The healthy balance of our body's internal chemistry is in large part due to the work of the kidneys. Each kidney is about the size of your fist and weighs about 150 grams. These organs are located on either side of the spine at approximately waist height.
ROLE OF KIDNEYS
The normal function of the kidney is to maintain the body's internal environment by purifying the blood and maintaining water and electrolyte composition. Hence, in disease with the kidneys the symptoms are referred anywhere in the body.The second function of the kidney is to remove the products of metabolism produced from the food we take. Another offshoot of this is that all the drugs we consume are also removed by the kidneys.
Other functions include production of hormones like Erythropoietin, Vitamin-D and Renin. Erythropoietin is concerned with blood production, Vitamin-D is related to bone modelling and bone growth and Renin to Blood pressure.
1. Elimination of Waste Products
Blood flows into the kidneys through the renal (renal refers to the kidney) artery. An artery is a blood
vessel which carries blood away from the heart and through the body. Thus the renal artery takes
blood from the heart and delivers it to the kidneys. Once the blood reaches the kidneys, waste
products are filtered out into the urine and the cleansed blood flows back to the heart through the
renal vein. Veins carry blood flowing from various organs back to the heart just as an artery carries
blood flowing away from the heart. Within the kidneys, there are very small filtering units called
nephrons. Approximately 1 million nephrons are found in each kidney.
The nephron is composed of a small cluster of blood vessels called the glomerulus (where the actual
filtering process occurs) and a minuscule tube called a tubule. The fluid filtered from the blood
plasma is modified and infact largely reabsorbed as it travels along the tubules. The remainder (the
urine) finds its way into the ureter, a larger tube draining all the tubules, which carries the urine to
the bladder from each kidney. Every two minutes the entire blood supply circulates through the
kidneys, and is thus continuously cleansed.
2. Production of Red Blood cells and Bone Formation
The Production of red blood cells and the formation of healthy bones are both dependent on the
proper functioning of our kidneys. First, the kidneys release the hormone erythropoietin which
promotes the maturation of erythrocytes (red blood cells) in the bone marrow. A shortage of this
hormone may cause anaemia. The measurement that gives information on the number of red blood
cells in the body is called the hematocrit. Patients generally experience fatigue when their hematocrit
is low. Secondly, the kidneys affect bone formation by regulating calcium and phosphorus
concentrations in the blood and by producing an active form of Vitamin D, which promotes calcium
absorption from the food.
3. Regulation of Blood Pressure
High Blood pressure (hypertension) can be both a cause and a consequence of kidney disease.
Prolonged high blood pressure damages the blood vessels of many organs and can lead to heart
disease and stroke as well as kidney failure. Control of the bodys blood pressure is another function
of the kidneys. These organs monitor concentrations of sodium, potassium, calcium, phosphorus,
chloride and bicarbonate as well as body fluid levels and remove excess amounts of salts and fluids
in the urine. When the kidneys fail to perform these vital functions, the blood pressure may rise and
swelling may occur. In severe cases heart failure may result. The kidneys also secrete a substance
called rennin. Rennin stimulates the production of a hormone which causes an elevation in blood
pressure. When the kidneys do not work properly, too much rennin may be produced and this can
lead to high blood pressure.
4. Control of the Body's Chemical and Fluid Balance
The waste by-product of this filtering process, as previously mentioned, is called urine. When the
kidneys fail to function properly, waste products which should be eliminated in the urine are retained
in the blood. This results in a very serious condition known as uremia. Symptoms of uremia include
nausea, weakness, fatigue, disorientation, shortness of breath and swelling in the arms and legs.
Some of the waste products that build up in the blood can be measured and their increased
concentration can be used to evaluate the seriousness of the problem. The substance most
commonly measured for this purpose is called creatinine. This substance is a waste product that
results from the metabolism in the muscle tissues. Kidney disease is often associated with high levels
of creatinine.
