Kidney is a Paired Organ Whose Functions Include Removing Waste Products From the Blood and...

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The excretory system of kidneys

Excretion is the removal of metabolic wastes that have travelled in the bloodstream atsome stage before removal. Components of the excretory system are kidneys, liver,lungs and

skin. Kidney is a paired organ whose functions include removing waste products from the bloodand regulating the amount of fluid in the body. The basic units of the kidneys are

microscopically thin structures called nephrons, which filter the blood and cause wastes to beremoved in the form of urine. Together with the bladder, two ureters, and the single urethra, the

kidneys make up the body¶s urinary system. Human beings, as well as members of all other vertebrate species, typically have two kidneys.

Like kidney beans, the body¶s kidneys are dark red in color and have a shape in whichone side is convex, or rounded, and the other is concave, or indented. The kidneys of adult

humans are about 10 to 13 cm (4 to 5 in) long and about 5 to 7.5 cm (2 to 3 in) wide²about thesize of a computer mouse.

The kidneys lie against the rear wall of the abdomen, on either side of the spine. They are

situated below the middle of the back, beneath the liver on the right and the spleen on the left.

Each kidney is encased in a transparent, fibrous membrane called a renal capsule, which helps protect it against trauma and infection. The concave part of the kidney attaches to two of the

body¶s crucial blood vessels²the renal artery and the renal vein²and the ureter, a tubelikestructure that carries urine to the bladder.

A primary function of kidneys is the removal of poisonous wastes from the blood. Chief among these wastes are the nitrogen-containing compounds urea and uric acid, which result from

the breakdown of proteins and nucleic acids. Life-threatening illnesses occur when too many of

these waste products accumulate in the bloodstream. Fortunately, a healthy kidney can easily ridthe body of these substances.

Structure of the kidney contain cortex, the outermost layer of the kidney. Beneath the

cortex lies the medulla, an area that contains between 8 and 18 cone-shaped sections known as pyramids, which are formed almost entirely of bundles of microscopic tubules. The tips of these

pyramids point toward the center of the kidney. The cortex extends into the spaces between the pyramids, forming structures called renal columns. At the center of the kidney is a cavity called

the renal pelvis.

The task of cleaning, or filtering, the blood is performed by millions of nephrons,

remarkable structures that extend between the cortex and the medulla. Under magnification,nephrons look like tangles of tiny vessels or tubules, but each nephron actually has an orderly

arrangement that makes possible filtration of wastes from the blood. The primary structure in thisfiltering system is the glomerulus, a network of extremely thin blood vessels called capillaries.The glomerulus is contained in a cuplike structure called Bowman¶s capsule, from which extends

a narrow vessel, called the renal tubule. This tube twists and turns until it drains into a collectingtubule that carries urine toward the renal pelvis. Part of the renal tubule, called the loop of Henle,

becomes extremely narrow, extending down away from Bowman¶s capsule and then back upagain in a U shape. Surrounding the loop of Henle and the other parts of the renal tubule is a



network of capillaries, which are formed from a small blood vessel that branches out from theglomerulus.

Blood enters the kidney through the renal artery. The artery divides into smaller andsmaller blood vessels, called arterioles, eventually ending in the tiny capillaries of the

glomerulus. The capillary walls here are quite thin, and the blood pressure within the capillariesis high. The result is that water, along with any substances that may be dissolved in it²typically

salts, glucose or sugar, amino acids, and the waste products urea and uric acid²are pushed outthrough the thin capillary walls, where they are collected in Bowman's capsule. Larger particles

in the blood, such as red blood cells and protein molecules, are too bulky to pass through thecapillary walls and they remain in the bloodstream. The blood, which is now filtered, leaves the

glomerulus through another arteriole, which branches into the meshlike network of blood vesselsaround the renal tubule. The blood then exits the kidney through the renal vein. Approximately

180 liters (about 50 gallons) of blood moves through the two kidneys every day.

