Mediastinum: The central compartment of the thoracic cavity where the heart is located, surrounded by vital structures and enclosed by the pericardium.
Apex beat: The point of maximal impulse of the heart, located in the left 5th intercostal space at the midclavicular line, approximately 9 cm from the midline, and where mitral valve sounds are best heard.
Base of the Heart: The posterior part of the heart opposite the apex, mainly formed by the left atrium, and it receives pulmonary veins, superior vena cava (SVC), and inferior vena cava (IVC).
Superior border of the heart: A line connecting the inferior border of the 2nd left costal cartilage to the superior border of the 3rd right costal cartilage, formed by the atria and auricles.
Right border of the heart: A line from the 3rd right costal cartilage to the 6th right costal cartilage, formed by the right atrium, extending between the SVC and IVC.
Left border of the heart: A line connecting the left ends of the superior and inferior borders, mainly formed by the left ventricle.
The heart is situated in the mediastinum, the central compartment of the thoracic cavity. It rests on the diaphragm near the midline and is surrounded by vital structures, enclosed within the pericardium. The apex beat is located in the left 5th intercostal space at the midclavicular line, about 9 cm from the midline, and is the best site for auscultating mitral valve sounds. The base of the heart lies opposite the apex and is primarily formed by the left atrium, which receives pulmonary veins, SVC, and IVC. The superior border of the heart is a line connecting specific costal cartilages and is formed by the atria and auricles. The right border runs from the 3rd to the 6th right costal cartilage and is formed by the right atrium, extending between the SVC and IVC. The left border connects the ends of the superior and inferior borders and is mainly formed by the left ventricle.
Understanding the precise anatomical location and borders of the heart is essential for accurate clinical assessment and effective auscultation.
Anterior (sternocostal) surface
The anterior surface of the heart is primarily formed by the right ventricle and right atrium.
Diaphragmatic (inferior) surface
The diaphragmatic surface rests on the central tendon of the diaphragm and is formed by both ventricles.
Right pulmonary surface
The right pulmonary surface is mainly formed by the right atrium.
Left pulmonary surface
The left pulmonary surface is mainly formed by the left ventricle and creates the cardiac impression on the left lung.
Pericardium
A double-walled sac surrounding the heart, consisting of a superficial fibrous pericardium and a deep serous pericardium with parietal and visceral layers.
Fibrous pericardium
The outer, tough, fibrous layer of the pericardium that encloses the heart and the serous layers.
The anterior (sternocostal) surface of the heart is mostly formed by the right ventricle and right atrium. The diaphragmatic (inferior) surface rests on the central tendon of the diaphragm and is formed by both ventricles. The right pulmonary surface is mainly formed by the right atrium, while the left pulmonary surface is mainly formed by the left ventricle, which also creates the cardiac impression on the left lung. The pericardium is a double-walled sac that surrounds the heart, comprising a superficial fibrous layer and a deeper serous layer divided into parietal and visceral layers. The visceral layer of the serous pericardium, also called the epicardium, lines the surface of the heart.
Recognizing the external surfaces of the heart and its protective coverings helps in understanding its spatial relationships and is essential for clinical interventions.
Epicardium: The outermost layer of the heart wall, also known as the visceral pericardium, providing a protective covering.
Myocardium: The middle layer composed of cardiac muscle tissue, responsible for the heart's contractile function.
Endocardium: The innermost layer lining the heart chambers, made of endothelial tissue, forming the endothelial lining.
Intercalated discs: Specialized junctions connecting cardiac muscle fibers, containing desmosomes and gap junctions, facilitating synchronized contraction.
Fibrous skeleton of the heart: Dense connective tissue forming rings around the heart valves, fusing together, and merging with the interventricular septum, providing structural support and electrical insulation.
Functional syncytium: A network of interconnected cardiac muscle fibers behaving as a single coordinated unit, enabling synchronized contraction.
