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Simplified Heart Anatomy
- Project Medify
- Sep 11, 2020
- 3 min read
By Gauri Bhatia
Introduction
Lub, dub. Lub, dub. This is the sound our hearts constantly make. It is the rhythm they repeat throughout our lives and the beat that keeps us alive. We feel it in our pulse, all over our bodies, and in our chest, right above where our heart sits. But what in the heart actually makes these sounds? What are the parts of the heart? And how is our heart connected to the rest of our body?
What Is the Heart?
The heart, although it may be the mere size of a human fist, is an essential organ of the body. Similar to the brain, lungs, and liver, the heart is an organ composed of specialized cells working together, forming its respective tissue. The heart is also the center of the circulatory system in the body. It pumps oxygen-rich blood to the entire body so that the body cells can use this oxygen to function; this allows humans to live. The human heart weighs about 8 to 10 ounces in females and 10 to 12 ounces in males.
Now, Let’s Dive Into Heart Anatomy
The heart is enclosed by a sac, the pericardium, which protects it and keeps it in place. The heart is also made out of three layers of tissue: the epicardium, myocardium, and endocardium, which are the outer, middle, and inner layers of the heart, respectively.
For now, think of the heart a bit like the box diagram below. The heart, like this diagram, has four chambers: two right chambers and two left chambers. The top right chamber is called the right atrium, and the top left chamber is called the left atrium. The bottom right chamber is called the right ventricle, and the bottom left chamber is called the left ventricle. Simple enough, right? A “wall” made out of muscle, the septum, separates the right and left sides. Between each atrium and ventricle is one valve which makes sure the blood flows in only one direction (from atrium to ventricle). The valve on the right side of the heart is called the right atrioventricular valve, also known as the tricuspid valve. The valve on the left is called the left atrioventricular valve, also referred to as mitral valve or the bicuspid valve (cuspid means flaps or points).
The Heart Doesn’t Work Alone!
The diagram above doesn’t fully capture the heart as there are many veins, arteries, and capillaries around the heart that are essential to the circulatory system. Veins are the blood vessels that bring oxygen-poor blood back to the heart. Arteries carry oxygen-rich blood away from the heart (think artery = away). Capillaries are the smallest blood vessels that connect the arteries and veins. Capillaries are so small that red blood cells flow through them single file.
There are two veins called the superior vena cava and the inferior vena cava which empty oxygen-poor blood into the right atrium of the heart. From there the blood goes into the right ventricle, which pushes it through the pulmonary semilunar valve and then into the pulmonary artery. This artery carries the deoxygenated blood to the lungs so that it can become oxygen-rich once again. After passing through the lungs, the blood travels to the pulmonary vein, which carries the now oxygen-rich blood back to the heart, and then into the left atrium. The pulmonary artery is the only artery to carry oxygen-poor blood and the pulmonary vein is the only vein in the entire body to carry oxygen-rich blood. Once the blood is in the left atrium, it goes through the bicuspid valve into the left ventricle, which has the thickest walls of any chamber in the heart. The left ventricle pushes blood, with the help of the aortic semilunar valve, into the aorta. The aorta is the thickest and biggest artery which supplies blood to the rest of the body organs. Since the heart is also an organ and needs a supply of oxygenated blood to function, the heart has its own set of arteries, called the coronary arteries which lie on top of the exterior wall of the heart.
The sound the heart makes when it beats (and what we hear with a stethoscope) is caused by two different sets of valves. The first sound, “lub,” is caused when the atrioventricular valves (the valves between the atria and ventricles) close. The second sound, “dub,” happens when the semilunar valves (the pulmonary semilunar valves and aortic semilunar valves) close. The repeated opening and closing of these valves causes the characteristic sounds that ensure that blood is flowing properly through the heart.
Sources
NHS Inform. (2020, February 13). How your heart works. Retrieved from
Lewis, Tanya. (2016, March 22). Human Heart: Anatomy, Function, & Facts. Retrieved from
Texas Heart Institute. (n.d.) Heart Anatomy [Photograph]. Retrieved from
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