CIRCULATORY SYSTEM PART II

COMPOSITION OF BLOOD 

BLOOD CELLS 

There are three types of blood cells. These are
1. Red blood cells( erythrocytes)
2. White blood cells( leucocytes)
3. Platelets ( thrombocytes)

RED BLOOD CELLS 

1. They are round discs, concave on two sides
2. They are very small and numerous
3. They do not have nucleus
4. Their cell membrane is permeable to gases such as oxygen.
5. They contain haemoglobin, which gives the red colour to the blood.
6. Haemoglobin transports oxygen from the lungs to the cells.
7. Red blood cells are made in the red bone marrow.

FUNCTION OF THE RED BLOOD CELLS 

They transports oxygen from the lungs to the cells and carbon dioxide from the cells to the lungs

WHITE BLOOD CELLS 

1. White blood cells are larger than red blood cells but smaller in number.
2. They have nucleus but no haemoglobin
3. There are two main types of white blood cells, they are

• Phagocytes
• Lymphocytes

4. The phagocytes function by surrounding and ingesting any bacteria that may enter the body.
5. The lymphocytes function by producing antibodies to fight diseases.
6. White blood cells are also produced in the red bone marrow and lymph nodes

FUNCTION OF THE WHITE BLOOD CELLS 

Their function is to defend the body against diseases.

BLOOD PLATELETS 

1. They are tiny or minute fragments of cells.
2. They do not have nucleus
3. They circulate inactivated cells in the blood.
4. They are produced in the red bone marrow.