Endocardium of the heart: structure, function, common pathology

The heart is one of the most important organs of the most complex system, which is usually called the human body. This is her motor, supplying blood to the remotest corners, so that all organs receive sufficient nutrition and can work without interruption. Despite the seeming simplicity of the organ from the outside, its internal structure seems quite interesting. Take at least its walls, which in fact consist not of one, but of three different layers, the tissues of which have their characteristics: endocardium, myocardium, epicardium. Each of these layers has its own structure and functions, the violation of which causes certain malfunctions in the work of the heart. In this article, we will talk about the inner shell of the main blood vessel, called the endocardium.

Histology of the epicardium

For the uninitiated in questions of medicine and biology of the reader, the meaning of the word "histology" may seem incomprehensible. We are talking about the division of biology, which studies the structure, features of vital activity and the functioning of various tissues of any living organism, including man. So, we are now talking about the structure of the epicardium, its development and the functions performed.

The human heart can otherwise be called the most voluminous blood vessel, which acts as a pump, ensuring the uninterrupted movement of blood in the body. Pumping function - one of the main functions of the heart, which is provided by reducing the central muscle layer of the body - the myocardium.

It would seem that if the myocardium is able to ensure the working capacity of the heart, i.e. Pumping the blood, why then need an endocardium? To understand this, you need to carefully consider the structure of the endocardium, which is the inner shell of the heart and tightly adjacent to the myocardium, lining the left and right ventricles and atria.

Endocardium is a continuous shell, filling any irregularities in the structure of the myocardium, covering the heart chambers and valves, posterior medial and anterolateral papillary muscles, tendon filaments. In the area of attachment to the heart of large vessels, the endocardium smoothly passes into the internal vascular membrane, similar in structure and functions.

Both the heart wall as a whole, and the epicardium itself, have a layered structure. It is divided into 4 layers:

• The outer layer, consisting of cells of connective tissue and adjacent directly to the myocardium. It has a loose structure and contains thick elastic, collagen and reticular fibers that go deep into the muscle layer, where they smoothly pass into the connecting stroma (stroma) of the myocardium.
• Muscular-elastic layer consisting of smooth elongated myocytes and elastin fibers and resembling in structure the middle layer of blood vessels. Due to this layer the endocardium moves after the myocardium during the contractile movements of the latter.
• Subendothelial layer. It, like the outer one, consists of loose connective tissue.
• Endothelial layer.

Ideally smooth endothelial cells (endotheliocytes) are attached to a cell-free structure called the basal membrane. The endothelial layer can be considered as a kind of flat epithelium, because its cells have a small bulge only in the nucleus, while the cytoplasm uniformly fills the free space (externally, when viewed from above, the endotheliocytes resemble a blot or omelet). The cells of the endothelium have microscopic dimensions and fit tightly to each other, leaving no space between them.

The surface of the endothelium is very smooth, and this is not accidental, because it is with it directly contact the blood cells. And one of the important functions of the endocardium is the provision of an opportunity for blood cells to pass through the heart cavity and adjacent vessels (both large and small) unhindered, without damage. By the way, damage to endotheliocytes entails a disruption of blood coagulability.

In addition to the fact that the endocardium lines the inner surface of the heart, it is also able to form peculiar folded structures inside the organ. Endocardial folds are usually called the valves of the heart valves, the atrial side of which is lined with an endothelium and has a smooth surface, and the ventricular irregularities are attached to the tendon filaments. The heart valves regulate the flow of blood through the heart.

The heart is a vital organ, the formation of which occurs at the very beginning of the embryonic period. The development of the endocardium begins already from the second week of the life of the embryo, when groups of cells appear in the embryonic leaf, which in the future form blood vessels, including the heart. The doubled fold of the mesoderm is converted into primary endocardial tubes, which are subsequently combined into one two-layered structure, called the primary heart tube. The endocardium is formed from the inner layer of this tube, and the outer layer of it gives rise to the myocardium and epicardium.

A feature of the endocardium is that the blood vessels contain only its outer layer, connected to the myocardium. The main part of the endocardium nutrients from the blood receives a diffuse way.

