Blog

Introduction to the heart | Internal structure of the heart | Valves of the heart | Major blood vessels | Cardiac muscle and conduction system | Microscopic anatomy of the heart | Blood supply to the heart | Developmental anatomy of the heart | Clinical relevance | Conclusion

Anatomy of Heart:

The anatomy of the heart is a fascinating topic that encompasses various aspects of its structure and function. Let’s delve deeper into the intricacies of the heart’s anatomy, including its external features, blood supply, venous supply, and lymphatic drainage.

Starting with the external features, the heart is a conical vaulted muscular organ that is situated in the middle mediastinum, which is the central compartment of the chest cavity. It is enclosed within a double-layered protective sac called the pericardium. The Greek name for the heart is “cardia,” from which we derive the attributive term “cardiac.” Similarly, the Latin name for the heart is “cor,” from which we have the adjective “coronary.”

The heart is positioned obliquely behind the body of the sternum (breastbone) and adjacent parts of the costal cartilages (cartilages that connect the ribs to the sternum). Approximately one-third of the heart lies to the right of the median plane, while two-thirds are located to the left. This orientation allows for the direction of blood flow from the atria (upper chambers) to the ventricles (lower chambers) to be downwards, forwards, and to the left.

In terms of size, the heart measures about 12×9 cm and weighs approximately 330g in males and 250g in females. However, these measurements may vary depending on factors such as age, overall health, and body size.

Moving on to the blood supply of the heart, this vital organ requires a constant and rich supply of oxygen and nutrients to function properly. The heart has its own blood supply, known as the coronary circulation, which consists of arteries and veins that nourish the heart muscle. The coronary arteries, including the left and right coronary arteries, arise from the aorta (the main artery that carries oxygenated blood from the heart to the rest of the body) and provide oxygen and nutrients to the different regions of the heart muscle. The coronary veins, on the other hand, drain the deoxygenated blood from the heart muscle and return it to the right atrium of the heart.

In addition to the blood supply, the heart also has venous drainage. The venous blood from the heart is collected by cardiac veins, which drain into a large vein called the coronary sinus. The coronary sinus then empties into the right atrium, completing the venous circulation of the heart.

Lastly, the heart also has a lymphatic drainage system, which helps in maintaining its fluid balance and removing waste products. The lymphatic vessels in the heart collect excess fluid and waste products from the heart muscle and transport them to lymph nodes for filtration before returning the lymph to the bloodstream.

In conclusion, the anatomy of the heart is a complex and intricate system that includes its external features, blood supply, venous supply, and lymphatic drainage. Understanding the detailed anatomy of the heart is crucial for comprehending its functioning and the various conditions that may affect it. Further studies and research in this field continue to contribute to our knowledge of the heart and its vital role in maintaining overall health and well-being.

External Features

The external features of the heart are an essential aspect of its anatomy. Understanding the anatomical description of the heart provides a solid foundation for studying its complex structure and function. Let’s take a closer look at the external features of the human heart.

The heart is comprised of four chambers: the right atrium, left atrium, right ventricle, and left ventricle. The atria are located above and behind the ventricles and are separated from the ventricles by an atrioventricular groove, which is a groove on the surface of the heart. Similarly, the ventricles are separated from each other by an interventricular groove, which is subdivided into anterior and posterior parts.

The heart also has distinct surfaces and borders. The apex of the heart is directed downwards, forwards, and to the left. The base, or posterior surface, is directed backward, while the anterior/sternocostal, inferior, and left lateral surfaces are other surfaces of the heart. These surfaces are demarcated by upper, inferior, right, and left borders.

The anatomical description of the heart’s surfaces and borders is crucial in understanding its orientation and location within the chest cavity. It provides a framework for further exploration of the heart’s internal structures and their functions, including the intricate network of blood vessels, valves, and muscle fibers that work together to pump blood and maintain circulation.

Having a comprehensive knowledge of the external features of the heart is fundamental in the study of its anatomy. It serves as a basis for further understanding the complex interplay between the heart’s structure and function, and how it contributes to overall cardiovascular health.

Grooves or sulci

The atria and ventricles of the heart are separated by a circular groove known as the atrioventricular or coronary sulcus. This groove is further divided into anterior and posterior parts. The anterior part consists of right and left halves.

The right half of the anterior part of the atrioventricular sulcus is oblique and lies between the right auricle and right ventricle. This area is responsible for loading the right coronary artery, which is a major blood vessel that supplies oxygenated blood to the right side of the heart.

On the other hand, the left part of the anterior part of the atrioventricular sulcus is small and located between the left auricle and left ventricle. It lodges the circumflex branch of the left coronary artery, which is another important blood vessel that supplies oxygenated blood to the left side of the heart.

The arrangement and location of these grooves, or sulci, on the surface of the heart are critical for understanding the vascular supply to the heart muscle. The coronary arteries play a vital role in nourishing the heart tissue and ensuring its proper functioning.

The anatomy of the coronary sulcus is of great importance for medical students, particularly those studying medicine or dentistry. It is a crucial topic that may be examined during viva examinations or other assessments related to the anatomy of the heart.

The coronary sulcus is partially obscured by the ascending aorta and pulmonary trunk in its anterior aspect. The interatrial groove, which is faintly visible, is located posteriorly, while the anterior interventricular groove is closer to the left margin of the heart, running downward and to the left.

At the lower end of the groove, it separates the apex of the heart from the rest of the inferior border. The posterior interventricular groove is located on the diaphragmatic or inferior surface of the heart, nearer to the right margin of this surface. The two interventricular grooves meet at the inferior border near the apex of the heart.

The point where the posterior interventricular groove intersects with the coronary sulcus is known as the crux of the heart. This is an important anatomical landmark and holds significance in understanding the overall structure and orientation of the heart.

A thorough understanding of the coronary sulcus and its relationship with other grooves and landmarks on the heart’s surface is essential for medical and dental students in order to accurately describe and identify different structures of the heart during clinical examinations and procedures.

The apex of the heart

The apex of the heart is formed exclusively by the left ventricle, and it is directed downward, forward, and to the left. It is overlapped by the anterior border of the left lung, which is an important anatomical relationship to consider.

