Final answer:
ADH's primary function is to conserve water in the body by affecting the kidneys' collecting ducts to reabsorb more water, leading to less water being excreted in urine and overall conservation of body fluids.
Step-by-step explanation:
The function of antidiuretic hormone (ADH), also known as vasopressin, is to promote water conservation in the body. ADH is secreted by the hypothalamus and released from the posterior pituitary gland and acts on the kidneys. Its main action is to make the collecting ducts of the kidneys more permeable to water, which leads to the reabsorption of more water back into the bloodstream, thus reducing urine volume and conserving body water.
Additionally, ADH can act as a vasoconstrictor, which helps in increasing blood pressure during situations like hemorrhaging, further aiding in the body's fluid management.