The heart wall is comprised of three layers: the outer epicardium, the middle myocardium, and the inner endocardium. The heart wall is comprised of three layers, the epicardium outer , myocardium middle , and endocardium inner. These tissue layers are highly specialized and perform different functions. During ventricular contraction, the wave of depolarization from the SA and AV nodes moves from within the endocardial wall through the myocardial layer to the epicardial surface of the heart.

The Heart Wall : The wall of the heart is composed of three layers, the thin outer epicardium, the thick middle myocardium, and the very thin inner endocardium. The dark area on the heart wall is scarring from a previous myocardial infarction heart attack.

The outer layer of the heart wall is the epicardium. The epicardium refers to both the outer layer of the heart and the inner layer of the serous visceral pericardium, which is attached to the outer wall of the heart. The innermost layer of the heart wall, the endocardium , is joined to the myocardium with a thin layer of connective tissue.

The endocardium lines the chambers where the blood circulates and covers the heart valves. It is made of simple squamous epithelium called endothelium , which is continuous with the endothelial lining of the blood vessels. Once regarded as a simple lining layer, recent evidence indicates that the endothelium of the endocardium and the coronary capillaries may play active roles in regulating the contraction of the muscle within the myocardium.

The endothelium may also regulate the growth patterns of the cardiac muscle cells throughout life, and the endothelins it secretes create an environment in the surrounding tissue fluids that regulates ionic concentrations and states of contractility. Endothelins are potent vasoconstrictors and, in a normal individual, establish a homeostatic balance with other vasoconstrictors and vasodilators. In order to develop a more precise understanding of cardiac function, it is first necessary to explore the internal anatomical structures in more detail.

The septa are physical extensions of the myocardium lined with endocardium. Located between the two atria is the interatrial septum. Normally in an adult heart, the interatrial septum bears an oval-shaped depression known as the fossa ovalis , a remnant of an opening in the fetal heart known as the foramen ovale. The foramen ovale allowed blood in the fetal heart to pass directly from the right atrium to the left atrium, allowing some blood to bypass the pulmonary circuit.

Within seconds after birth, a flap of tissue known as the septum primum that previously acted as a valve closes the foramen ovale and establishes the typical cardiac circulation pattern. Between the two ventricles is a second septum known as the interventricular septum.

Unlike the interatrial septum, the interventricular septum is normally intact after its formation during fetal development. It is substantially thicker than the interatrial septum, since the ventricles generate far greater pressure when they contract.

The septum between the atria and ventricles is known as the atrioventricular septum. It is marked by the presence of four openings that allow blood to move from the atria into the ventricles and from the ventricles into the pulmonary trunk and aorta. Located in each of these openings between the atria and ventricles is a valve , a specialized structure that ensures one-way flow of blood.

The valves between the atria and ventricles are known generically as atrioventricular valves. The valves at the openings that lead to the pulmonary trunk and aorta are known generically as semilunar valves. The interventricular septum is visible in the image below. In this figure, the atrioventricular septum has been removed to better show the bicupid and tricuspid valves; the interatrial septum is not visible, since its location is covered by the aorta and pulmonary trunk.

Since these openings and valves structurally weaken the atrioventricular septum, the remaining tissue is heavily reinforced with dense connective tissue called the cardiac skeleton , or skeleton of the heart. It includes four rings that surround the openings between the atria and ventricles, and the openings to the pulmonary trunk and aorta, and serve as the point of attachment for the heart valves.

The cardiac skeleton also provides an important boundary in the heart electrical conduction system. Figure 8. This anterior view of the heart shows the four chambers, the major vessels and their early branches, as well as the valves.

The presence of the pulmonary trunk and aorta covers the interatrial septum, and the atrioventricular septum is cut away to show the atrioventricular valves. One very common form of interatrial septum pathology is patent foramen ovale, which occurs when the septum primum does not close at birth, and the fossa ovalis is unable to fuse.

