The heart pumps blood throungh two pathways:
Pulmonary circulation pumps blood from the heart to the lungs and back to
the heart again.Blood picks up oxygen and releases carbon dioxide ir the lungs.
Systemic circulation pumps blood from the heart to the rest of the body.
Cells absorb much of oxygen and load the blood with carbon dioxide.
The heart muscle beats in an orderly and coordinated way. A small group of cardiac
muscle fiber, the sinoatrial node (SA node). is also called the peacemaker.When the
peacemaker fires, an electrical impulse causes the atria to contract. Another group
of muscle fiber, the atrioventricular node(AV node), causes the ventricles to
contract. the nervous system influences the SA node, increasing or decreasing
heart rate to meet the body's needs.