The river in your blood
Doctors can put a tube of blood in a machine that spins it very fast. The blood separates into layers. The red cells sink to the bottom, and on top is a clear, pale yellow liquid. That is plasma.
Plasma is more than half of your blood, about 55 percent. The cells float in it like boats on a river.
Mostly water
Plasma is about 90 percent water. That is one big reason your body needs you to drink water every day.
The rest is a mix of useful things: proteins, salts, sugar for energy, and tiny bits of food from your meals.
Some proteins in plasma help your blood clot at a cut. Others are antibodies, the germ catchers your white blood cells make.
A delivery service
Food: after your stomach and intestines break down your meals, the good parts soak into your plasma, which carries them to every cell.
Messages: your body sends chemical messages called hormones (HOR-moanz) through the plasma. Some hormones tell you when you are hungry, and some help you grow.
Waste: plasma carries waste away from your cells to your kidneys and liver, which clean it out.
Heat: plasma carries warmth around your body too.
Giving plasma
Kind grown-ups can give plasma to help people who are sick or hurt. A machine keeps the plasma and gives the red cells back to the donor.
Donated plasma helps people with bad burns or big injuries, and people whose blood needs help clotting.
A donor's body makes new plasma quickly, in about a day, mostly from the water they drink.