T3, T4, and calcitonin are:

Correct Answer: A

Rationale: Rationale: 1. T3, T4, and calcitonin are hormones secreted by the thyroid gland. 2. Thyroid gland is responsible for producing and releasing these hormones. 3. T3 and T4 regulate metabolism, while calcitonin helps regulate calcium levels. 4. Parathyroid glands secrete parathyroid hormone, not T3, T4, or calcitonin. 5. These hormones are not secreted in response to declining plasma levels of calcium. 6. T3, T4, and calcitonin are not steroids, they are peptide hormones. Therefore, the correct answer is A.

Correct Answer: B

Rationale: The correct answer is B: Portal capillaries. The hypothalamus and adenohypophysis are connected by a system of blood vessels called the hypothalamic-pituitary portal system, which includes portal capillaries. These capillaries carry releasing and inhibiting hormones from the hypothalamus to the adenohypophysis to regulate the secretion of pituitary hormones. The other choices are incorrect because: A: Islets of Langerhans are clusters of cells in the pancreas involved in insulin and glucagon production, not connected to the hypothalamus or adenohypophysis. C: The corpus callosum is a structure that connects the two cerebral hemispheres and is not related to the hypothalamus or adenohypophysis. D: The medulla oblongata is part of the brainstem responsible for autonomic functions and is not involved in connecting the hypothalamus and adenohypophysis.

Correct Answer: C

Rationale: Step-by-step rationale: 1. Hypocalcemic tetany is associated with low levels of calcium in the blood. 2. Parathyroid hormone (PTH) plays a crucial role in calcium regulation. 3. A deficiency of PTH can lead to decreased calcium levels, causing tetany. 4. Therefore, choice C is correct as hypocalcemic tetany may be caused by a deficiency of PTH. Summary: A: Incorrect. Hypocalcemic tetany leads to muscle spasms, not flaccid paralysis. B: Incorrect. Curare blockade affects neuromuscular transmission, not calcium levels. D: Incorrect. Insulin deficiency is associated with hyperglycemia, not hypocalcemia leading to tetany.

Correct Answer: C

Rationale: Rationale: 1. Myxedema is caused by hypothyroidism, which can be effectively treated with thyroxine. 2. Thyroxine is a synthetic form of thyroid hormone that helps restore thyroid hormone levels. 3. Myxedema symptoms such as fatigue, weight gain, and cold intolerance improve with thyroxine treatment. Summary of Incorrect Choices: A. Diabetes mellitus and hyperglycemia are not directly related to thyroid hormone levels. B. Hyperglycemia is not primarily treated with thyroxine. D. Graves' disease is a thyroid disorder characterized by hyperthyroidism, which requires different treatments than hypothyroidism.

Correct Answer: D

Rationale: Step-by-step rationale: 1. Hypocalcemic tetany results from low blood calcium levels. 2. Parathyroid hormone (PTH) regulates calcium levels by increasing calcium release from bones and reabsorption in the kidneys. 3. A deficiency in parathyroid activity leads to decreased calcium levels, causing tetany. 4. Choice D is correct as it directly links hypocalcemic tetany to parathyroid dysfunction. Summary: A: Incorrect, calcitonin lowers blood calcium levels. B: Incorrect, TSH regulates thyroid function, not calcium levels. C: Incorrect, osteoclasts break down bone tissue but are not directly related to hypocalcemic tetany.