The major tropic action of growth hormone is to signal the __________ to release __________.

• A. thyroid; T₃ and T₄
• B. pancreas; glucagon
• C. hypothalamus; thyroid-releasing hormone
• D. adrenal medulla; epinephrine
• E. liver; insulin-like growth factors (IGFs)

Answer: (E)

Verified step by step guidance

1. Understand the role of growth hormone: Growth hormone (GH) is a peptide hormone that stimulates growth, cell reproduction, and regeneration in humans and other animals. It is crucial for development and metabolism.
2. Identify the target organ: Growth hormone primarily targets the liver. The liver is responsible for producing various proteins and hormones that are essential for growth and metabolism.
3. Determine the hormone released by the liver: When stimulated by growth hormone, the liver releases insulin-like growth factors (IGFs). These factors play a significant role in promoting growth and development, particularly in bones and tissues.
4. Differentiate from other options: The thyroid releases T3 and T4, which are involved in metabolism regulation. The pancreas releases glucagon, which raises blood glucose levels. The hypothalamus releases thyroid-releasing hormone, which stimulates the thyroid gland. The adrenal medulla releases epinephrine, which is involved in the fight-or-flight response.
5. Conclude the correct answer: Based on the understanding of growth hormone's action, the correct answer is that growth hormone signals the liver to release insulin-like growth factors (IGFs).