As much as 20—25 percent of the general population may have a patent foramen ovale, but fortunately, most have the benign, asymptomatic version. Patent foramen ovale is normally detected by auscultation of a heart murmur an abnormal heart sound and confirmed by imaging with an echocardiogram. Despite its prevalence in the general population, the causes of patent ovale are unknown, and there are no known risk factors. In nonlife-threatening cases, it is better to monitor the condition than to risk heart surgery to repair and seal the opening.

Coarctation of the aorta is a congenital abnormal narrowing of the aorta that is normally located at the insertion of the ligamentum arteriosum, the remnant of the fetal shunt called the ductus arteriosus. If severe, this condition drastically restricts blood flow through the primary systemic artery, which is life threatening. In some individuals, the condition may be fairly benign and not detected until later in life. Detectable symptoms in an infant include difficulty breathing, poor appetite, trouble feeding, or failure to thrive.

In older individuals, symptoms include dizziness, fainting, shortness of breath, chest pain, fatigue, headache, and nosebleeds. Treatment involves surgery to resect remove the affected region or angioplasty to open the abnormally narrow passageway. Studies have shown that the earlier the surgery is performed, the better the chance of survival. A patent ductus arteriosus is a congenital condition in which the ductus arteriosus fails to close.

The condition may range from severe to benign. Failure of the ductus arteriosus to close results in blood flowing from the higher pressure aorta into the lower pressure pulmonary trunk. This additional fluid moving toward the lungs increases pulmonary pressure and makes respiration difficult. Symptoms include shortness of breath dyspnea , tachycardia, enlarged heart, a widened pulse pressure, and poor weight gain in infants.

Treatments include surgical closure ligation , manual closure using platinum coils or specialized mesh inserted via the femoral artery or vein, or nonsteroidal anti-inflammatory drugs to block the synthesis of prostaglandin E2, which maintains the vessel in an open position.

If untreated, the condition can result in congestive heart failure. Septal defects are not uncommon in individuals and may be congenital or caused by various disease processes.

Tetralogy of Fallot is a congenital condition that may also occur from exposure to unknown environmental factors; it occurs when there is an opening in the interventricular septum caused by blockage of the pulmonary trunk, normally at the pulmonary semilunar valve.

This allows blood that is relatively low in oxygen from the right ventricle to flow into the left ventricle and mix with the blood that is relatively high in oxygen.

Symptoms include a distinct heart murmur, low blood oxygen percent saturation, dyspnea or difficulty in breathing, polycythemia, broadening clubbing of the fingers and toes, and in children, difficulty in feeding or failure to grow and develop.

It is the most common cause of cyanosis following birth. Other heart defects may also accompany this condition, which is typically confirmed by echocardiography imaging. Tetralogy of Fallot occurs in approximately out of one million live births. Normal treatment involves extensive surgical repair, including the use of stents to redirect blood flow and replacement of valves and patches to repair the septal defect, but the condition has a relatively high mortality. Survival rates are currently 75 percent during the first year of life; 60 percent by 4 years of age; 30 percent by 10 years; and 5 percent by 40 years.

Septal defects are commonly first detected through auscultation, listening to the chest using a stethoscope. In this case, instead of hearing normal heart sounds attributed to the flow of blood and closing of heart valves, unusual heart sounds may be detected.

This is often followed by medical imaging to confirm or rule out a diagnosis. In many cases, treatment may not be needed. Some common congenital heart defects are illustrated in Figure 9. Figure 9. The right atrium serves as the receiving chamber for blood returning to the heart from the systemic circulation. The two major systemic veins, the superior and inferior venae cavae, and the large coronary vein called the coronary sinus that drains the heart myocardium empty into the right atrium.

