Cardiovascular System : The Classical World

Introduction

The cardiovascular system consists of the heart and blood vessels. The lower parts of the heart (the ventricles) pump the blood, and the vessels carry the blood through the body and back to the heart. The cardiovascular system works closely with the respiratory system since the blood vessels carry both oxygen and carbon dioxide that are inhaled and exhaled by the lungs. The largest vessels are closest to the heart, and the farther from the heart the smaller they are. Arteries always carry blood away from the heart. They then become arterioles and finally hair-like microscopic capillaries, which link up with the smallest veins, the venules, which enlarge to veins and finally the largest veins, the superior or inferior vena cava, before entering the heart.

The heart itself is divided into four chambers. The upper chambers, the atria, are the receiving rooms. The lower chambers, the ventricles, are the pump stations. The right atrium receives deoxygenated blood from the superior or inferior vena cava, and passes it through a one-way door, the tricuspid valve, into the right ventricle. From there the deoxygenated blood is pumped into the pulmonary arteries through the pulmonary semilunar valve. In the lungs it is oxygenated and comes back through the pulmonary venules and veins to be received by the left atrium. The now oxygenated blood is passed through the bicuspid, or mitral, valve into the left ventricle, from where it is pumped through the largest artery, the aorta, into the systemic circulation to the rest of the body, starting with the coronary circulation to provide oxygen and nutrients to the heart muscle tissue.

The pumping and movement of blood is caused by electrical impulses conducted from the sinoatrial node in the right atrium that initiates a cycle of contraction and relaxation of the heart muscle. The force of the contractions of the heart contributes towards blood pressure, the force of the circulating blood on the walls of the arteries. Systolic pressure (during the period of contraction) is measured first; then diastolic (during relaxation). 120/80 would be considered normal.