Which statement best defines tropic hormones?

• A. Messengers carried by the bloodstream to other organs to influence secretion of additional hormones by another gland.
• B. Proteins that are produced by exocrine glands.
• C. Directly stimulate only the cells where they are produced.
• D. Secretions that are stored in glands and released on demand.

Answer: (A)

Tropic hormones are signaling substances whose main job is to regulate other endocrine glands. They travel through the bloodstream to distant targets and prompt those glands to increase or decrease their hormone output. This is exactly what the statement describes: they are messengers carried by the bloodstream to other organs to influence secretion of additional hormones by another gland.

Examples help: thyroid-stimulating hormone (TSH) prompts the thyroid to release thyroid hormones; adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex to secrete cortisol; follicle-stimulating hormone (FSH) and luteinizing hormone (LH) stimulate the gonads to produce sex hormones.

The other descriptions don’t fit tropic hormones. Exocrine glands produce non-hormonal secretions into ducts rather than hormones; hormones that directly stimulate only the cells where they’re produced act locally and aren’t regulating another gland; and secretions stored and released on demand refer to substances stored for immediate use rather than regulatory hormones controlling other glands.