The superior vena cava drains blood from regions superior to the diaphragm: the head, neck, upper limbs, and the thoracic region. It empties into the superior and posterior portions of the right atrium. The inferior vena cava drains blood from areas inferior to the diaphragm: the lower limbs and abdominopelvic region of the body. It, too, empties into the posterior portion of the atria, but inferior to the opening of the superior vena cava.

Immediately superior and slightly medial to the opening of the inferior vena cava on the posterior surface of the atrium is the opening of the coronary sinus. This thin-walled vessel drains most of the coronary veins that return systemic blood from the heart.

The majority of the internal heart structures discussed in this and subsequent sections are illustrated in Figure 8. While the bulk of the internal surface of the right atrium is smooth, the depression of the fossa ovalis is medial, and the anterior surface demonstrates prominent ridges of muscle called the pectinate muscles.

The right auricle also has pectinate muscles. The left atrium does not have pectinate muscles except in the auricle.

The atria receive venous blood on a nearly continuous basis, preventing venous flow from stopping while the ventricles are contracting. While most ventricular filling occurs while the atria are relaxed, they do demonstrate a contractile phase and actively pump blood into the ventricles just prior to ventricular contraction. The opening between the atrium and ventricle is guarded by the tricuspid valve.

The right ventricle receives blood from the right atrium through the tricuspid valve. They are composed of approximately 80 percent collagenous fibers with the remainder consisting of elastic fibers and endothelium. They connect each of the flaps to a papillary muscle that extends from the inferior ventricular surface. There are three papillary muscles in the right ventricle, called the anterior, posterior, and septal muscles, which correspond to the three sections of the valves.

When the myocardium of the ventricle contracts, pressure within the ventricular chamber rises. Blood, like any fluid, flows from higher pressure to lower pressure areas, in this case, toward the pulmonary trunk and the atrium. To prevent any potential backflow, the papillary muscles also contract, generating tension on the chordae tendineae. This prevents the flaps of the valves from being forced into the atria and regurgitation of the blood back into the atria during ventricular contraction.

The image below shows papillary muscles and chordae tendineae attached to the tricuspid valve. Figure In this frontal section, you can see papillary muscles attached to the tricuspid valve on the right as well as the mitral valve on the left via chordae tendineae. The walls of the ventricle are lined with trabeculae carneae , ridges of cardiac muscle covered by endocardium.

In addition to these muscular ridges, a band of cardiac muscle, also covered by endocardium, known as the moderator band reinforces the thin walls of the right ventricle and plays a crucial role in cardiac conduction. It arises from the inferior portion of the interventricular septum and crosses the interior space of the right ventricle to connect with the inferior papillary muscle.

When the right ventricle contracts, it ejects blood into the pulmonary trunk, which branches into the left and right pulmonary arteries that carry it to each lung. The superior surface of the right ventricle begins to taper as it approaches the pulmonary trunk. At the base of the pulmonary trunk is the pulmonary semilunar valve that prevents backflow from the pulmonary trunk.

After exchange of gases in the pulmonary capillaries, blood returns to the left atrium high in oxygen via one of the four pulmonary veins. While the left atrium does not contain pectinate muscles, it does have an auricle that includes these pectinate ridges.

Blood flows nearly continuously from the pulmonary veins back into the atrium, which acts as the receiving chamber, and from here through an opening into the left ventricle. Most blood flows passively into the heart while both the atria and ventricles are relaxed, but toward the end of the ventricular relaxation period, the left atrium will contract, pumping blood into the ventricle. This atrial contraction accounts for approximately 20 percent of ventricular filling.

The opening between the left atrium and ventricle is guarded by the mitral valve. Recall that, although both sides of the heart will pump the same amount of blood, the muscular layer is much thicker in the left ventricle compared to the right.

Like the right ventricle, the left also has trabeculae carneae, but there is no moderator band. The mitral valve is connected to papillary muscles via chordae tendineae.

