In this lesson, the following essential questions were examined:

• What are the major structures and their functions of the circulatory system?
• How do the principal structures of the circulatory system move blood through the body?

The human circulatory system is made up of the heart, blood vessels, and blood. The heart is a muscular pump with two atria that receive blood from the vena cava and pulmonary vein.

Deoxygenated blood from the vena cava collects in the right atrium, while oxygenated blood from the pulmonary vein collects in the left atrium. The right atrioventricular valve opens to move deoxygenated blood into the right ventricle. Simultaneously, the left atrioventricular valve opens to move oxygenated blood into the left ventricle.

The pumping action (muscle contraction/relaxation) is coordinated by Purkinje fibres in the septum. Nodes in the right atrium conduct electrical impulses to these fibres, which induce rhythmic muscle contraction. This gives a "lub dub" sound to the blood moving through the chambers of your heart.

From the ventricles, semilunar valves open and close at the pulmonary artery trunk and aorta trunk. Deoxygenated blood moves from the right ventricle to the lungs, while oxygenated blood that has returned from the lungs is pumped through the aorta from the left ventricle.

Arteries such as the aorta take blood away from the heart. Veins, such as the vena cava and pulmonary vein, return blood to the heart. Blood moves from arteries to capillaries to engage in energy and matter exchange. Blood moves from the capillaries to the veins, and blood is moved back to the heart to be reoxygenated.

Lesson Glossary

endocardium: the innermost layer of tissue that lines the chambers of the heart

This sheet of shiny white tissue also lines the body's blood vessels to help form a continuous lining through the circulatory system. This lining helps blood flow smoothly and prevents the formation of clots.

myocardial fibres: a specialized cardiac muscle that can contract as well as conduct electrical impulses; not found anywhere else in the body

pulmonary: having to do with the lungs

Purkinje fibres: specialized fibres that transmit electrical impulses to the cardiac muscles in the heart to induce rhythmic muscle contraction

systemic: a body system in general