The apex of the heart is situated in the left fifth intercostal space, approximately 9 cm lateral to the midsternal line and just medial to the midclavicular line. This location of the apex of the heart is significant in the anatomy of the heart, as it serves as a point of reference for clinical examinations and procedures. In living subjects, pulsations of the heart may be visible or palpable over the region of the apex.

It’s worth noting that in children below 2 years of age, the apex of the heart is typically located in the left fourth intercostal space along the midclavicular line. This age-specific variation is important to consider when assessing the anatomy of the heart in pediatric patients.

Understanding the precise location and position of the apex of the heart is crucial for healthcare professionals in accurately identifying and examining the heart’s structures during clinical assessments, such as palpation of heartbeats and determination of cardiac landmarks for diagnostic purposes.

The base of the heart

The base of the heart, also known as the posterior surface, is primarily formed by the left atrium and a small part of the right atrium. It is the posterior aspect of the heart, which is oriented towards the back of the body.

In relation to the base of the heart, one can observe the openings of the four pulmonary veins, which drain oxygenated blood from the lungs and open into the left atrium. Additionally, the superior and inferior vena cava, which are large veins that carry deoxygenated blood from the systemic circulation, open into the right atrium at the base of the heart.

The base of the heart is located in close proximity to the thoracic vertebrae five (T5) to thoracic vertebrae eight (T8) when the body is in a lying posture. In an erect posture, it descends by one vertebra. It is separated from the vertebral column by the pericardium (the sac-like membrane that surrounds the heart), the right pulmonary veins, the esophagus (the tube that connects the mouth to the stomach), and the aorta (the main artery that carries oxygenated blood from the heart to the rest of the body).

Understanding the anatomy of the base of the heart is important in clinical assessments and procedures, such as imaging studies, cardiac surgeries, and interventions involving the pulmonary veins, vena cavae, esophagus, and aorta.

Borders of the heart

The borders of the heart provide an understanding of the external structure and shape of the heart.

1. Upper border: The upper border of the heart is slightly oblique and is formed by the two atria, with the left atrium being the main contributor. It is located towards the top of the heart and is important in identifying the superior extent of the heart.
2. Right border: The right border of the heart is more or less vertical and is formed by the right atrium. It extends from the superior vena cava to the inferior vena cava (IVC), which are the major veins that carry deoxygenated blood from the upper and lower parts of the body back to the heart.
3. Inferior border: The inferior border of the heart is nearly horizontal and is formed mainly by the right ventricle, with a small part near the apex being formed by the left ventricle. It extends from the IVC to the apex of the heart, which is the pointed tip at the bottom.
4. Left border: The left border of the heart is oblique and curved. It is formed mainly by the left ventricle, and partially by the left auricle (a small, ear-like extension of the left atrium). It separates the anterior and left surfaces of the heart and extends from the apex to the left auricle.

Surfaces of the heart

The anterior or sternocostal surface of the heart is formed mainly by the right atrium and right ventricle, and partially by the left ventricle and left auricle.

The left atrium is not visible on the anterior surface as it is covered by the aorta and pulmonary trunk. Most of the sternocostal surface is covered by the lungs, but a part of it that lies behind the cardiac notch of the left lung is uncovered. This uncovered area is dull on percussion and is clinically referred to as the area of superficial cardiac dullness.

The inferior or diaphragmatic surface of the heart rests on the central tendon of the diaphragm. It is formed in its left two-thirds by the left ventricle, and in its right one-third by the right ventricle. It is transversed by the posterior interventricular groove and is directed downwards.

The left surface of the heart is formed mostly by the left ventricle, with the upper end being formed by the left auricle. In its upper part, the surface is crossed by the coronary sulcus, which is a groove that contains important coronary vessels. The left surface is related to the left phrenic nerve, the left pericardiacophrenic vessels, and the pericardium.

Structures of the heart

Now let’s learn about the structure of anatomy of the heart. The structure of the human heart mainly deals with the valves of the heart.

Valves

The valves of the heart play a crucial role in maintaining the unidirectional flow of blood and preventing regurgitation or backflow of blood in the opposite direction. There are two pairs of valves in the heart: atrioventricular (AV) valves and semilunar valves.

The right atrioventricular valve, also known as the tricuspid valve, is located between the right atrium and right ventricle. It is called tricuspid because it has three cusps or leaflets. The left atrioventricular valve, also known as the bicuspid valve or mitral valve, is located between the left atrium and left ventricle. It is called bicuspid because it has two cusps or leaflets.

The semilunar valves include the aortic valve and pulmonary valve, and they are located at the exit of the aorta and pulmonary artery, respectively. Each of these valves has three semilunar cusps or leaflets that are shaped like half-moons, hence the name semilunar valves.

The cusps of the heart valves are made up of folds of the endocardium, which is the inner lining of the heart, and are strengthened by an intervening layer of fibrous tissue. These valves open and close in response to pressure changes during the cardiac cycle, allowing blood to flow in one direction and preventing backflow, thus ensuring efficient blood circulation and maintaining proper cardiac function. Any dysfunction or disease of the heart valves can result in various cardiac conditions and may require medical intervention, such as valve repair or replacement, to restore normal heart function.

Atrioventricular Valves

The atrioventricular valves, also known as AV valves, are composed of several components:

1. Fibrous ring: The cusps of the AV valves are attached to a fibrous ring that surrounds the valve orifice. This fibrous ring provides structural support and serves as an attachment site for the cusps.
2. Cusps: The cusps of the AV valves are oblate and project into the ventricular cavity. Each cusp has an attached margin that is attached to the fibrous ring, and a free margin that is not attached to any structure. The cusps have atrial and ventricular surfaces, and their margins are serrated due to the attachment of chordae tendinae, which are thin tendinous cords.
3. Chordae tendinae: The chordae tendinae are thin tendinous cords that connect the free margins and ventricular surfaces of the cusps to the apices of the papillary muscles, which are small muscular projections from the walls of the ventricles. The chordae tendinae prevent the eversion or flipping inside out of the cusps into the atrial cavity during ventricular contraction, and they also limit the amount of ballooning of the cusps towards the ventricular cavity.
4. Papillary muscles: The papillary muscles are responsible for actively contracting and pulling on the chordae tendinae during ventricular contraction, helping to keep the AV valves competent and preventing regurgitation of blood back into the atria. The number and arrangement of papillary muscles vary in each AV valve. The tricuspid valve has three papillary muscles: anterior, inferior, and septal, with the anterior papillary muscle being the largest. The mitral valve has two papillary muscles: anterior and posterior.
5. Blood vessels: Blood vessels are present only in the fibrous ring and in the basal one-third of the cusps of the AV valves. The central two-thirds of the cusps borrow nutrition directly from the blood in the cavity of the heart.
6. Cusp characteristics: The tricuspid valve has three cusps – anterior, posterior (or inferior), and septal – that span across the three walls of the right ventricle. The mitral valve has two cusps – anterior (or aortic) and posterior – and lies between the mitral and aortic orifices. The cusps of the mitral valve are smaller and thicker than those of the tricuspid valve.