Diseases of the endocardium

As you can see, the endocardium is a very important structural part of the cardiac wall, on the strength of which blood flow intensity and even qualitative blood parameters depend, which delivers oxygen and nutrients to various tissues of the body. Despite the fact that the tissues of the endocardium itself have a small number of blood vessels, it together with the myocardium provides the regulatory function of the circulation (both as an atraumatic surface along which the blood flows unimpeded over the main blood vessel and as heart valves that ensure the correct direction of blood flow ).

But, like any human organ, the endocardium is not immune from disease. It can be as congenital pathologies (heart defects associated with the underdevelopment of the valve system, due to which the organ can not function normally), and acquired, most often associated with the inflammatory process in the endocardium.

By and large, endocardial inflammation can be considered one of the most common pathologies of the inner layer of the heart, although according to statistics endocarditis is considered a rare disease (1 person out of 25,000). It would seem, how can the inner shell of our "motor" in general, where access from the outside is limited for all media except blood, can inflame? But you need to take into account the fact that the most common factor in the development of inflammation is an infection that can easily spread throughout the body along with blood, and therefore can get into the heart.

It turns out that any bacterial infection that exists in the body, can provoke inflammation of the endocardium? Yes, the scientists concluded that although the most common causative agent of the disease is considered to be all known streptococci and staphylococci, the presence of gram-negative microorganisms, chlamydia, rickettsia, certain fungi and viruses can lead to the development of the disease.

However, it is not necessary to be very frightened, because in order for an infectious agent to provoke inflammation, certain prerequisites are needed, namely: congenital and acquired heart disease and its valves, plus weakened immunity. The most dangerous in terms of development of endocarditis are congenital pathologies such as stenosis of the aortic valve, defect of the interventricular septum, general arterial trunk, transposition of the main vessels, prolapse of the mitral valve, etc. The acquired pathologies include: rheumatic heart valve disease, aortic and mitral insufficiency, narrowing aorta and the like.

In principle, the development of inflammation on the intact endocardium is the exception to the rule, indicating low immunity. Most often the inflammatory process develops against the background of already existing cardiac pathology.

Congenital and acquired heart defects are associated with a violation of hemodynamics (the formation of turbulent blood flow and high blood pressure on the walls of blood vessels), which can cause damage to the inner shell of the heart. Damage to the endocardium, in turn, leads to violations in the system of blood clotting and the formation of thrombi, on which subsequently the pathogenic microorganisms settle. Thrombotic elements do not in themselves cause inflammation, although they can flow to the brain and other organs by detachment, causing blood vessels to clog (in the case of the brain, this can be a stroke). Settled on thrombotic formations, bacteria contribute to the further destruction of the inner layer of the heart, which further disturbs hemodynamics and the heart as a whole.

Inflammation of the endocardial layer is most often observed in the area of the valves of the heart valves, which are more prone to damage by the blood flow. It is in the area of the heart valves that the infection that causes the inflammatory process and the proliferation of connective tissue, leading to thickening of the endocardium, is most often deposited. In addition, detachment of the upper layer of the endocardium, the formation of clots and filaments of a special fibrin protein covering the defects of tissues, and again leading to their thickening can be observed.

In order for infectious (endogenous, bacterial, fungal, viral, septic, etc.) infectious endocarditis to develop, the body should have a focus of infection, which can be venereal pathologies, bacterial lesions of the gastrointestinal tract, caries, stomatitis and even respiratory infections . By the way, quite often this pathology is diagnosed in children aged 8-13 years precisely against the backdrop of inadequate treatment of infectious respiratory pathologies that significantly reduce the body's defenses.

In addition, the bacterial factor can get into the blood and during medical manipulations: colonoscopy, bronchoscopy, catheterization, implantation, biopsy, dental treatment, etc. For example, the prevalence of pathology among drug users is due to the use of non-sterile needles and syringes. But cores can get an infection during the implantation of prostheses and shunts.

The main symptoms of endocarditis are: fever against the background of relative health, the appearance of heart murmurs and hemorrhages on the skin and eye proteins, myalgia, pain in the chest and head, cough, shortness of breath, hyperhidrosis at night, edematous syndrome, weight loss, etc. .

Treatment of infective endocarditis is primarily the introduction of effective antimicrobial agents into the body - antibiotics. A fourth of patients undergo surgery because of the high likelihood of developing various complications, most often irreversible.

