Circulatory system

• The heart is located between the lungs, behind the sternum (breastbone), and to the left side of the body.
• The heart has four chambers - two atria and two ventricles.
• Blood flows from the right atrium into the right ventricle through the atrioventricular valve.
• Blood flows from the left atrium into the left ventricle through the bicuspid or mitral valve.
• Valves prevent backflow of blood during contraction of the ventricles.
• The septum separates the right and left sides of the heart.
• Pulmonary veins carry oxygen-rich blood from the lungs to the left atrium.
• Vena cava carries deoxygenated blood from the body to the right atrium.
• Aorta carries oxygen-rich blood from the left ventricle to the rest of the body.
• Coronary arteries supply blood to the heart muscle itself.
• Arterioles are small vessels that regulate blood flow to different parts of the body by controlling their diameter.
• Arterioles are small branches that lead to capillaries, which deliver nutrients and oxygen directly to cells.
• Cardiac output = stroke volume x heart rate
• Capillaries are tiny, thin-walled vessels where exchange between the bloodstream and tissues occurs.
• Veins return blood back to the heart.
• Cardiac cycle is made up of 3 stages: cardiac diastole, atrial systole, ventricular systole.
• Stage 1: cardiac diastole (relaxation), Atrioventricular valves open and semi-lunar valves closed. Elastic recoil, lowers the pressure inside the heart chambers. Blood flows into ventricles from veins but ventricles and atria relax.
• Stage 2: Atrial systole- contraction of atria as blood flows into ventricles.
• Stage 3: Ventricular systole - contraction of ventricles pushes blood out through arteries. Pressure increases so AV valves close and semilunar valves open.
• The right side of the heart receives deoxygenated blood from the body via the vena cava and pumps it to the lungs via pulmonary artery. The left side of the heart receives oxygenated blood from the lungs via the pulmonary vein and pumps it around the rest of the body via the aorta.
• Blood flow during cardiac cycle: Deoxygenated blood enters right atrium via vena cava, oxygenated blood enters left atrium via pulmonary vein, deoxygenated blood leaves right ventricle via pulmonary artery, oxygenated blood leaves left ventricle via aorta.
• The circulatory system consists of the heart, vessels and blood.
• Heart rate refers to the number of times the heart beats per minute.
• Blood vessels are classified by their structure and function.
• Haemoglobin is a protein with a quaternary structure, made up of four polypeptide chains and a haeme group that contains an iron ion.
• the haeme group that contains the iron ion, gives haemoglobin a red colour.
• each haemoglobin molecule can carry four oxygen molecules, so it has a high affinity for oxygen.
• oxygen dissociation curve shows how much oxygen is bound to haemoglobin at different partial pressures of oxygen.
• It is a reversible reaction.

  
• The partial pressure of oxygen is a measure of oxygen concentration. So, the greater the concentration of dissolved oxygen in cells, the higher the partial pressure.
• The partial pressure of carbon dioxide is a pressure measuring the concentration of carbon dioxide in a cell.
• when cells respire they use up oxygen, so this lowers the pO2, so red blood cells deliver oxyhaemoglobin to respiring tissues, where it unloads tissues.