There are two papillary muscles on the left—the anterior and posterior—as opposed to three on the right. The left ventricle is the major pumping chamber for the systemic circuit; it ejects blood into the aorta through the aortic semilunar valve. With the atria and major vessels removed, all four valves are clearly visible, although it is difficult to distinguish the three separate cusps of the tricuspid valve. Regular aerobic exercise can help strengthen cardiac muscle tissue and lower the risk of heart attack, stroke , and other cardiovascular conditions.

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People should call the emergency services if they suspect a heart attack. What to know about cardiac muscle tissue. Medically reviewed by Dr. Payal Kohli, M. Cardiac muscle tissue Function Structure Cardiomyopathy Tips for healthy tissue Summary Cardiac muscle tissue, or myocardium, is a specialized type of muscle tissue that forms the heart.

What is cardiac muscle tissue? Share on Pinterest A person can strengthen cardiac muscle tissue by doing regular exercise. How does cardiac muscle tissue function? How is it structured? What conditions affect it. Additionally, glycogen granules are present in the myofibrils to support the additional energy requirement. The myocardium has the largest oxygen requirement and is most critically affected by the reduction in blood flow.

Reduction in blood flow i. Also, cardiac muscles are resistant to fatigue. Essentially, cardiac muscles create their own action potential , i.

These specialized cells form the myocardial conduction system that consists of the sinoatrial node , atrioventricular node , the bundle of His , and Purkinje fibers. The conducting myocardial cells are specialized muscle cells that function in the same way as neurons.

These conducting cells initiate and spread the action potential throughout the heart while the contracting myocardial cells take up this action potential to pump the heart rhythmically and regularly. To understand the circulatory system, it is important to understand what is the function of the myocardium. The primary function of the cardiac muscles is to stimulate contractions and relaxation in the heart. The contraction action results in the pumping of the blood from the ventricles to the whole body while the relaxation action of the cardiac muscles allows the atrium to receive blood.

This beating of the heart pumps the blood throughout the body ensuring that each cell and tissue of the body receives the blood supply.

Cardiac muscles are essentially under the control of an autonomous nervous system that releases the timed nervous impulses signaling the heart cells to contract and relax in a rhythmic pattern. So, what actually happens in cardiac muscles when your heart beats? Released Tropomyosin alters its position thereby allowing myosin to attach to actin. Myosin, then, utilizes the stored ATP molecules and reduce the length of each sarcomere.

The cardiac muscle undertakes twitch-type contractions wherein there is a long refractory period followed by brief relaxation periods. The relaxation action is vital for the heart in order to fill the atrium with blood for the next cycle. All the cardiac muscles work in harmony resulting in the generation of the force on the walls of the chamber of the heart. The sheets of the cardiac muscles are placed in a planar fashion wherein each muscle is perpendicular to each other.

This creates the effect that when the heart contracts, it does so in multiple directions. Thus, contraction of the multiple layers of the cardiac muscle fiber results in the shrinkage of the ventricle and atrium from top to bottom as well as from side to side. This produces a strong pumping and twisting force in the ventricles, forcing blood throughout the body. It is important to note that cardiac muscle undergoes aerobic metabolism, principally utilizing lipids , and carbohydrates.

Myocardial dysfunction can be categorized into two types: primary due to genetic cause and secondary myocardial diseases mostly acquired causes but maybe precipitated due to genetic reasons. Cardiomyopathies are diseases that result due to dysfunctional myocardium. Globally, cardiomyopathy is one of the foremost causes of morbidity and mortality. Clinically, cardiomyopathies can be categorized into five categories:.

Very high quantity and continuous supply of oxygen and energy is the basic requirement of the cardiac tissues. The oxygen supply is transported to the heart via the coronary arteries. However, these arteries are highly disposed to the formation of atheromas, i. Incase these atheromas are large, they obstruct or reduce the passage of the blood and oxygen to the cardiac cells thereby leading to the condition known as myocardial infarction or heart attack. The reduction in the oxygen supply to the cardiac cells is known as myocardial ischemia.