[1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12]

Consequences of endocarditis

Inflammation of the endocardium quite often causes the development of other equally dangerous pathologies of the inner shell of the heart. For example, a pathology of newborns, such as  fibroelastosis of the endocardium. The disease consists in a thickening of the heart wall, as a result of which the chambers of the heart have a smaller size. This situation causes the development of severe form of congestive heart failure, which in turn can lead to death, which is often observed among children with this diagnosis.

Intensive treatment in some cases allows you to translate the disease into a chronic form and increase the remission interval, and in rare cases even cure the disease. It is important that the child's organism actively responds to drug therapy.

The etiology of endocardial fibroelastosis (a fairly rare pathology) is still not fully understood, however, there are all the prerequisites to suspect as an underlying predisposing factor the intrauterine infection of the fetus, which becomes the cause of the inflammatory process with subsequent thickening of the tissues. Other causes of the pathology include subendocardial ischemia (impaired blood supply to the subendocardial layer of the myocardium), decreased lymphatic drainage of the cardiac tissues, and a general deficiency of carnitine. 

Secondary fibroelastosis of the endocardium can develop against the background of congenital and acquired heart defects (aortic stenosis, genetic mutation in the form of the absence of physiological holes in the heart, damage to the myocardium, etc.).

Treatment of the disease consists in lifelong admission of cardiac glycosides, anticoagulants, glucocorticosteroids.

Another rare disease with endocardial damage of the heart can be called  endocardial fibrosis. Here some clarification is required: pathology is more correctly called endomyocardial fibrosis, since it affects not only the endocardium, but also the middle shell of the heart (myocardium), and is manifested by inflammation and thickening of the endocardial and myocardial layers of the heart. Most often, the changes are diagnosed in the tops of the ventricles of the heart, but sometimes they can be found on the atrioventricular valves, consisting of the endocardium.

The main causes of this pathology, common in the tropics and subtropics, scientists consider the inflammatory process, the presence of infection in the body, malnutrition (malnutrition, deficiency of vitamins and minerals, intoxication with serotonin contained in plantain, actively consumed by local people).

The main symptom of the disease is progressive heart failure, which causes the death of most patients within 1-2 years after the onset of the disease.

Effective drug therapy in this case has not yet been developed, since the etiology of the disease has been studied very little. In some cases, surgical intervention involving endocardiectomy, which is performed in conjunction with the plasticity of antrioventricular valves located between the atria and ventricles of the heart, helps.

Inflammatory pathologies of the heart shells can lead to a disruption of the metabolism, for example, calcium, in the tissues of the organ even in the absence of endocrine diseases. Calcium, along with many other elements of Mendeleev's table (sodium, potassium, zinc, magnesium, etc.), is a substance necessary for our body to carry out vital activity, however its excess can cause calcification of various tissues and organs, including number and endocardium. The whole point is that calcification can develop against a background of various inflammatory pathologies, accompanied by proliferation of fibrous tissues.

Calcinosis is most often diagnosed in the aortic valve region, resulting in the formation of calcareous growths on its walls that disrupt hemodynamics (normal blood flow) and provoke the development of organic lesions of various heart tissues.

Among the most common causes of calcification of the myocardium can be considered and rheumatic lesions of body tissues provoking degenerative changes in them. Rheumatism is considered as an infectious-allergic disease with a wave-like current that affects mainly the heart and blood vessels. The causative agent of it becomes streptococcus, an immune response to the substances released by it and provokes the appearance of symptoms of the disease.

Rheumatism is manifested by mucoid edema of the heart tissues, softening and necrosis of collagen fibers and penetration of fibrin filaments into them, inflammatory reactions proceeding at the cellular level with the formation of specific rheumatic granulomas in the endocardium (connective tissue that forms the inner membrane and heart valves) and other heart tissues.

In principle, endocarditis can be considered one of the most vivid manifestations of rheumatism. And at the same time, endocardial inflammation caused by a bacterial infection, in itself, can provoke the development of rheumatism. Thus, endocarditis can be considered as a cause, and as a consequence of rheumatism of the heart and blood vessels. Moreover, the disease becomes chronic and difficult to treat.

[13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24]