The Smooth Layer Of Endothelial Cells Which Line The Interior Of The Heart And Heart Valves Is The

17.1C: Layers of the Heart Walls

It is composed of three layers: the outer epicardium, the middle myocardium, and the inner endocardium. The outer epicardium is the outermost layer of the heart wall. Objectives for Learning

  • Recognize the layers of the heart wall that are called the epicardium, myocardium, and endocardium
  • And

Key Points

  • The epicardium is a thin layer of connective tissue and fat that protects the heart by acting as an additional layer of defense against injury. It is seen as a continuation of the serous pericardium
  • However, this is not the case. In the heart, the myocardium is made up of cardiac muscle cells known as cardiomyocytes that receive neurological stimulation from the sinoatrial (SA) and atrioventricular (AV) nodes through the Purkinje fibers
  • The myocardium is also known as the heart muscle. Cardiomyocytes are shorter than skeletal myocytes and have fewer nuclei than their skeletal counterparts. Cardiac muscle is striated in appearance
  • A smooth, non-adherent surface for blood collecting and pumping is provided by endothelial cells in the endocardium, which may also aid in the regulation of contractility. Infective endocarditis is a term used to describe an infection or inflammation of the endocardium.

Key Terms

  • Purkinje fibers: A bundle of nerve fibers found underneath the endocardium and responsible for supplying neurological impulses to the heart muscle tissues of the mycardium. endocardium: Heart valves are lined by a thin serous membrane that lines the inside of the heart and valves. A cardiomyocyte is a cardiac muscle cell (or myocyte) that is found in the heart and contributes to the formation of cardiac muscle tissue.

The heart wall is made up of three layers: the epicardium (outer layer), the myocardium (middle layer), and the endocardium (inner layer) (inner). These layers of tissue are highly specialized and serve a variety of tasks in the body. It is believed that the wave of depolarization from the SA and AV nodes travels from within the endocardial wall, through the myocardial layer, and finally to the epicardial surface of the heart during ventricular contraction.


The Heart Wall: The heart wall is formed of three layers: the thin outside epicardium, the thick middle myocardium, and the extremely thin inner endocardium. The outer epicardium is the thickest layer, while the middle myocardium is the thinnest one. It is scarring from a past myocardial infarction that is causing the black spot on the heart wall (heart attack). The epicardium is the outer layer of the heart wall that surrounds the coronary arteries. As well as the outside layer of the heart, the epicardium also refers to the inner layer of the serous visceral pericardium, which is linked to the heart’s outer wall by a fibrous band of tissue.

It is located underneath the pericardium.


The myocardium is the middle layer of the heart wall, and it is the thickest layer of the heart wall. It is made up of heart muscle tissue and is the thickest layer of the heart wall. It is made up of cardiac muscle cells, which are also known as cardiomyocytes. Cardiomyocytes are specialized muscle cells that contract in the same way as regular muscle cells, but are distinguished by their form and size. Heart muscle cells are shorter and have fewer nuclei than skeletal muscle cells when compared to skeletal muscle cells.

Cardiomyocytes, because of their continual rhythmic contraction, require a specific blood supply to give oxygen and nutrients to the cardiac muscle tissue and to eliminate waste products such as carbon dioxide from the heart muscle tissue.


The endocardium is the innermost layer of the heart wall, and it is formed of endothelial cells, which offer a smooth, elastic, non-adherent surface for blood collecting and pumping while also serving as a protective barrier against infection. As a barrier between the blood and the heart muscle, the endocardium may govern metabolic waste disposal from heart tissues and the composition of the extracellular fluid in which cardiomyocytes bathe, both of which are important in the regulation of heart function.

Moreover, this tissue covers the heart’s valves, and it is histologically continuous with the vascular endothelium of the major blood arteries that enter and exit the heart on both sides.

Infection of the endocardium can result in a major inflammatory illness known as infective endocarditis, which is a life-threatening condition. This, as well as other possible issues with the endocardium, may result in valve damage and disrupt the proper flow of blood through the heart.

Blood Vessels and Endothelial Cells

We have now moved on from the tissues that are derived from the embryonicectodermandendoderm to the tissues that are derived from the mesoderm. This layer of cells, which is sandwiched between the ectoderm and the endoderm, develops and diversifies to perform a wide range of supporting activities throughout the body. It is responsible for the formation of the body’s connective tissues, blood cells, and blood vessels, as well as muscle, the kidney, and a variety of other structures and cells. We’ll start with the blood vessels.

