Final answer:
Antidiuretic hormone (ADH), also known as vasopressin, is released by the posterior pituitary when blood pressure decreases or blood ionic concentration increases, promoting water retention in the kidneys and helping to restore normal blood pressure and fluid balance.
Step-by-step explanation:
The hormone that is produced by the hypothalamus and secreted from the posterior pituitary when blood pressure decreases or blood ionic concentration increases is known as antidiuretic hormone (ADH), also termed vasopressin.
ADH's main function is to regulate water reabsorption in the kidneys, ensuring body fluid balance and blood pressure regulation. If the body is dehydrated or under stress, which could be indicated by an increase in blood ionic concentration, the osmoreceptors in the hypothalamus detect this change and signal the release of ADH.
Consequently, ADH travels to the kidneys and promotes water reabsorption by increasing the permeability of the collecting ducts through the insertion of aquaporins. This action conserves water and contributes to increasing blood volume and pressure, effectively managing the body's fluid balance.
Key mechanisms involved in ADH's function include vasoconstriction and the promotion of water recovery in the kidneys under physiological stress or significant fluid loss. ADH also has a negative feedback loop; as blood osmolarity decreases, the hypothalamus reduces ADH secretion, normalizing urine production and maintaining homeostasis.