The human blood

The human blood consist of a 55% of fluid called plasma and other 45% is cellular components consist of red blood cells, white blood cells and platelets. 

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Plasma is yellow liquid in our blood. 90% of plasma is water. The rest are dissolved substances which include nutrients such as glucose, amino acid and vitamins, proteins like antibody, hormones, enzymes, albumins and fibrinogen and inorganic ions such as sodium, calcium, chlorides and phosphates. Main function of plasma are to transport nutrients to tissue, to remove waste products from tissues, to distribute hormone, enzymes, antibodies and other proteins and to distribute heat energy from the liver and muscles to all other part of the body.

Red blood cell (erythrocytes) transport oxygen from the lungs to all parts of the body. They contain a red pigment called haemoglobin which combines with oxygen molecules to form oxyhaemoglobin. They also carry carbon dioxide from our body cells to our lungs. Red blood cells are made in the bone marrow. The lifespan of red blood cells is about 120 days. When red blood cells are worn out, they are destroyed in the liver and spleen.

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White blood cells (leucocytes) are much larger than red blood cells and they each have a nucleus. They are usually irregular in shape, colourless and do not contain haemoglobin. There are several types of white blood cells. White blood cells are formed from bone marrow cells. The lifespan of white blood cells depends on the type of white blood cells. It varies from a few hours to a few months. They play a vital role in the body’s defence against diseases. Unlike red blood cells, white blood cells can squeeze through the walls of the blood capillaries into the space among the cells to destroy the bacteria.

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Platelets are cells fragments produced by large cells in the bone marrow. Under a high-powered microscope, they appear as under tiny oval-shape structures without nucleus. They play an importance role in blood clotting. When a blood vessel breaks, the platelets release clotting factors.

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The Transport System in Human

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The transport system in human is called circulatory system. The human circulatory system is a called double circulatory system because the blood flows through the heart twice in a complete circuit. The human double circulatory system consists of the pulmonary circulation which transports blood between the heart and the lungs and the systemic circulation which transports blood between the heart and all other parts of the body.

A circulatory system has four basic characteristics, Circulating fluid, pumping device, blood vessel and valves. The circulating fluid is called blood which transports useful and waste materials. Pumping device is the heart; blood is moved through the body by muscular contractions of the heart. Blood vessels are a complex network of blood vessel carries materials to the tissue and back to the heart. There are three main types of blood vessels; arteries, veins and capillaries. Valves are present in some blood vessels to prevent backflow and ensure that bloods flows in one direction only.