Circulatory system

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Pulmonary circulation

Circulation between lungs and heart

Systemic circulation

Circulation between body and heart

Capillaries

Thinnest of all blood vessels. Their walls are one cell thick to allow for gas exchange

Arteries

Carries blood AWAY from the heart.

• Contains high pressure blood

• Thick outer layer and thick inner layer of muscle and elastic fibres

• Narrow central tube

Veins

Carries blood TO the heart

• Contains low pressure blood

• Thin outer wall and thin inner layer of muscle and elastic fibres

• Wide central tube

Red blood cells

AKA erythrocytes, they make up 45% of the blood. They carry oxygen through the body and remove carbon dioxide. They contain hemoglobin. They are disc-shaped to maximize surface area and are flexible to fit through the tiny capillaries.

White blood cells

AKA leukocytes, they make up about 1% of the blood. They act as the body’s defense system by attacking invaders and producing anti-bodies

Platelets

Help close and repair wounds. When needed, they form irregular shapes to plug over a wound.

Plasma

Blood cells and platelets are suspended in it. It about 55% of total blood.