During а hоt dаy, wаter is lоst thrоugh sweat. This decreases blood (fluid) volume. Blood volume decrease, which increases osmolarity of blood. Increasing osmolarity of the blood is detected by osmoreceptors in the hypothalamus. The sense of thirst is enhanced partially as a result of antidiuretic hormone (ADH). Drinking of fluids reverses the declining water volume. What is the control center?