Anatomy of the Circulatory System

The Heart

Location and Size
The heart is the size of a person’s fist: hollow, cone-shaped, and weighs less than a pound. It is enclosed within the inferior mediastinum and middle cavity of thorax. The apex is located at the left hip and rests on diaphragm. The heart is located within the fifth intercostal, where a stethoscope is placed.

Coverings
Coverings of the heart include the pericardium (double sac of serous membrane), the epicardium (visceral pericardium, located at the external surface of the heart), parietal pericardium (continuous at the heart base), fibrous pericardium (reinforced by dense connective tissue, protects heart), and serous fluid (produced by serous pericardial membrane).

Layers
There are three layers, which are the epicardium, myocardium, endocardium. The epicardium is the external surface of the heart. The myocardium are thick bundles of cardiac muscle that contract. The endocardium are thin sheets of endothelium that line heart chambers

Chambers and Associated Great Vessels
There are four chambers or cavities, which include two atria and two ventricles. They help blood flow smoothly. The superior atria are receiving chambers. Blood flows into atria under low pressure from veins and continues on to fill ventricles. The inferior ventricles are discharging chambers. Blood is pumped out and into circulation

Systemic vs. Pulmonary Circuits
Pulmonary arteries carry blood to lungs. Oxygen is picked up and CO2 is unloaded. Pulmonary circulation occurs from the right side of heart to lungs, to left side of heart. It carries blood to lungs, then back to heart. Systemic circulation occurs from the left side of heart through body tissues, and back to right side of heart. It supplies oxygen and nutrient-rich blood to all organs.


Major Valves
The atrioventricular valve prevents backflow into atria when ventricles contract It is comprised of a bicuspid valve (2 flaps), tricuspid valve (3 flaps), and chordae tendinae (anchors flaps). Semilunar valves guard bases of two large arteries leaving the vent. There are pulmonary and aortic semilunar valves.