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Transcript:
Antidiuretic hormone, also known commonly
as arginine vasopressin, is a nine amino acid peptide produced in a part of the
brain called the hypothalamus. Within hypothalamic neurons, the hormone is
packaged in secretory vesicles with a carrier protein called neurophysin, and
both are released upon hormone secretion.
The hormone is released from the pituitary
gland, a small gland at the base of the brain. Therefore, ADH follows the simple
neuroendocrine pathway, in which the stimulus attaches to sensory neuron in
hypothalamus and a hormone is secreted.
·
Solubility
ADH is soluble in water because it contains
a hydroxyl group at the end of the peptide chain. Since hydroxyl group makes the
molecule polar, it can dissolve in polar solvent such as water.
·
Function
The single most important effect of
antidiuretic hormone is to conserve body water by reducing the loss of water in
urine. A diuretic is an agent that increases the rate of urine formation.
Injection of small amounts of antidiuretic hormone into a person or animal
results in antidiuresis or decreased formation of urine, and the hormone was
named for this effect.
Antidiuretic hormone is a peptide hormone
that increases water permeability of the kidney's collecting duct and distal
convoluted tubule by inducing translocation of aquaporin-CD water channels in
the kidney nephron collecting duct plasma membrane.
·
Receptor
Antidiuretic hormone binds to receptors on
cell’s surface in the collecting ducts of the kidney and promotes reabsorption
of water back into the circulation. In the absence of antidiuretic hormone, the
collecting ducts are virtually impermeable to water, and it flows out as urine.
·
Regulation
The production of ADH is a negative
feedback system. The most important variable regulating antidiuretic hormone
secretion is plasma osmolarity, or the concentration of solutes in blood.
Osmolarity is sensed in the hypothalamus by neurons known as an osmoreceptors,
and those neurons, in turn, stimulate secretion from the neurons that produce
antidiuretic hormone. When osmolarity is high in the blood, the pituitary gland
releases less ADH. Then, kidneys remove water from blood so more water is lost
in urine, which lowers the osmolarity.
On the other hand, the hypothalamus
releases more ADH when the water level in blood is low. Then, kidneys remove
less water from the blood so less water is lost in urine.
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