The heart is a muscle that is responsible for the circulation of the blood around the entire body. It is situated in the mediastinum of the thorax, while the great vessels radiate their branches to the head and neck, the thorax and abdomen and the upper and lower limbs. It uses rhythmic electrical impulses that cause the ventricles to contract and force the blood out of the heart so that the returning blood maybe return in a circular fashion. In this article, the major anatomy of the heart will be discussed, such as the borders, surfaces, the chambers and the great vessels. A brief overview of some common pathological findings is also mentioned.
The superior border of the heart as seen from an anterior view is made by the atria and their auricles. The larger part of the right ventricle and some of the left ventricle contribute to the inferior border. It should be noted that the heart is not a rectangle or a square with clear sides, and therefore at a certain angle some structures will be only partially visible.
The left border is marked out by the left auricle and left ventricle. Finally, the right border is comprised of the sliver of the right atrium that can be seen between the superior vena cava and the inferior vena cava.
According to the heart’s normal anatomic position, there are three surfaces to the heart and first is the anterior surface which is also known as the sternocostal surface and is made up of the right ventricle. The diaphragmatic surface which is just inferior to the latter, contains the larger portion of the right ventricle, with a small portion of the left ventricle. Lastly the pulmonary surface which is to the left and fills the space known as the cardiac impression in the left lung, and contains the left ventricle.
There are two atria, one for each side of the body. They make up two of the four cardiac chambers along with the two ventricles. The left atrium forms the base of the heart. It has smooth walls and an auricular appendage which is rigid with pectinate muscles. The interatrial septum is almost completely transverse as it slopes posteriorly and to the right. The four pulmonary veins empty into this chamber, which in turn passes its hematologic contents into the left ventricle via the mitral valve as it relaxes.
The right atrium collects blood from the superior vena cava and the coronary sinus which pump it in through the posterior wall, which is smooth. The anterior wall is rigid due to the pectinate muscles and is separated from the posterior wall by the crista terminalis, which is a ridge and presents itself on the external surface as the sulcus terminalis. The superior and inferior vena cava open opposite each other on the posterior superior and inferior wall respectively. The right atrioventricular valve, known as the tricuspid valve, opens into the right ventricle.
The right ventricle is lined with trabeculae carneae and has a tricuspid valve, whose cusps are attached to the fibrous ring around the orifice of the valve, while the free edges are each attached to two or three papillary muscles, septal, anterior and posterior. The moderator band is a free appendage of muscle that extends from the interventricular septum to the anterior wall of the ventricle and contains purkinje fibers that are part of the heart's electrical conducting system. The supraventricular crest marks the separation of the outflow and inflow tracts and the conus arteriosus which is the outflow tract, leads to the pulmonary valve, which has three cusps, just as the aortic valve does.
The left ventricle is conical and its apex is the apex of the heart. It is slightly bigger and almost twice as thick as the right ventricle, since it does most of the work when pumping the blood around the body. Trabeculae carneae line the inner walls and two papillary muscle are present, that connect themselves to the mitral valve via the chordae tendinae. The muscles contract and the valve is closed, forcing the blood up towards the aorta and out of the heart. On the posterior superior wall the aortic orifice can be seen with a three cusped valve. These cusps on the valve prevent backflow of the blood into the heart. Just above the cusps there are slight dilations in the aortic wall and these are known as the aortic sinuses.
The first branches of the aorta are the right and left coronary arteries which carry the blood supply to the heart. They originate on the distal side of the aortic valve, from their corresponding aortic sinuses.
The right coronary artery can be found in the atrioventricular groove and makes a circle around the posterior surface of the heart. Its branches include:
- the sinoatrial nodal branch
- the right marginal branch
- the atrioventricular nodal branch
- the posterior interventricular branch
These branches supply the right atrium, the majority of the right ventricle, the diaphragmatic surface of the left ventricle, part of the intraventricular and interatrial septa, the sinoatrial node and the atrioventricular node.
The left coronary artery runs between the left auricle and the pulmonary trunk. It gives several branches including a circumflex branch that sometimes branches further to give a sinoatrial nodal branch. It also gives off an anterior interventricular branch. The areas supplied by thesebranches are the left atrium, most of the left ventricle, a small area of the right ventricle, the interventricular septum and the sinoatrial node.
On the posterior side of the heart there is a groove known as the coronary groove which contains the coronary sinus, which receives blood from the great cardiac vein, the middle cardiac vein, the small cardiac veins, the left marginal vein and the left posterior ventricular veins.
The other veins of the heart include the anterior cardiac veins which directly enter the right atrium and the smallest cardiac veins that open into all the chambers of the heart.
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.