Most hormones of the endocrine system are regulated by a:

Correct Answer: A

Rationale: The correct answer is A: Negative feedback mechanism. This is because most hormones in the endocrine system are regulated by a negative feedback loop, where the release of a hormone is inhibited once a certain level of that hormone is reached in the body. This helps maintain homeostasis. Incorrect choices: B: Positive feedback mechanism - This is less common in hormone regulation as it leads to amplification of a response rather than maintaining balance. C: Hormone-receptor complex - While hormones bind to receptors to exert their effects, this is not the primary mechanism of hormone regulation. D: Hormone-gene complex - While hormones can affect gene expression, this is not the primary mechanism of hormone regulation in the endocrine system.

Correct Answer: B

Rationale: The correct answer is B: Insulin. Insulin is a protein hormone produced by the pancreas that regulates blood sugar levels. Proteins are large molecules made up of amino acids, and insulin fits this definition. Oxytocin (A) is a peptide hormone, not a protein. TSH (C) and ADH (D) are both peptide hormones as well, not proteins. In summary, insulin is the only option that fits the criteria of being a protein hormone.

Correct Answer: C

Rationale: The correct answer is C: Parthormone. The anterior pituitary gland secretes hormones such as Growth hormone, Follicle stimulating hormone, and Thyroid stimulating hormone, but not Parthormone. Parthormone is actually produced by the parathyroid glands, not the anterior pituitary gland. Parathormone plays a key role in regulating calcium levels in the blood. Therefore, choice C is incorrect as it does not belong to the hormones secreted by the anterior pituitary gland.

Correct Answer: C

Rationale: The correct answer is C: Hyperpigmentation. Addison's disease is a condition characterized by adrenal insufficiency, leading to decreased production of cortisol and aldosterone. Hyperpigmentation is a common symptom due to elevated levels of ACTH stimulating melanin production. Other choices are incorrect because Addison's disease typically presents with hypotension, weight loss, and bradycardia, rather than hypertension, weight gain, or tachycardia.

Correct Answer: A

Rationale: The pituitary gland is often referred to as the 'master gland' because it plays a crucial role in regulating other endocrine glands in the body. It secretes hormones that control various bodily functions, such as growth, reproduction, and metabolism. The other choices, thyroid, thymus, and hypothalamus, are important glands as well, but they do not have the same broad control over the endocrine system as the pituitary gland. The thyroid regulates metabolism, thymus is involved in immune function, and hypothalamus regulates body temperature, hunger, and thirst. However, none of these glands have the overall regulatory function and influence on other glands as the pituitary gland does.