Thirst And Fluid Balance

Intracellular Fluid

Fluid contained within cells.

Extracellular Fluid

All body fluids outside of cells.

Intravascular Fluid

Fluid found within blood vessels.

Interstitial Fluid

Fluid that bathes cells and fills the space between cells.

Isotonic

Having equal osmotic pressure to the contents of a cell.

Osmometric Thirst

Thirst produced by an increase in the osmotic pressure of the interstitial fluid relative to the intracellular fluid.

Osmoreceptor

A neuron that detects changes in the solute concentration of the interstitial fluid surrounding it.

Circumventricular Organs

Specialized brain regions with a rich blood supply located along the ventricular system; they include the OVLT and SFO.

OVLT

A circumventricular organ that lacks a blood-brain barrier and contains most osmoreceptors.

SFO

A circumventricular organ containing some osmoreceptors; it also detects angiotensin in the blood and helps initiate drinking.

Adipsia

Lack of Drinking

Vasopressin (ADH)

A hormone released by the posterior pituitary that helps conserve water by causing the kidneys to reabsorb water and excrete concentrated urine.

Volumetric Thirst

Thirst produced by hypovolemia, or a reduction in the volume of intravascular fluid (puking)

Hypovolemia

A reduction in the volume of intravascular fluid.

Renin

A hormone secreted by the kidneys that causes the conversion of angiotensinogen to angiotensin II.

Angiotensin II

A peptide hormone that constricts blood vessels, causes retention of sodium and water, and produces thirst and a salt appetite.

Median Preoptic Nucleus (MPON)

A brain region that receives input from the OVLT, SFO, and nucleus of the solitary tract; its output drives drinking behavior