Endothelial cells have a remarkable ability to adapt their quantity and configuration to meet the needs of the surrounding environment.

Tissue development and repair would be difficult without the assistance of endothelial cells, which are responsible for expanding and rebuilding the network of blood arteries.

It is thought that by inhibiting the production of new blood vessels by the use of medications that act on endothelial cells, it would be possible to slow the progression of tumor growth (discussed in Chapter 23).

Endothelial Cells Line All Blood Vessels

Blood vessels that are the biggest in size are arteries and veins, which have a strong, resistant wall of connective tissue and several layers of smooth muscle cells to protect them (Figure 22-22). The endothelium, an extremely thin single sheet of endothelial cells that lines the inside of the wall and is divided from the surrounding outer layers by a basallamina, lines the inside of the wall. The quantity of connective tissue and smooth muscle in the vascular wall varies depending on the size and function of the vessel, but the endothelium lining is always there.

These are connective-tissue cells, which are closely linked to vascular smooth muscle cells, that wrap themselves around the tiny vessels in the body (Figure 22-24).

Figure 22-22

An illustration of a cross section of a tiny artery. Endothelial cells, despite their inconspicuousness, are an essential component of the body. Contrast this with the capillary in Figures 22-23 and 23.

Figure 22-23

Capillaries. (A) Cross section of a tiny capillary in the pancreas as seen via an electron microscope.

It is composed of a single endothelial cell that is surrounded by a basal lamina to create the wall. Take note of the little “transcytotic” vesicles, which, according to one theory, are responsible for cell division (more.)

Figure 22-24

Pericytes. An image taken with a scanning electron microscope shows pericytes wrapping their processes around a tiny blood artery (a post-capillary venule) in the cat’s mammary gland. Pericytes can be found around capillaries as well, although they are considerably more sparingly dispersed (more.) The transport of materials through the vascular system, as well as the movement of white blood cells in and out of the circulation, is controlled by endothelial cells, which line every capillary from the heart down to the tiniest capillary.

Pericyte recruitment in particular is dependent on the secretion of PDGF-B by endothelial cells, and pericytes are absent from numerous parts of the body in mutants lacking this signal protein or its receptor.

This reflects the importance of signals exchanged in both directions between the pericytes and endothelial cells during the development of the embryonic blood vessels.

In the case of the endothelial cells, for example, mechanoreceptors allow them to sense the shear stress caused by the flow of blood over their surface; by signaling this information to the surrounding cells, they enable the blood vessel to adjust its diameter and wall thickness to match the flow of blood.

New Endothelial Cells Are Generated by Simple Duplication of Existing Endothelial Cells

Pericytes. An image taken with a scanning electron microscope shows pericytes wrapping their processes around a tiny blood artery (a post-capillary venule) in the mammary gland of a cat. Also found around capillaries, although in much smaller numbers and with a different pattern of distribution, is the pericyte (more.) The transport of materials through the vascular system, as well as the movement of white blood cells in and out of the circulation, is controlled by endothelial cells, which line every capillary from the heart down to the tiniest capillary in the human body.

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Because the endothelial cells’ secretion of PDGF-B is critical for the recruitment of pericytes, pericytes are absent from numerous parts of the body in mutants lacking this signal protein or its receptor.

This reflects the importance of signals exchanged in both directions between the pericytes and endothelial cells during the development of the embryonic blood vessel.

Example: Endothelial cells include mechanoreceptors that allow them to feel shear stress caused by the flow of blood across their surface; by transmitting this information to the surrounding cells, they enable the blood artery to adjust its diameter and wall thickness to accommodate the flow of blood.

According to the findings in Chapter 15, endothelial cells also regulate quick responses to brain signals for blood vessel dilatation by releasing the gas NO to cause smooth muscle relaxation within the vessel wall.

New Capillaries Form by Sprouting

Capillaries, which sprout from existing tiny vessels, are the vessels that give rise to new vessels in the adult. Angiogenesis is a process that happens in response to certain signals and may be studied in naturally transparent tissues like as the cornea of the eye, which makes it a handy observation site. Abrasives applied to the cornea cause the formation of new blood vessels to develop from the rim of tissue around the cornea, which has a plentiful supply of oxygen and nutrients, inward toward the cornea’s centre, which ordinarily has none.

