Circulatory System

It is a system of blood vessels with a pump and valves to ensure one-way flow of blood.

In Mammals

Mammals have a four-chambered heart and a double circulation. This means that for every one circuit of the body, the blood passes through the heart twice.

• Advantage of Double Circulation: Blood travelling through the small capillaries in the lungs loses a lot of pressure ****that was given to it by the pumping of the heart, meaning it cannot travel as fast. By returning the blood to the heart after going through the lungs its pressure can be raised again before sending it to the body, meaning cells can be supplied with the oxygen and glucose they need for respiration faster and more frequently.

The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs (the pulmonary circulation); The left side of the heart receives oxygenated blood from the lungs and pumps it to the body (the systemic circulation).

In Fish

Fish have a two-chambered heart and a single circulation. This means that for every one circuit of the body, the blood passes through the heart once

Heart, to the Gills, to the Body then back to the Heart.

→ Single Circulation vs Double Circulation In single circulation, the low-pressure blood just continue and carries on around the fish’s body, therefore the blood travels more slowly. However, in double circulation, the low-pressure blood is delivered back to the heart, which raises its pressure again to transport to the whole body. Therefore it travels faster than single circulation.

The Heart Structure

Blood Flow / Cycle

Oxygenated Blood: Lungs → Pulmonary Vein → Left Atrium → AorticVentricular Valve → Left Ventricle → Semilunar Valve → Aorta → Body

Deoxygenated Blood: Superior Vena Cava & Inferior Vena Cava → Right Atrium → AorticVentricular Valve → Right Ventricle → Semilunar Valve → Pulmonary Artery → Back to Lungs

The wall that seperates the left ventricle and right ventricle is called septum.

It forms a barrier in the four-chamber of heart. It prevents oxygenated and deoxygenated blood from mixing. In the absence of septum double circulation has not occurred properly.

Different Thickness

Ventricle is THICKER than Atrium, because it pumps blood out from heart.

Right is THICKER than Left side, because Right side (Aorta) pumps blood out to the body.

BOTH To withstand high pressure.

Coronary Heart Disease

CHD is the blockage of Coronary Arteries