The circulatory system

• Chordae tendinae


  holds the flaps of the valve in position
• Blood flows from the right side to the left side of the heart through the valves.
• The heart is divided into four chambers
• The pulmonary semilunar valve prevents blood flowing back into the right ventricle when it contracts
• Left atrium receives oxygenated blood from lungs via pulmonary vein, left ventricle pumps it out to rest of body via aorta
• Right atrium receives deoxygenated blood from the body via vena cava, right ventricle pumps it to lungs via pulmonary artery
• The aortic semilunar valve prevents blood flowing back into the left ventricle when it relaxes
• Ventricles are thicker than atria as they need more strength to pump blood around the body
• Coronary circulation - Blood supply to the heart muscle itself
• Valves prevent backflow of blood between adjacent chambers
• Arteries carry blood away from the heart, so have elastic walls that can stretch under high pressure
• Capillaries are very thin walled with no smooth muscle or elastin fibres, allowing diffusion between cells
• Blood pressure is highest in the aorta and lowest in the capillaries
• Blood is carried through veins back towards the heart
• Veins contain one-way valves which stop blood flowing backwards
• The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs
• Pulmonary veins carry oxygenated blood from the lungs to the left atrium
• Veins contain valves which stop blood flowing backwards when the heart contracts