Water concentration of body is monitored by osmoreceptors in hypothalamus, which detect concentration of electrolytes in extracellular fluid. When osmolarity (plasma sodium concentration) increases above normal because of water deﬁcit, feedback system operates.
Osmoreceptors are sensory receptor primarily found in hypothalamus ( located in vascular organ of lamina terminalis, a circumventricular organ ) of most homoeothermic organisms that detects changes in osmotic pressure. They contribute to osmoregulation controlling fluid balance in the body. They are defined functionally as neurons that have an intrinsic ability to detect changes in osmolality.
Urine formation begins with ﬁltration of large amounts of ﬂuid through glomerular capillaries into Bowman’s capsule. Glomerular Filtration takes place through the semipermeable walls of the glomerulus and glomerular capsule.
The filtrate in the glomerulus is very similar in composition to plasma with the important exceptions of plasma proteins and blood cells.