In the adrenal medulla:

Correct Answer: C

Rationale: Rationale for Choice C: Plasma norepinephrine levels are generally unchanged after adrenalectomy in the adrenal medulla because norepinephrine is mainly produced by postganglionic sympathetic nerve endings rather than the adrenal medulla. Adrenalectomy removes the adrenal gland, which primarily secretes epinephrine, not norepinephrine. Therefore, plasma norepinephrine levels would not be significantly affected by adrenalectomy. Summary of other choices: A: Incorrect. Epinephrine is formed from norepinephrine, not tyrosine, through methylation and hydroxylation. B: Incorrect. The majority of cells in the adrenal medulla are epinephrine-secreting cells, not just 10%. D: Incorrect. The half-life of catecholamines in the circulation is very short, around 2 minutes, not 10 minutes.

Correct Answer: D

Rationale: The correct answer is D: acromegaly. After body growth is completed, excess GH production can lead to acromegaly, a condition characterized by the enlargement of bones and tissues. This occurs because GH continues to stimulate bone and tissue growth. Kidney failure (A) is not directly related to excess GH production. Tetany (B) is caused by low calcium levels, not excess GH. Gigantism (C) occurs when excess GH is produced during the growth years, leading to abnormal height, not after growth is completed. Therefore, the correct answer is D as it directly correlates with the scenario provided.

Correct Answer: D

Rationale: The correct answer is D because corticosteroids are produced by the adrenal cortex, not the adrenal medulla. Cortisol is a type of corticosteroid, making choice A incorrect. Androgens are indeed produced by the adrenal cortex, making choice B correct. Calcitonin is produced by the thyroid, not the adrenal cortex, making choice C incorrect. Therefore, the only pair that is incorrect is corticosteroid and adrenal medulla.

Correct Answer: D

Rationale: The correct answer is D: Epiglottis. The epiglottis is a flap of tissue that covers the trachea during swallowing, preventing food from entering the lungs. When food is swallowed, the epiglottis closes off the trachea to ensure that the food goes down the esophagus into the stomach. Incorrect choices: A: The pyloric sphincter is a valve located between the stomach and the small intestine, regulating the flow of partially digested food. B: The trachea is the windpipe that connects the larynx to the bronchi, allowing air to pass into the lungs. C: The pharynx is the throat area where the pathways for both food and air cross, but it is the epiglottis that specifically prevents food from entering the lungs.

Correct Answer: B

Rationale: The correct answer is B: Pituitary gland. The pituitary gland is considered the most influential endocrine gland because it controls the functions of other endocrine glands by secreting various hormones that regulate growth, reproduction, metabolism, and other bodily functions. It is often referred to as the "master gland" due to its crucial role in maintaining hormonal balance and homeostasis in the body. Rationale: A: Pineal gland - The pineal gland primarily regulates the sleep-wake cycle through the secretion of melatonin and is not as influential in overall endocrine function as the pituitary gland. C: Thyroid gland - The thyroid gland regulates metabolism through the production of thyroid hormones, but it does not have the same level of control over other endocrine glands as the pituitary gland. D: Adrenal gland - The adrenal gland produces hormones like cortisol and adrenaline, which are important for stress response and metabolism, but it does not have the same regulatory influence over other