Endocardium
Encyclopedia
The endocardium is the innermost layer of tissue that lines the chambers of the heart. Its cells
are embryologically
and biologically
similar to the endothelial
cells that line blood vessel
s.
The endocardium underlies the much more voluminous myocardium, the muscular tissue responsible for the contraction of the heart. The outer layer of the heart is termed epicardium
and the heart is surrounded by a small amount of fluid enclosed by a fibrous sac called the pericardium
.
The endocardial endothelium may also act as a kind of blood-heart barrier (analogous to the blood-brain barrier), thus controlling the ionic composition of the extracellular fluid in which the cardiomyocytes bathe.
, ischemia
of the myocardium can extend to the endocardium, disrupting the inner lining of the heart ("transmural" infarction
). Less extensive infarctions are often "subendocardial" and do not affect the endocardium. Subendocardial infarctions are much more dangerous than transmural infarctions because they create an area of dead tissue surrounded by a boundary region of damaged myocyte
s. This damaged region will conduct impulses more slowly, resulting in irregular rhythms. The damaged region may enlarge or extend and become more life-threatening.
During depolarization the impulse is carried from endocardium to epicardium, and during repolarization the impulse moves from epicardium to endocardium.
In infective endocarditis
, the endocardium (especially the endocardium lining the heart valve
s) is affected by bacteria.
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
are embryologically
Embryology
Embryology is a science which is about the development of an embryo from the fertilization of the ovum to the fetus stage...
and biologically
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
similar to the endothelial
Endothelium
The endothelium is the thin layer of cells that lines the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. These cells are called endothelial cells. Endothelial cells line the entire circulatory system, from the heart...
cells that line blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s.
The endocardium underlies the much more voluminous myocardium, the muscular tissue responsible for the contraction of the heart. The outer layer of the heart is termed epicardium
Epicardium
Epicardium describes the outer layer of heart tissue . When considered as a part of the pericardium, it is the inner layer, or visceral pericardium, continuous with the serous layer....
and the heart is surrounded by a small amount of fluid enclosed by a fibrous sac called the pericardium
Pericardium
The pericardium is a double-walled sac that contains the heart and the roots of the great vessels.-Layers:...
.
Function
Recently, it has become evident that the endocardium, which is primarily made up of endothelial cells, controls myocardial function. This modulating role is separate from the homeometric and heterometric regulatory mechanisms that control myocardial contractility. Moreover, the endothelium of the myocardial (heart muscle) capillaries, which is also closely appositioned to the cardiomyocytes (heart muscle cells) is involved in this modulatory role. Thus, the cardiac endothelium (both the endocardial endothelium and the endothelium of the myocardial capillaries) controls the development of the heart in the embryo as well as in the adult, for example during hypertrophy. Additionally, the contractility and electrophysiological environment of the cardiomyocyte are regulated by the cardiac endothelium.The endocardial endothelium may also act as a kind of blood-heart barrier (analogous to the blood-brain barrier), thus controlling the ionic composition of the extracellular fluid in which the cardiomyocytes bathe.
Role in disease
In myocardial infarctionMyocardial infarction
Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...
, ischemia
Ischemia
In medicine, ischemia is a restriction in blood supply, generally due to factors in the blood vessels, with resultant damage or dysfunction of tissue. It may also be spelled ischaemia or ischæmia...
of the myocardium can extend to the endocardium, disrupting the inner lining of the heart ("transmural" infarction
Infarction
In medicine, infarction refers to tissue death that is caused by a local lack of oxygen due to obstruction of the tissue's blood supply. The resulting lesion is referred to as an infarct.-Causes:...
). Less extensive infarctions are often "subendocardial" and do not affect the endocardium. Subendocardial infarctions are much more dangerous than transmural infarctions because they create an area of dead tissue surrounded by a boundary region of damaged myocyte
Myocyte
A myocyte is the type of cell found in muscles. They arise from myoblasts.Each myocyte contains myofibrils, which are long, long chains of sarcomeres, the contractile units of the cell....
s. This damaged region will conduct impulses more slowly, resulting in irregular rhythms. The damaged region may enlarge or extend and become more life-threatening.
During depolarization the impulse is carried from endocardium to epicardium, and during repolarization the impulse moves from epicardium to endocardium.
In infective endocarditis
Endocarditis
Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves . Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, or even on intracardiac devices...
, the endocardium (especially the endocardium lining the heart valve
Heart valve
A heart valve normally allows blood flow in only one direction through the heart. The four valves commonly represented in a mammalian heart determine the pathway of blood flow through the heart...
s) is affected by bacteria.