Why do we need a circulatory system? • The cells in your body must be supplied with Nutrients (in the Plasma) and Oxygen (by the Erythrocytes) so that they can respire to generate the energy needed for life. • The waste products from respiration (Carbon Dioxide and Heat) have to be carted away and excreted. • The army that defends your cells, the Lymphocytes, has to be delivered to the site of the conflict. • The patch-up merchants, ie the Platelets, that stop excessive bleeding also have to delivered. We have a closed system - what does that mean? The same blood that run to your toes one minute, is re-circulated to your head the next Here’s another version of the human circulatory system Anatomy of the heart Mammals have a heart with 4 chambers 3 1 4 2 Not all hearts have 4 chambers – Reptiles and Amphibia have 3 chambered hearts the septum between the ventricles is incomplete The heart carries Deoxygenated and Oxygenated Blood - Three types of blood vessels arteries, which carry blood away from the heart to either the lungs or body tissues, capillaries which are minute vessels which deliver nutrients, water, and oxygen to the body cells and pick up cellular wastes, and the veins which transport blood back to the heart. Arteries – high pressure vessels Veins – Low pressure vessels Muscles contraction helps push blood flow back to the heart What is blood made up of: Cellular component • Red blood cells( Erythrocytes) - their function is to transport oxygen • White blood cells (Leucocytes) - their function is to fight of infection • Platelets ( Thrombocytes) - their function is to form network over any holes that become apparent in the capillary beds The source of all blood cells – Bone marrow Structure of Red Blood cells • Red blood cells – biconcave to increase surface area and allow greater flexibility White blood cells, also known as leukocytes, are larger than erythrocytes, have a nucleus, and lack haemoglobin. They function in the cellular immune response.