Week 6 · Chapter 4: 4-2 How the Kidneys Work; 4-3 Various Organs; Column: The Mystery of the Human Body · 3 lessons
1
Kidneys: the blood cleaners
Science P6: Term 1, Chapter 4, pp. 38–45
GoalExplain how the kidneys clean the blood and make urine.
New words
kidney · one of two organs that filter wastes and extra water from the bloodurine · the liquid waste made by the kidneysbladder · the bag that stores urine until it leaves the bodyexcretion · getting rid of wastes made by the body
Explanation
The body makes wastes all the time, for example when cells use nutrients. These wastes go into the blood. The blood carries them to the two kidneys. Each kidney is bean-shaped and about the size of a fist. They sit on each side of the back, below the ribs. The kidneys filter the blood: they take out wastes and extra water and leave the useful things in the blood. The wastes and extra water leave the kidneys as urine. The urine flows to the bladder, which stores it until it leaves the body. Getting rid of wastes like this is called excretion. Do not mix it up with feces: feces are undigested food from the large intestine, not wastes made by the kidneys.
blood with wastes→kidneys filter→urine→bladder stores→leaves the body
Worked examples
Hana drinks a lot of water on a hot day, and she needs the toilet more often. The kidneys remove extra water from the blood, so the body keeps the right amount.
Think of a coffee filter or tea strainer: water passes through, but bigger pieces stay behind. A kidney is a much more clever filter, because it also keeps useful substances in the blood.
Where are the kidneys? Not in the stomach area. Put your hands on your lower back, one on each side, just under the ribs. That is where the two kidneys are.
Class activity
Filter model. With a grown-up, put a few dry lentils or rice grains in a cup of water. Pour the water through a coffee filter or strainer into another cup. The lentils stand for wastes and stay behind. This model is not for eating. Then draw the kidney region on an outline of a body.
Practice
1
How many kidneys do people usually have?
Two.
2
What do the kidneys take out of the blood?
Wastes and extra water.
3
Where is urine stored?
In the bladder.
4
Are feces made by the kidneys?
No. They are undigested food from the large intestine.