The heart wall consists of three layers: the epicardium (visceral pericardium), which covers the outer surface; the myocardium, made of cardiac muscle fibers that are striated, short, branched, and interconnected via intercalated discs; and the endocardium, which lines the interior chambers of the heart with endothelial tissue. Cardiac muscle fibers are interconnected by intercalated discs that contain desmosomes, which anchor fibers together, and gap junctions, which allow ions and action potentials to pass freely, enabling the heart to behave as a functional syncytium. The fibrous skeleton of the heart provides structural support, prevents overstretching of the valves, and insulates the atria from the ventricles electrically. The myocardial thickness varies: atria have thin walls, while the left ventricle has the thickest wall to effectively supply systemic circulation.
The microscopic structure of the heart wall, including specialized muscle fibers, connective tissue, and junctions, underpins its mechanical strength and ability to contract in a coordinated manner, which is essential for effective pumping of blood.
Atrioventricular (AV) valves are valves located between the atria and ventricles. They include the mitral valve (bicuspid valve) on the left side and the tricuspid valve on the right side. These valves prevent backflow of blood into the atria during ventricular contraction. They are anchored by chordae tendineae, which are strong fibrous cords attaching the valve cusps to papillary muscles on the inner ventricular walls, ensuring proper closure and preventing prolapse.
Semilunar valves are located at the bases of the large arteries leaving the ventricles. They include the aortic semilunar valve and the pulmonary semilunar valve. These valves prevent backflow of blood into the ventricles after blood is ejected during systole.
Heart valves are essential for ensuring unidirectional blood flow through the heart chambers. The AV valves (mitral and tricuspid) close during ventricular contraction to prevent blood from flowing back into the atria. They are held in place and prevented from prolapsing into the atria by chordae tendineae, which are connected to papillary muscles. These muscles contract with the ventricles to maintain tension on the chordae tendineae, aiding in valve closure.
The semilunar valves (aortic and pulmonary) close after blood is ejected from the ventricles, preventing any backflow into the ventricles. Their structure, with cusps that fill with blood to close the opening, ensures a tight seal.
Heart valves work together to maintain unidirectional blood flow through the heart chambers, which is vital for efficient circulation.
The closure of these valves produces characteristic heart sounds: the lub (first sound) is caused by the AV valves closing, and the dub (second sound) results from the semilunar valves closing. These sounds can be auscultated at specific anatomical landmarks.
The structure and function of heart valves are crucial for maintaining unidirectional blood flow and generating the characteristic sounds heard during a heartbeat.
Right coronary artery: A coronary artery that originates from the ascending aorta and supplies oxygenated blood to the right atrium, right ventricle, and parts of the conduction system of the heart.
Left coronary artery: A coronary artery that arises from the ascending aorta, supplying oxygenated blood primarily to the left side of the heart, including the left ventricle and left atrium.
Anterior interventricular branch (LAD): A branch of the left coronary artery located in the anterior interventricular sulcus, responsible for supplying both ventricles.
Circumflex branch: A branch of the left coronary artery that curves around the heart in the coronary sulcus, supplying parts of the left atrium and ventricle.
Coronary sinus: A large venous structure on the posterior aspect of the heart that drains deoxygenated blood from the myocardium into the right atrium.
Great cardiac vein: A vein that runs alongside the anterior interventricular branch, draining blood from the anterior surfaces of the heart into the coronary sinus.
The right and left coronary arteries branch from the ascending aorta to supply oxygenated blood to the myocardium. The anterior interventricular branch, also known as the LAD, is located in the anterior interventricular sulcus and supplies both ventricles. The coronary sinus collects deoxygenated blood from the myocardium via various veins, including the great cardiac vein, and drains into the right atrium. Myocardial ischemia occurs when there is a partial obstruction of coronary arteries, leading to reduced blood flow, hypoxia, and potential weakening of cardiac cells. Complete obstruction results in myocardial infarction, where heart tissue dies and is replaced by scar tissue, possibly disrupting conduction and causing sudden death.
Coronary circulation is essential for myocardial oxygenation; impairment of this system can lead to ischemia and infarction, with serious clinical consequences for heart function and health.
Sinoatrial (SA) node: The natural pacemaker of the heart that initiates the heartbeat and sets the pace for the heart’s rhythm.