Urine production begins with the substances that the blood leaves behind during its

passage through the kidney²the water, salts, and other substances collected from the glomerulusin Bowman¶s capsule. This liquid, called glomerular filtrate, moves from Bowman¶s capsule

through the renal tubule. As the filtrate flows through the renal tubule, the network of bloodvessels surrounding the tubule reabsorbs much of the water, salt, and virtually all of the nutrients,

especially glucose and amino acids, that were removed in the glomerulus. This important process, called tubular reabsorption, enables the body to selectively keep the substances it needs

while ridding itself of wastes. Eventually, about 99 percent of the water, salt, and other nutrientsis reabsorbed.

At the same time that the kidney reabsorbs valuable nutrients from the glomerular filtrate,it carries out an opposing task, called tubular secretion. In this process, unwanted substances

from the capillaries surrounding the nephron are added to the glomerular filtrate. These

substances include various charged particles called ions, including ammonium, hydrogen, and potassium ions.

Together, glomerular filtration, tubular reabsorption, and tubular secretion produce urine, which

flows into collecting ducts, which guide it into the microtubules of the pyramids. The urine isthen stored in the renal cavity and eventually drained into the ureters, which are long, narrow

tubes leading to the bladder. From the roughly 180 liters (about 50 gallons) of blood that thekidneys filter each day, about 1.5 liters (1.3 qt) of urine are produced.

Diseases of the kidney range from mild infection to life-threatening kidney failure. Themost common form of kidney disease is an inflammation of the kidney, called pyelonephritis.

Most such inflammations are caused by a bacterial infection that starts in the bladder and spreadsto the kidney. Sometimes an obstruction that interferes with the flow of urine in the urinary tract

can cause the disease. Symptoms of pyelonephritis include fever, chills, and back pain.Antibiotic drugs are usually given to fight the infection, which can scar the kidneys and impair

their function if left untreated.



Glomerulonephritis, another common kidney disease, is characterized by inflammation of some of the kidney's glomeruli (glomerulus is a round cluster of interconnected capillaries found

in the cortex of a kidney, which remove body waste to be excreted as urine)

This condition may occur when the body¶s immune system is impaired. Antibodies and

other substances form large particles in the bloodstream that become trapped in the glomeruli.This causes inflammation and prevents the glomeruli from working properly. Symptoms may

include blood in the urine, swelling of body tissues, and the presence of protein in the urine, asdetermined by laboratory tests. Glomerulonephritis often clears up without treatment. When

treatment is necessary, it may include a special diet, immunosuppressant drugs, or plasmapheresis, a procedure that removes the portion of the blood that contains antibodies.

Other common kidney disorders include kidney stones, which are small, crystallizedsubstances, such as calcium, that form in the kidney or other parts of the urinary tract. Smaller

kidney stones can pass out of the body on their own, although this can be painful. Larger stonesmay require surgery, or they may be broken into smaller pieces with sound waves in a procedure

called ultrasonic lithotripsy.

The kidneys may be harmed when ever injury or disease affects the rest of the body. For

example, diabetes mellitus (a disease caused by a malfunctioning pancreas that produces little or no insulin) can result in impaired blood flow through the kidneys. The bacteria that cause

tuberculosis can travel from the lungs and infect the kidneys. Injured muscles can release largeamounts of protein into the bloodstream, blocking the nephrons. Drug use, including long-term

use of some prescription medications as well as illegal drugs, can also cause kidney damage.Certain birth defects may cause the kidneys to have abnormal shapes or to function improperly.

Treatment of severe kidney disease may include kidney dialysis, a procedure in which blood is circulated through a machine that removes wastes and excess fluid from the

bloodstream. Some patients use dialysis for a short time, while their kidneys recover from injuryor disease. Others must use dialysis for their entire lives or until they undergo a kidney

transplant. Kidney transplants are the most common of all transplant operations and haveexcellent success rates. Unfortunately, there are not enough kidneys available for the people who

need them. More than 38,000 people in the United States alone wait for a kidney transplant eachyear, and fewer than 12,000 of them receive this life-sustaining organ . As one kidney is enough

to survive, it is worthwhile to donate to a relation or any other person for God¶s sake. This is particularly if the recipient is still economically viable. Can any member of Unilorin forum

afford to be so generous? As stated below, you may want to will your kidney to someone whomight need it immediately after your death.

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