The kidneys (two in number) are situated in the abdominal cavity on the two sides of the body. They contain a network of very minute tubelike structures through which blood is strained, and the unwanted materials like extra amount of water, salts, waste products of digestion and other biochemical processes, are separated from the blood. This forms the urine, which goes down from the kidneys through two tubes called the ureters, to the bladder. The urine is passed out of the body through a duct called urethra.The skin provides another arrangement for getting rid of excess salts and water in the blood. This is achieved by minute glands called the sweat glands which are situated under the skin. When the blood flows through the sweat glands, they separate some salts and water, along with some other unwanted materials, from the blood. The separated fluid comes to the surface in the form of sweat, and evaporates. This helps to keep the body temperature normal during hot summer days.The Endocrine SystemThis system consists of many glands situated at various places in the body. The important ones among them are: the pituitary, the pineal (both in the head), the thyroid, the parathyroids (both in the neck), the thymus (in the thoracic cavity), adrenals, and the sex glands (in the abdominal cavity). A special feature of these glands is that there are no ducts to carry their secretions(called hormones) outside the glands. Hence they are also called the ductless glands. The hormones prouced in the endocrine glands are thrown directly in the blood flowing through them and are thus made available to different organs and tissues of the body. The hormones (e,g. pituitrin, thyroxin, adrenalin, etc.) are very much essential for a proper development of the body, and are found to be intimately concerned with many important functions like metabolism, growth, sexual maturity, emotional set-up, action of the heart and the lungs, and so on. A deficiency as well as an excess of the secretion of hormones may lead to many disorders.