The proper functioning of the AV valves is essential for maintaining unidirectional blood flow through the heart, preventing regurgitation or backflow of blood into the atria during ventricular contraction, and ensuring efficient cardiac function. Any dysfunction or disease of the AV valves can result in various cardiac conditions and may require medical intervention, such as valve repair or replacement, to restore normal heart function.

Semilunar Valves

The semilunar valves, namely the aortic valve and pulmonary valve, are so named because of the semilunar or crescent shape of their cusps. These valves share similarities in their structure and function.

1. Cusps: Each semilunar valve has three cusps or leaflets that are attached directly to the walls of the aorta or pulmonary artery, without the presence of a fibrous ring like the atrioventricular valves. The cusps form small pockets or sinuses with their mouths directed away from the ventricular cavity. The free margin of each cusp contains a central fibrous nodule, and on each side of this nodule, a thin smooth margin called the lunule extends up to the base of the cusp.
2. Closure during ventricular diastole: The semilunar valves are closed during ventricular diastole, the relaxation phase of the cardiac cycle, when the ventricles are filling with blood. During this time, each cusp bulges towards the ventricular cavity, closing the valve and preventing backflow of blood into the ventricles.
3. Sinuses: Opposite the cusps, the walls of the aorta and pulmonary artery are slightly dilated to form the aortic and pulmonary sinuses. These sinuses help to maintain smooth blood flow and prevent turbulence, and they also serve as sites for the origin of the coronary arteries, which supply blood to the heart muscle. The anterior and left posterior aortic sinuses are the points of origin for the coronary arteries.

The semilunar valves play a crucial role in preventing backflow of blood from the aorta and pulmonary artery into the ventricles during diastole, ensuring efficient forward flow of blood through the systemic and pulmonary circulations, respectively. Any dysfunction or disease of the semilunar valves can lead to conditions such as aortic or pulmonary valve stenosis or regurgitation, which may require medical intervention, such as valve repair or replacement, to restore normal heart function.

Clinical anatomy of the heart

The clinical anatomy of the heart encompasses the complex structure and function of this vital organ. The heart’s rhythmic contractions are accompanied by distinct sounds that provide important diagnostic clues. The first heart sound, commonly referred to as “S1,” is generated by the cessation of the atrioventricular valves (the mitral and tricuspid valves) closing tightly as the ventricles contract to pump blood out of the heart. This sound is often described as a “lub” and marks the beginning of systole, the phase of the cardiac cycle when the heart is actively pumping blood.

Similarly, the second heart sound, known as “S2,” is produced by the closure of the semilunar valves (the aortic and pulmonary valves) at the end of systole, when the ventricles relax and begin to fill with blood again. This sound is often described as a “dub” and marks the beginning of diastole, the phase of the cardiac cycle when the heart is relaxed and refilling with blood.

Learn More about Heart Sounds: Click Here

Abnormalities in the structure or function of the heart valves can result in conditions such as stenosis and incompetence, which can significantly impact cardiac function. Stenosis refers to the narrowing of the valve orifice, often due to the fusion or thickening of the cusps, which can obstruct blood flow and impede the heart’s ability to pump efficiently. Examples of stenotic conditions include mitral stenosis, aortic stenosis, and others. These conditions may present with symptoms such as chest pain, fatigue, and shortness of breath, and may require medical intervention or surgical repair to alleviate the obstruction.

On the other hand, incompetence, also known as regurgitation, occurs when the valve fails to close properly, resulting in backflow of blood into the previous chamber. This can cause increased workload on the heart and lead to symptoms such as palpitations, fluid retention, and reduced exercise tolerance. Aortic incompetence or aortic regurgitation, for example, occurs when the aortic valve does not close properly during diastole, allowing blood to flow back into the left ventricle. Management of incompetence may involve medication to reduce symptoms or surgical intervention to repair or replace the affected valve.

In addition to stenosis and incompetence, other conditions related to the clinical anatomy of the heart may include congenital heart defects, infections of the heart valves (endocarditis), and structural abnormalities such as ventricular septal defects or atrial septal defects. Diagnostic tools such as echocardiography, cardiac catheterization, and electrocardiography are commonly used to evaluate the structure and function of the heart and identify any abnormalities.

In summary, understanding the clinical anatomy of the heart, including the origin of heart sounds, the concepts of stenosis and incompetence, and other related conditions, is crucial in diagnosing and managing various cardiac conditions. Regular monitoring, appropriate medical interventions, and lifestyle modifications can help maintain heart health and prevent complications associated with heart valve abnormalities.

Fibrous Skeleton

The fibrous skeleton of the heart is a complex structure composed of fibrous rings that surround the atrioventricular and arterial orifices, along with additional masses of fibrous tissue. This anatomical feature plays several critical roles in maintaining the normal functioning of the heart.

Firstly, the fibrous skeleton provides structural support and attachment points for the cardiac muscles. The atria, ventricles, and the membranous part of the interventricular septum are anchored to the fibrous rings, which help to maintain the shape and integrity of the heart. This allows the heart to effectively pump blood in a coordinated manner during each cardiac cycle.

Secondly, the fibrous skeleton acts as an insulating barrier that prevents electrical signals from directly passing between the atria and ventricles, except for the atrioventricular bundle or bundle of His. This electrical insulation is essential for the proper functioning of the heart’s conduction system, which controls the rhythm and coordination of the heartbeats.

Furthermore, the fibrous skeleton helps to ensure the competence of the cardiac valves. The fibrous rings provide a rigid foundation for the attachment of the valve cusps, allowing them to open and close properly during each cardiac cycle, thereby preventing backflow of blood and maintaining unidirectional blood flow.

