Decreased blood volume and pressure will activate the renin-angiotensin system and production of angiotensin II. This peptide will activate supraoptic and paraventricular nucleus in hypothalamus stimulating the synthesis of antidiuretic hormone (vasopressin). This hormone is further transported to the posterior pituitary gland where it is released into the blood flow. Vasopressin binds to V1-receptors located on vascular smooth muscles leading to vasoconstriction increasing systemic vascular resistance. On the other hand, vasopressin bind to V2-receptors located on the basolateral membrane of collecting duct. This process leads to the insertion of water channels (aquaporins) into the apical membrane of collecting duct cells increasing water reabsorption by kidneys. This process leads to increased blood volume. As a result, activation of V1-receptors and V2-receptors results increases blood pressure.
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