Such observations suggest that endothelial cells that are to become a new capillary grow out from the side of an existing capillary or tiny venule by spreading lengthy pseudopodia, so pioneering the construction of a capillary sprout that then hollows out to form a tube, as seen in the illustration (Figure 22-25).

In the embryo, endothelial cells on the arterial and venous sides of the developing network of vessels differ in their surface properties: the plasma membranes of the arterial cells contain the transmembrane protein Eph-B2 (see Chapter 15), whereas the membranes of the venous cells contain the corresponding receptor protein, Eph-B4, which is a receptor tyrosine kinase (see Chapter 15).

These molecules are responsible for the transmission of a signal at areas of cell-cell contact, and they are required for the creation of a well organized network of vessels.

Figure 22-25

Angiogenesis. A new blood capillary is formed when an endothelial cell protrudes from the wall of an existing tiny vessel, forming a new blood vessel. The cells in the translucent tail of a live tadpole were seen, and this figure was created as a result of those findings. (Adapted from C.C. Speidel, Am. J. Anat., vol (more.) Studies in culture have demonstrated that endothelial cells in a media containing appropriate growth factors will spontaneously form capillary tubes, even if they are segregated from all other types of cells in the culture medium (Figure 22-26).

Figure 22-26

In vitro development of capillaries. The spontaneous development of intracellular vacuoles in endothelial cells in culture results in a network of capillary tubes that seems to connect from cell to cell, forming an endothelial cell network. The photos below depict the many phases of the production process. Thearrow(more.)

Angiogenesis Is Controlled by Factors Released by the Surrounding Tissues

Almost every cell in a vertebrate’s body, in almost every tissue, is within 50–100 microns of one or more capillaries. What process is responsible for ensuring that the blood artery system extends into every nook and crevice of the body? How is it able to adapt so precisely to the local requirements of the tissues, not only during normal development but also in the face of a wide range of pathological situations? To meet the high metabolic demands of the healing process, wounding, for example, causes a burst of capillary development around the site of the damage to occur in the immediate vicinity of the wound (Figure 22-27).

However, a tiny sample of tumor tissue placed in the cornea, which typically lacks blood vessels, induces the vascular edge of the cornea, which is located near the implant, to develop rapidly toward it. The growth rate of the tumor rises dramatically once the blood vessels reach it.

Figure 22-27

In response to injury, new capillary development occurs. When the cornea is cut, the reaction to injury may be seen on scanning electron micrographs taken from casts of blood vessels surrounding the corneal border. It is possible to create castings by injecting a resin into the vessels and allowing it to cure (more.) In all of these instances, the invading endothelium cells respond to signals provided by the tissue that they are invading by releasing their own proteins. A protein known as vascular endothelialgrowth factor (VEGF), which is related to platelet-derived growth factor, plays a critical role in the transmission of signals in the blood vessels (PDGF).

  1. The latter control, on the other hand, is quite well known.
  2. A protein called HIF increases expression of the VEGF gene (and of other genes whose products are needed when oxygen is in short supply).
  3. There are at least four components to the endothelial cells’ reaction to the injury.
  4. Second, the endothelial cells begin to move in the direction of the signal source.
  5. Cells form tubes and differentiate at the fourth stage of the process.

(Other growth factors, such as several members of the fibroblast growth factorfamily, can also induce angiogenesis, but they have an effect on cells other than endothelial cells.) During the formation of new arteries, which transport oxygen-rich blood to the tissue, the oxygen concentration increases, HIF-1 activity decreases, VEGF synthesis is shut off, and angiogenesis comes to a complete end (Figure 22-28).

  • As is true of all signaling systems, it is just as vital to turn the signal off correctly as it is to turn it on correctly.
  • This degradation is dependent on the ubiquitylation of HIF-1, a process that necessitates the expression of a different gene product, which is faulty in a rare condition known asvon Hippel-Lindau (VHL) syndrome.
  • These cells possess high levels of HIF-1, regardless of whether or not oxygen is available, resulting in the overproduction of VEGF on a continuous basis.
  • The over-rich food given by the additional blood vessels appears to boost the proliferation of the mutant cells that create the VEGF, resulting in a vicious cycle that promotes tumor development and spread.

Loss of the VHL gene product results in the development of various cancers, in addition to hemangioblastomas, through processes that may be distinct from those that affect angiogenesis.

