Heart and blood

• The circulatory system is responsible for delivering oxygen, nutrients, hormones, and other necessary substances to the body's cells.
• Arteries carry blood away from the heart. They have thick muscular and elastic fibre walls. They have a small lumen and have high pressure. They carry oxygenated blood, with an exception for the pulmonary artery.
• Veins carry blood towards the heart. They have thinner walls than arteries but thicker than capillaries. They have a large lumen and have low pressure. They often contain valves to stop the back flow of blood. They carry deoxygenated blood, with the exception of the pulmonary vein.
• Capillaries are the smallest blood vessel in the body. They connect arteries and veins. They are one cell thick to allow quick diffusion from the blood. They also have a large lumen.
• The left side of the heart has thicker muscles surrounding it because it is on the left side that blood is pumped all around the body.
• The heart is composed of four chambers: two atria and two ventricles.
• Heart valves are structures within the heart that ensure the one-way flow of blood.
• The vena cava (vein) brings blood to the heart on the right side. The pulmonary artery from the right side of the heart takes deoxygenated blood to the lungs. The pulmonary vein on the left side of the heart brings oxygenated blood to the heart. The aorta (artery) on the left side of the heart takes oxygenated blood all around the body.
• There are two types of white blood cell:

  Phagocytes

  Lymphocytes
• Phagocytes engulf bacteria and are there to protect the body from infection and disease. They are very flexible.
• Lymphocytes engulf bacteria but can also stick them together to do this easier. They are there to protect the body from infection and also produce anti-bodies.
• Red blood cells are also called erythrocytes. They are the cells that carry oxygen around the body. They have no nucleus to maximize space for oxygen and the haemoglobin. They are red coloured because of the haemoglobin.
• Platelets are cells that help to clot open wounds. They have no nucleus to maximize space to stick to other platelets to form a clot.
• Plasma is straw coloured and contains dissolved substances such as glucose, urea and carbon dioxide. Plasma also carries all other types of blood.