The Circulatory System - Human Heart – and Lymphatic System
Human Circulatory System
The human circulatory system consists of the heart, blood, red blood cells, white blood cells, platelets, and the lymphatic system. Blood and lymph are the two fluids in the circulatory system. Lymph is that almost colourless fluid that contains white blood cells and which is carried by the lymphatic system. The larger circulatory system is composed of two systems namely the cardiovascular system and lymphatic system. Cardiovascular system is to do with the heart, blood, and blood vessels. The lymphatic system is to do with the lymph, lymph nodes, and lymph vessels. The circulatory system transports the following in the body:
- Transport water and dissolved minerals to the tissue cells.
- Transport oxygen from lungs to cells for cell metabolism.
- Transport nutrients from digestive system to the cells for cell metabolism.
- Transport waste products of cell metabolism to kidneys and lungs.
- Transport hormones and blood cells to help fight diseases in the body.
Blood Flow in the Heart
The size of a human heart is about the size of a mango fruit or a clenched fist. The heart is like a compartment of two pumps (one pump on right side and the other on left side) that pump oxygenated blood to the body and de-oxygenated blood to the lungs as follows:
- Pulmonary circulation: Through vena cava, the right side of the heart receives blood rich in carbon dioxide through right atrium, this blood moves to right ventricle, and on to pulmonary artery, and on to the lungs where carbon dioxide is released and oxygen is absorbed.
- Systemic circulation: Through pulmonary vein, the left side of the heart receives blood rich in oxygen through left atrium, this blood moves on to the left ventricle, and on to aorta, and on to the body where oxygen is used by the cells and carbon dioxide wastes is absorbed by blood. Exchange of nutrients and oxygen for metabolism, and waste products takes place between the blood capillaries and the cells.
- This blood rich in carbon dioxide wastes in 2 above repeat the process again as in number 1 above.
- Coronary Circulation:This is the circulation of blood in the heart muscle. The coronary arteries supply heart with oxygen rich blood which they tap immediately after the aortic valve (from 2 above) and on to the heart muscle. The carbon dioxide rich blood is removed from the heart muscle through coronary veins and on to right atrium to continue with circulation as in 1 above.
In a human heart, the two atria will contract and relax simultaneously, and also the two ventricles will contract and relax simultaneously. This contraction and relaxation of the two atria and two ventricles is what generate the energy for the heart to pump blood. The initiator of the impulse is a nerve originating at sinoatrial node, and has an automatic influence from nervous system. The sinoatrial node is therefore the pacemaker. Once the nerve impulses have been generated, they spread to the atrioventricular node where they are picked by Purkinje fibers and the impulses are amplified several times by Purkinje fibers giving the heart sufficient power for pumping the blood.
An adult man has an average of 5 British litres of blood. The heart will need only 1 minute to pump the entire 5 litres of blood throughout the body. For a guy running marathon, the heart will pump no less than 30 litres of blood in 1 minute. If the heart does not pump the blood for 3 minutes to the brain, the brain will be damaged. If the heart does not pump the blood for 3 minutes to the heart muscles, the heart muscles will be damaged resulting in a heart attack, and then death. A healthy man at rest will have a heart rate of between 60 and 74 beats per minute.
Closure and opening of heart valves, and contraction and relaxation of the heart muscle produces heart sounds represented and magnified as lubb-dubb-pause-lubb-dubb-pause in a doctor’s stethoscope. Any abnormal gaps in the hearts sound of lubb-dubb-pause-lubb-dubb-pause may be an indication that the doctor is dealing with a likely candidate for heart attack, or that the heart muscle and valves of the subject are in trouble.
Red blood cells and platelets
Red blood cells are biconcave disk-shaped cells with no nucleus. The red blood cells contain hemoglobin which helps the red cells in transportation of oxygen and carbon dioxide. It is this hemoglobin that gives these cells the red colour. The red blood cells are composed of many linked amino acids and mineral iron. The red blood cells are produced in red bone marrow and have an average live of 120 days.
Platelets, also known as thrombocytes, are biconcave disk-shaped blood cells that are smaller in size than red blood cells. The platelets are for obstructing blood from bleeding when a tissue is damaged. The platelets will coagulate to form a blood clot.
Lymphatic System and White Blood Cells
Lymph is that almost colourless body fluid that contains white blood cells and is carried by the lymphatic system. The lymphatic system is a part of the circulatory system. The lymphatic system consists of lymph, capillaries called lymphatic vessels for carrying lymph, and lymph nodes. Blood contains lymph. When blood flows through the capillaries, the lymph fluid will slowly diffuse into the surrounding tissues. Once blood is in the tissues, it is collected by lymphatic vessels for circulation in the lymphatic system. The lymph fluid will then flow through lymph nodes. There are more than 100 lymph nodes located along the lymphatic vessels in human body. The lymph contains the white blood cells called lymphocytes that generate antibodies as well as fight disease causing organisms, dead blood cells and toxic wastes.
The spleen is a part of the lymphatic systems and is composed of lymph node tissue. The spleen is a big lymph node that acts as a reservoir for blood, destroy old blood cells and produce lymphocytes. All lymph nodes produce lymphocytes. Lymphocytes are of the types B-lymphocytes and T-lymphocytes which can be stimulated by foreign bodies and antigens to produce immunity. The lymph fluid is then drained by lymphatic trunks and these lymphatic trucks join any of the two main collecting ducts called (1) the thoracic duct and (2) the right lymphatic duct. From these two main ducts, the lymph will enter the veins to become part of the plasma. This happens just before the blood reaches the right atrium of the heart. After this, the blood circulation process repeats all over again.
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