Open-loop negative feedback refers to the phenomenon of

Open-loop negative feedback refers to the phenomenon of

• A. Negative feedback with a modifiable set point
• B. Blood flow in the hypothalamic-hypophyseal portal system
• C. Blood flow to the pituitary via dural-penetrating vessels
• D. Negative feedback involving an unvarying, fixed set point

Answer: (D)

In regulation, a negative feedback loop compares the current state to a reference value, called the set point, and acts to reduce the difference. When that reference value is fixed and does not change in response to disturbances, the system has an unvarying set point. The feedback then works to pull the variable back toward this constant target, but the target itself isn’t adjusted by the loop. That combination—negative feedback that uses a constant, unchanging reference—is what open-loop negative feedback describes. If the reference could shift in response to signals or conditions, the set point would be variable, which goes beyond open-loop behavior and into adaptive or closed-loop regulation. The other options describe mechanisms or anatomical details not about fixed versus changeable set points.

In regulation, a negative feedback loop compares the current state to a reference value, called the set point, and acts to reduce the difference. When that reference value is fixed and does not change in response to disturbances, the system has an unvarying set point. The feedback then works to pull the variable back toward this constant target, but the target itself isn’t adjusted by the loop. That combination—negative feedback that uses a constant, unchanging reference—is what open-loop negative feedback describes.

If the reference could shift in response to signals or conditions, the set point would be variable, which goes beyond open-loop behavior and into adaptive or closed-loop regulation. The other options describe mechanisms or anatomical details not about fixed versus changeable set points.