In addition to the fibrous rings, there are specific masses of fibrous tissue within the fibrous skeleton. The frigonum fibrosum dextrum, located between the atrioventricular rings behind and the aortic ring in front, is a large mass of fibrous tissue. In some mammals, such as sheep, a small bone called the os cordis is present within this mass of fibrous tissue. Another smaller mass of fibrous tissue, known as the trigonum fibrosum sinistrum, is present between the aortic and mitral rings. The tendon of the infundibulum, located close to the pulmonary valve, binds the posterior surface of the infundibulum to the aortic ring, providing additional stability and support to the heart’s anatomy.

The fibrous skeleton of the heart plays a crucial role in maintaining the structural integrity, electrical conduction, and proper functioning of the cardiac valves. Understanding the anatomy and function of the fibrous skeleton is essential in the diagnosis and management of various cardiac conditions, such as arrhythmias, valve diseases, and congenital heart defects.

The Musculature of the Heart

The musculature of the heart consists of specialized cardiac muscle fibers that are arranged in intricate patterns to facilitate the pumping action of the heart. These cardiac muscle fibers are organized in long loops that are attached to the fibrous skeleton of the heart. When these muscle fibers contract, they generate the force necessary to propel blood out of the cardiac chambers, similar to wringing out water from a wet cloth.

The atrial muscle fibers are arranged in two layers – a superficial transverse layer and a deep anteroposterior (vertical) layer. The superficial transverse layer runs horizontally across the atria, while the deep anteroposterior layer runs vertically from the anterior to the posterior part of the atria. This arrangement allows for coordinated contraction of the atrial walls, facilitating the filling of the ventricles with blood.

The ventricular muscle fibers are also organized in superficial and deep layers. The superficial fibers arise from the fibrous skeleton of the heart and undergo a spiral or helical course. This spiral arrangement allows for a twisting motion during ventricular contraction, resulting in an efficient ejection of blood from the ventricles into the arteries.

The complex arrangement of cardiac muscle fibers in the atria and ventricles is crucial for the coordinated contraction and relaxation of the heart, which ensures effective pumping of blood throughout the circulatory system. Dysfunction or disruption of the cardiac muscle fibers can lead to various cardiac disorders, such as cardiomyopathy, heart failure, and arrhythmias. Understanding the organization and function of the cardiac musculature is essential in the diagnosis and management of these conditions.

Thorax

The superficial fibers of the ventricular musculature have distinct courses that contribute to the efficient pumping action of the heart. The fibers that start from the tendon of the infundibulum (1) pass across the diaphragmatic surface of the heart and curve around the inferior border to reach the sternocostal surface. From there, these fibers cross the anterior intraventricular groove to reach the apex of the heart, where they form a vortex and ultimately end in the anterior papillary muscle of the left ventricle.

Similarly, the fibers that arise from the right atrioventricular (AV) ring take a similar course as the aforementioned fibers but end in the posterior papillary muscle of the left ventricle. On the other hand, the fibers that arise from the left AV ring lie along the diaphragmatic surface of the heart and cross the posterior interventricular groove to reach the papillary muscles of the right ventricle.

In contrast, the deep fibers of the ventricular musculature have an “S-shaped” course. These fibers arise from the papillary muscle of one ventricle and turn in the interventricular groove to end in the papillary muscle of the other ventricle. The fibers of the first layer circle around the right ventricle, cross through the interventricular septum, and end in the papillary muscle of the left ventricle. The fibers of the second and third layers have decreasing courses in the right ventricle and increasing courses in the left ventricle.

This intricate arrangement of the ventricular musculature allows for coordinated contraction and relaxation of the ventricles, which is essential for the effective pumping of blood out of the heart and into the systemic and pulmonary circulation. Any disruption in this complex arrangement of fibers can result in impaired cardiac function and contribute to conditions such as heart failure, arrhythmias, and valvular disorders. Therefore, understanding the organization and function of the ventricular musculature is crucial in the clinical anatomy of the heart and in the diagnosis and management of cardiac diseases.

Arteries supplying the heart

The heart is endowed with two coronary arteries, arising from the ascending aorta. Both arteries run in the coronary sulcus.

Course

The course of the right coronary artery, one of the main arteries that supply blood to the heart, follows a specific path on the surface of the heart. It first passes forwards and to the right to emerge on the surface of the heart between the root of the pulmonary trunk and the right auricle. From there, it runs downwards in the right anterior coronary sulcus, which is a groove that marks the boundary between the right atrium and right ventricle, and reaches the junction of the right and inferior borders of the heart.

The right coronary artery then winds around the inferior border of the heart, following the groove between the right ventricle and diaphragmatic surface of the heart. Here, it runs backward and to the left in the right posterior coronary sulcus, which is a groove that marks the boundary between the right atrium and right ventricle on the posterior surface of the heart. The artery continues its course in the posterior interventricular groove, which is a groove that runs along the posterior surface of the interventricular septum, the wall that separates the left and right ventricles of the heart.

Finally, the right coronary artery terminates by anastomosing, or connecting, with a circumflex branch of the left coronary artery at the crux of the heart. The crux is the point where the posterior interventricular groove and the left atrioventricular groove meet. This anastomosis between the right coronary artery and the left circumflex branch of the left coronary artery helps to provide collateral blood supply to the heart and ensures adequate oxygen and nutrient delivery to the cardiac muscle. Any obstruction or blockage in the right coronary artery can result in reduced blood flow to the areas of the heart it supplies, which can lead to myocardial ischemia and potentially result in a heart attack. Therefore, a thorough understanding of the course of the right coronary artery is important in the clinical management of coronary artery disease and other cardiac conditions.

Branches

The right coronary artery gives rise to several branches, which can be categorized into large branches and small branches.

Large branches of the right coronary artery include:

1. Marginal branch: Also known as the acute marginal branch or the right marginal artery, this branch runs along the right margin, or border, of the heart and supplies blood to the right ventricle.
2. Posterior interventricular branch: Also known as the posterior descending artery, this branch runs along the posterior interventricular groove on the posterior surface of the heart, alongside the posterior interventricular septum, and supplies blood to the posterior walls of both ventricles.

