Hormone release stops when the stimulus that triggered it – like thirst or high blood sugar is satisfied or corrected. This is called:

Correct Answer: B

Rationale: The correct answer is B: negative feedback system. In a negative feedback system, the body's response to a stimulus works to counteract the initial stimulus, bringing the body back to its set point. In the context of the question, hormone release stops when the stimulus is satisfied, which is characteristic of a negative feedback system. A: Positive feedback system amplifies the initial stimulus rather than counteracting it. C: Lock and key system refers to how enzymes bind to specific substrates, not related to hormone regulation. D: Solar system is unrelated to physiological processes.

Correct Answer: D

Rationale: The correct answer is D: Both A & B. The thyroid and parathyroid glands work together to regulate calcium levels in the blood. The parathyroid gland releases parathyroid hormone, which increases calcium levels, while the thyroid gland secretes calcitonin, which decreases calcium levels. Therefore, both glands play a crucial role in maintaining calcium homeostasis. Choice A, the thyroid gland, is incorrect as it primarily regulates metabolism. Choice C, the adrenal medulla, is incorrect as it is responsible for releasing adrenaline and noradrenaline, not regulating calcium levels.

Correct Answer: B

Rationale: The correct answer is B: Weight gain. Addison's disease is characterized by adrenal insufficiency, leading to symptoms such as salt craving, hypoglycemia, and hyperpigmentation due to increased melanin production. Weight loss, not weight gain, is commonly associated with Addison's disease due to decreased cortisol levels. Salt craving is due to sodium loss, hypoglycemia results from insufficient cortisol levels, and hyperpigmentation is caused by elevated ACTH levels stimulating melanin production. Weight gain is not a typical symptom, making it the correct answer.

Correct Answer: D

Rationale: The correct answer is D, receptor-mediated stimulus. Hormones can be stimulated by hormonal, humoral, or neural factors, but not directly by receptors. Hormonal stimulus involves other hormones triggering hormone release, humoral stimulus involves changing blood levels of ions or nutrients triggering hormone release, and neural stimulus involves direct nerve stimulation triggering hormone release. Receptor-mediated stimulus is not a recognized type of hormone stimulus because hormones do not directly respond to receptors in this context.

Correct Answer: A

Rationale: Aldosterone is the correct answer because it specifically acts on the kidneys to increase the reabsorption of sodium. It is produced by the adrenal glands in response to low blood pressure or low sodium levels. Aldosterone binds to receptors in the kidneys, leading to increased sodium reabsorption and potassium excretion. Angiotensin plays a role in stimulating the release of aldosterone, but it does not directly affect sodium reabsorption. ADH regulates water reabsorption, not sodium. ACTH stimulates the adrenal glands to produce cortisol, not aldosterone. Therefore, aldosterone is the hormone responsible for the reabsorption of sodium in the kidneys.