URINARY SYSTEM

The urinary system consists of two kidneys, urinary bladder, two ureters, which carry urine from the kidneys to the urinary bladder, and urethra, which carries urine from the bladder to the outside of the body. The primary function of the urinary system is to remove the excess fluid and waste material from the blood. In addition, the kidneys function as glands producing hormones that are important in the production of red blood cells, in the regulation of blood pressure, and in the formation of bone.

The kidneys are the most important organs for fluid excretion. The kidneys, a pair of bean-shaped organs, are located against the back of the abdominal wall on either side of the spine at the level of the lowest ribs. Each kidney is generally about the size of the person's fist. The right kidney is slightly lower than the left. The kidney is surrounded by a renal capsule and a renal fat pad and is held in place by the renal fascia. The two layers of the kidney are the cortex and the medulla.

On the medial side of each kidney there is a relatively small area called the hilum where the renal artery and the nerves enter and the renal vein and ureter exit.

The hilum opens into a cavity called the renal sinus, which is filled with fat and connective tissue. In the center of the renal sinus the urinary channel is enlarged to form the renal pelvis.

Urinary System (models)

Several large urinary tubes (called calyces) extend to the renal pelvis from the kidney tissue. The calyces that open directly into the renal pelvis are called major calyces, and the smaller calyces that open into major calyces are called minor calyces. There are 8 to 20 minor calyces and 2 or 3 major calyces per kidney. At the hilum the renal pelvis narrows to form the ureter. Ureters are muscular tubes, one from each kidney, that propel the urine to the bladder. The bladder is a muscular bag that stores the urine. The urethra is the narrow tube through which the urine leaves the bladder during urination.