Small branches of the right coronary artery include:

1. Nodal branch: In approximately 60% of cases, the right coronary artery gives rise to a nodal branch, which supplies blood to the sinoatrial (SA) node, the natural pacemaker of the heart that regulates the heart’s electrical activity.
2. Right atrial branches: These branches supply blood to the right atrium, the upper chamber of the heart.
3. Infundibular branch: This branch supplies blood to the infundibulum, which is the conical-shaped portion of the right ventricle that leads to the pulmonary trunk.
4. Terminal branches: These branches supply blood to the terminal portion of the right coronary artery and its surrounding tissues.
5. Right ventricular branches: These branches supply blood to the right ventricle, the lower chamber of the heart.
6. Conus branch: Also known as the conal branch or the conal artery, this branch supplies blood to the conus arteriosus, which is the conical-shaped portion of the right ventricle just below the pulmonary valve.

The branches of the right coronary artery play a crucial role in supplying oxygen and nutrients to various regions of the heart, including the right atrium, right ventricle, and the conducting system of the heart. Any blockage or obstruction in these branches can result in reduced blood flow to the corresponding areas, which can lead to myocardial ischemia and potentially result in various cardiovascular conditions, such as angina, myocardial infarction (heart attack), or arrhythmias.

Conducting system

The conducting system of the heart, also known as the cardiac conduction system, is a network of specialized myocardial fibers responsible for initiating and conducting electrical impulses that regulate the heartbeat. This intricate system is crucial for maintaining the coordinated rhythm and contraction of the heart.

1. Sinoatrial node or SA node: Located in the upper part of the right atrium near the opening of the superior vena cava, the SA node is often referred to as the “natural pacemaker” of the heart. It generates electrical impulses that set the rhythm of the heart and determine the heart rate. The impulses generated by the SA node spread across the atria, causing them to contract and push blood into the ventricles.
2. Atrioventricular node or AV node: Positioned in the lower part of the right atrium, near the atrioventricular septum, the AV node acts as a relay station that delays the electrical impulses coming from the SA node. This delay allows the atria to complete their contraction and ensures that the ventricles receive the blood from the atria before they contract.
3. Atrioventricular bundle or AV bundle or bundle of HIS: After passing through the AV node, the electrical impulses travel down the AV bundle, also known as the bundle of HIS. The AV bundle is a specialized group of fibers that conducts the impulses rapidly from the atria to the ventricles, ensuring synchronized contraction of the ventricles.
4. The right and left branches: The AV bundle further divides into two branches, the right bundle branch and the left bundle branch. These branches extend along the interventricular septum, transmitting the electrical impulses to the respective ventricles.
5. Purkinje fibers: The right and left bundle branches give rise to Purkinje fibers, which are fine and rapidly conducting fibers that spread throughout the ventricular walls. The Purkinje fibers play a crucial role in delivering the electrical impulses to the individual ventricular muscle cells, causing them to contract in a coordinated manner.

In summary, the conducting system of the heart comprises the SA node, AV node, AV bundle, right and left bundle branches, and Purkinje fibers, all working together to ensure the proper initiation, conduction, and coordination of the cardiac impulses, leading to the synchronized contraction of the heart chambers and efficient pumping of blood throughout the body. Any disruption in this complex system can result in various cardiac conduction disorders, which may require medical intervention for proper management.

Clinical anatomy of the heart

Clinical anatomy of the heart is a specialized field of study that focuses on the detailed understanding of the anatomical structures and their clinical significance in relation to heart function, diseases, and surgical interventions. One important aspect of clinical anatomy of the heart is the understanding of the conducting system and its role in cardiac arrhythmias.

Cardiac arrhythmias, which refer to abnormal heart rhythms, can occur due to defects or damage to the conducting system of the heart, disrupting the normal rhythm of contraction. The conducting system, including the SA node, AV node, AV bundle, bundle branches, and Purkinje fibers, is responsible for generating and conducting electrical impulses that regulate the heartbeat. Any disruption in this system can result in arrhythmias, which can have various clinical manifestations and require medical intervention for proper management.

The blood supply to the conducting system is also of clinical significance. The right coronary artery is responsible for supplying the majority of the conducting system, except for a part of the left branch of the AV bundle, which is usually supplied by the left coronary artery. Vascular lesions, such as atherosclerosis or arterial blockages, in the coronary arteries can affect the blood flow to the conducting system and may lead to arrhythmias.

In clinical practice, a thorough understanding of the anatomy of the heart and its conducting system is crucial for diagnosing and managing cardiac arrhythmias. Cardiac surgeons and interventional cardiologists often rely on their knowledge of the clinical anatomy of the heart to plan and perform surgical interventions, such as pacemaker implantation, ablation procedures, or coronary artery bypass grafting (CABG), to correct arrhythmias or restore normal heart function.

In conclusion, a comprehensive understanding of the clinical anatomy of the heart, including the conducting system and its blood supply, is essential for the diagnosis and management of cardiac arrhythmias. It plays a crucial role in guiding surgical interventions and other medical treatments for patients with heart rhythm disorders.

Veins of the heart

The veins of the heart play a vital role in draining deoxygenated blood from the cardiac muscle and returning it to the right atrium of the heart. There are several main veins that make up the venous drainage system of the heart.

1. Great cardiac vein: This is the largest and most important vein of the heart. It runs alongside the left anterior descending artery, which is a major branch of the left coronary artery, and drains the blood from the front and sides of the heart. The great cardiac vein usually runs in the anterior interventricular groove and eventually empties into the coronary sinus.
2. Middle cardiac vein: This vein typically runs in the posterior interventricular groove, parallel to the posterior descending artery, which is a branch of the right coronary artery. It drains the posterior part of the ventricles and usually empties into the coronary sinus.
3. Right marginal vein: This vein runs along the right margin of the heart and drains the blood from the right ventricle. It usually empties into the coronary sinus or directly into the right atrium.
4. Posterior vein of the left ventricle: This vein drains the posterior part of the left ventricle and usually empties into the coronary sinus.
5. Oblique vein of the left atrium: This vein runs in the posterior left atrioventricular groove and drains the blood from the left atrium. It may also empty directly into the left atrium or into the coronary sinus.
6. Anterior cardiac veins: These veins are smaller in size and drain the blood from the anterior surface of the right ventricle. They may empty directly into the right atrium or into the coronary sinus.
7. Venae Cordis minimi: Also known as Thebesian veins, these are small veins that drain directly into the right atrium. They are unique as they drain the blood from the walls of the heart itself, bypassing the coronary sinus.

