In the context of the hypothalamus and pituitary gland, what is a tropic hormone?

• A. A hormone that acts only within the hypothalamus as a neurotransmitter and is not released into the bloodstream
• B. A hormone that directly stimulates a skeletal muscle fiber to contract
• C. A hormone that primarily lowers blood glucose by increasing cellular uptake of glucose
• D. A hormone that stimulates another endocrine gland to secrete its hormones

Answer: (D)

Verified step by step guidance

1. Step 1: Understand the definition of a tropic hormone. Tropic hormones are hormones that regulate the function of other endocrine glands by stimulating them to release their own hormones.
2. Step 2: Recognize that the hypothalamus and pituitary gland are key players in the endocrine system, where the hypothalamus releases hormones that control the pituitary, and the pituitary releases tropic hormones that regulate other glands.
3. Step 3: Differentiate tropic hormones from other types of hormones, such as those that act directly on target tissues (e.g., skeletal muscle) or those that act locally within the brain (e.g., neurotransmitters).
4. Step 4: Identify that a tropic hormone's primary role is to stimulate another endocrine gland, not to act directly on non-endocrine tissues or to function solely within the brain.
5. Step 5: Conclude that the correct description of a tropic hormone is 'a hormone that stimulates another endocrine gland to secrete its hormones,' which aligns with the function of pituitary tropic hormones like TSH, ACTH, and LH.