The nephron is surrounded by peritubular capillaries. A human kidney contains about a million nephrons. The collecting duct at the end of each nephron adjusts the amount of water and sodium in the urine, so that when the body needs to conserve water the urine is concentrated. The cells of the collecting ducts have receptors for two hormones involved in the regulation of urine volume and contents. ADH is produced in the brain.
Aldosterone is a steroid hormone that causes the reabsorption of sodium.
Aldosterone is produced in the adrenal gland. Nitrogenous wastes are continually created in the body by the breakdown of proteins, amino acids, and nucleotides. The major forms of nitrogenous wastes produced by animals are ammonia, urea, and uric acid. Habitat, phylogeny, and embryonic pattern of development predict which form a particular species of animal will use the most. Read sections 43.1, 43.2, 43.3, and 43.4.