The Circulatory System Science Matters Chapter 8 Introduction Living things need a transport system to carry things around the body. In humans its called The Circulatory system. The parts of the system are: The Heart, The Blood The Blood Vessels (tubes through which the blood flows). Parts of the circulatory system The Blood The blood brings oxygen and nutrients to the cells and it takes waste (CO2, urea) away from the cells. The blood flows around the body in a continuous cycle about every 30 seconds An adult human contains about 5 litres of blood which if lost can be replaced William Harvey (1578 1637) An English doctor who discovered that blood flows around the body Functions of the Blood 1. Transport Blood carries oxygen, digested food, waste materials, hormones
2. Defence against Disease Destroys harmful bacteria & viruses. Forms a clot when we get cut preventing blood loss 3. Body Temperature Keeps the body at 37 o C Composition of the blood Plasma Plasma is a straw coloured liquid Made up of 90% water + dissolved substances (glucose, urea, proteins) The function of Plasma is to transport substances and heat Red Blood Cells (RBC) They are bi-concave elastic discs Red blood cells carry oxygen around the body They contain a substance called Haemoglobin Haemoglobin has the ability to pick up oxygen. White Blood Cells (WBC) They have no definite shape These cells fight infection Some white blood cells make antibodies, chemicals that inactivate bacteria and viruses Other white blood cells engulf (eat)and destroy bacteria and viruses
Platelets These cells are involved in clotting the blood. The platelets clump together and block the wound. They are not real cells just tiny bits of other cells. Blood Clotting Blood Vessels Arteries Capillaries Veins Thick Wall Small Lumen (space in middle) Blood under high pressure Very thin wall 1 cell thick, tiny lumen Blood pressure lower Thin walls but large lumens No blood pressure No Valves No Valves Valves to stop backflow of blood Carry blood away from heart Usually carry oxygen rich blood Carry blood from arteries to veins Blood looses oxygen as if flows through Carry blood to the heart Blood low in oxygen Blood vessels are the tubes that carry blood around the body
There are 3 types of blood vessel 1. Arteries carry blood away from the heart 2. Capillaries join arteries to veins 3. Veins carry blood towards the heart The Human Heart Structure of the heart
The heart is divided in two by a wall of muscle called the septum. The left side holds oxygenated (pure) blood The right side holds de-oxgenated (impure) blood The left and right sides are split into 2 chambers the atria on top and ventricles on the bottom Ventricles and atria are separated by valves Valves stop the backflow of blood Walls on the left ventricle are thicker than the right Right side pumps de-oxygenated blood to lungs Left side pumps oxygenated blood from the lungs to ALL parts of body Blood vessels of the heart Aorta Carries oxygenated blood from the left side of the heart to all parts of the body Vena cava Carries de-oxygenated blood from all the main organs of the body to the right side of the heart Pulmonary Artery Carries de-oxygenated blood from the right side of the heart to the lungs Pulmonary vein Carries oxygenated blood from the lungs to the left side of the heart
How the heart pumps blood Blood flows from the veins into both atria Deoxygenated blood from around the body goes into the right atrium and oxygenated blood from the lungs goes into the left atrium The walls of the atria contract, open the valves and push the blood into the ventricles. The ventricles contract close the valves to the atria and open the valves to the arteries The Aorta carries the oxygenated blood from the left ventricle all around the body where it delivers food and oxygen to the cells and collects waste. The Pulmonary Artery carries deoxygenated blood from the right ventricle to the lungs where it gets rid of CO 2 and collects Oxygen The Vena Cava take deoxygenated blood back from around the body into the right atrium. The pulmonary vein takes the oxygenated blood from the lungs back to the left atrium The Heartbeat Adults heart beats about 70 times per minute. The sound a doctor hears in his stethoscope is the heart valves opening and closing during heartbeat Our heart pumps faster when we exercise because we need to get greater amounts of oxygen to our muscles and brain When heart rate increases so too does our rate of breathing because we need to take in more oxygen
Pulse Each time it beats blood rushes down the arteries putting pressure on their walls and causing them to expand. Where an artery is close to the skin surface (temple, neck, wrist) you can feel this throbbing called a pulse. Pulse rate varies with age, gender, health, fitness.