THE CIRCULATORY SYSTEM

BLOOD VESSELS

OBJECTIVES

• Differentiate the 3 types of blood vessels

• Explain the form and function of each type of blood vessel

Blood Vessels

• Blood circulates the human body in a network of blood vessels

• There are 3 types of blood vessels in the human body:

– Arteries

– Veins

– Capillaries

Form & Function

• The structure of each blood vessel is related to its function in the circulatory system

• Arteries and veins are linked by capillaries

• Arteries branch into smaller and smaller blood vessels called arterioles.

• Veins branch into smaller and smaller blood vessels called venules.

• The smallest branch of both form a dense network of capillaries.

ARTERIES (FUNCTION)

• Carry blood away from the heart and deliver it to all the cells of the body

• Usually carry oxygen rich blood (oxygenated blood)

– There is an exception: pulmonary artery which carries oxygen poor blood (deoxygenated blood) to the lungs. This blood has a high concentration of Carbon dioxide (CO2).

ARTERIES- STRUCTURE

• Have very strong muscular walls

• The muscular walls are thicker than those of veins

• They have a smaller lumen than a similar sized vein

• Muscular walls have lots of elastic fibers

• Blood is under high pressure

ARTERIES (FORM &FUNCTION)

• The thick walls allow the vessel to withstand the high pressure of the blood running through it.

• The elastic fibers in the walls allow them to recoil after the blood has passed so that the vibrations are dampened.

• Smaller lumen allows blood to maintain high pressure as it is pumped to the smaller arteries

STRUCTURE OF AN ARTERY

Connective tissue

Smooth muscle and elastic fiber

Epithelial tissueLumen

VEINS (FUNCTION)

• Carry blood towards the heart and deliver it to the heart

• Usually carry oxygen poor blood (deoxygenated

blood)

– There is an exception: pulmonary vein which carries oxygen rich blood (oxygenated blood) to the heart to then be pumped to the cells of the body.

VEINS- STRUCTURE

• Have muscles in walls but not as thick as arteries.

• Walls are not elastic as in arteries

• Have a larger lumen than a similar sized artery

• Valves are positioned at sites along the walls to prevent backflow of blood

• Blood is under low pressure

• Usually found deep between skeletal muscles

VEINS (FORM & FUNCTION)

• The wide lumen allows for the easy flow of blood.

• As surrounding skeletal muscles contract they help to push the blood along the veins.

• Valves in walls help the blood that is under low pressure, to move in one direction.

Connective tissue

Smooth muscle and elastic fiber

Epithelial tissue

STRUCTURE OF A VEIN

Lumen

CAPILLARIES (FUNCTION)

• They are in direct contact with the cells and tissues of the body

• Blood cells (red blood cells and white blood cells) flow in single file in the lumen of the capillary

• They are the site of exchange of substances from the blood and the tissue fluid

– Oxygen leaves blood Carbon dioxide enters blood

– Nutrients leave blood Metabolic waste enters blood

CAPILLARIES (STRUCTURE)

• No muscles in their walls

• Smallest of all blood vessels

• Walls are only one cell thick, so they are extremely thin

• They are the most abundant of all blood vessels

CAPILLARIES – FORM & FUNCTION

• Blood cells (red blood cells and white blood cells) flow in single file in the lumen of the capillary

• The thin walls allow for the easy movement of nutrients and oxygen from the bloodstream and into the tissues (cells) and the movement of carbon dioxide and other waste products out of the tissues (cells) and into the bloodstream

• Slow flow of blood through capillaries allows for movement of substances (diffusion)

STRUCTURE OF

CAPILLARY

Difference in Structure

NOTE:

• The largest artery is the aorta, it is the artery that carries blood away from the heart to the body

• The largest vein is the vena cava, it is the vein that returns blood to the heart from the body. The superior vena cava returns blood from the upper body and the inferior vena cava returns blood from the lower body

Form & Function: Identify the blood vessels below and uses phrases at the bottom to describe the function of each structure.

N a m e : Name: Name:

* Medium-sized blood vessels * Tough, flexible and thick walls* Smallest blood vessels * Carries blood back to the heart * Walls are only one-cell thick * Largest blood vessels* Exchanges oxygen and waste with the blood* Thin Walls due to less blood pressure * Carries blood away from the heart