The relatively constant internal environment of the body is maintained by _______.

Correct Answer: C

Rationale: The correct answer is C: homeostasis. Homeostasis refers to the body's ability to maintain a stable internal environment despite external changes. It involves various physiological mechanisms to regulate temperature, pH, blood sugar levels, and more. Negative feedback (choice A) is a key component of homeostasis, where the body reverses a deviation from the set point to restore balance. Positive feedback (choice B) amplifies a response and does not contribute to maintaining stability. Metabolism (choice D) is the sum of all chemical processes in the body and is necessary for homeostasis but does not directly regulate the internal environment.

Correct Answer: D

Rationale: The correct answer is D because alcohol inhibits the release of antidiuretic hormone (ADH) from the pituitary gland. ADH helps regulate water balance by promoting water reabsorption in the kidneys, reducing urine output. Alcohol impairs this process, leading to increased urine production and dehydration. Choices A, B, and C are incorrect because ADH decreases urine production, prevents dehydration, and is produced in the neurohypophysis (posterior pituitary), not the adenohypophysis (anterior pituitary).

Correct Answer: B

Rationale: The correct answer is B: epinephrine. During the alarm phase of the general adaptation syndrome, the body activates the fight-or-flight response to cope with stress. Epinephrine, also known as adrenaline, is released by the adrenal glands in response to stress or danger. It increases heart rate, boosts energy, and enhances focus, preparing the body to either fight the stressor or flee from it. Estrogen (A) is a sex hormone, not involved in the fight-or-flight response. Angiotensinogen (C) and renin (D) are part of the renin-angiotensin-aldosterone system, regulating blood pressure and fluid balance, not directly related to the fight-or-flight response.

Correct Answer: B

Rationale: Correct Answer: B - Secretion of ACTH is regulated by a hypothalamic secretion. Rationale: 1. The hypothalamus secretes corticotropin-releasing hormone (CRH). 2. CRH stimulates the anterior pituitary to release adrenocorticotropic hormone (ACTH). 3. ACTH then stimulates the adrenal cortex to release cortisol. 4. This feedback loop demonstrates how ACTH secretion is regulated by a hypothalamic secretion. Summary: A - Incorrect. ACTH is secreted by the anterior pituitary, not the posterior pituitary. C - Incorrect. ACTH causes the release of hormones from the adrenal cortex, not the adrenal medulla. D - Incorrect. ACTH is a tropic hormone as it acts on another endocrine gland (adrenal cortex).

Correct Answer: B

Rationale: The correct answer is B: hormones. Hormones are chemical signals produced by glands that travel through the bloodstream to affect the behavior of other glands and tissues. Enzymes (choice A) are catalysts for chemical reactions, not signaling molecules. Carbohydrates (choice C) are energy sources and structural components, not signaling molecules. Metabolites (choice D) are the byproducts of metabolism, not signaling molecules. Hormones are specifically designed to regulate physiological processes in the body by acting on target cells, making them the most fitting choice among the options provided.