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Layers of the Heart

Layers of the Heart
The heart consists of three layers in all. This Bodytomy article explains the structure and function of each of these layers.
Dr. Sumaiya Khan
Human heart.
The heart is one of the most important organs present in the human body. This organ is responsible for pumping blood to all parts of the body. Thus, it is considered as the main organ of the circulatory system. The heart is made up of specialized, smooth muscle tissue known as cardiac muscles or myocardium. Given below are details regarding the different layers of the heart wall along with details regarding their anatomical structure and function.
The pericardium is the double-walled sac that contains the heart and roots of the great vessels that leave from or enter the heart. There are two layers of the pericardial sac: fibrous pericardium and the serous pericardium. The serous pericardium is further divided into two layers, which are the parietal and the visceral pericardium. The parietal pericardium is inseparably fused to the fibrous pericardium, while the visceral pericardium is actually a part of the epicardium, which is the outermost single layer of the pericardium. The visceral layer extends into the starting point of great vessels, thus, becoming one with the parietal layer of the serous pericardium. This happens where the aorta and pulmonary trunk leave the heart and where the two venae cavae (superior and inferior vena cava) and pulmonary veins enter the heart. In between the parietal and visceral layers lies a space which is known as the pericardial cavity. It is lubricated by pericardial fluid. This is the region that makes it susceptible to excess accumulation of fluid, as is seen in pericardial effusion.
The myocardium is the basic muscle that makes up the heart. This muscle is involuntary and is striated in nature. The cardiac muscle structure consists of basic units of cardiac muscle cells known as myocytes. Coordinated contraction of the cardiac muscles is what makes the heart propel blood to various parts of the body. It is the function of the coronary arteries to supply blood and oxygen to the cardiac muscles. This is the thickest of all the layers. As is common knowledge, the cardiac muscle function is to ensure that the heart beats around 72 times per minute. Thus, the cardiac muscles cannot afford to rest even for a single second. So, it is absolutely essential that these muscles get blood supply and nutrition continuously, as any kind of disruption in the blood and nutrition supply to these muscles can result in death of a part of the cardiac muscle, which is known as myocardial infarction or heart attack. This could in turn lead to a complete cessation of the functioning of heart muscles, known as the cardiac arrest.
The endocarium is the innermost, thin, and smooth layer of epithelial tissue that lines the inner surface of all the heart chambers and valves. This layer is made of thin and flat cells that are in direct contact with the blood that flows in and out of the heart. Each heart valve is formed by a fold of endocardium with connective tissue between the two layers. However, rather than just being an inner lining of the heart, the endocardium also has an endocrine function. This is one of the layers of the heart that has a single cell lining that secretes the hormone endocardin, which is responsible for prolonging myocardial contraction.
Each layer is specialized in its structure and function. Thus, all three layers function together to ensure proper functioning of the heart and to ensure that it pumps blood properly to all the organs in the body.