2Assessment CriteriaP5 – Describe the structure and function of the cardiovascular system M2 – Explain the function of the cardiovascular systemStructure of the cardiovascular system: heart (atria, ventricles, bicuspid valve, tricuspid valve, aortic valve, pulmonary valve, aorta, vena cava – superior and inferior, pulmonary vein, pulmonary artery); bloodvessels (arteries, arterioles, capillaries, veins, venuoles)Function of the cardiovascular system: delivery of oxygen and nutrients; removal of waste products;thermoregulation (vasodilation and vasoconstriction of vessels); function of blood (oxygen transport,clotting, fighting infection)
3Structure of the Heart BLOOD VESSELS OF THE HEART Several blood vessels are attached to the heart. They bring either oxygenated or deoxygenated blood to the heart and take it away. This can be highlighted by the simplified diagram.
4Chambers of the HeartThe heart is divided into two parts by a muscular wall called the septum; each part contains an atrium and a ventricle.The atria are smaller than the ventricles as all they do is push the blood down into the ventricles. This does not require much force so they have thinner muscular walls.The ventricles have much thicker muscular walls because they need to contract with greater forces in order to push blood out of the heart.The left side of the heart is larger because it needs to pump blood all around the body, whereas the right side pumps deoxygenated blood to the lungs, which are in close proximity to the heart.
5Valves of the HeartThere are 4 main valves in the heart that regulate blood flow ensuring it moves in only one directions. They open to allow blood to pass through and then close to prevent back-flow. The tricuspid valve is located between the right atrium and right ventricle and the bicuspid valve lies between the left atrium and left ventricle. The semilunar valves can be found between the right and left ventricles and the pulmonary artery and aorta respectively
7The Heart WallThe pericardium surrounds and protects the heart due to the strong fibrous tissue it contains. It is covered in pericardial fluid to prevent friction caused by movement from the pumping action of the heart. The heart wall is made up of three different layers:Endocardium – this is the inner layer and consists of very smooth tissue to enable the blood to flow freely through the heart.Myocardium – this is the middle layer and consists of cardiac muscle tissue. Cardiac muscle cells only respire aerobically (using oxygen) and are connected by intercalated discs in order to allow a co-ordinated wave of contraction.Epicardium – this is the outer layer of the heart, but at the same time forms the inner layer of the pericardium.
9Blood Vessels 5 different types of Blood Vessel These carry blood from the heart, distribute it around the body and then return it back to the heart.Arteries carry blood away from the heart. The heart beat pushes blood through the arteries by surges of pressue and the elastic artery walls expand with each surge, which can be felt as a pulse in the arteries near the surface of the skin
10Arteries branch off into smaller vessels called arterioles, which in turn divide into microscopic vessels called capillaries.Capillaries have a single-cell layer of endothelium cells and are only wide enough to allow on red blood cell to pass through at a given time.This slows the blood flow, which allows time for exchange of substances with the tissues to take place by diffusion
11Blood the flows from the capillaries to the venules, which increase in size and eventually form veins, which return the blood under low pressure to the heart.Heart>Arteries>Arterioles>Capillaries>Venules>Veins>Heart
12Structure of Blood Vessels Arteries, arterioles, venules and beins all have a similar structure. Their walls consist of three layers:The tunica externa is the outer layer, which contains collagen fibres. This layer needs to be elastic in order to stretch and withstand large fluctuations in blood volume.The tunica media is the middle layer, which is made up of elastic fibres and smooth muscle. The elastic fibres stretch when blood is forced into the arteries. The smooth muscle can contract in the walls of the small arteries and arterioles, which ensures that the amount of blood flowing to various organs varies according to demandThe tunica interna is made up of thin epithelial cells which are smooth and reduce friction between the blood and the vessel walls