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Vasopressin, also known as antidiuretic hormone (ADH) or arginine vasopressin (AVP), is a hormone that plays a crucial role in regulating water and sodium balance in the body. It primarily affects the kidneys, increasing water reabsorption and thus decreasing urine output, and also constricts blood vessels, which can raise blood pressure. Vasopressin is synthesized in the hypothalamus and released from the posterior pituitary gland.
Vasopressin is a hormone that plays a key role in maintaining osmolality (the concentration of dissolved particles, such as salts and glucose, in the serum) and therefore in maintaining the volume of water in the extracellular fluid (the fluid space that surrounds cells). This is necessary to protect cells from sudden increases or decreases in water content, which are capable of interfering with proper cell function. Normal serum osmolality ranges from about 285 to 300 milliosmoles per kilogram (mOsm/kg) in healthy people. Vasopressin and a hormone called oxytocin evolved from a single primordial neurohypophyseal hormone called vasotocin, which is present in lower vertebrates.
Special nerve cells called osmoreceptors in the hypothalamus are very sensitive to changes in serum osmolality. The osmoreceptors are closely associated with the same nerve cells that produce and secrete vasopressin. Serum osmolality that increases or decreases by as little as 1 percent can cause respective decreases or increases in vasopressin release.
This stimulation leads to the separation of vasopressin from molecules of neurophysin, to which vasopressin is loosely attached within the secretory cells. Vasopressin is then released from the posterior pituitary gland, leading to the subsequent retention of water by the kidneys. This inhibition leads to a decrease in vasopressin secretion and a subsequent increase in water excretion. The osmoreceptors are also closely linked to the thirst centre, which is stimulated by high serum osmolality and is inhibited by low serum osmolality in the same way as is vasopressin secretion.
In the kidneys, vasopressin acts on the cells of the collecting ducts. These cells contain receptors for vasopressin that are linked to vesicles that contain special water channels (aquaporins). When the cells are stimulated by vasopressin, the aquaporins fuse with the region of the cell membrane that is exposed to urine, allowing water to enter the cells. The water is then returned to the circulation. This causes the volume of urine to decrease and the urinary content of sodium, chloride, and other substances to increase. When this occurs, the urine is said to be concentrated.
Vasopressin, also known as antidiuretic hormone (ADH) or arginine vasopressin (AVP), is a hormone that regulates water and sodium balance in the body. It increases water reabsorption in the kidneys and constricts blood vessels.
Vasopressin is synthesized in the hypothalamus and is released from the posterior pituitary gland.
In healthy people, normal serum osmolality ranges from about 285 to 300 milliosmoles per kilogram (mOsm/kg).
Osmoreceptors are special nerve cells in the hypothalamus that are highly sensitive to changes in serum osmolality. They are closely associated with the nerve cells that produce and secrete vasopressin.
In the kidneys, vasopressin acts on the cells of the collecting ducts. It stimulates aquaporins (water channels) to fuse with the cell membrane, allowing water to enter the cells and return to circulation, which decreases urine volume and concentrates the urine.
The thirst centre is closely linked to osmoreceptors. It is stimulated by high serum osmolality and inhibited by low serum osmolality in the exact same way that vasopressin secretion is regulated.
