HeartThe heart is a muscular organ that pumps blood around the body by circulating it through the circulatory/vascular system. It is found in the middle mediastinum, wrapped in a two-layered serous sac called the pericardium. The heart is shaped as a quadrangular pyramid, and orientated as if the pyramid has fallen onto one of its sides so that its base faces the posterior thoracic wall, and its apex is pointed toward the anterior thoracic wall. The great vessels that originate from the heart, radiate their branches to the head and neck, the thorax and abdomen and the upper and lower limbs.
The heart holds a special position in anatomical sciences. For instance, you can live without your spleen or with only one kidney, you can even regrow your liver–but you cannot live without a heart. This page will introduce you to the anatomy of the heart.
|Borders||Superior (atria, auricles), inferior (right and left ventricles), left (left auricle, left ventricle), right (right atrium) borders|
|Surfaces||Sternocostal (right ventricle), diaphragmatic (mostly right ventricle, portion of left ventricle), pulmonary (cardiac impression) surfaces|
|Chambers||Atria (left and right), ventricles (left and right)|
|Emerging/ Entering Vessels||Pulmonary veins (-> left atrium), superior and inferior vena cavae (-> right atrium), aorta (left ventricle ->), pulmonary artery (right ventricle ->)|
|Valves||Mitral, tricuspid, aortic, pulmonary valves|
Right coronary artery (sinoatrial nodal branch, right marginal branch, atrioventricular nodal branch, posterior interventricular branch)
Left coronary artery (circumflex branch, anterior interventricular branch)
Coronary sinus (great, middle and small cardiac veins, left marginal vein, left posterior ventricular veins)
The heart has five surfaces: base (posterior), diaphragmatic (inferior), sternocostal (anterior), and left and right pulmonary surfaces. It also has several margins: right, left, superior, and inferior:
- The right margin is the small section of the right atrium that extends between the superior and inferior vena cava.
- The left margin is formed by the left ventricle and left auricle.
- The superior margin in the anterior view is formed by both atria and their auricles.
- The Inferior margin is marked by the right ventricle.
Inside, the heart is divided into four heart chambers: two atria (right and left) and two ventricles (right and left).
The right atrium and ventricle receive deoxygenated blood from systemic veins and pump it to the lungs, while the left atrium and ventricle receive oxygenated blood from the lungs and pump it to the systemic vessels which distribute it throughout the body.
The left and right sides of the heart are separated by the interatrial and interventricular septa which are continuous with each other. Furthermore, the atria are separated from the ventricles by the atrioventricular septa. Blood flows from the atria into the ventricles through the atrioventricular orifices (right and left)–openings in the atrioventricular septa. These openings are periodically shut and open by the heart valves, depending on the phase of the heart cycle.
Although there are a lot of structures in the heart diagrams, you shall not worry, we’ve got them all covered for you in these articles and video tutorials. Be sure to check out the heart anatomy quiz which will help you to master the heart anatomy.
Heart valves separate atria from ventricles, and ventricles from great vessels. The valves incorporate two or three leaflets (cusps) around the atrioventricular orifices and the roots of great vessels.
The cusps are pushed open to allow blood flow in one direction, and then closed to seal the orifices and prevent the backflow of blood. Backward prolapse of the cusps is prevented by the chordae tendineae–also known as the heart strings–fibrous cords that connect the papillary muscles of the ventricular wall to the atrioventricular valves.
There are two sets of valves: atrioventricular and semilunar. The atrioventricular valves prevent backflow from the ventricles to the atria:
- The right atrioventricular/tricuspid valve is between the right atrium and right ventricle. It has three cusps/leaflets: anterior/anterosuperior, septal, and posterior/inferior.
- The left atrioventricular/bicuspid valve is also called the mitral valve since it only has two cusps and resembles a miter in shape. It is between the left atrium and left ventricle and has two cusps/leaflets: anterior/aortic and posterior/mural.
Semilunar valves prevent backflow from the great vessels to the ventricles.
