling through the bloodstream to target tissues. Enzymes (A) are catalysts that accelerate chemical reactions. Antibodies (B) are proteins produced by the immune system to neutralize pathogens. Proteins (C) are essential macromolecules for various cellular functions but do not specifically regulate metabolic functions in other cells like hormones do.

Correct Answer: A

Rationale: The correct answer is A because steroid hormones are lipid-soluble molecules that can pass through the cell membrane and bind to intracellular receptors in the nucleus. This binding activates or inhibits gene transcription, leading to changes in protein synthesis and cellular responses. Choice B is incorrect because cAMP activity is typically associated with peptide hormones, not steroid hormones. Choice C is incorrect because steroid hormones do not stimulate glycogen synthesis. Choice D is incorrect because steroid hormones do not directly affect blood pressure regulation.

Correct Answer: B

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.