Part of that extra thickness is caused by the protein keratin, which is nourished in deeper layers of the skin but forms a surface layer of dead cells on the epidermis. This extra thickness may also explain why your hands and feet become wrinkled when you soak in the tub.
Antidiuretic hormone (ADH), also called arginine vasopressin (AVP), is a hormone that helps regulate water balance in the body by controlling the amount of water the kidneys reabsorb while they are filtering wastes out of the blood. This test measures the amount of ADH in the blood.
ADH is produced in the hypothalamus and stored in the pituitary gland. It's released from there into the bloodstream, and it affects how the kidneys work by letting them know how much water they need to keep in or get out of the body. You may not know it, but you can actually see it at work pretty easily!