In endocrine physiology, what mechanism controls most hormone concentrations in the blood?

• A. Neural reflex arcs that directly maintain constant hormone levels without endocrine glands
• B. Negative feedback loops that reduce further hormone secretion when levels rise
• C. Positive feedback loops that amplify hormone secretion until an endpoint is reached
• D. Random secretion patterns independent of target tissue responses

Answer: (B)

Verified step by step guidance

1. Understand that hormone concentrations in the blood are primarily regulated to maintain homeostasis, ensuring that levels stay within a narrow, optimal range.
2. Recognize that negative feedback loops are a common physiological mechanism where an increase in hormone levels triggers responses that inhibit further hormone secretion, thus preventing excessive accumulation.
3. Contrast negative feedback with positive feedback loops, which amplify hormone secretion but are typically involved in specific, time-limited processes rather than ongoing regulation.
4. Note that neural reflex arcs can influence hormone secretion but do not usually maintain constant hormone levels independently without endocrine gland involvement.
5. Conclude that the primary mechanism controlling most hormone concentrations in the blood is negative feedback loops, which reduce further hormone secretion when hormone levels rise.