ACCESS HE Human Biology. Blood ACCESS HE Human Biology. Clare Hargreaves-Norris

Introduction The circulatory system is comprised of: Blood, this fluid transports vital substances to all areas of the body. Blood is transported in vessels known as arteries, veins and capillaries. The heart acts as a pump to move the blood around the body. Clare Hargreaves-Norris

The blood has three main functions Functions Of The Blood The blood has three main functions Clare Hargreaves-Norris

1. Transportation Red blood cells carry oxygen to the cells of the body. Carbon dioxide is carried back to the lungs. Nutrients such as glucose, vitamins and minerals are transported around the body. Hormones are secreted into the blood and attach to the plasma so that they can be transported around the body to their target organs. All waste materials such as urea are carried in the blood to be removed and excreted. Clare Hargreaves-Norris

2. Defence Leucocytes (white blood cells) fight against disease and microbe entry. Leucocytes engulf the bacteria and destroy them (phagocytosis). Lymphocytes (specialised leucocytes) produce antibodies which give the body future resistance to re-infection. Coagulation. Platelets start the clotting process to prevent excessive blood loss and to stop infection from gaining entry into the body. Clare Hargreaves-Norris

3. Regulation The blood regulates body heat by absorbing it from the liver and muscles as it passes by, and then transports it around the body. Clare Hargreaves-Norris

Composition of blood Blood is made from Plasma (55%) a straw-coloured fluid Erythrocytes (red blood cells) Leucocytes (white blood cells) Thrombocytes (platelets) Clare Hargreaves-Norris

Remaining 10% consists of other substances: Structure Function Plasma 90% water. Remaining 10% consists of other substances: - blood proteins, - mineral salts, nutrients, waste material, - gases, enzymes, hormones, antibodies. Renews the cellular fluid. Maintains the pH of the blood at 7.4. Makes the blood viscous. Provides energy to the cells. Produces chemical reactions. Protects against infection. Clare Hargreaves-Norris

Erythrocytes (red blood cells) Structure Function Erythrocytes (red blood cells) Minute biconcave discs. They obtain their red colour from haemoglobin combining with oxygen to form oxyhaemoglobin. Made in the red bone marrow. They take approximately 7 days to form. They then function for approximately 4 months. They are then destroyed by the liver or spleen. To carry oxygen around the body to the cells. To take carbon dioxide away from the cells. Clare Hargreaves-Norris

Leucocytes (white blood cells) Structure Function Leucocytes (white blood cells) Are colourless cells, contain a nucleus, and are larger than red blood cells. There are fewer leucocytes than erythrocytes. There is approximately 1 leucocyte to every 600 erythrocytes. To fight infection. 2 main types of leucocytes: Granulocytes (75%) Neutrophils - digest bacteria & cell debris. Basophils – release histamine and heparin. Eosinophils – combat inflamation. Agranulocytes (25%). Lymphocytes (23%) - produce antibodies to kill foreign proteins. Monocytes (2%) - ingest foreign proteins. Clare Hargreaves-Norris

Platelets (Thrombocytes). Platelets are formed in the red bone marrow. Structure Function Platelets (Thrombocytes). Platelets are formed in the red bone marrow. They are tiny fragments that are even smaller than red blood cells. They produce thrombokinase. Thrombokinase starts the ‘clotting cascade’. Clotting cascade is a chain of reactions resulting in a blood clot. This is an essential part of homeostasis to prevent blood loss. Clare Hargreaves-Norris

Blood clotting Platelets produce a substance called thrombokinase. This sets off a chain of reactions resulting in the laying of fibres. The fibres cover the wound thus preventing blood loss. When the blood clots it forms a scab. A scab is a natural protective seal (plaster) to the area. This process is known as the ‘Clotting Cascade’. Clare Hargreaves-Norris

Factors affecting the blood clotting process The health and efficiency of the blood supply can be affected by: Smoking Alcohol Poor nutrition intake Anti-coagulant drugs such as warfarin and aspirin. Clare Hargreaves-Norris