More Info

When you go for a checkup, your doctor uses a stethoscope to listen carefully to your heart. The first sound (the lub) happens when the mitral and tricuspid valves close. The next sound (the dub) happens when the aortic and pulmonary valves close after the blood has been squeezed out of the heart.

Capillaries

Capillaries are extremely small vessels located within the tissues of the body that transport blood from the arteries to the veins.Capillary walls are thin and are composed of endothelium (a single layer of overlapping flat cells). The flow of blood is controlled by structures called precapillary sphincters.

Deoxygenated Blood

Deoxygenated blood enters the right atrium of the heart from the superior and inferior vena cava (veins). The atria contract, forcing blood from the right atrium into the right ventricle.

Oxygenated Blood

The oxygenated blood returns to the left atrium of the heart via the pulmonary veins (carrying oxygenated blood).As the atria contract, blood from the left atrium is forced into the left ventricle. the circulatory system is also called the cardiovascular system. the cardiovascular system carries needed substances to cells and carries waste products away from cells. in addtion blood cells fight disease.  

the heart:

each time the heart beats, it pushes blood through the blood vessels of the cardiovascular system.