In man, a closed type of circulatory system is found, which consists of the following components.
A fluid with cells, substances & other dissolved.
A pumping pulsatile organ.
Blood vessels are tubes i.e. Arteries, Veins, and capillaries.
It is composed of a liquid called blood plasma & blood cells.
Weight of blood in our body is about 1/12th of our body.
Average adult body has about 5 litres of blood.
In a healthy person, plasma consulates about 55% and cell or cell like bodies about 45% by volume of the blood.
Water constitutes about 90-92% of plasma & 8-10% are dissolved substances.
A cubic millimetre of blood contains 5 to 5.5 million red blood cells in males and 4 to 4.5 million in females.
In the RBCs of mammals, the muscle is lost when they get mature.
95% of the cytoplasm of RBCs is filled with haemoglobin which transports O2 & CO2 the remaining 5% consists of enzymes & other proteins.
RBCs are biconcave & have an elastic cell membrane.
In the embryonic and foetal life they are formed in the liver and spleen. In adults, they are formed in the red bone marrow of short & flat bones, such as the sternum, ribs & vertebrae.
The average life span of RBCs is 120 days.
The average lifespan of red blood cell is about four months (120 days) after which it breaks down in liver & spleen by phagocytosis
These are colourless.
They are not confined to blood vessels only as they also migrate out into the tissue fluid .
One cubic millimetre of blood contain 7000 to 8000 WBC’s
Their life span ranges from months to even years, depending on the body’s needs.
WBC’s function as the main agents in the body’s defence system.
Leukocytes are divided into two main types.
They are not cells but are fragments of large cells of bone marrow called megakaryocytes they do not have any nucleus & any pigment.
One cubic millimetre of blood contains 250000 platelets.
They play an important role in blood clotting. The clot serves as a temporary seal at the damaged area.
