Sweat is water, salt, some urea. Sweat gland is coiled tubule in dermis, straightens as exits through epidermis. With kidney failure, urea is excreted by sweat glands and forms urea-frost on skin surface. Urochrome is yellow pigment derived from heme breakdown and is excreted by kidneys. Liver also excretes cholesterol and excess fat-soluble vitamins.
Expiration also results in unavoidable loss of water.
Nitrogenous wastes are products of metabolism of amino acids, nucleotides and creatine phosphate. Amino acid metabolism produces urea as main nitrogenous end product in humans. Are bean-shaped, reddish brown organs. About size of a fist. Located on either side of vertebral column just below diaphragm.