37.1 The Circulatory System

Myocardium

• Thick middle muscle layer of the heart; pumps blood through the circulatory system.

Atrium

• Upper chamber of the heart that receives and holds blood that is about to enter the ventricle.

Ventricle

• Lower chamber of the heart that pumps blood out of the heart.

Pulmonary Circulation

• Pathway of circulation between the heart and the lungs.

Systemic Circulation

• Pathway of circulation between the heart and the rest of the body except the lungs.

Valve

• Flap of connective tissue between an atrium and a ventricle, or in a vein, that prevents backflow of blood.

Pacemaker

• Small group of cardiac muscle cells in the right atrium that “set the pace” for the heart as a whole; also known as the sinoatrial node.

Aorta

• Large blood vessel in mammals through which blood travels after it leaves the left ventricle.

Artery

• Large blood vessel that carries blood from the heart to the tissues of the body.

Capillary

• Smallest blood vessel; brings nutrients and oxygen to the tissues and absorbs carbon dioxide and waste products.

Vein

• In plants, a cluster of vascular tissue in leaves; in animals, a blood vessel that returns blood to the heart.

Atherosclerosis

• Condition in which fatty deposits called plaque build up on the inner walls of the arteries.

Key Concept

• The human circulatory system consists of the heart, a series of blood vessels, and the blood that flows through them.

Key Concept

• As blood flows through the circulatory system, it moves through three types of blood vessels—arteries, capillaries, and veins.