What is blood for?


Blood is a red, oozy fluid that is found inside our bodies. It’s an important part of our bodies and we wouldn’t be able to stay alive without it. Every part of your body needs blood, from your brain all the way to your toes, and your body has to keep it ‘fresh’ so it makes new blood every single day.

My seven-year-old wants to know why blood is so important to our bodies – what is it for? So, let’s find out about what blood is made of and what jobs it does inside us:

Blood is made up of a special liquid called ‘plasma’, which contains a mixture of important chemicals, and three different types of cells (red blood cells, white blood cells and platelets). About half of your blood is plasma and the other half is cells. (You can find out more about cells here – they are the building blocks that all living things are made up of.)

Plasma is a yellowy-coloured liquid which carries important chemicals around your body. The cells in your body need food for energy and have to listen to important chemical messages from your brain. They also need to be able to get rid of waste products that could be harmful. Plasma helps your cells by carrying digested food and hormones (special chemical messages) all over your body, and taking waste products, like carbon dioxide and urea, away. Your plasma can also carry heat and help your body to stay at the right temperature to keep working properly.

Red blood cells carry oxygen to cells all over your body. They collect the oxygen from your lungs when you breathe in and take it to cells in other parts of your body. They can do this because they contain a special protein called ‘haemoglobin’ which can pick up oxygen molecules from the air you breathe. The haemoglobin in red blood cells is what makes your blood look red.

White blood cells fight off germs and help your body to stay healthy. There are different kinds of white blood cells – some spot germs, like viruses and bacteria, and warn your body about infection; others fight off the germs and keep you disease-free. If you get ill, your body will make lots and lots of white blood cells to get rid of all the germs and make you better.

Platelets are important when you cut yourself because they travel to the site of the wound and clump together to make a scab. A scab acts as a quick-fix to stop germs and dirt from getting into your body, while your skin repairs itself underneath.

In order to do its job, your blood travels around your body through a network of tubes called ‘blood vessels‘. The amount of blood you have will depend on the size of your body, so a child may have about 2.5 litres of blood, whilst a grown-up will probably have about twice that amount.



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