Biology 12 Circulatory System Arteries: • Thick elastic walls, 3 layers (an inner, smooth endothelial; a middle which • is thick elastic and muscular; and an outer layer of connective tissue) • Carry blood away from the heart. • Usually carry blood which is high in oxygen concentration • Exception = pulmonary artery carries deoxygenated blood • Usually carry blood which is high in pressure. • Have a Pulse. Arterioles: • Small arteries just visible to the naked eye. Veins: • • • • • •
Carry blood towards the heart 3 layers (inner endothelial cells, thin middle layer (not as elastic as arteries) and an outer connective tissue layer) Have one way valves (pocket valves) to ensure return of blood to the heart. Non elastic walls, no pulse Usually carry blood low in oxygen concentration (exception: Pulmonary Vein) Blood usually is of low pressure
Venules: • These are small veins which drain blood away from the capillaries.
Blood vessels controlled by nerves-arteries/arterioles vaso-constricted or vaso-dilated Vaso-constriction: • helps prevent heat loss eg. “white” fingers and toes • shunt blood away from areas of body. eg. reduce blood flow to gut and kidneys so that blood flow to skeletal muscles can be increased during exercise. • helps ensure blood flow to brain and heart is not affected Vaso-dilation: • open up blood vessels: example - in skin to help regulate body temp. • in skeletal muscle during exercise: example - “redness” in face Capillaries: • Small thin walled (one cell thick). Made of endothelial cells. • Where exchange of nutrients, gases and waste takes place. • Arterioles lead and branch into net-works of capillaries called Capillary Beds. At the junction of the arterioles and the capillary beds are special sphincter muscles which can contract to shut off the blood flowing into the capillary bed. This can happen as a result of shock or trauma or due to cold temperatures.
Capillary bed exchange:
Arterial Side: • blood pressure is greater than osmotic pressure - water is forced into extracellular fluid and into the tissues • oxygen and other nutrients diffuse into tissues Venous side: • because blood pressure drops in capillaries (larger surface area), osmotic pressure is greater than blood pressure. (plasma proteins help make blood hypertonic) • wastes like ammonia, urea and carbon dioxide diffuse into blood. • water also diffuses back into blood.
Blood Velocity and Pressure Velocity of blood varies in different parts of the system and is related to the total cross sectional area of the various vessels. Velocity of the blood decreases as the blood pressure decreases. Both decrease due to the increased cross sectional area, which become the greatest in the capillaries. There the blood moves much slower in the capillaries than in the aorta. The wavy pattern on the graph is due to the systole and diastole of the heart ventricles causing the artery and arteriole walls to expand and spring back to their original diameter.
Connections: Maintaining blood volume • The blood pressure (BP) at the arterial side of a capillary bed is approximately: 40 mmHg • The osmotic pressure (OP) at arterial side of the capillary bed is approximately: 25 mmHg • Therefore, BP is greater than OP at the arterial side of the capillary bed and water is forced out of the blood into the tissues. • • •
The blood pressure at the venule side of the capillary bed drops to approximately: 15 mmHg The osmotic pressure at the venule side of the capillary bed is approximately: 25 mmHg Therefore, OP is greater than BP at the venule side of the capillary bed and water diffuses into blood.
Blood Circulation: This is divided into two systems; the Pulmonary system which circulates blood through the lungs and the Systemic system which circulates blood around the rest of the body. Blood Flow through the Body: • •
notice that there are 2 carotid arteries and 2 jugular veins, one on each side of the neck this diagram does not show all the major blood vessels that you must know (see next page)
Major blood vessels • The following diagram presents an easier way to memorize the major blood vessels.
The Lymphatic System The thoracic duct empties into the subclavian vein