AP BIOLOGY

Detailed explanation-1: -Osmolality of body fluids is monitored by hypothalamic osmoreceptors, which regulate both water intake (thirst) and renal conservation of water through adjustments in the rate of ADH secretion (see Chapter 9).

Detailed explanation-2: -An osmoreceptor is a sensory receptor primarily found in the hypothalamus of most homeothermic organisms that detects changes in osmotic pressure. Osmoreceptors can be found in several structures, including two of the circumventricular organs – the vascular organ of the lamina terminalis, and the subfornical organ.

Detailed explanation-3: -Osmoreceptors are therefore defined functionally as neurons that are endowed with an intrinsic ability to detect changes in ECF osmolality, and it is now known that both cerebral and peripheral osmoreceptors contribute to the body-fluid balance.

Detailed explanation-4: -First, a region in the brain called the anterior hypothalamus has a cluster of neurons called supraoptic nuclei, which have osmoreceptors that sense even tiny changes in osmolarity, as small as 1 mOsm/L. These neurons are always sampling the blood that passes by.

Detailed explanation-5: -Osmoreceptors regulate sodium and water balance in a manner that maintains the osmotic pressure of the extracellular fluid (ECF) near an ideal set point.