Introduction The human heart is four-chambered consisting of two atria and two ventricles. The heart is pear shaped and about the size of a fist. The heart is located beneath the protective ribs on the left side. The heart is an involuntary muscle, meaning that unlike the leg or arm muscles, the cardiac muscle is not under voluntary control. Different animals may have different chambered hearts or none at all. Following is the general anatomy of the human heart. Diagram of the Heart Top Superior/Inferior Vena Cava The Superior Vena Cava and the Inferior Vena Cava both bring deoxygenated blood to the heart.
Generally, the Superior Vena Cava carries blood from the upper part of the body while the Inferior Vena Cava carries blood from the lower part of the body. Like all veins, the Superior and Inferior Vena Cava are made of smooth muscle. Unlike arteries which require their elasticity to withstand the pumping of the heart, veins are more inelastic. These two large major veins feed into the right atrium. Top Right Atrium The blood collects here. As directed by the pacemaker (sinoatrial node), located in the upper wall of this atrium, the two atria (left and right) are simultaneously contracted.
This allows the continuation of blood flow through the tricuspid valve between the right atrium and the right ventricle. This valve does nothing more than allow the blood to flow into the right ventricle without letting blood reenter the right atrium. Top Right Ventricle From the right atrium, blood collects into the right ventricle. The AV node, located in the lower wall of the right atrium sends a signal via the bundle of His to the Purkinje fibers that make the ventricles contract and make blood flow from the right ventricle through the pulmonary semilunar valve to the pulmonary artery.
Like all other valves 1, the pulmonary semilunar valve prevents blood from moving backward. Top Pulmonary Artery Note that this is the only artery that caries deoxygenated blood. This artery takes the blood to the lungs. In the lungs, membrane surface area is increased with the presence of cellular sacs called the alveoli. These tiny sacs contain capillaries that serve to oxygenate blood with inspiration and release carbon dioxide with expiration. Top Pulmonary Vein After gas exchange occurs (CO 2 exchanges with O 2), the blood comes back to the heart via the pulmonary vein.
Top Left Atrium The blood, now oxygenated, collects in the left atrium. When the right atrium is contracted, the left atrium is contracted simultaneously. The blood passes through the mitral or bicuspid valve to the left ventricle. Top Left Ventricle This ventricle collects the blood and contracts the same time as the right ventricle. Blood is then passed through the aortic semilumar valve to the aorta. Top Aorta The aorta, the largest artery, carries the blood to the rest of the body. Some of the blood branches off into the coronary artery.
The heart itself requires blood to sustain itself; hence, the coronary artery supplies the heart muscle with this necessary oxygen. Top Layers of the Heart Pericardium Surrounds heart * A double layered sac often characterized as tough tissue * Outer layer serves to hold the heart in place support of the heart by attaching to various structures in chest cavities * The inner layer is also known as the epicardium * Located directly on top of the heart muscle Top Myocardium Commonly referred to as cardiac muscle.
* Forms walls of the heart’s four chambers: two atria and two ventricles. * The level of thickness depends on the chamber, for example the left ventricle’s thickness of myocardium is greatest since it must pump blood at the highest pressure systemically. Top Endocardium * Comprised of thin endothelial and connective tissue that line the innermost layer of the heart * Is white and shiny in appearance * Helps prevent blood clots from forming within the chambers Top Circulation of Blood Systemic Circulation.
The aorta branches into three arteries ( Brachiocephalic artery, Left common carotid artery, and Left Subclavian) but continues and eventually branches into the femoral artery, located in the thigh. The brachiocephalic artery, then divides into the right common carotid artery (up the throat to the brain) and the right subclavian (right arm). The left common carotid artery goes up the throat and into the brain. The left subclavian artery supplies the left arm. Circulation of Blood Within Heart (keep clicking to view the entire animation) Top.