Atrial volume receptors are low pressure baroreceptor

Baroreceptor

Baroreceptors are sensors located in the blood vessels of several mammals. They are a type of mechanoreceptor that detects the pressure of blood flowing through them, and can send messages to the central nervous system to increase or decrease total peripheral resistance and cardiac output...

s that are found in the atria

Atrium (anatomy)

In anatomy, the atrium , sometimes called auricle , refers to a chamber or space. For example, the term is used for a portion of the lateral ventricle in the brain and the blood collection chamber of the heart...

 of heart.

When these receptors detect pressure drop in the atria, which is indicative for a decrease in blood volume, signal is transmitted from the atrial volume receptors to the hypothalamus

Hypothalamus

The Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...

 of brain. The hypothalamus, in turn, increases the production of vasopressin

Vasopressin

Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's...

 (ADH, AVP, or arginin vasopressin). Furthermore, low volume also stimulates sympathetic nerves, which stimulate renin

Renin

Renin , also known as an angiotensinogenase, is an enzyme that participates in the body's renin-angiotensin system -- also known as the Renin-Angiotensin-Aldosterone Axis -- that mediates extracellular volume , and arterial vasoconstriction...

 release from Juxtaglomerula cells of the afferent arteriole in kidneys. Renin leads to the activation of Angiotensin II, a potent agent in increasing blood pressure.