WJEC Biology 3 - Blood and Circulation

  • Created by: Molly
  • Created on: 27-04-13 13:57

William Harvey

William harvey was an english physician. He was able to explain how blood moves around the body in a circle - travelling from the left side of the heart in ateries and then back to the right side of the heart in veins. 

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White Blood Cells (phagocyte)

Includes Nucleus, cell membrance lysosome, engulfed bacterium.

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Red Blood Cell

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Functions of four main parts of the blood

Platelets’ (thrombocytes) function is to clot the blood. Clotting of the blood seals the wound, and stops pathogens from entering our blood and causing problems.

White blood cells (phagocytes and lymphocytes) kill pathogenic bacteria and combat viruses.

Red blood cells (erythrocytes) contain haemoglobin which reacts with oxygen. They distribute the oxygen to the cells, which is essential for their functions.

Plasma’s (intravascular fluid) function is transport. It carries all of the other components of the blood.

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Differences between Red and White blood cells


                      Red Blood Cells                                             White Blood Cells

Shape             Bi-concave                                                              Irregular

Function         Carry and distribute oxygen                               To fight pathogens

Nucleus?        No. This saves space to carry oxygen.         Yes. Sometimes more than one.

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The double circulatory system

Most mammals, including humans have a double circulatory system. There are two separate circulations, one to the lungs (the pulmonary circulation) to oxygenate the blood and the other to the organs to supply oxygen. This means that the right side of the heart is smaller as it only has to pump blood to the lungs, whereas the left side has to pump to the whole body.

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The double circulatory system diagram


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The Heart

The heart is made mainly of muscle and is responsible for pumping blood around the body, it has its own supply of blood fed through coronary vessels on the outside of the heart. The blood flows to the organs through arteries and returns to the heart through veins.

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The heart diagram


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The path of Blood

Deoxygenated blood enters through the vena cava into the right atrium

>        It passes through the atrioventricular tricuspid valve into the right ventricle

>        The blood then passes through the semi lunar valve out the pulmonary artery

>        The blood travels to the lungs and becomes oxygenated, then travels back through the pulmonary vein

>        The oxygenated blood enters the left atrium and passes through the atrioventricular bicuspid valve into the left ventricle

>        The blood passes up through the semi lunar valves and out through the aorta to the body

>        The blood loses its oxygen in the cells and becomes deoxygenated, then returning to the heart through the vena cava.

Valves are small ‘flaps of skin’ which prevent the backflow of blood; they are found in the heart (tricuspid and bicuspid atrioventricular, and semi- lunar valves) and in the veins.

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Blood Vessels

Arteries: When blood flows out of the heart it enters the arteries. Blood in the arteries is at a high pressure. Because of this, arteries need strong walls to withstand this pressure. They have elastic tissue in their walls which stretch and recoil with the force.

In the veins, the blood is under much lower pressure. The blood slows much more slowly, so there is no need for veins to have such thick, strong elastic walls. The lumen of the veins is much wider than arteries so that the blood is not slowed. Veins have valves to stop the backflow of blood.

Capillaries: No cell is ever very far away from a capillary. Their function is to take oxygen, nutrients (et cetera), and remove waste from the cells. To do this then need to be very thin, to allow substances to diffuse easily.  

Blood flows through very small blood vessels called capilleries. Substances needed by cells pass/diffuse out of the blood flows out of the blood to the tissues, and substances produced by the cells pass/diffuse in the blood, through the walls of the capilleries. The thin walls of the capilleries are an advantage for diffusion. Capillieres form extensive networks so that every cell is near to a capillary carrying blood

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