5.2 Moving blood through the body

Chambers

The heart consists of four muscular chambers.

• Septum: separates the two chambers on the left hand side from the two on the right.

• Atria: upper chambers, receive blood transporting it to the ventricles,

• Ventricles: lower chambers, pump blood out to the body.

Valves

The four valves control the direction of the blood.

• Chordae tendinae - strong tendons that hold the atrioventricular valves in position.

• Veins - contain valves to prevent the back-flow of blood.

• Valves snapping shut causes the heart’s thumping sounds.

Blood vessels

• Arteries - muscular blood vessels that carry blood away from the heart.

• Arterioles - small arteries; direct blood flow to various tissues.

• Capillaries - microscopic blood vessels that connect arterioles and venules, enable the exchange of substances between blood and surrounding tissues.

• Veins - carry blood towards the heart.

• Venules - small veins.

Blood vessel layers

Arteries

• Present tunica interna,

• Well developed tunica media,

• Relatively thin tunica externa.

Capillaries

• Present tunica interna,

• No tunica media,

• No tunica externa.

Veins

• Present tunica interna,

• Relatively thin tunica media,

• Well developed tunica externa.

Artery structure

• Elastic walls - expansion and contraction with changes in blood pressure.

• Muscular walls - allows vasoconstriction and vasodilation to control blood flow.

• Narrow lumen size - helps maintain high pressure in arteries.

Vein structure

• Walls are not elastic or muscular.

• Thin walls.

• Valves present - prevent backflow of blood.

• Large lumen size.

Double circulation

All mammals including humans have double circulation:

• Systematic circulation,

• Pulmonary circulation.

Pulmonary circulation

• Takes deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the left atrium.

• Right ventricle - the pump for the pulmonary circulation.

Systematic circulation

• Takes oxygenated blood from the left ventricle to all the tissues of the body and returns deoxygenated blood to the right atrium.

• Left ventricle - the pump for the systematic circulation.

Cardiac cycle

Also known as the heart beat - the sequence of events that occurs in one complete beat of the heart.

• Diastole: the filling phase of the cycle when heart muscle relaxes,

• Systole: pumping phase of cycle when heart muscle contracts.

Rate of blood flow

Depends on:

• Vasoconstriction and vasodilation of blood vessels throughout the body,

• How fast the heart is beating,

• How much blood is pumped with each beat.

Heart rate: beats per minute.

Stroke volume: volume (mL) of blood forced from a ventricle with each contraction.

Cardiac output: the volume (mL) of blood leaving one of the ventricles every minute.