In general, most of the veins of the heart, including the great cardiac vein, middle cardiac vein, right marginal vein, posterior vein of the left ventricle, and oblique vein of the left atrium, drain into the coronary sinus, which is a large vein that runs in the posterior part of the atrioventricular groove and empties into the right atrium. However, the anterior cardiac veins and venae Cordis minimi have a direct route of drainage into the right atrium.

Lymphatics of Heart

The lymphatic system of the heart is an important component of the cardiovascular system, responsible for draining excess interstitial fluid and immune cells from the cardiac tissue. The lymphatics of the heart are closely associated with the coronary arteries and typically form two main trunks.

The right lymphatic trunk accompanies the right coronary artery and runs along its course. It usually drains lymph from the right atrium, right ventricle, and a portion of the interventricular septum. The right lymphatic trunk then typically terminates by emptying into the right brachiocephalic lymph nodes, which are located near the junction of the right subclavian and right internal jugular veins.

Nerve supply of heart

The nerve supply of the heart plays a crucial role in regulating its functions, including heart rate and coronary artery dilation. The heart receives both parasympathetic and sympathetic nerves, which have opposing effects on cardiac activity.

The parasympathetic nerves, also known as the cardioinhibitory nerves, reach the heart via the vagus nerve (cranial nerve X). These nerves originate from the medulla in the brainstem and have inhibitory effects on the heart, slowing down the heart rate when stimulated. The parasympathetic nerves mainly innervate the atria and the atrioventricular (AV) node, helping to regulate the conduction of electrical impulses and controlling the heart rate during rest and relaxation.

On the other hand, the sympathetic nerves, derived from the upper four to five thoracic segments of the spinal cord, are known as the cardio-acceleratory nerves. These nerves have excitatory effects on the heart, increasing the heart rate and dilating the coronary arteries when stimulated. The sympathetic nerves play a crucial role in the “fight or flight” response, helping the heart to respond to stress, exercise, and other physiological demands.

Both the parasympathetic and sympathetic nerves form complex networks of nerve fibers called cardiac plexuses, which are located around the heart. There are two main cardiac plexuses – the superficial cardiac plexus and the deep cardiac plexus.

The superficial cardiac plexus is located below the arch of the aorta in front of the right pulmonary artery. It is formed by branches from the superior cervical cardiac annexe of the left sympathetic chain and the inferior cervical cardiac arm of the left vagus nerve. The superficial cardiac plexus is connected to the deep cardiac plexus, the right coronary artery, and the left anterior pulmonary plexus.

The deep cardiac plexus is situated in front of the bifurcation of the trachea and behind the arch of the aorta. It is formed by all the cardiac branches derived from all the cervical and upper thoracic ganglia of the sympathetic chain, as well as the cardiac branches of the vagus and recurrent laryngeal nerves, except those that form the superficial plexus. The deep cardiac plexus distributes branches to the corresponding coronary and pulmonary plexuses and also provides separate branches to the atria.

Developmental components

1. Right atrium:
   • Rough anterior part: Atrial chamber proper.
   • Smooth posterior part: Formed by the consumption of right horn of sinus venosus and interatrial septum.
   • Demarcating part: Crista terminalis.
2. Left atrium:
   • Rough part: Atrial chamber proper.
   • Smooth part: Formed by the digestion of pulmonary veins and interatrial septum.
3. Right ventricle:
   • Rough part: Proximal portion of bulbus cordis.
   • Smooth part: Conus cordis or middle portion of bulbus cordis.
4. Left ventricle:
   • Rough part: Whole primitive ventricular chamber.
   • Smooth part: Conus cordis or middle portion of bulbus cordis.
5. Interventricular septum:
   • Thick muscular in the lower part, separating the two ventricles.
   • Thin membranous in the upper part, formed by fusion of inferior atrioventricular cushion and right and left conus swellings. The membranous part not only separates the two ventricles but also separates the right atrium from the left ventricle.
6. Truncus arteriosus or distal part of bulbus cordis:
   • Forms the ascending aorta and pulmonary trunk, separated by a spiral septum.
   • The spiral septum is responsible for the triple reaction of the ascending aorta or pulmonary trunk. Initially, the pulmonary trunk is anterior to the ascending aorta, then it shifts to the left, and finally, the right pulmonary artery is posterior to the ascending aorta.
7. Heart becomes fully functional at the end of the second month of intrauterine life.

Pericardium

The pericardium, a double-walled sac that surrounds the heart, plays a crucial role in protecting and supporting this vital organ throughout life. Comprised of fibrous and serous layers, the pericardium serves as a dynamic structure that facilitates the heart’s pulsations from ‘womb to tomb’, ensuring its smooth functioning.

The pericardium starts developing early during embryogenesis, forming a protective covering around the developing heart within the womb. It provides mechanical support to the growing heart and helps maintain its proper position within the chest cavity. As the heart continues to develop, the pericardium grows along with it, adapting to its changing shape and size.

Once the heart is fully formed and starts functioning, the fibrous layer of the pericardium acts as a tough outer coat that prevents overstretching and excessive movement of the heart. It also serves as a barrier, protecting the heart from infections and inflammation that may occur in the surrounding organs.

The serous layer of the pericardium, on the other hand, is a thin, slippery membrane that lines the inner surface of the fibrous layer and directly covers the heart. It produces a small amount of lubricating fluid that allows the heart to beat smoothly and minimizes friction between the heart and the surrounding structures during its pulsations.

The pericardium also plays a role in maintaining the normal rhythm of the heart. It contains specialized nerve endings that help in regulating the heartbeat by providing sensory feedback to the brain. These nerve endings are sensitive to changes in pressure and stretch within the pericardium, sending signals to the brain to adjust the heart’s rate and rhythm as needed.

Furthermore, the pericardium is involved in the complex interplay between the heart and the autonomic nervous system, which controls the involuntary functions of the body, including heart rate and blood pressure. The nerves that innervate the pericardium are part of this intricate network, and their interactions with the heart and the brain contribute to the overall regulation of the heartbeat.

