The human excretory system:Kidney|DigitalWorldEdu

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Today you will learn The Human excretory system with details. 

The human excretory system

Excretion is the removal of the waste products of chemical reactions, excess water, and salts taken in with food from the body. Excretion must not be confused with the passing of faeces because most of the contents of the faeces have not taken part in chemical reactions. The main organs of the excretory system are bladder and the kidneys these two organs play most important role in excretory system.

You have two kidneys just above your waist at the back. Blood is carried to and from the kidneys by a special artery and vein. I he kidneys remove chemical substances like urea and other unwanted substances from the blood. They also control the quantity of water within body.

The kidneys make urine from urea, water, and other wastes from the blood. Urea s produced by break down of proteins. Urine travels to the bladder through tubes, one of each kidney. The bladder is a bag which stores urine. A ring of muscle at the bottom of the bladder keeps the bladder closed until you attend the rest room (urinate). A tube carries urine out of the body.

Human excretory system

How the Kidney Work

Each kidney receives blood through a renal artery. Inside each kidney, this artery divides into capillaries which carry blood to over a million tiny structures called Bowman's capsules. Inside a Bowman's capsule the capillary divides again forming a ball of intertwined capillaries the glomerulus (plural: glomeruli).

A diagram of a inside of a kidney showing the distribution of the glomeruli

The blood pressure inside each glomerulus is so high that liquid is forced out through its walls into the Bowman's capsule. This liquid contains urea, but also many useful substance such as glucose, amino acids, vitamins, and mineral salts. The liquid flows out of the Bowman's capsules into long, coiled kidney tubules, or nephrons. Here all the useful substances are absorbed back into the blood stream. The liquid left behind is urine, which consists of urea and unwanted mineral salts dissolved in water. The urine flows down the ureters to the bladder.

The excretion of urea

Enlarged view of a nephron or kidney tubule

Carbon dioxide is not the only harmful waste product made inside the body. Another is urea, which is produced in the liver. As you know, the amino acids in proteins are needed for body-building. But you do not need all thea acids that you digest and absorb. Excess proteins cannot be stored by the body because they contain substances that would poison you. They are broken down in the liver and the waste products are carried by the blood to the kidneys. The main breakdown product of proteins is urea, and this is excreted in the urine.If you have eaten a lot of protein, the amount of urea in your urine increases. Without the excretion of this urea and unwanted mineral salts, your body would be poisoned.

There are approximately a million nephrons in a kidney.

Waste products in plants

In animals, waste products are removed from the body by definite excretory systems. Such systems are not found in plants. This does not mean that plants do not produce waste products. They do, but the amount of waste produced is much less than that produced by animals. Waste products in plants are transported to parts of the plant that will be shed, such as leaves, petals, fruits, and bark.

The waste products occur in many different forms. Some are oils and they produce the odours in leaves. Eucalyptus, lavender, and clove oils are all waste products. Other waste materials are deposited as crystals in leaves and fruits. When the leaves and fruits fall from the trees, the waste products are removed. The 'gritty pieces in some kinds of pears are crystals of waste materials. Most waste materials are removed from deciduous trees in autumn when they shed their leaves. As evergreen trees shed their leaves regularly throughout the year, waste products are removed continuously.

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