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Human Transport System: Blood and Heart

The human blood is made up of red cells, white cells, platelets, and plasma.

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The red blood cells, also known as erythrocytes are microscopic cells that do not contain the nucleus. They are produced by stem cells in the bone marrow. They contain hemoglobin, the red pigment which is useful in the transport of oxygen from the lungs to the rest of the body (Williams and Gray 1989).

The leukocytes (white blood cells) are also produced in the bone marrow while others are produced in the thymus gland. Their primary function is to protect the body against diseases. They are divided into lymphocytes (which detect and engulf foreign bodies for them to be removed), granulocytes, and macrophages which destroy these foreign bodies. They are also important in disposing of dead cells and foreign particles.

Platelets, just like red blood cells, have no nucleus. They are useful in the blood clotting process after physical injury. They stick to the walls of the blood vessels, thus sealing the opening in the vascular wall. In addition, they produce coagulation chemicals that form clots. Of late it has been discovered that they also produce proteins that kill harmful organisms in the body.

Plasma refers to the fluid medium in which other blood components are dissolved. It is made up of water, salt, sugar, fat, and proteins. It is pale yellow in color.

Structure and functions of blood vessels

The major blood vessels are arteries, veins, and capillaries.

Arteries have a comparatively narrow lumen with thick muscular walls. Their main function is to transport blood away from the heart. They all carry oxygenated blood apart from the pulmonary artery. They also have no valves apart from the pulmonary artery blood flows in them at high pressure.

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Veins, on the other hand, have a comparatively larger lumen with less tissue on their walls. They mainly transport blood towards the heart. Unlike arteries, they all have valves. They carry deoxygenated blood apart from the pulmonary vein. Blood flows in them at low pressure.

Capillaries are very narrow (about one cell thick) to allow for the exchange of materials between them and the surrounding cells. They are supplied with blood by arterioles (smaller versions of arteries) and drained by venules (smaller versions of veins). They replenish the cells with oxygenated blood and rid them of deoxygenated blood (Williams and Gray 1989).

Diseases of the heart

Heart Attack

A heart attack (also known as myocardial infarction) is caused by the blocking of the flow of blood in the coronary artery by a blood clot. This results in the damage of parts of the heart muscles. This may lead to sweating, prolonged pains in the upper abdomen, and deep pains in the chest, which may last for several minutes.


Angina is the discomfort that arises when part of one’s heart does not receive sufficient blood rich in oxygen. It is characterized by severe chest pain. The pain may also be felt in the jaws, shoulder, neck, arms, or back. It sometimes may feel like indigestion.

Diseases of the blood

Sickle cell Anaemia

Sickle cell anemia is a disease that is passed on from parents to their offspring. It is characterized by the abnormal development of red blood cells. These cells tend to be hard, sticky, and crescent in shape. They die prematurely and hence one has a shortage of red blood cells, leading to anemic conditions which include lack of breath and tiredness (Ganong 2003).

Iron deficiency Anaemia

Iron deficiency anemia results from insufficient intake of iron in one’s diet. Since iron is a key raw material in the manufacture of haemoglobin, it interferes with the same process. It may also be caused by parasitic infections such as hookworms. This is mainly due to intestinal bleeding caused by the same. Its main symptoms include fatigue, weakness and pallor (Ganong 2003).


Ganong, F., 2003. Review of medical physiology (21 ed.). New York: Lange Medical Books/McGraw-Hill.

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Williams, W. and Gray, D., 1989. Gray’s anatomy (37th ed.). New York: C. Livingstone.

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