Circumventricular organs

Circumventricular organs are specialized areas in the brain located around the ventricles (fluid-filled spaces), designed to monitor substances in the blood because they have a weaker blood-brain barrier. Unlike most parts of the brain that tightly filter blood substances, these organs allow essential signals—such as detecting toxins, hormones, or metabolic changes—to pass freely. This enables the brain to respond promptly to changes in blood chemistry, regulating functions like thirst, hunger, blood pressure, and immune responses effectively.