The binding of a steroid hormone to its receptor would lead to the __________.

Correct Answer: A

Rationale: The correct answer is A because the binding of a steroid hormone to its receptor triggers a series of events that ultimately lead to the transcription of DNA for the gene that is 'turned on'. This process involves the hormone-receptor complex entering the nucleus, binding to specific DNA sequences, recruiting transcription factors, and initiating gene expression. Choice B is incorrect because steroid hormones do not typically use second messengers for signaling. Choice C is incorrect because while some hormones can activate enzymes indirectly, steroid hormones primarily act through gene transcription. Choice D is incorrect because cAMP is typically associated with signaling pathways involving non-steroid hormones like adrenaline.

Correct Answer: C

Rationale: The correct answer is C: Pretracheal fascia. This layer surrounds the thyroid gland, forming the false capsule. It separates the thyroid from the strap muscles anteriorly and the trachea and esophagus posteriorly. The Carotid sheath (A) encloses the common carotid artery, internal jugular vein, and vagus nerve. The Investing layer (B) covers the sternocleidomastoid and trapezius muscles. The Prevertebral fascia (D) surrounds the vertebral column and deep neck muscles, not directly related to the thyroid gland.

Correct Answer: C

Rationale: The correct answer is C because the hypothalamus does not directly secrete ACTH, TSH, and gonadotropins. It secretes releasing hormones that regulate the secretion of these hormones from the anterior pituitary gland. Choice A and B are correct because the hypothalamus does secrete releasing hormones and controls the anterior pituitary gland. Choice D is incorrect because the hypothalamus synthesizes oxytocin and ADH, which are stored in the posterior pituitary gland.

Correct Answer: D

Rationale: The correct answer is D, the anterior pituitary gland, because it secretes TSH, ACTH, and growth hormone. The anterior pituitary gland is also known as the adenohypophysis, and it plays a key role in regulating various bodily functions through the release of different hormones. The other choices are incorrect because the neurohypophysis (choice A) secretes hormones like oxytocin and vasopressin, the pancreas (choice B) secretes insulin and glucagon, and the adrenal medulla (choice C) secretes adrenaline and noradrenaline.

Correct Answer: D

Rationale: Correct Answer: D Rationale: Calcitonin and parathyroid hormone regulate plasma calcium levels. Calcitonin decreases calcium levels by inhibiting bone breakdown, while parathyroid hormone increases calcium levels by stimulating bone breakdown and increasing calcium reabsorption. Therefore, both hormones work together to maintain calcium homeostasis. The correct answer, choice D, highlights that both hormones control plasma calcium levels. Summary of Other Choices: A: Incorrect. Calcitonin is secreted by the thyroid gland, not the parathyroid glands. B: Incorrect. Calcitonin decreases plasma calcium levels, while parathyroid hormone increases plasma calcium levels. C: Incorrect. Parathyroid hormone increases plasma calcium levels, whereas calcitonin decreases plasma calcium levels.