What is inside blood

A scab, a hard crust, forms on a scraped knee. What in the blood helped?

Platelets helped, by plugging the cut and helping the blood clot. A clot is blood that has thickened into a lump.

Rule

Rule: Red cells carry oxygen. White cells fight germs. Platelets help blood clot. Plasma carries food and hormones.

Blood is a connective tissue with a liquid matrix. It moves food, gases and hormones around the body. Hormones are chemical messengers.

By volume means by how much space each part fills. Pus is a thick, yellowish fluid.

• Plasma — the pale liquid part. It is about 55% of blood by volume.
• Formed elements — cells and platelets floating in plasma. They are about 45%.
• Red blood cells — they carry oxygen. They hold haemoglobin. This red protein is rich in iron. Each cell lasts about four months.
• White blood cells — they defend the body against germs. They gather where germs enter. Pus can form there.
• Platelets — small pieces that plug a cut and help blood clot.