Kidney, Kidney Stone and Kidney Failure

The kidneys remove wastes from the blood, producing urine. The urine flows through the ureters into the bladder and even­tually leaves the body through the urethra. 

Blood enters the kidney through the renal artery. In the medulla and cortex, the renal artery divides into increasingly smaller ves­sels, each of which ends in a filtering unit called a nephron. Within each nephron, much of the blood's fluid content filters through the glomerulus into the convoluted tubule. Cells in the tubule wall absorb needed substances from this fluid, leaving the waste materials that make up urine.

Kidney is a complex organ in human beings and all other vertebrates. The two kidneys perform many vital functions, of which the most important is the production of urine. This fluid carries various waste materials out of the body. If the kidneys fail to function, poisons built up in the body, eventually causing death.

The kidneys look like purplish-brown kidney began and are about the size of an adult's fist. They lie below the middle of the back on each side of the spine. The right kidney, located under the liver, is a little lower than the left one. Some people are born with only one kid­ney, but they lead a normal life.

How the kidneys produce urine. Human kidneys consist of three layers. These layers are, in order, the cortex on the outside of the organ, the medulla, and the pelvis. Blood flows into the medulla through the renal artery. In the medulla and cortex, the renal artery branches into increasingly smaller arteries. Each of these arteries ends in a blood filtration unit called a nephron. Two healthy kidneys contain a total of about 2 million nephrons, which filter about 190 litres of blood daily.

A nephron consists of a network of tiny blood vessels, the glomerulus, surrounded by Bowman's capsule, a two-layer membrane that opens into a convoluted tu­bule. Pressure forces much of the blood plasma (fluid portion of the blood) through the glomerulus and into Bowman's capsule. The resulting tubular fluid, which contains water and dissolved chemicals, then passes into the convoluted tubule. The portion of the blood that remains in the glomerulus flows into small vessels called capillaries, which surround the convoluted tu­bule. As the tubular fluid flows through the tubule, substances needed by the body are absorbed by the cells of the tubule wall. These substances, which include amino acids, glucose, and about 99 per cent of the than rejoin  the blood in the capillaries. The capillaries return the blood to the heart by way of the renal vein.

Substances not absorbed in the tubule are wastes that the body cannot use. Other wastes are secreted into the tubular fluid by the tubular cells of the kidney. These various substances, which include ammonia, urea, uric, acid, and excess water, make up urine. The urine passes from the convoluted tubules into larger collecting tu­bules and then into the pelvis layer of the kidney. A tube called the ureter carries urine from each kidney into the urinary bladder. Urine collects in the bladder until it passes out of the body through another tube, the ure­thra. Healthy kidneys produce from 1 to 2 litres of urine daily.

Other functions of the kidneys. In addition to pro­ducing urine, the kidneys secrete a hormone called erythropoietin, which controls the production of red blood cells. The kidneys also convert vitamin D from an inactive form to an active form. The active form of this vitamin is essential for normal bone development.

In addition the kidneys help maintain the blood pressure of the body by releasing an enzyme called renin. See Hypertension (Causesl).

Kidney diseases. If one kidney is lost in an accident or by disease, the other may enlarge and do the work of both. But if both kidneys are damaged or lost, waste materials accumulate in the body, causing death.

Kidney infection, called pyelonephritis, ranks as the most common kidney disease. Most cases result from infection that spreads upward from the bladder. Unless it is complicated by blockage of the urinary tract, pyelonephritis rarely leads to kidney failure.

The kidneys also can be damaged by antibodies produced to fight bacteria or viruses elsewhere in the body, Such reactions lead to inflammation of the glomerulus. This type of inflammation is called glomerulonephritis, formerly known as Bright's disease.

Long-term or severe high blood pressure can seriously damage the kidneys, as can diabetes. Cysts, kidney stones, and tumours may block the flow of urine. The blocked urine can damage the kidneys by exerting pressure, or it may lead to pyelonephritis. Kidney disorders may also result from birth defects, injuries, or accidental poisoning, or as a side effect of certain medications.

Many people who have lost their kidneys or have suffered kidney damage are kept alive by a dialysis ma­chine. A tube connects this machine to an artery in the patient's arm. Blood flows into the machine, which removes wastes. Another tube carries the blood back into a vein in the arm. A patient may have to undergo this process, called haemodialysis, for several hours, three times a week.

Some kidney patients can use peritoneal dialysis, a connuous procedure that does not involve being connected to a machine. In this process, a container of dial­ysis solution is emptied into the patient's abdominal cavity through a permanently implanted tube. The solution remains there for several hours, picking up wastes from the bloodstream. The patient then drains the used solution and replaces it with a fresh supply.

Other kidney patients have their diseased kidneys replaced with a healthy one in a kidney transplant. A re­placement organ from a close relative is desirable be­cause it closely matches the patient's tissues. But most replacement organs come from unrelated donors who have died in accidents or from other causes. The pa­tient's body always attempts to reject these "foreign" or­gans. However, modern medicines are usually able to control the rejection process and save the transplanted kidney. Related articles: Bladder, Nephritis, Elimination, Tissue transplant, Gout, Urea, Human body (Trans-Vision), Uraemia , Kidney stone, and Urine.

Kidney Stone

Kidney stone is a hard object that forms in the kid­neys. Kidney stones range in size from microscopic to about as large as a golf ball. They occur chiefly in men and can cause intense pain if they become stuck in the urinary tract. Most kidney stones consist of calcium salts. In many cases, doctors cannot determine why the stone forms. Some people who develop kidney stones absorb an unusually high amount of calcium from their diet. Excess calcium is eliminated in the urine. However, some of the calcium may crystallize before it leaves the body, forming a stone.

Most kidney stones pass out of the body with the urine, often accompanied by severe pain. When a stone becomes stuck, it may need to be removed by a doctor. In some cases, the doctor can remove it by inserting a flexible tube into the ureter (tube that carries urine from the kidneys to the bladder). Doctors also may use a laser or a machine called a Hthotripter to treat kidney stones. In laser treatment, an optical fibre—a thin thread of glass or plastic—is inserted into the ureter until it reaches the

stones. The laser then produces a beam of energy that travels through the fibre and breaks the stones into frag­ments, which are eliminated with the urine. A lithotripter focuses shock waves on the stones while the patient sits in a water bath. The waves break up the stones. See also Kidney. Kidney transplant. See Tissue transplant.