Circulatory System

The Mammalian Circulatory System Mammals have a closed circulatory system which means the blood does not bathe the cells directly. Blood is pumped through a series of vessels. Blood circulates in one direction only.

Blood Circulates in 3 Cycles There are 3 major cycles or loops for blood flow. Pulmonary Circulation- the flow of blood between the heart and lungs Systemic Circulation- the route from the heart to the rest of the body Cardiac Circulation- the path taken by blood from the heart to the heart, the most common site of heart attacks.

Circulatory System – Structure and Function The function of the circulatory system is to carry nutrients and wastes to and from different places in the body. The three main structures of the circulatory system are: The vessels that connect all the parts The blood to carry dissolved nutrients and wastes The heart to pump blood

Three Types of Blood Vessels The function of vessels is to direct fluid from one area to another. ARTERIES carry blood away from the heart. Most arteries carry oxygenated blood. VEINS carry blood toward the heart. Most veins carry deoxygenated blood. CAPILLARIES link veins with arteries. All exchange of wastes and nutrients occurs in capillaries.

1A. The ARTERY Arteries carry blood away from the heart. thick muscle and elastic fibres Elastic fibres allow the artery to stretch under pressure. The thick muscle contracts to push the blood along.

Veins carry blood towards the heart. 1B. The VEIN Veins carry blood towards the heart. thin muscle, valves and elastic fibres Veins have valves which stop the blood from going in the wrong direction. When body muscles surrounding the veins contract to move the body, they also squeeze the veins and push the blood along the vessel.

1C. The CAPILLARY Capillaries link arteries with veins. The wall of a capillary is only one cell thick. Nutrients go from the blood to the cells. Wastes go from the cells to the blood.

1C. The Capillary Bed A collection of capillaries is known as a capillary bed. artery vein capillaries body cell Capillaries are the only site for exchange of materials from the blood to the cells.