The Cardiovascular System

Assessment CriteriaP5 – Describe the structure and function of the cardiovascular system

M2 – Explain the function of the cardiovascular system

Structure 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); blood vessels (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)

Structure of the HeartBLOOD 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.

Chambers of the Heart• The 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.

Valves of the Heart There 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

The Heart Wall• The 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.

Blood 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

• Arteries 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

• Blood 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

Structure 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 demand

The tunica interna is made up of thin epithelial cells which are smooth and reduce friction between the blood and the vessel walls

Functions of the CV System• Delivering Oxygen + Nutrients

• Removal of Waste

• Thermoregulation

• Vasodilation/Constriction

• Oxygen Transport

• Clotting

• Fighting Infection

Thermoregulation• Increased Energy used during

exercise

• CV System controls distribution and redistribution of body heat

Vasodilation/Vasoconstriction• Vasodilation = Increased diameter

of blood vessels /Expand

• Resistance Decreases

• Increased Blood Flow

• Vasoconstriction = Decreased diameter

• Blood flow shut down

• Decreased blood flow

Delivering O2 / Removing Waste• Delivering Oxygen

• Increased O2 delivered to muscles

• Nutrients delivered

• Removing Waste

• Transported to: Kidneys, Liver, CO2 to Lungs

Blood• Made from

• Plasma

• Red Blood Cells

• White Blood Cells

• Platelets

Oxygen Transport• Demand increases

during exercise

• Blood carries the oxygen from the lungs to the body

• Waste is also transported away

Clotting• White blood cells

help to clot

• Platelets PLUG the damage

• Coagulation factors in plasma help to strengthen the plug

Fighting Infection

• Antibodies and White blood cells defend against viruses and bacteria