At the skeletal muscle sarcomere, Ca2+ ions do each of the following, except:

Correct Answer: d

Rationale: Rationale for Correct Answer (D): 1. Ca2+ ions do not directly break down ATP into ADP + inorganic phosphate at the sarcomere. 2. This breakdown occurs through the enzymatic action of myosin ATPase. 3. Ca2+ ions primarily bind to troponin to initiate muscle contraction by moving tropomyosin. 4. Ca2+ ions help expose active sites on actin, facilitating cross-bridge formation. Summary of Incorrect Choices: A. Correct - Ca2+ binds to troponin to move tropomyosin, not to uncover it. B. Correct - Ca2+ aids in exposing active sites on actin, not troponin. C. Correct - Ca2+ is stored in the sarcoplasmic reticulum, but it is released into the cytoplasm to trigger muscle contraction, not stored in the terminal cisternae.

Correct Answer: D

Rationale: Rationale: 1. Insulin, cortisol, thyroxine, and oxytocin are all hormones produced by various glands in the body. 2. Insulin is produced by the pancreas, cortisol by the adrenal glands, thyroxine by the thyroid gland, and oxytocin by the hypothalamus and released by the pituitary gland. 3. Each of these hormones plays a different role in the body, such as regulating blood glucose levels, metabolism, stress response, and reproductive functions. 4. Therefore, the correct answer is D: they are all hormones. Summary: A: Incorrect. Hypothalamic-releasing hormones are specific hormones that stimulate the release of other hormones from the pituitary gland. B: Incorrect. Adenohypophysis secretes different hormones, not these specific ones. C: Incorrect. Insulin, for example, decreases blood glucose levels, while cortisol increases blood glucose levels.

Correct Answer: B

Rationale: The correct answer is B: stimulates osteoclastic activity. Parathyroid hormone (PTH) acts on bones to stimulate osteoclasts, which are responsible for breaking down bone tissue to release calcium into the bloodstream. This process helps increase blood calcium levels. Choices A, C, and D are incorrect because PTH actually increases plasma calcium levels, is not an iodine-containing hormone, and does not stimulate osteoblastic activity.

Correct Answer: C

Rationale: Ketoacidosis is most related to excess fatty acid catabolism. During this process, the body breaks down fatty acids into ketones, leading to an accumulation of ketones in the blood and causing metabolic acidosis. Adrenocortical insufficiency (A) is related to cortisol deficiency, not ketoacidosis. Cushing syndrome (B) is associated with excess cortisol production, not ketoacidosis. Hyperglycemia (D) is high blood sugar levels and is not directly related to the mechanism of ketoacidosis.

Correct Answer: D

Rationale: Step-by-step rationale: 1. The anterior pituitary gland is connected to the hypothalamus by the portal capillaries. 2. This connection allows for the transport of releasing hormones from the hypothalamus to the anterior pituitary. 3. Releasing hormones stimulate the anterior pituitary to release specific hormones. 4. This communication pathway is essential for regulating hormone production and maintaining homeostasis. Summary of other choices: A: Incorrect. The neurohypophysis refers to the posterior pituitary, not the anterior pituitary. B: Incorrect. ADH and oxytocin are released from the posterior pituitary, not the anterior pituitary. C: Incorrect. Releasing hormones are produced by the hypothalamus, not the anterior pituitary.