The importance of the pericardium in heart health is evident in various clinical conditions. Pericarditis, which is inflammation of the pericardium, can cause chest pain, difficulty breathing, and abnormal heart rhythms. Pericardial effusion, a buildup of fluid within the pericardial sac, can compress the heart and impair its function. In some cases, surgical interventions such as pericardiectomy may be required to remove a diseased or damaged pericardium.

In addition to its anatomical and physiological functions, the pericardium has also been associated with emotional and cultural symbolism related to the heart. It has been metaphorically referenced in literature, poetry, and music to convey emotions such as love, passion, and vulnerability. The heart, enclosed and protected by the pericardium, has been used as a symbol of the seat of emotions and the essence of human existence.

In conclusion, the pericardium is a remarkable structure that plays a crucial role in supporting and protecting the heart throughout life. Its fibrous and serous layers work together to facilitate the heart’s pulsations, regulate its rhythm, and provide mechanical support. Beyond its physiological functions, the pericardium also holds cultural and emotional significance as a symbol of the heart’s essence. Understanding the importance of the pericardium can deepen our appreciation for the complexity and resilience of the human heart.

Dissection

Dissection is a fundamental technique used in anatomy to study the internal structures of the body. When it comes to the heart, understanding the anatomy of the pericardium and its relationship with the heart is crucial for a comprehensive dissection.

To begin the dissection of the heart, the student must have a basic understanding of the directional terminology and make precise cuts to reveal the internal structures clearly. A vertical incision is made on each side of the pericardium, immediately anterior to the line of the phrenic nerve. These incisions are then joined by a transverse cut about 1 cm above the diaphragm, creating a flap of pericardium that can be turned upwards and sideways to expose the pericardial cavity.

Within the pericardial cavity, the student can observe that the turned flap of pericardium comprises a fibrous layer and a parietal layer of the visceral pericardium, which closely surrounds the heart. The visceral layer of the pericardium is also known as the epicardium, which is the outermost layer of the heart wall.

To further explore the pericardium, a probe can be passed from the right side behind the ascending aorta and pulmonary trunk until it appears on the left side, just to the right of the left atrium. This probe is positioned in the transverse sinus of the pericardium, which is a potential space located between the ascending aorta and pulmonary trunk anteriorly, and the superior vena cava and pulmonary veins posteriorly.

Lifting the apex of the heart upwards allows the student to insert a finger behind the left atrium into a cul-de-sac, which is bounded by the inferior vena cava on the right and below, and the lower-left pulmonary vein above and to the left. This cul-de-sac is known as the oblique sinus of the pericardium, and understanding its location and anatomy is important for a thorough dissection.

As the dissection progresses, the student can then define the borders, surfaces, grooves, apex, and base of the heart. The borders of the heart include the right border, which is formed by the right atrium, the inferior border, which is formed by the right ventricle, and the left border, which is formed by the left ventricle. The surfaces of the heart include the anterior surface, which is formed by the right ventricle and part of the left ventricle, and the diaphragmatic surface, which is formed by the left ventricle and part of the right ventricle. The apex of the heart is the pointed tip located at the inferior and leftmost part, while the base of the heart is the broader superior part.

Overall, a careful dissection of the pericardium and the heart allows the student to gain a deeper understanding of the anatomy and relationships of these vital structures. It helps in identifying the different layers of the pericardium, exploring the potential spaces within the pericardial cavity, and defining the borders, surfaces, grooves, apex, and base of the heart, providing a hands-on experience that enhances the knowledge of cardiac anatomy.

Features

The pericardium, which gets its name from the Greek words meaning “around the heart,” is a protective fibroserous sac that surrounds the heart and its major blood vessels, known as the great vessels. Located in the middle mediastinum of the thoracic cavity, it consists of two layers – the fibrous pericardium and the serous pericardium.

The fibrous pericardium is a tough, outer layer that envelops the heart and fuses with the vessels that enter and leave the heart, creating a barrier that helps protect the heart from external damage. The heart is nestled within the fibrous and serous pericardial sacs, and as it develops during embryonic development, it invaginates itself into the serous sac without disrupting its continuity.

The last part of the heart to enter the pericardial sac is the region of the atria, which gives rise to the visceral pericardium that reflects back as the parietal pericardium. This results in the adherence of a layer of serous pericardium to the inner surface of the fibrous pericardium, forming the parietal layer, while the visceral layer of serous pericardium adheres to the outer layer of the heart, forming its epicardium. This double-layered serous pericardium, composed of the parietal and visceral layers, helps reduce friction between the heart and the surrounding structures during the heart’s contraction and relaxation movements.

Overall, the pericardium serves as a protective barrier, providing support and lubrication to facilitate the smooth movement of the heart within the thoracic cavity, while also helping to maintain the integrity of the heart’s structure.

Fibrous Pericardium

The fibrous pericardium, composed of fibrous tissue, has several notable features. Its apex is blunt and is located at the level of the sternal angle, where it fuses with the roots of the great vessels and the pretracheal fascia. The base of the fibrous pericardium is broad and seamlessly blends with the central tendon of the diaphragm, making them inseparable.

Anteriorly, the fibrous pericardium is connected to the upper and lower ends of the body of the sternum by weak superior and inferior sternopericardial ligaments. Posteriorly, it is related to the principal bronchi, the esophagus with the nerve plexus around it, and the descending thoracic aorta. On each side, it is in close proximity to the mediastinal pleura, the mediastinal surface of the lung, the phrenic nerve, and the pericardiacophrenic vessels.

These anatomical relationships of the fibrous pericardium are important in understanding its role in protecting the heart and its surrounding structures. Its fusion with the central tendon of the diaphragm helps anchor the heart in place, while its connections to the sternum and other adjacent structures provide stability and support to the pericardial sac. Additionally, its relationship with the bronchi, esophagus, and other nerves and vessels highlights the need for careful consideration during surgical procedures in this area to avoid damage to these vital structures.

Serous pericardium

The serous pericardium is a delicate, double-layered serous membrane that is lined by mesothelium. It consists of two layers, the parietal pericardium and the visceral pericardium (also known as the epicardium), each with its unique characteristics.

The parietal pericardium is the outer layer of the serous pericardium and is fused with the fibrous pericardium. It forms a continuous membrane with the fibrous pericardium, providing a protective covering for the heart and anchoring it within the fibrous pericardial sac.

