Body Systems - Year 8 Science: Circulatory System

Circulatory System Functions

FUNCTIONS

• Circulate blood.
• Bring O2 , water & nutrients to the cells.
• Take CO2 & other wastes away from the cells.
• Maintain body T0 & hydration.
• Fight disease.
• Blood clotting.

Circulatory system

The cardiovascular system consists of the :

• Heart
• Blood vessels
• Blood
• Pulmonary circuit ( blood flow between the heart and lungs )
• Systemic circuit – ( blood flow between the heart and the body )

The heart acts to pump blood around the body to provide nutrients and oxygen as well as removing waste and carbon dioxide.

Vessels transport blood to and from the heart around the body.

Structure of arteries

• Thick muscle layer – control the flow of blood
• Thick elastic layer – smooth surges from the heart
• No valves
• Muscular walls allow blood to be pumped through arteries  under high pressure

Structure of veins

• Thin muscle layer
• Thin elastic layer
• Valves: to prevent blood “back flowing”
• Lack of elastic muscle tissue causes veins to have low pressure
• Blood moves easily from high pressure to low pressure

Structure of capillaries

• No muscle
• No elastic
• No valves
• Thin layer of cells only – easy diffusion for gases.
• Numerous and highly branched – large surface area to help diffusion.
• Narrow diameter - bring RBC close to the cells and allow WBC to escape.

Blood vessels

The Blood vessels are intricate networks of hollow tubes that transport blood throughout the entire body.

There are three major types of blood vessels:

ARTERIES - carry blood away from the heart

CAPILLARIES – allow the exchange of gases, nutrients & wastes between the blood and the tissues

VEINS – carry blood back to the heart.

2 other types:

Venules: Smallest veins which extend from capillaries

Arterioles: smallest arteries merge into capillaries