Figure 22-28

The regulatory system that regulates blood vessel expansion in response to a tissue’s requirement for oxygen (or lack thereof). When there is a lack of oxygen, the release of VEGF is triggered, which in turn encourages angiogenesis.


A single cell layer of endothelial cells borders all blood arteries and regulates the passage of nutrients and waste products between the circulation and the surrounding tissues. Signals from endothelial cells coordinate the growth and development of connective tissue cells, which produce the layers that surround the blood vessel wall and help it to function properly. Extending the walls of existing tiny capillaries can result in the formation of new blood vessels, which are formed by the expansion of endothelial cells, which have the ability to generate hollow capillary tubes even when isolated in culture.

A homeostatic system guarantees that blood arteries penetrate every part of the body and that they do not get blocked.

In the presence of hypoxia, VEGF works on endothelial cells, prompting them to proliferate and infiltrate the hypoxic tissue in order to provide it with new blood vessels.


THE OBJECTIVES:By the completion of this laboratory session, you should be able to:1. Identify and explain the light and electron microscopic structure of the different types of blood and lymphatic vessels. Explain the structural changes that occur in the three different kinds of capillaries and how these changes relate to variations in permeability. Understanding the layers of the atrial and ventricular walls, together with the variances in thickness of these layers, can help you to better comprehend how your heart works.

  1. Recognize the components of the cardiac skeleton and comprehend the structural and functional link between the cardiac skeleton and the cardiac muscle.
  2. SLIDES FOR THIS LABORATORY:18, 47, 55, 59, 64, 66, 67, 78, 80, 81, and Supplemental Slides 115-121, 128, 129.
  3. The tunica intima is made up of two layers: an endothelial layer that lines the lumen of the artery and a subendothelial layer that is primarily made up of loose connective tissue.
  4. The tunica medium is mostly made of smooth muscle cells that are organized circumferentially around the circumference of the body.
  5. Finally, the tunica adventitia is mostly formed of loose connective tissue that is composed of fibroblasts and collagen fibers that are linked with each other.
  6. The tunica medium is a vascular wall that makes up the majority of the aorta’s wall thickness.
  7. Although the border between thetunica intima and the media is not easily discernible, the internal elastic laminais only the most inner of the several elastic lamellae that exist within the wall.
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Slide number 67 The carotid artery (elastic artery) meets the big vein (jugular).

Keep an eye out for the intima, media, and adventitia.

When comparing the aorta to the carotid artery, the aorta has a thicker intima and more elastic lamellae in the media.

It is important to note that the elastic and collagen fibers are easily visible on this slide.

Keep an eye out for the association between age and histological type.

Aorta of a newborn human, stained with Verhoeff Van Gieson stain (Supplemental Slide 117).

Additional Slide 119Aorta of a person aged seven years, stained with Verhoeff Van Gieson stain.

Supplemental Slide 121Aorta of a 22-year-old human, stained with the Verhoeff Van Gieson stain.

Elastic laminae are prevalent on both the internal and exterior surfaces.

Sliding door 81Spermatic cable On this slide, multiple muscle arteries are mixed together with atypical veins of thepampiniform plexus to generate a complex structure.

Also take note of the smooth muscle arrangement in these veins along the outer longitudinal axis.

Take note of the huge quantity of smooth muscle that is grouped in a circular pattern in the media of the muscular arteries.

47 Verhoeff’s hematoxylin and mucicarmine methyl green were used to stain the submaxillary gland.

Internal and exterior elastic laminae (or membranes) are coloured black and may be easily distinguished from one another.

ARTERIOLESThe tunica intima of arterioles is made up of a continuous endothelium and a very thin subendothelial layer that surrounds it.

The tunica medium is composed of two layers of smooth muscle cells in most instances.

The tunica adventitia is a thin sheath of connective tissue that is difficult to distinguish from other connective tissue.

You can find a large number of vessels in the connective tissue that surrounds the oviduct.

Identify the different layers of vessels that are present.

The endothelial cells that make up the wall have been severely reduced.

There is no smooth muscle to be found.

Capillaries and venules are the primary vessels through which exchange occurs between the blood vascular space and the interstitium.

A considerable amount of fluid and cell exchange occurs through the venule’s wall, which is unexpected considering how small it is.

Appendix on slide 55.

