The organum vasculosum of the lamina terminalis (OVLT) is one of the circumventricular organs of the brain . Other circumventricular organs are the subfornical organ (SFO) and the area postrema in the brainstem. The OVLT and the SFO are both strongly interconnected with the medial preoptic nucleus of the hypothalamus (the nucleus medianus), and together these three structures comprise the so called "AV3V" region - the region anterior and ventral to the third ventricle. The AV3V region is very important in the regulation of fluid and electrolyte balance, by controlling thirst, sodium excretion, blood volume regulation, and vasopressin secretion. The Subfornical organ is one of the circumventricular organs of the brain and is involved in thirst-regulation. ... The brain stem is the stalk of the brain below the cerebral hemispheres. ... In the anatomy of mammals, the hypothalamus is a region of the brain located below the thalamus, forming the major portion of the ventral region of the diencephalon and functioning to regulate certain metabolic processes and other autonomic activities. ...

The OVLT is outside the blood brain barrier, and so neurons in this region can respond to factors that are present in the systemic circulation. The blood-brain barrier is a physical barrier between the blood vessels in the central nervous system, and the central nervous system itself. ...

Some neurons in the OVLT are osmoreceptors, being sensitive to the osmotic pressure of the blood. These neurons project to the supraoptic nucleus and paraventricular nucleus to regulate the activity of vasopressin-secreting neurons. These neurons also project to the nucleus medianus (also called the medial preoptic nucleus) which is involved in controlling thirst. An osmoreceptor is a sensory receptor primarily found in the hypothalamus of most homeothermic organisms that detects changes in osmotic pressure. ... Osmotic pressure or turgor (also called turgor pressure) is the pressure produced by a solution in a space that is enclosed by a differentially permeable membrane. ... In biology, the supraoptic nucleus is a nucleus of magnocellular neurosecretory cells in the hypothalamus, their axons extend into posterior pituitary. ... The paraventricular nucleus (PVN) is an aggregation of neurons in the hypothalamus, adjacent to the third ventricle. ... Arginine vasopressin (AVP), also known as argipressin or antidiuretic hormone (ADH), is a human hormone that is mainly released when the body is low on water; it causes the kidneys to conserve water by concentrating the urine and reducing urine volume. ... Drinking is the act of consuming a liquid through the mouth, almost always largely consisting of water. ...