Answer: blood.
- A blood
- B nerves
- C only lymph
- D air
Correct answer: A. blood
Explanation: The bloodstream transports hormones to their target organs.
The hypothalamus releases hormones that direct the pituitary, which releases its own trophic hormone to a target gland; that gland's hormone output then feeds back (dashed lines) to suppress both the pituitary and hypothalamus once levels are sufficient - a self-correcting loop running the entire endocrine system.
Concept context
The endocrine glands, hormone classification and mechanism of action, and negative feedback regulation.