The heart is a complex organ made up of several layers of tissue and other key components that are vital to its operation. First, the heart wall is comprised of three layers of tissue, each with a unique function:
- Epicardium: fibrous tissue making up the outermost section of the heart and serving as a layer of protection.
- Myocardium: middle layer comprising the majority of the heart, made up of interlacing bundles of tissue that facilitate the heart's contraction.
- Endocardium: thin innermost layer of tissue made up of smooth muscle and small blood vessels creating the surface of the heart's valves.
This is all encased inside a pericardium, a fluid-filled, fibroserous sac with an inner and outer layer that holds a lubricating fluid between them. This fluid serves to reduce the friction caused by the heart as it beats.
To keep the myocardium working properly, a continued supply of nutrients and oxygen must be carried through a complex network of blood vessels called coronary arteries and waste supplies must be removed.
Inside the heart is an internal cavity made up of four chambers, each with its own unique purpose: the right and left atria and the right and left ventricles.
The two atria receive the deoxygenated blood—the right from systemic veins and the left from pulmonary veins—while the ventricles pump oxygenated blood out from the heart.
The left ventricle is the thicker of the two and pumps oxygenated blood to all tissues throughout the body, while the right pumps blood to the lungs only.
There are also four valves in the heart that facilitate the movement of blood between the chambers of the heart. The tricuspid valve connects the right atrium and right ventricle, while the mitral valve connects the left atrium and left ventricle.
The pulmonary valve connects the right ventricle and the pulmonary artery, which carries the blood to the lungs. And the aortic valve connects the left ventricle to the aorta, which carries blood to all other parts of the body.