SCIENCE

Look again at the diagram of the Excretory System. You will see how the kidneys are connected with the rest of the Excretory System. Do you see the ureters? Each ureter is really a narrow tube which runs from each kidney to the bladder. The bladder, really the urinary bladder is a muscular bag which is found towards the bottom of the abdominal area. Touch your tummy. Do you feel it? You sure do know exactly where it is when it is full!

Coming from the bladder you will see the urethra, another tube. This tube takes the urine from the bladder towards the outside of the body.

Look again at the diagram. Do you see the renal artery and the renal vein? They take the blood to and from the kidneys.

The kidneys produce a fluid called urine. This urine consists of urea and other waste products from the liver, and water.

N.B. Urine should consist of approximately 95% water, 2% urea, 1% sodium chloride and much smaller amounts of other salts, etc.

Urine from the kidneys trickles down the ureters to the bladder. The bladder then gradually expands like a balloon as more and more urine collects inside it. The bladder varies in size according to the amount of urine it contains.

The bladder, when full, is emptied through the relaxing and contracting of muscles of the bladder and other muscles nearby. Children, do remember that the urine of a healthy person should be a clear pale yellowish fluid. If yours is different, do let your parents know. Also, remember to drink lots of water and eat lots of fruits.

We have looked at the main organ(s) of the Excretory System, the kidneys. The lungs are also involved in excretion. They help to get rid of carbon dioxide. This gas, produced in our bodies, as we already learnt, can cause harm if it remains inside.

Do you know that your skin is not just a simple covering? It is also an organ of excretion. The skin is the largest organ of excretion, actually the largest organ of the body. Just think about it! it helps get rid of waste matter including urea and salt, dissolved in water. (Here you ever tasted your perspiration? Doesn’t it taste salty? Have you ever taken note of when it is that you perspire?) Our perspiration or sweat is produced when our body temperature rises. This often happens when we exercise and do much physical activity. Evaporation of the sweat helps to cool down the body and maintain the body temperature.

Complete the following exercises 1. Match the organs with the substances they excrete.

Organ Lungs Kidneys Skin

Urine = urea + water

Substance Urea Sweat Carbon dioxide Water

2. Excretion refers to ....................... ..................... 3. The main organs of excretion are ......................

4. The urinary bladder is the organ of excretion. T/F

5. Of what is urine composed?

Until next week, goodbye Boys and Girls, and continue to revise!