The heart is one of the most important organs in your body. It lies in the center of your thoracic cavity in a sac called the pericardium. Within this sac it contracts freely to pump blood to your lungs for oxygenation. It pumps the oxygenated blood to the rest of your body and returns wastes. To understand the intricate functioning of your heart and blood flow it is important to know the anatomy of the heart, your blood vessels, and the blood itself.
The Heart
The heart is a muscular organ whose primary function is to pump blood through the the lungs and the entire body. It is composed of four chambers -- the left and right ventricles, which are the pumping chambers, and the left and right atria, which prime the pumping chambers. The heart chambers are separated by valves. The right atrium and ventricle are separated by the tricuspid valve while the left atrium and ventricle are separated by the mitral valve. The right ventricle communicates with the circulation of the lungs via the pulmonary arteries. The pulmonary valve regulates blood flow between the right ventricle and pulmonary arteries. On the left side of the heart the aortic valve separates the left ventricle and the aorta and regulates blood flow from the left side of the heart out to the body's general circulation.
Composition of Blood
Blood is composed of a proteinaceous fluid called plasma and cellular elements including red blood cells, which carry oxygen, white blood cells, which act as immune cells, and platelets, which help to create blood clots. Blood also carries other necessary nutrients and hormones to tissues and sweeps away waste products.
Blood Vessels
The blood vessels are like a closed system of pipes that carry blood from the heart to the tissues and back to the heart. Blood vessels that flow away from the heart are called arteries. Arteries are compared of three tissue layers -- the outer connective tissue layer is called the adventitia; the middle layer is a muscular layer called the media; and the inner layer has endothelial cells that line the inside of the blood vessel. Large arteries also contain elastic fibers between the tissue layers that allow the vessels to stretch to accommodate large volumes of blood at high pressures.
Veins are blood vessels that carry blood toward the heart. They also have three tissue layers, though their muscle layers are much thinner than arteries and they have less elastic tissue. These characteristics of veins allow them to hold large volumes of blood at low pressures.
Capillaries are tiny blood vessels that arise from arteries and terminate at veins. They exists in tissue and they allow oxygen to diffuse out of the blood and into the tissues while carbon dioxide and other wastes from the tissue diffuse back into the blood to be carried away.
Great Vessels
The great vessels are the major blood vessels, both arteries and veins. The great vessels include the superior vena cava, which brings blood directly into the heart from the upper body, the inferior vena cava, which brings blood directly into the heart from the lower body, the pulmonary arteries, which carry blood from the heart to the lungs, the pulmonary veins which return blood to the heart from the lungs, the aorta, which is the largest artery in the body and carries body directly from the heart to the rest of the body, the brachiocephalic arteries and veins, the left common carotid artery, and the left subclavian artery.
References
- "Pathophysiology of Disease"; Stephen J. McPhee, M.D., Gary D. Hammer, M.D., Ph.D.; 2010
- "Ganong's Review of Medical Physiology"; Kim E. Barrett, Ph.D., Susan M. Barman, Ph.D., Scott Boitano, Ph.D., Heddwen Brooks, Ph.D., 2010
- "Hurst's the Heart, Ch. 3"; Joseph F. Malouf, M.D., William D. Edwards, M.D., A. Jamil Tajik, M.D., James B. Seward, M.D., FACC; 2008.
