Summarizing Mammalian Heart and Blood Vessels

Summary

The heart muscle pumps blood through three divisions of the circulatory system: coronary, pulmonary, and systemic. There is one atrium and one ventricle on the right side and one atrium and one ventricle on the left side. The pumping of the heart is a function of cardiomyocytes, distinctive muscle cells that are striated like skeletal muscle but pump rhythmically and involuntarily like smooth muscle. The internal pacemaker starts at the sinoatrial node, which is located near the wall of the right atrium.

Electrical charges pulse from the SA node causing the two atria to contract in unison; then the pulse reaches the atrioventricular node between the right atrium and right ventricle. A pause in the electric signal allows the atria to empty completely into the ventricles before the ventricles pump out the blood. The blood from the heart is carried through the body by a complex network of blood vessels; arteries take blood away from the heart, and veins bring blood back to the heart.

Glossary

angina

pain caused by partial blockage of the coronary arteries by the buildup of plaque and lack of oxygen to the heart muscle

aorta

major artery of the body that takes blood away from the heart

arteriole

small vessel that connects an artery to a capillary bed

artery

blood vessel that takes blood away from the heart

atherosclerosis

buildup of fatty plaques in the coronary arteries in the heart

atrioventricular valve

one-way membranous flap of connective tissue between the atrium and the ventricle in the right side of the heart; also known as tricuspid valve

bicuspid valve

(also, mitral valve; left atrioventricular valve) one-way membranous flap between the atrium and the ventricle in the left side of the heart

capillary

smallest blood vessel that allows the passage of individual blood cells and the site of diffusion of oxygen and nutrient exchange

capillary bed

large number of capillaries that converge to take blood to a particular organ or tissue

cardiac cycle

filling and emptying the heart of blood by electrical signals that cause the heart muscles to contract and relax

cardiomyocyte

specialized heart muscle cell that is striated but contracts involuntarily like smooth muscle

coronary artery

vessel that supplies the heart tissue with blood

coronary vein

vessel that takes blood away from the heart tissue back to the chambers in the heart

diastole

relaxation phase of the cardiac cycle when the heart is relaxed and the ventricles are filling with blood

electrocardiogram (ECG)

recording of the electrical impulses of the cardiac muscle

endocardium

innermost layer of tissue in the heart

epicardium

outermost tissue layer of the heart

inferior vena cava

drains blood from the veins that come from the lower organs and the legs

myocardial infarction

(also, heart attack) complete blockage of the coronary arteries and death of the cardiac muscle tissue

myocardium

heart muscle cells that make up the middle layer and the bulk of the heart wall

pericardium

membrane layer protecting the heart; also part of the epicardium

semilunar valve

membranous flap of connective tissue between the aorta and a ventricle of the heart (the aortic or pulmonary semilunar valves)

sinoatrial (SA) node

the heart’s internal pacemaker; located near the wall of the right atrium

superior vena cava

drains blood from the jugular vein that comes from the brain and from the veins that come from the arms

systole

contraction phase of cardiac cycle when the ventricles are pumping blood into the arteries

tricuspid valve

one-way membranous flap of connective tissue between the atrium and the ventricle in the right side of the heart; also known as atrioventricular valve

vasoconstriction

narrowing of a blood vessel

vasodilation

widening of a blood vessel

vein

blood vessel that brings blood back to the heart

vena cava

major vein of the body returning blood from the upper and lower parts of the body; see the superior vena cava and inferior vena cava

venule

blood vessel that connects a capillary bed to a vein