Ceistr

Surface area to volume ratio

In large organisms the surface area to volume ratio is not large enough for diffusion alone to supply substances like oxygen

Circulatory system

A system used to transport substances like oxygen and glucose to cells in large organisms.

Suitable medium

In mammals

Means of moving the medium

Animals often have a pump

Mechanism to control flow

Valves are used in veins to prevent any backflow of blood.

Close system of vessels

The circulatory system in most animals and plants is closed and branched to deliver substances to all parts of the body.

Double circulatory system

In mammals

Atria

Thin-walled and elastic chambers of the heart that stretch when filled with blood.

Ventricles

Thick muscular chambers of the heart that pump blood around the body or to the lungs.

Left atrioventricular valve (bicuspid valve)

The valve between the left atrium and left ventricle.

Right atrioventricular valve (tricuspid valve)

The valve between the right atrium and right ventricle.

Aorta

A vessel connected to the left ventricle that carries oxygenated blood to all parts of the body except the lungs.

Pulmonary artery

A vessel connected to the right ventricle that carries deoxygenated blood to the lungs for oxygenation and removal of carbon dioxide.

Pulmonary vein

A vessel connected to the left atrium that brings oxygenated blood back from the lungs.

Vena cava

A vessel connected to the right atrium that brings deoxygenated blood back from the tissues except the lungs.

Myogenic

Refers to the heart’s ability to initiate its own contraction.

Sinoatrial node

A region of specialised fibres in the right atrium that acts as the pacemaker of the heart.

Atrioventricular node

A node located between the two atria that passes on excitation to the ventricles.

Bundle of His

A bundle of fibres that carries the wave of excitation down to the apex of the heart.

Purkyne fibres

Fibres that branch from the bundle of His and carry the electrical wave upwards to cause ventricular contraction.

Cardiac diastole

The stage where both atria and ventricles relax

Atrial systole

The stage where the atria contract

Ventricular systole

The stage where the ventricles contract