In circumstances where the body requires prolonged or increased levels of a hormone, the DNA of target cells will specify the synthesis of more receptors on the surface of the cells of the target organ. This is known as ________.

Correct Answer: C

Rationale: Step 1: Up-regulation refers to the process where cells increase the number of receptors in response to increased hormone levels. Step 2: This allows cells to become more sensitive to the hormone and maintain homeostasis. Step 3: The other choices are incorrect because they do not accurately describe the phenomenon of up-regulation. Step 4: Option A refers to sensitivity reaction in general, not specifically related to hormone receptors. Step 5: Option B does not accurately describe the process of increasing receptor numbers. Step 6: Option D mentions a reaction to a stressor, which is not directly related to the regulation of hormone receptors.

Correct Answer: C

Rationale: The correct answer is C: positive feedback. Oxytocin release is triggered by the positive feedback mechanism. When oxytocin is released in response to a stimulus, it further stimulates the release of more oxytocin, intensifying the effect. This continuous loop enhances the initial response, leading to a cascade effect. Negative feedback (choice A) works to maintain homeostasis by counteracting the initial stimulus, which is not the case for oxytocin release. Neutral feedback (choice B) does not play a significant role in regulating hormone release. Choice D is incomplete and irrelevant.

Correct Answer: A

Rationale: Rationale: 1. Hashimoto's disease is characterized by the immune system attacking the thyroid gland, leading to hypothyroidism. 2. It is an autoimmune condition where the body produces antibodies that target and destroy thyroid cells. 3. This results in a decrease in thyroid hormone production. 4. Graves disease (choice B) is a form of hyperthyroidism caused by an overactive thyroid gland. 5. Myxedema (choice C) refers to severe hypothyroidism but is not autoimmune. 6. Acromegaly (choice D) is a disorder caused by excess growth hormone production, unrelated to thyroid function.

Correct Answer: B

Rationale: The correct answer is B: right atrium of the heart. Atrial natriuretic hormone (ANH) is produced by specialized cells in the right atrium of the heart called atrial myocytes. When the heart senses an increase in blood volume or pressure, these cells release ANH to help regulate fluid and electrolyte balance by promoting sodium and water excretion by the kidneys. Choices A, C, and D are incorrect because ANH is not produced by the kidney tubules, adrenal cortex, or pancreas. The primary site of ANH production is specifically within the cardiac atria.

Correct Answer: B

Rationale: Correct Answer: B - aldosterone Rationale: 1. Aldosterone is a hormone produced by the adrenal glands that primarily regulates salt and water balance, not fuel metabolism. 2. Insulin helps in lowering blood sugar levels by facilitating glucose uptake by cells. 3. Glucagon stimulates the release of glucose from the liver to raise blood sugar levels. 4. Cortisol plays a role in mobilizing energy stores during stress. Summary: Aldosterone does not directly impact fuel metabolism like insulin, glucagon, and cortisol do. Insulin lowers blood sugar levels, glucagon raises blood sugar levels, and cortisol mobilizes energy stores during stress.