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 blood vessels

There are three types of blood vessels; arteries, veins and capillaries. Arteries are blood vessels which carry blood away from the heart. Arteries deliver oxygenated blood except the pulmonary artery. The walls of arteries are much thicker and stronger than those of veins because they have to withstand the high pressure of blood coming from the heart. Veins are blood vessels which carry blood back to the heart. Veins deliver deoxygenated blood except pulmonary veins. Veins are thinner walls than arteries because blood pressure in the veins is much lower than in the arteries. Since the blood in the veins may be moving against gravity, they contain valve to prevent the blood from flowing back. Capillaries are tiny blood vessels which connect arteries and veins. They have walls which are only one cell thick. Oxygen and nutrients move from the blood through the capillary walls into the body cells. At the same time, carbon dioxide and other waste products move from the cells into the blood.

Source: http://academic.kellogg.edu/herbrandsonc/bio201_mckinley/f23-1_walls_of_an_arter_c.jpg

Structure of the human heart

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The function of the heart is to pump the blood to all parts of body. The heart is made up of two pumps located side by side. The right side of the heart pumps deoxygenated blood it receives from the tissue to the lungs. Carbon dioxide is removed in the lungs. The left side of the heart pumps oxygenated blood it receives from the lungs to the rest of the body. Oxygen is removed in the tissue for respiration.

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.