Types of Thirst

1. Osmomatric Thirst

The term means to the fact that three detectors or actually responding to change in the concentration of the inter-stitial fluid that surrounds them. Osmosis means the movement of water through semipermeable membrane from a region of low solute concentration to one of high solute concentration.
Semipermeable membrane -- A membrane that allows some but not all molecules to pass through osmomatric thirst produce by an increase in the osmomatric pressure of the inter-stitial fluid relative to intra-cellular, thus produce cellular dehydration.
Osmosis receptors -- Neurons that detect in the solute concentration of the intra-stitial fluid that surrounds in and are responsible of osmomatric thirst and located in the region of the anterior of hypothalamus.
Thirst osmomatric -- Thirst produce by increase in the relative osmatic pressure of extra cellular fluid which results from loss of cellular fluid.
Thirst volumetric -- Thirst produce by decrease amount of extra cellular fluid in the body.

2. Volumetric Thirst

This type of thirst is associated with the decrease volume of the blood or blood plasma or decrease in intra vascular volume and it occur mostly through evaporation or through loss of blood, vomiting and diarrhea.
Receptors of kidney -- These are the receptors which controlled the secretion of Angiotensin.
Angiotensin is a peptide hormone that constrict blood vessels causes the retension of sodium and water produce thirst and salt appetite.
Receptors of Heart and Blood -- These are also known as arterial baror receptors. These are associated with the volumetric thirst lie within the heart which contains sensory neurons when the blood plasma fall in the vessels. These receptors detect the change and stimulate processes.

Organum Vasculosum of the Lamina terminals (OVLT)

A circum ventricular organ located anterior portion of the third ventricle served by fenestrated capillaries and it is known to be blood brain barrier.

Sub Fornical Organ (SFO)

A small organ located in the lateral ventricle attached to the underside of the fornics contain neurons that detect the presence of angiotensin in the blood and excite neural circuits that initiate drinking.
Neural Mechanism of Thirst
1) Some part of anterior third ventricle and dorsal.
2) Hormones get signals from angiotensin.