Human body
Blood vessels carry blood throughout the body, which moves because of the beating of the heart. Venules and veins collect blood low in oxygen from tissues throughout the body. These collect in progressively larger veins until they reach the body's two largest veins, the superior and inferior vena cava, which drain blood into the right side of the heart. From here, the blood is pumped into the lungs where it receives oxygen and drains back into the left side of the heart. From here, it is pumped into the body's largest artery, the aorta, and then progressively smaller arteries and arterioles until it reaches tissue. Here blood passes from small arteries into capillaries, then small veins and the process begins again. Blood carries oxygen, waste products, and hormones from one place in the body to another. Blood is filtered at the kidneys and liver.
Atrioventricular nodal branch
The atrioventricular nodal branch is a cardiac artery that is crucial because it feeds the atrioventricular node, necessary for the excitation and contraction of the ventricles. Most frequently (in over 80% of humans) it arises as a distal branch from the right coronary artery near the crux of the heart. In some people, the atrioventricular node instead receives blood from the circumflex branch of the left coronary artery, otherwise known as the left circumflex coronary artery or LCX. Very rarely, in approximately 2% of people, the vascular supply to the atrioventricular node arises from both the right coronary artery and the left circumflex branch.