The |kidneys| are responsible for filtering toxins, wastes, ingested water, and mineral salts out of the bloodstream. |Kidneys| are also responsible for regulating the acidity of the ~blood~ by excreting alkaline salts when necessary. The two, bean-shaped organs are located in the ~posterior~ (back) part of the abdomen, flanking the |vertebral column| and approximately between the twelfth thoracic and third |lumbar vertebrae|. Often, the left |kidney| is positioned up to an inch higher than the right |kidney|. Each |kidney| is about 4-5 inches long and about two inches thick, weighing 4-6 ounces in the average adult. Because of the high degree of vascularity (presence of ~blood~ vessels), the |kidneys| are colored a dark reddish-brown.
Each |kidney| features a concave lateral side, where an opening, called the |hilus|, admits the |renal artery|, the |renal vein|, ~nerves~, and the |ureter|. Within the |kidney| is the ~renal~ (referring to the |kidney|) ~sinus~, or cavity. Within the |renal sinus| are the functional group of the filtration called the |nephrons|, of which there are more than a million within each |kidney|. At the top of each |kidney| is an adrenal (also called suprarenal) gland. In a general sense, ~blood~ which passes into the |kidney| transmits soluble waste through the |nephrons|, and this liquid, called ~urine~, is passed down the |ureter| and into the |bladder| to await discharge.
