Right hand side. When the heart is relaxed, deoxygenated blood from the body enters the heart via the venae cavae. Then it enters the right atrium. From the right atrium it contracts and pushes blood down through the tricuspid valve and into the right ventricle. Then the right ventricle contracts, the tricuspid valve closes and blood is pushed up and out of the heart through the semi lunar valve and into the pulmonary artery which takes blood to the lungs. The heart then relaxes and the semi lunar valves close to stop blood flowing back into the heart. The blood then flows to the lungs where it becomes oxygenated and ready to be returned to the heart for distribution around the body.
Left hand side of the hearts blood flow. When the heart is relaxed, oxygenated blood from the lungs enters via the pulmonary vein. Blood then enters the left atrium. The left atrium contracts and pushes blood down through the bicuspid valve and into the left ventricle. Then the left ventricle contracts and the bicuspid valve closes to prevent blood flowing back into the heart. The blood is then pushed up and out of the heart through the semi lunar valve into the aorta which is the big artery leaving the heart taking blood to the rest of the body. The heart then relaxes and the semi lunar valves close to prevent blood flowing back into the heart.
Components of blood
Blood is the medium in which all the cells are carried to transport nutrients and oxygen to the cells of the body. Blood is made up of four components. These are red blood cells, white blood cells, platelets and plasma. Blood is made up of 55% plasma and 45% solids.
Red blood cells
99% of red blood cells are red blood cells or erythrocytes. They are red in colour due to the prescience of a red coloured protein called haemoglobin. Haemoglobin has a massive attraction for oxygen and the main role of the red blood cell is to take on and transport oxygen to the cells.
White blood cells
White blood cells are colourless or transparent and are fewer than red blood cells. (1:700 ratio of white to red). The role of the white blood cells also known as leucocytes are to fight infection. They are part of the body’s immune system. They destroy bacteria and other dangerous organisms.
Platelets
Platelets are not full cells but rather parts of cells. They act by stopping blood loss through clotting. They become sticky when in contact with the air to form the initial stage of repair. Platelets also need a substance called factor 8 to enable them to clot. A haemophiliac is a person whose blood does not clot. This is because they are short of platelets but rather factor 8 which enables the platelets to become active.
Plasma
Plasma is the liquid part of the blood which is straw coloured in appearance. It is the solution in which all the solids are carried.
Blood Vessels
In order for the blood to make its journey around the body it is carried through 5 different types of blood vessels; Arteries, arterioles, capillaries, venules and veins.
Arteries and Arterioles
Arteries are the large blood vessels that leave the heart. They have thick muscular walls which contract and relax to send blood to all parts of the body. The main artery leaving the heart leaving the heart is the aorta. It then splits up into smaller vessels which are called arterioles which are just little arteries. Artery walls contain elastic cartilage and smooth muscle. With this flexible wall it allows the vessels to expand and contract. This helps push blood along the length of the arteries. This is called peristalsis and means how smooth muscle contracts. Arteries do not contain any valves as they are not required and they carry oxygenated blood. The pulmonary artery is an exception as it carries deoxygenated blood away from the heart.
Capillaries
Once the arteries and arterioles have divided they will eventually send blood into the smallest blood vessels. The capillaries are found in all parts of the body especially the muscles. They are so small their walls are 1 cell thick. There are tiny spaces within these thin cell walls which allow oxygen and other nutrients to pass through. This is called diffusion. The blood flows very slowly through the capillaries to allow for this process. In the capillaries the blood will also pick up waste products of metabolism, carbon dioxide and lactic acid.