Sliding door 81Spermatic cable In addition, Slide 81 is excellent for tiny boats.

Compared to arteries, veins have the same three layers as arteries, but their borders are less clear, and their elastic components are not as well developed.

The pancreas is seen on slide 80.

Vascular structure that is not surrounded and maintained by solid tissue is referred to be thevein.

In addition, major veins such as the vena cava have this structure as a general rule.

This slide depicts a vein that is more average in size (medium).

Due to the fact that these massive, thin-walled capillaries commonly collapse to the point of invisibility during tissue processing, lymphatics can be difficult to demonstrate convincingly in normal tissues.

In the beginning, lymphatic capillaries are blind-ended, and as they grow in number, they combine to form lymphatic vessels, which eventually discharge into the circulation through lymphatic ducts (thoracic and right lymphatic).

These lymphatic vessels, like the veins (pampiniform plexus) of the spermatic cord, have extremely thick walls for lymphatic vessels.

HEARTSlide 64The heart and the AV valve are depicted.

Keep in mind that the atrial and ventricular walls differ in thickness (which corresponds to differences in pressure and work loads).

The muscle of the atria and the musculature of the ventricles are not continuous with one another.

Consider the AV valve leaflet and the connection of the leaflet to the heart’s fibrous structure.

Its top oratrial surface is thick and resembles atrial endocardium, while its lower orventricular surface is thin and resembles ventricular endocardium.

When you look at the fibrous skeleton, you will notice that it is formed of highly dense connective tissue and that it is histologically similar to atendon (the fibrous skeleton of the heart is actually made up of circular tendons).

Identify the Purkinje fibers that have been longitudinally sectioned in the subendocardial layer.

Supplemental Slide 128Heart is available.

This part depicts one of the leaflets of themilunar valve as well as the fibrous structure of the human heart.

The interventricular septum’s membranous and muscular components are also found in close proximity to the valve.

This is the same region of the heart that was seen on Slide 128.

The color of the collagen that forms the connective tissue investments (including the membranous septum) on this slide is red, while the color of the elastic fibers is black. It is important to note that the atrial wall of the heart has a disproportionately bigger number of elastic fibers.

Endocardium – an overview

Fanning and Martin’s Neonatal-Perinatal Medicine will be published in 2020 by Richard J. MartinMBBS, FRACP

Endocardial Development: Formation of Cushion Tissue

It is the swelled extracellular matrix that causes septation to occur in certain sections of the heart tube between the endocardium and myocardial that causes the heart to begin to septate. The AV junction, the outflow tract, the leading edge of the main atrial septum, and the ridge of the interventricular septum are among the sections that make up the heart. The creation of a cushion at the AV junction and the outflow tract has shown a complicated series of inductive processes that had been previously unknown.

  1. There are also a number of proteases and homeobox genes involved.
  2. The cushions in the outflow tract are also occupied by cardiac neural crest cells, which are a kind of stem cell.
  3. The cushions eventually give rise to, or at the very least have a significant impact on, the future development of the heart’s septa and valves.
  4. As a result, it should come as no surprise that septation problems are so prevalent.
  5. Researchers have discovered that the phases in heart valve differentiation and maturation share similarities with the processes of cartilage, tendon, and bone formation.
  6. 71.8).
  7. In order for the tissue to move further, the osteum primum, which is located between the tip of this protrusion of the septum primum and the endocardial cushion, shuts.
  8. As a result, the septum primum acts as a flap across the foramen ovale, enabling only right-to-left flow across the atria to pass through the opening.
  9. The myocardium invaginates the ventricle from the outside curve of the ventricle and grows cranially.
  10. Endocardial cushions in the outflow tract generate ridges that spiral along the conotruncus, forming a spiral pattern (Fig.

71.9). Eventually, these ridges will develop together to form the conotruncus, which will contain the aorta and pulmonary arterial trunks. The endocardial cushions of the AV canal and outflow tract come together, resulting in the completion of ventricular septation.

Systems Toxicologic Pathology

In Haschek and Rousseaux’s Handbook of Toxicologic Pathology (Third Edition), Brian R. Berridge and Eugene Herman discuss toxicologic pathology.


Goldman-Cecil Medicine, edited by Lee Goldman MD (2020).

Cardiovascular System and Lymphatic Vessels1

In Pathologic Basis of Veterinary Disease (Sixth Edition), by Lisa M. Miller and Arnon Gal, published in 2017.

