Steroid hormones influence cellular activities by __________.

Correct Answer: B

Rationale: The correct answer is B because steroid hormones bind to DNA and form a gene-hormone complex, which then regulates gene expression. This directly influences cellular activities at the genetic level. Choices A, C, and D are incorrect because steroid hormones do not activate cyclic AMP, G proteins, or use calcium ions as second messengers for their cellular actions. Steroid hormones act through genomic mechanisms, not via the signaling pathways associated with choices A, C, and D.

Correct Answer: C

Rationale: Rationale: The isthmus of the thyroid gland is located between the 2nd and 3rd tracheal rings. These rings provide support to the trachea and help maintain its shape. Therefore, the correct answer is C. Summary of other choices: A: 1st and 2nd - Incorrect, as the isthmus is not related to the 1st tracheal ring. B: 1st, 2nd and 3rd - Incorrect, as the isthmus is only between the 2nd and 3rd tracheal rings. D: 2nd, 3rd and 4th - Incorrect, as the isthmus does not extend to the 4th tracheal ring.

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.