22.6:
Anatomy of the Heart
The human heart, a muscle about the size of a fist is made up of three layers of tissue. The outermost layer, the epicardium, is surrounded by the pericardium, a membrane that protects the heart and keeps it in place. In the middle is the myocardium, cardiac muscle cells that make up the majority of the heart's walls which are lined on the inside by the endocardium.
The heart is also organized into four chambers. The upper ones are known as atria. The right atrium receives blood from the coronary sinus, superior vena cava, and inferior vena cava. Whereas the left atrium receives blood from the pulmonary vein. The two lower chambers, the right and left ventricles pump blood.
In addition, there are four main valves, flats of connective tissue that ensure blood flows in one direction preventing backflow.
Specifically, atria ventricular separation occurs on the right side with the tricuspid valve and on the left via the mitral or bicuspid valve. The other two semilunar valves ensure that the blood leaves the heart. One exists in the pulmonary artery on the right side and is called the pulmonary valve. While the other is found on the left in the aorta and is similarly named the aortic valve.
22.6:
Anatomy of the Heart
The human heart is made up of three layers of tissue that are surrounded by the pericardium, a membrane that protects and confines the heart. The outermost layer, closest to the pericardium, is the epicardium. The pericardial cavity separates the pericardium from the epicardium. Beneath the epicardium is the myocardium, the middle layer, and the endocardium, the innermost layer. There are four chambers of the heart: the right atrium, the right ventricle, the left atrium, and the left ventricle. These compartments have two types of valves—atrioventricular and semilunar—that prevent blood from flowing in the wrong direction.
Blood Flow
The right atrium receives blood from the coronary sinus and the superior and inferior vena cavae. This blood goes into the right ventricle via the right atrioventricular (or tricuspid) valve, a flap of connective tissue that prevents the backflow of blood into the atrium. Then, the blood leaves the heart, traveling through the pulmonary semilunar valve into the pulmonary artery. Blood is then carried back into the left atrium of the heart by the pulmonary veins. Between the left atrium and the left ventricle, the blood is again passed through an atrioventricular valve that prevents backflow into the atrium. This atrioventricular valve is called the bicuspid (or mitral) valve. The blood passes through the left ventricle into the aorta via the aortic semilunar valve, leaving the heart to be pumped through the circulatory system to all organs, muscles, and tissue.
Lub-Dub
The distinct sound the heart makes—lub-dub, lub-dub, lub-dub—is caused by the contraction of the heart and the closing of the atrioventricular and semilunar valves. Backflow from the ventricles to the atria is prevented by the atrioventricular valves. When atrioventricular valves close, this produces the “lub” sound. The closing of the semilunar valves, which prevent the backflow of blood from the arteries to the ventricles, creates the “dub” sound. When a valve does not close or open completely, this distinct sound is changed, creating a heart murmur.
Cardiovascular Disease
Cardiovascular disease, disease of the heart and cardiovascular system, is the most common cause of human death in the United States. Heart health is crucial to the optimal functioning of organs and muscles. Disruption of normal heart pumping, caused by blood backflow, ineffective pumping, or decreased blood flow, results in less oxygen provided to all tissue in the body.
Suggested Reading
Buckberg, Gerald D., Navin C. Nanda, Christopher Nguyen, and Mladen J. Kocica. “What Is the Heart? Anatomy, Function, Pathophysiology, and Misconceptions.” Journal of Cardiovascular Development and Disease 5, no. 2 (June 4, 2018). [Source]
Anderson, Robert H, Reza Razavi, and Andrew M Taylor. “Cardiac Anatomy Revisited.” Journal of Anatomy 205, no. 3 (September 2004): 159–77. [Source]
Mitchell, Jamie R. “Is the Heart a Pressure or Flow Generator? Possible Implications and Suggestions for Cardiovascular Pedagogy.” Advances in Physiology Education 39, no. 3 (September 1, 2015): 242–47. [Source]