circulatory system

sinoatrial (SA) node

A region in the right atrium of the heart that sets the rate and timing at which all cardiac muscle cells contract; the pacemaker.

semilunar valve

A valve located at each exit of the heart, where the aorta leaves the left ventricle and the pulmonary artery leaves the right ventricle.

atrioventricular (AV) node

A region of specialized heart muscle tissue between the left and right atria where electrical impulses are delayed for about 0.1 second before spreading to both ventricles and causing them to contract.

atrioventricular (AV) valve

A heart valve located between each atrium and ventricle that prevents a backflow of blood when the ventricle contracts.

stroke volume

The volume of blood pumped by a heart ventricle in a single contraction.

diastole

The stage of the cardiac cycle in which a heart chamber is relaxed and fills with blood.

cardiac output

The volume of blood pumped per minute by each ventricle of the heart.

capillary bed

A network of capillaries in a tissue or organ.

vein

In animals, a vessel that carries blood toward the heart

venule

A vessel that conveys blood between a capillary bed and a vein

ventricle

A heart chamber that pumps blood out of the heart.

pulse

The rhythmic bulging of the artery walls with each heartbeat

vasoconstriction

A decrease in the diameter of blood vessels caused by contraction of smooth muscles in the vessel walls.

vasodilation

An increase in the diameter of blood vessels caused by relaxation of smooth muscles in the vessel walls

systolic pressure

Blood pressure in the arteries during contraction of the ventricles

systemic circuit

The branch of the circulatory system that supplies oxygenated blood to and carries deoxygenated blood away from organs and tissues throughout the body.

diastolic pressure

Blood pressure in the arteries when the ventricles are relaxed.

heart

A muscular pump that uses metabolic energy to elevate the hydrostatic pressure of the circulatory fluid (blood or hemolymph).

heart rate

The frequency of heart contraction (in beats per minute)

double circulation

A circulatory system consisting of separate pulmonary and systemic circuits, in which blood passes through the heart after completing each circuit.

electrocardiogram (ECG or EKG)

A record of the electrical impulses that travel through heart muscle during the cardiac cycle

cardiac cycle

The alternating contractions and relaxations of the heart.

Blood

A connective tissue with a fluid matrix called plasma in which red blood cells, white blood cells, and cell fragments called platelets are suspended.

capillary

A microscopic blood vessel that penetrates the tissues and consists of a single layer of endothelial cells that allows exchange between the blood and interstitial fluid.

arteriole

A vessel that conveys blood between an artery and a capillary bed.

artery

A vessel that carries blood away from the heart to organs throughout the body.

atrium (plural, atria)

A chamber of the vertebrate heart that receives blood from the veins and transfers blood to a ventricle