- The pulmonary semilunar valve is between the right ventricle and the opening of the pulmonary trunk. It has three semilunar cusps/leaflets: anterior/non-adjacent, left/left adjacent, and right/right adjacent.
- The aortic semilunar valve is between the left ventricle and the opening of the aorta. It has three semilunar cusps/leaflets: left/left coronary, right/right coronary, and posterior/non-adjacent.
Solidify your knowledge about heart valve anatomy with these articles, videos, and quizzes!
Blood flow through the heart
The blood flow through the heart is quite logical. It happens with the heart cycle, which consists of the periodical contraction and relaxation of the atrial and ventricular myocardium (heart muscle tissue). Contraction of the myocardium is called systole, while its relaxation is called diastole. Note that whenever the atria contract, the ventricles are relaxed and vice versa. Let’s put into words the heart blood flow diagram:
- The right atrium receives deoxygenated blood from the superior and inferior venae cavae and coronary sinus
- The right atrium contracts pushing blood through the right atrioventricular valve into the right ventricle. The right ventricle then contracts passing the blood into the pulmonary trunk via the pulmonary valve to reach the lungs
- In the lungs, the blood gets oxygenated then moves back into the heart entering the left atrium through the pulmonary veins.
- The left atrium contracts and pushes the blood into the left ventricle through the left atrioventricular valve.
- The left ventricle pushes oxygenated blood through the aortic semilunar valve into the aorta, from which blood is distributed throughout the body.
The heart cycle is regulated completely subconsciously by an autonomic nerve plexus called the cardiac plexus. Learn everything about the properties of heart muscle tissue which enable the proper heart cycle, heart innervation, and blood flow here.
The heart must also be supplied with oxygenated blood. This is done by the two coronary arteries: left and right.
Heart muscles work constantly (thank goodness!), so the heart has a very high nutrient need. The coronary arteries arise from the aortic sinuses at the beginning of the ascending aorta, and then circle the heart–giving off several branches. In this way, oxygenated blood reaches every part of the heart.
Venous blood from the heart is collected into the cardiac veins: middle, posterior, and small. They are all tributaries to coronary sinus–a large vessel that delivers deoxygenated blood from the myocardium to the right ventricle.
We’ve got you covered with coronary vasculature anatomy here. Check out our clinical cases as well to see how bad it is when something is wrong with coronary circulation.
Great vessels of the heart
The great vessels of the heart are the: aorta, pulmonary artery, pulmonary vein, and superior and inferior vena cava. Why are they called the great vessels? Because they are large in size; the diameter of the ascending aorta is 2.1 centimeters, which is like the size of an American nickel (five-cent coin), and they all carry blood to and from the heart. Oh, not to mention that the aorta gives off branches which supply the entire body with oxygenated blood.
Major branches of the aorta include the brachiocephalic trunk, the left common carotid artery and the left subclavian artery. The superior vena cava receives blood from the upper half of the body via the left and right brachiocephalic veins, and the inferior vena cava from the lower half, through the common iliac veins.
Systemic vasculature is a broad field of anatomy. For starters, we recommend you to go through these articles, and continue building your knowledge with video tutorials and quizzes.
There are many disorders that can affect the heart and its adjacent structures. Below are a collection of different diseases, to name but a few.
Angina Pectoris is a pain in the chest that comes and goes and is due to the lack of oxygenation of the myocardium. Stable angina is the most common form and occurs because of the severe narrowing of the coronary arteries. Pain is felt upon exertion and is treated with nitroglycerin.
Infective endocarditis is a bacterial or fungal infection of the heart and can include but is not limited to the cardiac valves. These vegetative growths can be acute or chronic and are dangerous because of the potential embolization risk if they were to fragment.
The variations of congenital heart disease usually have an unknown etiology. Certain syndromes that occur due to chromosomal abnormalities usually have secondary heart defects which can include atrial septal defects, ventricular septal defects, a patent ductus arteriosus and even in some cases transposition of the great vessels. Down syndrome and turner syndrome are among the most common and well known trisomy abnormalities.