Key Terms - Cardiovascular System

tachycardia

Abnormally fast resting heart rate, >100 beats per minute in adults.

end-diastolic volume (EDV)

Amount of blood contained in the ventricle at the end of ventricular filling.

end-systolic volume (ESV)

Amount of blood left in the ventricle at the end of contraction.

mechanoreceptor

An end organ that responds to changes in mechanical stress, such as stretch, compression, or distension.

vasodilation

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

hemoglobin

An iron-containing protein in red blood cells that reversibly binds oxygen.

mean arterial pressure (MAP)

A calculation of a single value for blood pressure that factors both the systolic and diastolic pressures. Calculated from 2/3 DBP + 1/3 SBP

atrioventricular (AV) node

A cluster of cells at the junction between the atria and ventricles. Receives electrical signal from SA node, slows impulse before passing it on.

ventricular fibrillation

A condition in which the heart's electrical impulses are disorganized, preventing the myocardium from contracting normally and resulting in an ineffective twitching of the ventricles with no measurable cardiac output.

ventricular tachycardia

A condition in which the rate of ventricular contraction is quite rapid; if rapid enough, will not allow the heart's chambers to fill with enough blood between beats to produce blood flow sufficient to meet the body's needs.

vasoconstriction

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

bradycardia

A heart rate of less than 60 beats per minute (bpm) in an adult (slow heart rate).

chemoreceptor

A sensory organ capable of reacting to a chemical stimulus, sense changes in oxygen content, pH, or carbon dioxide levels in the blood.

sinoatrial (SA) node

A specialized area of cardiac tissue, located in the right atrium of the heart, which initiates the electrical impulses that determine the heart rate; often termed the pacemaker for the heart.

Purkinje fibers

Collection of nerve fibers in the ventricles that distribute impulses to the right and left ventricles, causing them to contract together.

capillaries

Connect the arteries and veins, smallest of the blood vessels; these are where oxygen, nutrients, and wastes are exchanged within the tissues.

pericardium

Double-walled membranous sac that encloses the heart.

cardiac output

The volume of blood pumped out by the heart per minute. It is the product of heart rate x stroke volume.

premature ventricular contraction (PVC)

Ventricular contraction that occurs early in the cardiac cycle before the SA node initiates an electrical impulse, originating in an ectopic focus in the ventricles.

arterioles

The smallest arteries that transport blood from larger arteries to the capillaries.

veins

Class of blood vessels that transport blood from the capillaries back to the heart.

hematopoiesis

Blood cell production, which is also called hemopoiesis.

arteries

Blood vessels that transport blood away from the heart.

electrocardiogram (ECG)

Graphic representation of electrical impulses generated by the heart during a cardiac cycle.

myocardium

Layer of the heart wall composed of cardiac muscle.

ejection fraction (EF)

Measurement of the volume percentage of left ventricular contents ejected with each contraction. It is the BEST indicator of pump function.

extrinsic neural control

Redistribution of blood at the system or body level through sympathetic nervous system control, primarily through vasoconstriction of small arteries and arterioles.

muscle pump

Rhythmic squeezing of veins by the large muscles of the legs; increases blood return to the heart against gravity.

venules

Small vessels that transport blood from the capillaries to the veins.

intercalated disks

Specialized cell junctions in the myocardium where one muscle cell connects to the next.

baroreceptor

Stretch receptor located within the cardiovascular system that senses changes in blood pressure.

stroke volume

The amount of blood ejected from the left ventricle during contraction; the difference between the end-diastolic volume and the end-systolic volume.

diastolic blood pressure (DBP)

The amount of force (pressure) that blood exerts on the walls of the blood vessels as it passes through them while the heart is at rest. Is represented by the bottom number in a blood pressure reading.

systolic blood pressure (SBP)

The blood pressure measured during the period of ventricular contraction; in blood pressure readings it is the larger, upper number of the two measurements.

cardiac cycle

The complete cycle of electrical and mechanical events in the heart from the beginning of one heart beat to the beginning of the next.

hematocrit

The percentage of cells or formed elements in the total blood volume. More than 99% of the cells or formed elements are red blood cells.