Excretion

In living things

What is the difference between Excretion and

Egestion?

Excretion is the release of energy or metabolic waste that was produced by chemical reactions in the body.

Egestion is the removal of undigested food from the body.

SYSTEMS OR ORGANS INVOLVED IN EXCRETION

The kidney- urea, water, minerals

The lungs- carbon dioxideThe skin- sweat( water and

minerals)

THE KIDNEY - HOW IT WORKS

By the end, you will know about…NephronsUltrafiltrationSelective ReabsorptionControl of Water BalanceKidney Damage and possible treatments….

Excretion

We need to excrete certain things that may otherwise build up and be poisonous to us, eg:

Carbon dioxide (lungs) Urea (kidney) Faeces (from digestion)

The Kidney

You have two kidneys in your body. They are located towards your back,

near your waist. They filter the blood, andremove any harmful or excessive substances, eg. Urea, water, salts, hormones.

Inside the Kidney The kidney has an outer CORTEX. The middle section is the MEDULLA. There are pyramid-like structures in

the medulla. The centre part is knownas the PELVIS. The tube that carries urineto the bladder is the URETER.

The Nephron Nephrons are smallsubunits that make up the kidney.They do the filtering! There are millions ofthese tiny structuresinside the kidney, and alleventually drain into theureter.

Ultrafiltration Blood had to be filtered to stay “clean”. It has to be filtered under high pressure.

ULTRAfiltration! The blood enters the kidney through the RENAL ARTERY. It enters the GLOMERULUS – a tinyknot of capillaries.

Bowman’s Capsule As the blood goes from artery to glomerulus, it

creates extremely high pressure.

This forces everything small enough to leave the blood and enter the first part of the nephron; Bowman’s Capsule.

Proteins and cells are too big, so stay in the blood.

First Coiled Tubule After the filtrate trickles down from Bowman’s Capsule, it

contains water, salts, urea, glucose, any hormones and drugs.

However, the body needs to reabsorb the useful products back into the blood.

The first coiled tubule is the first section of the nephron, near the Bowman’s capsule. It is long and coiled. In the first coiled tubule, glucose is reabsorbed into the capillaries surrounding the nephron.

The Loop of Henlé

The next section of nephron is the Loop of Henlé. It is a long loop, that goes into the medulla of the kidney.

It is here that water and some useful salts are reabsorbed.

Second Coiled Tubule

This is the third section of the nephron. It is another coiled tubule.

Anything else that needs reabsorbing will be reabsorbed here (eg. water and more salt if necessary).

Collecting Duct All the leftover substances end up in the collecting

duct.

This includes urea, excess water and salts, any drugs and other waste products from the body’s chemical reactions.

If the body gets dehydrated, water gets absorbed from the collecting duct.

This leftover waste liquid is known as URINE.

Urine Urine can be important in diagnosis of

certain diseases. If there are certain substances in the urine

that should have been filtered out by the kidneys,

then it can be an indication of kidney damage. Glucose in the urine is an indication of diabetes.

Water Balance The levels of water in the body need to be

properly controlled to avoid death by dehydration.

This is an example of HOMEOSTASIS – keeping the environment inside you at a constant. Think of it like a driver trying to stick to the speed limit!

ADH Anti-diuretic hormone is produced by the

pituitary gland in the brain.

Changes in water levels in the blood are detected by the HYPOTHALAMUS in the brain. It controls release of ADH by the pituitary.

Water Balance cont… When you drink a lot, there is a lot of water

in your blood. Your hypothalamus detects this, and

stimulates the pituitary to release LESS ADH.

This means the collecting ducts become LESS permeable to water.

LESS water is reabsorbed into the blood. Therefore you produce a greater amount of

weak, pale urine.

Water Balance cont…

When you don’t drink enough, the hypothalamus stimulates the pituitary to release MORE ADH.

The collecting ducts become MORE permeable to water.

MORE water is reabsorbed into the blood.

Therefore you produce a small amount of very yellow, concentrated urine.

Kidney Damage The kidneys can be damaged due to

diabetes, high blood pressure, developing kidney stones, etc.

You can survive with one working kidney, as the blood can still be filtered by the remaining kidney.

If both kidneys fail, there are only two possible treatments to stop the toxins and salts building up to fatal levels in the body.

Treatments – Dialysis The patient is hooked up to a dialysis

machine – this is like an artificial kidney. The patient’s blood runs out of the body, through tubes into machine where excess fluids and toxins are drawn off. Tubes take blood back into the body.

Treatments - Transplants A donor kidney must be found that matches the patient’s own tissue type. The donor kidney must be removed from the donor less than an hour after death. The kidney is put in the groin, and attached to a vein and an artery. The patient will have to take anti-rejection drugs for

the rest of their life.