The visceral pericardium, or epicardium, is the inner layer of the serous pericardium that is directly attached to the surface of the heart, except along the cardiac grooves where it is separated from the heart by blood vessels. The visceral pericardium is continuous with the parietal pericardium at the roots of the great vessels, including the ascending aorta, pulmonary trunk, two venae cavae, and the coronary veins.

The space between the parietal pericardium and the visceral pericardium is known as the pericardial cavity. This cavity contains only a thin film of serous fluid, which acts as a lubricant, allowing the apposed surfaces of the pericardium to slide smoothly against each other during the beating of the heart. This fluid helps reduce friction and allows the heart to move freely within the pericardial sac during its rhythmic contractions.

Overall, the serous pericardium serves as a protective covering for the heart, allowing it to move and beat efficiently without friction, while also helping to maintain its position within the thoracic cavity.

Sinuses of Pericardium

The sinuses of the pericardium are spaces or gaps within the pericardial cavity that are formed by reflections of the serous pericardium. There are two main sinuses of the pericardium – the transverse sinus and the oblique sinus.

1. Transverse sinus: The transverse sinus is a horizontal gap that lies between the arterial and venous ends of the heart tube. It is bounded anteriorly by the ascending aorta and pulmonary trunk, posteriorly by the superior vena cava, and inferiorly by the left atrium. On each side, it opens into the general pericardial cavity. The transverse sinus allows for free movement of the great vessels and facilitates their connections to the heart.
2. Oblique sinus: The oblique sinus is a narrow gap located behind the heart. It is bounded anteriorly by the left atrium, and posteriorly by the parietal pericardium and the esophagus. On the right and left sides, it is bounded by reflections of the pericardium. The oblique sinus forms a cul-de-sac posterior to the left atrium and permits pulsations of the left atrium to take place freely.

During development, when the veins of the heart are crowded together, a pericardial reflection surrounds them and forms the oblique pericardial sinus. This sinus allows for the separation and movement of the veins as the heart increases in size. The transverse sinus and oblique sinus are important anatomical features of the pericardium that play a role in the movement and functioning of the heart within the pericardial sac.

Contents of the pericardium

The pericardium contains several important structures, including:

1. Heart with cardiac vessels and nerves: The heart, along with its blood vessels (coronary arteries and veins), and nerves (such as the cardiac plexus) are enclosed within the pericardium. The pericardium provides protection and support to the heart, helping to maintain its position within the thoracic cavity.
2. Ascending aorta: The ascending aorta, which is the first part of the main artery that carries oxygenated blood from the heart to the rest of the body, lies within the pericardium. It originates from the left ventricle of the heart and ascends before curving to form the aortic arch.
3. Pulmonary trunk: The pulmonary trunk, also known as the pulmonary artery, carries deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation. It lies within the pericardium before branching into the right and left pulmonary arteries that lead to the respective lungs.
4. Lower half of the superior vena cava: The superior vena cava is a large vein that carries deoxygenated blood from the upper body to the right atrium of the heart. The lower half of the superior vena cava, which is located close to the heart, lies within the pericardium.
5. Terminal part of the inferior vena cava: The inferior vena cava is a large vein that carries deoxygenated blood from the lower body to the right atrium of the heart. The terminal part of the inferior vena cava, which is the portion closest to the heart, is also contained within the pericardium.
6. Terminal parts of the pulmonary veins: The pulmonary veins are the four veins that carry oxygenated blood from the lungs back to the left atrium of the heart. The terminal parts of the pulmonary veins, where they enter the left atrium, are located within the pericardium.

The pericardium serves as a protective membrane that surrounds and supports these vital structures, helping to maintain their position and functioning properly within the thoracic cavity.

Blood Supply

The blood supply to the pericardium, specifically the fibrous and parietal pericardium, is mainly provided by branches from the following arteries:

1. Internal thoracic arteries: The internal thoracic arteries, also known as the internal mammary arteries, are branches of the subclavian arteries. They are located in the chest wall and give off branches that supply the anterior part of the pericardium, including the fibrous pericardium.
2. Musculophrenic arteries: The musculophrenic arteries are branches of the internal thoracic arteries that supply the diaphragm and the lower part of the anterior pericardium.
3. Descending thoracic aorta: The descending thoracic aorta, which is the continuation of the aortic arch, gives off small branches that supply the posterior part of the pericardium.

Additionally, the pericardium is also supplied by small branches from adjacent arteries, such as the bronchial arteries, phrenic arteries, and esophageal arteries.

The veins from the pericardium drain into corresponding veins, including the internal thoracic veins, musculophrenic veins, and azygos veins, which eventually drain into the superior vena cava or inferior vena cava, depending on their location.

The blood supply to the pericardium is important for maintaining the health and integrity of the pericardial tissue, as well as supporting its role in protecting the heart and aiding in its proper functioning.

Nerve Supply

Nerve supply plays an important role in the sensory innervation of the pericardium, which is the protective sac that surrounds the heart. The fibrous and parietal pericardium are innervated by the phrenic nerves, which are branches of the cervical plexus (C3-C5). These nerves are sensitive to pain, and irritation or inflammation of the fibrous and parietal pericardium can cause pericarditis, which is characterized by chest pain that may be sharp, stabbing, or aching in nature. The pain of pericarditis usually originates in the parietal pericardium alone, as it is the outer layer of the pericardium that is sensitive to pain.

In contrast, the epicardium, which is the innermost layer of the pericardium and also known as the visceral pericardium, is supplied by the autonomic nerves of the heart. These nerves, including sympathetic and parasympathetic nerves, regulate the functions of the heart but are not sensitive to pain. Therefore, conditions affecting the epicardium, such as inflammation or injury, may not cause localized pain.

It’s important to note that the pain associated with pericarditis and cardiac pain or angina may differ in characteristics and location. Pericardial pain from pericarditis is typically localized to the chest and may worsen with deep breathing or changes in body position. On the other hand, cardiac pain or angina usually presents as chest discomfort, pressure, or tightness that may radiate to the left arm, neck, jaw, or back. The origin of cardiac pain or angina is usually related to the cardiac muscle or the blood vessels of the heart.

Understanding the nerve supply and sensory innervation of the pericardium is crucial in diagnosing and managing conditions related to the pericardium and the heart. It helps healthcare professionals differentiate between pericardial pain and cardiac pain, which can guide appropriate treatment strategies and management plans for patients with these conditions.