Endocardium and Heart Valves

inTextbook of Clinical Echocardiography, edited by Catherine M. OttoMD, published in 2018.

Endocardial Definition

When doing an echocardiographic examination of left ventricular systolic function, it is critical to accurately identify the ventricular endocardium, regardless of whether M-mode, 2D, or 3D techniques are utilized. Speckle tracking stain is also the most accurate when used in conjunction with high-quality photographs of the myocardium. The physics of ultrasound instruments, anatomic considerations, and technical factors, including the ability of the sonographer, all have an impact on endocardial definition.

  1. As with other ultrasonic targets, lateral resolution is dependent on the depth of the target.
  2. Because it is not a flat surface anatomically, the endocardium is punctuated with a large number of trabeculations, which are most visible near the LV apex.
  3. Several technical elements influence endocardial definition during image capture, and precise inspection methodology is required for the best picture quality.
  4. Acoustic access may be improved in many ways, the first of which is patient placement, followed by the use of an echo-stretcher with an apical cutout, the patient being asked to cease breathing, and the transducer being carefully adjusted.
  5. When employing digitally acquired pictures, 2D endocardial borders are traced using the real-time motion of the images.
  6. During the same cardiac cycle, end-diastolic and end-systolic pictures are traced, with end-diastole defined as the commencement of the QRS complex and end-systole defined as the presence of minimum ventricular volume (Figure 1).
  7. Despite the fact that 3D imaging employs semiautomated boundary detection, it still relies on manual identification of anatomic landmarks and, in most cases, requires modification of the automated boundaries in order to get precise volumes measurements.

As with the speckle tracking strain pictures, the myocardium is visually evaluated and tweaked to confirm that it is tracking appropriately.

The Heart in Systemic Autoimmune Diseases

M.Sebastiani and C.Ferri, in Handbook of Systemic Autoimmune Diseases, published in 2017.

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3.1.4Endocarditis and Valvular Disease

Cardiovascular Pathology (Fourth Edition), 2016; authored by J.J.Maleszewski and J.P.Veinot.


The Musculoskeletal System (Second Edition), by NicholasManolios, was published in 2010.

Cardiac involvement

M.J. Koster and K.J. Warrington, in The Heart in Rheumatic, Autoimmune, and Inflammatory Diseases, published online in 2017.


(2015) David T.Durack’s Principles and Practice of Infectious Diseases (Eighth Edition) was published by Mandell, Douglas & Bennett in 2015.

Inhibition of Bacterial Adherence to Endocardium

The adhesion of bacteria to the endocardium, as well as the presence of localized deposits of platelets and fibrin on the endocardium, are critical early events in the progression of IE (seeChapter 82). Many of the hallmarks of a biofilm are present in a bacterial infection that has developed on the surface of a prosthetic valve or other implanted prosthetic material. Endocarditis might theoretically be prevented by using agents that inhibit adhesion or biofilm development. Anticoagulants and antiplatelet medicines were shown to be ineffective in preventing IE in animals in earlier studies79, but as our understanding of the factors of bacterial adherence grows, additional treatments to reduce bacterial adherence may be discovered.

80 IE could be prevented significantly with the use of a drug, an antibody, or a vaccine that prevented bacterial adherence to the endocardium or the formation of a biofilm.

However, at this time, no such medicine, antibody, or vaccination for the prevention of IE is available for human consumption.

Layers of the heart

Dr. Jana Vaskovi is the author of this article. Dr. Dimitris Mytilinaios, MD, PhD, was the reviewer. The most recent evaluation was performed on December 21, 2021. 6 minutes are allotted for reading. Throughout this article, the three layers of the heart (the epicardium, the myocardium, and the endocardium) will be discussed, as well as any clinical relationships that may exist between them. The heart is located in our body in the same manner that automobiles have their fuel pumps. The heart is a muscular organ that is located in the middlemediastinum and is responsible for pumping blood throughout the body.

Remembering the heart’s structure, it contains two atria and two ventricles, which combine to form elements and critical milestones in the heart’s life cycle.

But first, let’s take a look at hearthistochemistry, which is vital for understanding the function of the heart. The heart is composed of three layers of tissue on a histological level: the epicardium, the myocardium, and the endocardium.

