Class 4 The Cardiovascular System Cardiovascular system includes the blood, blood vessels, and heart. Small arteries that link to capillaries are called arterioles . Small veins that link to capillaries are called venules .
Capillaries feed and remove cell waste, thus connecting arterioles and venules.
The primary organ is the heart. The heart operates like a pump, receiving blood from veins, sending it to the lungs to become oxygenated, receiving it from the lungs, and sending it throughout the body. The heart is a sac enclosed in a muscle. The muscle is called the myocardium . The endocardium also covers heart valves.