Arteries, Arterioles, Veins, Venules, & Capillaries Three types of vessels: Arteries - carry blood away from the heart. Veins - transport blood back to the heart. Capillaries - connects arteries to the veins. Allows diffusion of food, oxygen, and other materials into cells. Allows diffusion of wastes and carbon dioxide out the cells.

Arteries Large hose-like vessels Carry blood away from the heart. Have thick, multi-layered muscular walls. Walls are capable of stretching to accommodate the “pulse” of blood when the heart beats. Walls of arteries are thicker and stronger than the walls of veins and capillaries. Artery walls contain large amounts of muscle and elastic tissue. Muscle and elastic tissue allows an artery to change its diameter. Elastic tissue allows the artery to expand when the heart pumps blood into it. The blood exerts pressure against the vessel walls as it moves through the vessel, this is referred to as blood pressure. When an artery widens, more blood can flow through it, blood pressure decreases. When an artery contracts, less blood can flow through it, blood pressure increases. By changing diameter, an artery helps regulate blood flow and pressure.

Arteries Capable of expanding and contracting to change and maintain the blood pressure. NO valves Blood spurts Blood inside them is high in oxygen & low in carbon dioxide except in pulmonary artery.

Arteries Blood inside is bright red (except pulmonary artery) Blood inside is under High pressure Examples: Coronary (heart), Brachial (arms), Carotid (head), Femoral (legs), Renal (kidney).

Arterioles Tiny branches from arteries. Cannot be seen with unaided eye - microscopic Thinner, less muscular walls (compared to arteries) Feed blood into the capillaries Narrower than arteries, but wider than capillaries

Capillaries Flow and pressure of blood is controlled by sphincters that are outside of the capillaries. Microscopic vessels ~ 8 µm in diameter. Erythrocytes (rbc’s) pass through in single file. Walls are only one cell thick (to facilitate diffusion of materials/exchange).

Capillaries Thinness allows for easy diffusion outward or inward through the single cell layer. Form capillary beds - networks of vessels linking arterial and venous blood.

Capillaries Oxygen , nutrients and other materials move out of the capillaries and into the extra-cellular fluid and then into cells. Carbon dioxide, wastes and other materials are picked up and move into the capillaries. Diffusion enables the movement of substances into and out of capillaries.

Venules Vessels larger than capillaries but smaller (i.e. narrower and thinner walls) than veins. Collect blood from capillaries.

Veins Larger inside diameter compared to arteries Take blood towards the heart Thinner, less muscular walls than arteries, but still 3 layers No stretching or contracting of walls except by external muscles. Contain valves to help return the blood to the heart (compensate for lower venous pressure, less muscle in walls, and large diameter).

Veins - Valves

Veins Blood: Moves smoothly. Low in oxygen except pulmonary circulation. Dull red. Low pressure. Examples: cardiac (heart), brachial (arms), jugular (head), femoral (legs), renal (kidney).

Varicose Veins When the valves don’t function properly, blood leaks backwards and pools in veins Veins sag, stretch and swell, creating bulging gnarled vessels

The circulatory system of arteries, veins and capillaries