Key facts about the layers of the heart

Epicardium Visceral layer of serous pericardiumComprised of mesothelial cells and fat and connective tissues
Myocardium Muscle layerComprised of cardiomyocytes
Endocardium Lines inner surface of heart chambers and valvesComprised of a layer of endothelial cells, and a layer of subendocardial connective tissue
Clinical relation Endocarditis


The epicardium is the heart’s outermost layer, and it is made up of a variety of cells. According to medical terminology, it is the visceral layer of the serouspericardium that attaches to the myocardium of the heart. From a histological standpoint, it is made up of mesothelial cells, just as the parietal pericardium. A layer of adipose and connective tissue lies underneath the mesothelial cells, which serves to link the epicardium to the myocardium and to cushion the heart. The epicardium contains nerves and blood arteries that provide the heart with oxygen and nutrients.

The sac is filled with serous pericardial fluid, which helps to avoid friction between the heart and the rest of the body during cardiac contractions.


The myocardial is the most important element of the heart in terms of function, and it is also the thickest of the three heart layers. Muscle contractions are made possible by the myofibril layer. Cardiomyocytes are the cells that make up the myocardium on a microscopic level. Cardiomyocytes are distinguished from skeletal muscle cells by the presence of a single nucleus in the center of the cell, which helps to identify them from the latter’s many nuclei spread along the cell’s perimeter. Cardiomyocytes contain large amounts of glycogen deposits as well as mitochondria.

  1. In addition, yellow lipofuscin granules are seen in cardiomyocytes.
  2. The amount of lipofuscin present in a cell increases with age.
  3. Adhesion junctions (fascia adhesion), desmosomes (maculae adhesiontes), and gap junctions are the three components that make up the discs (communicating junctions).
  4. As a result, the myocardium is sometimes referred to as a syncytium rather than a collection of cells that are partly independent of one another.
  5. As a result of the increased hydrostatic pressure that the ventricles must resist when pumping the blood into the systemic veins, the heart rate increases.


The endocardium is the heart’s deepest layer, and it is composed of a variety of cells. It is found on the inside surfaces of the heart chambers, as well as on the heart valves themselves. The endocardium is composed of two layers. The endothelial cells that line the inside of the heart chambers make up the inner layer. The second layer is located superiorly and consists of a subendocardial connective tissue that is continuous with the connective tissue of the myocardium and is located inferiorly.

Subendocardial layer contains branches of the heart’s conduction system, which are submerged in it. Make sure you understand everything by taking our quiz:

Clinical relations: Endocarditis

Endocarditis is a condition in which the endocardium becomes inflamed. The majority of the time, it is caused by an infectious agent. It mostly affects cardiac valves that have previously been damaged, and it is almost always caused by the bacterium Streptococcus viridans. It is Streptococcus aureus that causes the pathogenic bacteria in the case of a healthy heart. The pathophysiology is the same regardless of which bacterium is responsible. Once the germs transported by the circulation reach the heart valves, they begin to infiltrate the endocardium, causing it to rupture.

Parts of the vegetation can be dislodged and spread throughout the body by the circulation, resulting in the formation of secondary deposits of infection.

When the bacteria are not as aggressive, they can, on the other hand, remain in the heart for an extended period of time, resulting in valve abnormalities.

As a result, it is critical to notify your doctor if you have a valve problem so that they may prescribe antibiotics as a preventative measure.

For 2 to 6 weeks, intravenous antibiotics are used for the treatment of infectious endocarditis.


Every piece of material published on Kenhub has been evaluated by medical and anatomical professionals. It is based on scholarly literature and peer-reviewed research that we supply our clients with information. Kenhub does not give medical advice or recommendations. By reviewing our content quality rules, you may have a better understanding of our content development and review standards. References:

  • M. H. Ross and W. Pawlina are two of the most well-known scientists in the world (2011). Histology is the study of tissue (6th ed.). Lippincott Williams & Wilkins
  • Mescher, A. L. Philadelphia, PA: Lippincott Williams & Wilkins
  • Mescher, A. L. (2013). Basic Histology (Junqueira’s Basic Histology) (13th ed.). McGraw-Hill Education
  • Kumar, V., Abbas, A. K., and Aster, J. C. New York, NY: McGraw-Hill Education
  • Abbas, A. K., and Aster, J. C. (2013). Pathology for Beginners (Robbins Basic Pathology) (9th ed.). Elsevier Saunders Company, Philadelphia, PA.

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