The Excretory SystemBy Alarik Erlingsson

Structures of The Excretory System

Every living system produces chemical waste products, some of which are so toxic that if they’re not eliminated from the system, death is imminent.

Every cell in the body produces waste compounds, including salts, carbon dioxide, and ammonia, which is produced when the cell uses Amino Acids from proteins for energy.

Ammonia is converted to urea, but it too must be eliminated from the body

The process by which metabolic wastes are eliminated to maintain homeostasis is called excretion.

The Skin

The skin excretes excess water, salts, and small amounts of urea in sweat.

The skin releases sweat regularly in amounts so small that you don’t even notice, this way your body can excrete wastes all the time.

The Lungs

Blood transports carbon dioxide from body cells to the lungs.

When you exhale, your lungs excrete carbon dioxide and small amounts of water vapor.

The Liver

One of the liver’s principal activities is the conversion of nitrogen wastes, ammonia, into less toxic urea.

Urea is then sent through the blood stream to the kidneys for elimination.

The Kidneys

The kidneys are the major organs in excretion.

The kidneys filter out excess water, urea, and metabolic wastes from the blood.

The kidneys produce a waste product most commonly known as urine.

Ureters transport urine from the kidneys to the urinary bladder, where the urine is stored until it is released through the urethra.

Excretion and the Kidneys

Waste-laden blood enters the kidney through the renal artery, the blood is filtered, then the blood enters circulation again through the renal vein.

Each kidney has about one million individual processing units called nephrons.

Nephrons are where most of the work in the kidney takes place-impurities are filtered, wastes are collected, and purified blood is returned to circulation.

Blood purification is complex and involves two processes: filtration and reabsorption.

FiltrationFiltration is the passing of a liquid or gas through a filter to remove wastes.

Filtration mainly takes place in the glomerulus, a small yet dense network of capillaries located at the upper end of each nephron inside a cup=shaped structure called Bowman’s capsule.

Material filtered from the blood is called filtrate, which can be urea, water, salts, amino acids, glucose, and vitamins. Proteins and blood cells are too large for the filter.

Reabsorption Reabsorption is the process by which water and dissolved substances are taken back into the blood.

Substances, including salts, vitamins, amino acids, fats, and glucose, are removed from the filtrate by active transport and reabsorbed by the capillaries.

Because of osmosis, almost 99 percent of water that enters Bowman’s capsule is reabsorbed into the blood.

In effect the kidney throws away almost everything and then takes back everything. This way the kidney is able to remove drugs and toxic compounds from the blood.

Reabsorption Cont.

The loop of Henle is the section of the Nephron tubule responsible for conserving water and minimizing the volume of the filtrate.

The waste material, urine, is emptied into a collecting duct.

Urine Excretion

From the collecting ducts, urine flows to the ureter.

The ureters carry urine to the urinary bladder where urine is held until the urine leaves through the urethra.

The Kidneys and Homeostasis

The kidneys play a large role in homeostasis. Besides removing wastes, the kidneys also maintain blood pH and regulate water content of the blood.

The kidneys respond directly to the composition of the blood and are influenced by the endocrine system.

Control of Kidney Function

The activity of the kidneys is controlled by the blood itself for the most part.

Glands can release hormones that also influence kidney function.

As you may know, the color of urine indicates how hydrated you are. A pale yellow color shows that you are hydrated, a darker color indicates low water levels in your body.

Urine Testing

Medical professionals can learn a lot about a person’s health from a urine sample.

The presence of protein or glucose in urine can be indicators of diseases such as diabetes.

Although many substances are reabsorbed into the blood, drugs generally stay in the filtrate and are excreted in urine. This is why urine tests are used commonly for drug tests.

Kidney Disorders

The kidneys are the master chemists of the blood supply.

If anything happens to the kidneys, serious medical problems are sure to follow.

Three of these problems are kidney stones, kidney damage, and kidney failure.

Kidney Stones

Sometimes substances such as calcium, magnesium, or uric acid salts in the urine crystallize and form kidney stones.

When the kidney stones block a ureter, they cause great pain.

Kidney stones are often treated using ultrasound waves, which pulverize the stones and are then excreted in the urine.

Kidney Damage

Many diseases, injuries, and exposure to hazardous substances can cause impaired kidney function.

Most cases of kidney damage in the U.S. are related to diabetes or high blood pressure.

Excessive blood pressure damages the delicate filtering mechanism, and high blood sugar levels cause the kidneys to filter more blood than usual.

Kidney Failure

Kidney failure is when kidneys can no longer cleanse the blood and maintain homeostasis.

A patient with kidney failure must receive dialysis or undergo a kidney transplant.

During dialysis a machine performs the role of the kidneys. Most patients receive treatments three times a week four hours at a time.

In transplantation, a patient receives a kidney and a ureter from a compatible donor.

THE END