Blood circulation in human body - What is the function of blood in the human body?

Blood is the fluid necessary for life. 

It flows through the arteries, capillaries and veins of our body, and consists of a liquid part, called plasma, and blood cells that float in the plasma.
Adult body has about 6.5 liters of blood.
The blood is the most perfect transfer system: it brings food and oxygen to each cell, and takes out the unnecessary products, delivers hormones and other substances, helps the body to fight infection and to adapt the body heat.

Types of Blood Cells

There are three types of blood cells.
They are:  Red blood cells, which give the red color to the blood and carry oxygen,
White blood cells, of which there are several types and whose task is to fight infection, and finally,
the blood plates (Platelets) which help the blood to clot, thus preventing excessive bleeding and blood loss from injured blood vessel.
All blood cells are created in the bone marrow. 
If you look at the open bone, you will see in it reddish-gray cavity spongy substance. Under the microscope we can see a network of blood vessels and connective tissue fibers, between which are numerous, large cells, where blood cells are formed.

What is Blood Plasma?

Of the total volume of blood, approximately 55 percent is plasma, a clear, pale yellow fluid.
After a meal, little balls of fat float in the plasma and it gets dairy look. Therefore, we should not eat before taking blood for examination.
Plasma is like a river that carries substances important for our life, digested nutrients from the walls of the small intestines to the body tissues, and also unnecessary substances from the tissues to the kidneys.
But this is only one part of the work, which is conducted by the plasma.
Blood Plasma
Plasma also conveys antibodies that create resistance to disease, hormones that regulate various functions of the body and part of the carbon dioxide from the tissues to the lungs.
Plasma contains several hundred different substances.
In addition to these substances, plasma also contains water - about 91 percent, proteins - 7 percent and mineral salt - 0.9 percent. Salts and proteins are very important for maintaining the necessary balance between the water in the tissues and blood. Mineral salts in plasma also perform other functions of vital importance.
The plasma obtains mineral salts from the food that we enter into the body.

Q&A

What do Red Blood cells do?

Red blood cells give the red color to the blood and carry oxygen

What do White Blood cells do?

There are several types of White Blood cells, and their main task is to fight infection

What do platelets do?

Blood plates (Platelets) help the blood to clot, thus preventing excessive bleeding and blood loss from injured blood vessel.

Can you eat before a blood test?

After a meal, little balls of fat float in the plasma and it gets dairy look. Therefore, we should not eat before taking blood for examination.