Renal System | Research & Encyclopedia Articles

Renal System

The renal system is also known as the urinary system. Located in the retroperitoneal upper area of the abdominal cavity, the renal system is a collection of the organs and the structures that function in the removal of waste material from the body. In humans the renal system consists of the pair of kidneys, ureters, bladder, and the urethra.

The conversion of incoming nutrients to energy for the body's various processes generates waste. Much of this waste is soluble, that is, it can dissolve in water (and so in blood, which is largely comprised of water). This waste must be removed from the water and expelled from the body.

Waste removal takes place in the kidneys. These are the principle filtration units of the renal system. There are normally two kidneys in the human body. They are located on each side of the abdomen in the lower region of the back. Within the kidney, wastes are removed from the fluid. The wastes are concentrated into a waste product called urine.

Once produced, the urine passes from the body via the other components of the renal system. Tubes called ureters connect the kidneys to the urinary bladder. Each ureter is made of muscle and is between 16 and 18 in. (41 and 46 cm) long. Rhythmic contractions of the ureter force the urine downward into the bladder. The bladder is essentially a bag that holds the liquid until enough has accumulated that the need to urinate becomes evident. The bladder is also composed of muscle, which is capable of contraction. This forces the urine out the bottom of the bladder and into a narrow tube called the urethra. The urethra leads to the outside, via the penis in the male or via the urethral opening superior to vaginal opening in the female.

The urethra is susceptible to infection, because of growth of microorganisms from the outside that infiltrate the urethral tubes. While usually treatable with antibiotics, chronic infections can develop that are quite resistant to treatment. These infections can be uncomfortable and can restrict urination, which may in turn influence the chemistry of the renal system.

Two other important functions of the renal system, which are also performed by the kidneys, is regulating and maintaining the balance of electrolytes and the pH of the fluid that has been processed. The electrolyte balance is maintained by regulating the amount and the composition of the fluid. Fluid passing through the kidneys is monitored and the proper concentrations of ions such as hydrogen, sodium, potassium, chloride, bicarbonate, sulfate, and phosphate are ensured. The production of ammonia also helps to keep the processed fluid at a pH of between 7.37 and 7.43. This range is critical for the proper function of the body.

The ability of the renal system to function depends upon the presence of two hormones. The first of these is called the antidiuretic hormone, or ADH. This hormone is produced by the pituitary gland. The ADH acts to make the filtration components of the kidney more able to accept water. When ADH concentration in the body is high, the kidney produces a smaller volume of highly concentrated urine. This would be advantageous when water intake is restricted due to lack of available drinking water.

The second vital hormone is known as aldosterone. The presence of the hormone affects the absorption of sodium by the kidneys. As a result, the urine that is produced contains less sodium and more potassium than when the aldosterone concentration is lower. This mechanism allows the body to adjust for changing internal needs for electrolytes such as sodium and potassium. If this mechanism is faulty, the changing sodium and potassium levels in the body promote a condition called hypertension.

The performance of the renal system can also be adversely affected by diabetes mellitus. The excess glucose in the blood may not be removed by the kidneys, leading to the appearance of glucose in the urine. Protein may also be present in the urine, a condition called proteinuria, which is indicative of a breakdown in kidney function. Medical attention is necessary for both conditions to prevent serious and permanent damage to the renal system, especially to the kidney.