Answer: islets of Langerhans.
- A islets of Langerhans
- B the lung alveoli
- C the kidney nephrons
- D the gut villi
Correct answer: A. islets of Langerhans
Explanation: The islets of Langerhans secrete insulin and glucagon.
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.