The circulatory system in humans
This system consists mainly of: the heart, blood and blood vessel.
Circulatory System, or cardiovascular system, in humans, is the combined function of the heart, blood, and blood vessels to transport oxygen and nutrients to organs and tissues throughout the body and carry away waste products. Among its vital functions, the circulatory system increases the flow of blood to meet increased energy demands during exercise and regulates body temperature. In addition, when foreign substances or organisms invade the body, the circulatory system swiftly conveys disease-fighting elements of the immune system, such as white blood cells and antibodies, to regions under attack. Also, in the case of injury or bleeding, the circulatory system sends clotting cells and proteins to the affected site, which quickly stop bleeding and promote healing. Blood vessel
The blood vessels are tubes through which the blood travels around the body. There are three types of blood vessels, the artery, the vein and capillary.
- Artery: transport blood away from the heart. Blood leaving the heart is at high pressure so arteries have thick muscular and elastic walls to stop them bursting. The muscles in the walls stretch when the blood rushes into the artery from the heart.
- Capillary: The capillaries have walls that are one cell thick. Blood flow through them needs to be constant and even as they are easily damaged. The very thin walls allow for the rapid exchange of materials between blood and the cells of the body. There are so many capillaries that they can close to every cell in the body. The capillaries join up to form larger and larger blood vessels which eventually becomes veins.
3. Vein: Veins are wider tubes than arteries with thin walls that contain less muscle and elastic fibres. Body muscles that surround the veins squeeze them when they contract, such as the muscles in the leg when we walk. This help to push the blood along the vein. However, to make sure the blood only moves towards the heart, there are ‘one way’ valves along the walls of the veins.
The blood
- The blood consists of pale yellow liquid called plasma and cells (RBC and WBC).
- 55% blood Plasma
- 45%blood cells
- The plasma is about 90% water and 10% digested food (glucose, amino acids, fatty acids and glycerol) , hormone, dissolve gasses O2, mineral salts , vitamins, CO2 (as bicarbonate ions) and nitrogenous waste
There are 2 main types of blood cells
1) Red blood cells (erythrocytes) - contain haemoglobin a red pigment containing iron, this is important for oxygen transportation in the blood. These cells have biconcave disc and have no nucleus .RBC are made in the bone marrow, the life span is up to 120 days then they are destroyed in the liver.
2) White blood cells (leukocytes) - these are larger than RBC, contain a nucleus, don’t contain haemoglobin and are in smaller amount for every WBC there are 300 RBC. The main function is to defend the body against invading substance or organism.
Phagocytes –these engulf invading and digested organism inside of them (phagocytosis)
lymphocytes – these have antigen on the surface when and antigen is not recognize then they produce antibodies to destroy that substance or make them less harmful
Platelets – these are fragments used for blood to clot.
Blood types
Antigen -A substance that when introduced into the body stimulates the production of an antibody
Antibodies- any of various proteins produced in the blood in response to the presence of an antigen.
Donor’s blood type
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Recipient’s blood type
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A Antigen A
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B Antigen B
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AB Antigen A and B
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O
No antigens
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A antibody A anti-A
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√
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x
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x
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√
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B anti- B
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x
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x
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x
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√
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AB
No
antibodies
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√
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√
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√
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√
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O antibody A and B
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x
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x
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x
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√
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The “X” denotes cannot match and “√” denote proper matching of blood groups. The person with O blood can donate blood to anyone therefore called universal donor this is because antibodies in the recipient’s blood have no antigens in the donor blood to react with. However person with AB blood type can receive blood from people with any blood group therefore called universal recipient s b/c they do not contain any antibody to react with antigen of the other blood type.
The heart is divided into two parts the right and left sides made up of myocardium or cardiac muscles; this is separated by a layer of muscle called the septum.
The heart has four chambers:
The right atrium receives blood from the veins and pumps it to the right ventricle.
The right ventricle receives blood from the right atrium and pumps it to the lungs, where it is loaded with oxygen.
The left atrium receives oxygenated blood from the lungs and pumps it to the left ventricle.
The left ventricle (the strongest chamber) pumps oxygen-rich blood to the rest of the body. The left ventricle’s vigorous contractions create our blood pressure.
§ Cardiac Muscles—Contracts without fatigue
- Valve tendons—supports valves
- Tricuspid/bicuspid—prevents back flowing of blood
- Pulmonary Artery—carries deoxygenated blood to the lungs.
- Pulmonary vein—returns oxygenated blood from the lungs.
- Aorta—Carries oxygenated blood from the heart
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