Insulin, a small (51-amino-acid) protein, is synthesized by the beta cells of the pancreas. This hormone is released ________.

Correct Answer: C

Rationale: The correct answer is C because insulin is released when the body's glucose level rises. This is a key function of insulin to regulate blood sugar levels. When glucose levels increase after a meal, beta cells release insulin to help cells absorb and use glucose for energy. This process helps to maintain blood sugar within a healthy range. Choice A is incorrect because insulin release is not necessarily excessive in obese people, but rather it can be impaired due to insulin resistance. Choice B is incorrect because insulin is typically released in response to high blood sugar levels, not physical stress. Choice D is incorrect because insulin is released when blood sugar levels drop too low, not rise.

Correct Answer: A

Rationale: The correct answer is A: liver. Thyroid hormone affects the liver by regulating metabolism and energy production. It increases the breakdown of fats, proteins, and carbohydrates. The liver plays a crucial role in converting thyroid hormones into their active form. Summary: B: The spleen is not directly affected by thyroid hormone. C: The thyroid gland produces thyroid hormone but is not directly affected by it in adults. D: While the brain is indirectly influenced by thyroid hormone, it is not a primary target organ for its effects in adults.

Correct Answer: B

Rationale: The correct answer is B: hormonal, humoral, and neural. Hormonal regulation involves feedback loops where hormone levels control their own production. Humoral regulation involves substances in body fluids influencing hormone release. Neural regulation involves the nervous system influencing hormone production. Option A is incorrect because sensory mechanisms do not directly control hormone production. Option C is incorrect because sensory mechanisms are not typically involved in hormone regulation. Option D is incorrect because hormonal control is a key mechanism that was omitted.

Correct Answer: C

Rationale: The correct answer is C: growth hormone and LH. The anterior pituitary gland secretes these hormones. Growth hormone regulates growth, metabolism, and body composition, while LH (luteinizing hormone) plays a role in reproductive function. A: Anti-diuretic hormone and oxytocin are produced by the posterior pituitary gland. B: ACTH (adrenocorticotropic hormone) is secreted by the anterior pituitary, but insulin is produced by the pancreas. D: Thyroxine is released by the thyroid gland, and cortisol is produced by the adrenal glands, not the anterior pituitary.

Correct Answer: D

Rationale: The correct answer is D: parathyroid hormone. Calcitonin and parathyroid hormone regulate calcium levels in the blood. Calcitonin lowers blood calcium levels by inhibiting bone resorption, while parathyroid hormone increases blood calcium levels by promoting bone resorption. Thus, they have opposite effects on calcium regulation, making parathyroid hormone the antagonistic hormone to calcitonin. Thyroxine (A), growth hormone (B), and insulin (C) do not directly oppose the action of calcitonin in regulating calcium levels.