BLOOD VESSELS

By: Ms. Reis

Blood Vessels

3 types of blood vessels form a network of tubes throughout the body to transport the blood.

1. Arteries

2. Capillaries

3. Veins

Arteries

• Arteries – blood vessels that carry oxygenated blood away from the heart to tissues where it is needed.

• The aorta is the largest artery in the body carrying blood from the heart to the tissues.

Arteries

• Arteries have elastic walls that allow it to first expand as blood passes through then snap back again. This movement keeps blood flowing in the right direction, and provides an additional pumping motion to help force the blood through the blood vessels.

• Arteries branch at their ends into smaller arteries that then join capillaries.

Capillaries• Arteries and veins are linked together by

capillaries• Nearly every tissue within the body is

within 0.1 mm of a capillary.

Capillaries: the Site of Gas and Fluid Exchange

• Capillaries are the site of fluid and gas exchange between the blood and cells.

• Oxygen and nutrients diffuse from the blood into the surrounding tissue.

• Carbon dioxide and other wastes pass from the body tissues into the blood.

Capillaries

• Capillaries are tiny:Because of their small diameter red blood cells must travel through capillaries in single file.

• Capillaries have thin walls:The thin capillary wall allows substances to diffuse between the blood and tissues

Capillary

Capillaries

• Oxygenated blood, which appears red in colour, takes on a purple-blue colour as it leaves the capillary. The deoxygenated blood collects in small veins called venules.

Veins

• Veins – blood vessels that return deoxygenated blood back to the heart where it can become oxygenated.

• Once blood reaches the veins after passing the fine network of capillaries it is travelling very slowly.

Blood Vessels: A Comparison• Arteries have thicker walls than veins to

withstand the greater pressure that the blood exerts on the wall of the artery.

Blood Vessels: A Comparison

• Veins have thinner walls but a larger inner circumference. As a result veins lack the elasticity of the artery, but have a greater capacity to carry blood.

• The venous system contains twice as much blood as the arterial system.

ARTERY CAPILLARY VEIN

Wall is composed of 3 layers of cells

Wall is one cell thick

Thinner wall than artery

High elasticity No elasticity Little elasticity but has valves

Smaller diameter than veins

very narrow diameter

Larger diameter than arteries

Carries blood away from the heart

Site of gas exchange with tissue cells

Carries blood toward the heart

Varicose Veins

• If valves do not function properly gravity carries blood to the feet and blood pooling occurs. This results in veins distending/expanding.

• Both genetics and lifestyle are factors.