Anatomy of the urinary system

The urinary system is a group of organs in the body concerned with filtering out excess of fluid and other substances from the bloodstream. This system keeps the chemicals and water in your body balanced. It consists of two kidneys, which secrete the urine, the ureters, or ducts, which convey urine to the urinary bladder, where it is stored for some time; and the urethra, through which it is discharged from the body.

The kidneys are paired bean-shaped organs of purplish or brown colour. They have two surfaces, two borders, and an upper and lower extremity. There are three major regions of the kidney: the renal cortex, the renal medulla and the renal pelvis.

The kidneys are situated in the posterior part of the abdomen, behind the peritoneum. They are covered by the renal capsule. Each kidney is about 11.25 cm in length, 5 cm in breadth, and 2.5 cm in thickness. The left kidney is longer and narrower, than the right one. The weight of the kidney in the adults varies from 170 gm to 115 gm.

There are more than 1000000 nephrons in each kidney. The nephron carries out nearly all of the kidney's functions. Its chief function is to regulate the concentration of water and soluble substances like sodium salts by filtering the blood, reabsorbing what is needed and excreting the rest as urine. The nephron eliminates waste substances from the body, regulates blood volume and blood pressure, controls levels of electrolytes and metabolites, and regulates blood pH. The inflammation of nephrons in the kidneys is called nephritis.

The ureters are two tubes which measure from 25 to 30 cm in length. They convey the urine from the kidneys to the urinary bladder.

The urinary bladder is a triangle-shaped, hollow musculomembranous organ. It is located in the lower part of the abdomen and is held in place by ligaments that are attached to other organs and the pelvic bones. After the urine enters the bladder from the ureters, small folds in the bladder mucosa act like valves preventing backward flow of the urine.

The urethra is a tube that connects the urinary bladder with the outside of the body. Male and female urethra differs in shape and length. Male urethra length varies from 17.5 to 20 cm; and it is divided into three portions, the prostatic, membranous, and cavernous. The female urethra is a narrow membranous canal, about 4 cm. long.

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