The release of cortisol is stimulated by

Correct Answer: D

Rationale: The correct answer is D: adrenocorticotropic hormone (ACTH). ACTH is released by the pituitary gland in response to stress or low cortisol levels, stimulating the adrenal glands to release cortisol. Aldosterone (A) regulates electrolyte balance, angiotensin (B) regulates blood pressure, and antidiuretic hormone (C) regulates water balance, but they do not directly stimulate cortisol release. So, ACTH is the correct choice for stimulating cortisol production.

Correct Answer: D

Rationale: The correct answer is D because during protein kinase activation, enzymes phosphorylate many other enzymes, leading to a cascade of signaling events that can trigger multiple responses in a cell. This process amplifies and diversifies the cellular response to hormones. A: Choice A is incorrect because the number of receptors on the cell membrane does not directly relate to the ability of hormones to elicit multiple responses. B: Choice B is incorrect because receptors typically bind to one hormone molecule at a time, not multiple hormones simultaneously. C: Choice C is incorrect because the rapid metabolism of protein kinases does not directly explain why hormones can elicit multiple responses in a cell.

Correct Answer: D

Rationale: The correct answer is D because steroids act by binding to intracellular receptors, forming a hormone-receptor complex that directly interacts with the cell's DNA to regulate gene expression. This leads to changes in protein synthesis and cell function. A: Extracellular receptors do not have specificity for a single amino acid sequence on the hormone. Steroids act intracellularly. B: Formation of cyclic AMP is associated with G-protein coupled receptors, not steroid receptors. C: Second-messenger systems are typically involved in signaling cascades triggered by extracellular ligands, not steroids.

Correct Answer: A

Rationale: The correct answer is A because glucocorticoids, like cortisol, increase blood glucose levels through gluconeogenesis, elevate fatty acid levels for energy production, and promote amino acid breakdown for energy. This helps the body respond to stress by providing necessary energy sources. Additionally, glucocorticoids can enhance blood pressure to ensure adequate blood flow during stress. Option B is incorrect because glucocorticoids typically increase heart rate and blood pressure to support the stress response. Option C is incorrect as glucocorticoids do not stimulate the release of insulin; instead, they can have an anti-insulin effect. Option D is incorrect as glucocorticoids do not block neurotransmitters but rather modulate the stress response at various levels.

Correct Answer: A

Rationale: The correct answer is A: Adrenal gland. The adrenal gland is located atop the kidneys and is responsible for producing hormones such as adrenaline and cortisol. This gland plays a crucial role in the body's stress response and regulation of metabolism. The other choices are incorrect because the hypothalamus is located in the brain and regulates hormone secretion, the pancreas is located in the abdomen and is involved in insulin production, and the thyroid gland is located in the neck and controls metabolism.