Atrioventricular (AV) node: A specialized tissue that receives impulses from the SA node and relays them to the ventricles via the AV bundle.
Bundle of His (AV bundle): The pathway through which impulses travel from the AV node to the ventricles, splitting into pathways within the interventricular septum.
Purkinje fibers: Fibers that carry impulses from the bundle branches to the heart’s apex and ventricular walls, stimulating ventricular contraction.
Electrocardiogram (ECG): A recording of the electrical activity of the heart, showing specific waves and complexes that correspond to different phases of heart depolarization and repolarization.
Artificial pacemaker: A device implanted to restore normal heart rhythm when the natural pacemaking system is impaired, sending electrical impulses to stimulate heart contractions.
The SA node initiates the heartbeat and functions as the heart’s natural pacemaker. Impulses generated by the SA node travel to the AV node, which then passes the impulse through the bundle of His. This bundle splits into two pathways called bundle branches within the interventricular septum, guiding impulses toward the apex of the heart. From there, Purkinje fibers distribute the impulse throughout the ventricular walls, causing ventricular contraction.
Electrical activity in the heart is recorded by an ECG. The P wave indicates atrial depolarization, the QRS complex reflects ventricular depolarization, and the T wave shows ventricular repolarization. The atrial repolarization is masked by the larger QRS complex.
When the natural pacemakers become damaged or diseased, the heart’s rhythm can be maintained by the AV node, autorhythmic fibers in the AV bundle, bundle branches, or Purkinje fibers, though at a slower rate. If these are insufficient, an artificial pacemaker can be surgically implanted. It consists of a battery and impulse generator, connected via leads to the heart chambers, and can automatically adjust heart rate during activity.
The heart’s conduction system orchestrates rhythmic contractions, and technological interventions like artificial pacemakers can restore normal heart rhythm when natural pacemaking is impaired.
Tunica intima: The innermost layer of a blood vessel, composed of a simple layer of endothelial cells that line the lumen. It provides a smooth surface for blood flow and plays a role in vessel regulation.
Tunica media: The middle layer of a blood vessel, primarily made up of smooth muscle cells and elastic fibers. It is responsible for controlling vessel diameter through vasoconstriction and vasodilation.
Tunica externa (adventitia): The outermost layer of a blood vessel, consisting of connective tissue that provides structural support and anchors the vessel to surrounding tissues.
Elastic arteries: Large arteries characterized by a high content of elastic fibers in the tunica media, allowing them to accommodate pressure fluctuations during the cardiac cycle.
Muscular arteries: Medium-sized arteries with a thicker tunica media containing more smooth muscle, enabling precise regulation of blood flow through vasoconstriction and vasodilation.
Capillaries: The smallest blood vessels, composed of a single endothelial layer, facilitating exchange of gases, nutrients, and waste between blood and tissues.
Blood vessels are structured with three distinct layers: the tunica intima (endothelium), tunica media (smooth muscle), and tunica externa (connective tissue). The tunica intima's endothelium provides a smooth lining to reduce blood resistance. The tunica media varies among vessel types; elastic arteries contain more elastic fibers in this layer to handle pressure changes, while muscular arteries have a thicker tunica media with abundant smooth muscle for vasoconstriction and vasodilation. Capillaries are unique in consisting of only a single endothelial layer, which allows efficient exchange of gases and nutrients between the blood and surrounding tissues.
The histological differences in blood vessel walls—particularly in the composition of the tunica media—reflect their specialized functions in maintaining circulation and ensuring effective tissue perfusion.
| Aspect | Surface/Sectional Anatomy | Heart Wall Microscopic Anatomy | Valve Structure & Function |
|---|---|---|---|
| Main Structures | Anterior (sternocostal), Diaphragmatic (inferior), Right pulmonary, Left pulmonary surfaces | Epicardium (visceral pericardium), Myocardium, Endocardium | Atrioventricular valves (mitral, tricuspid), Semilunar valves (aortic, pulmonary) |
| Formed By | Right ventricle and atrium (anterior), Both ventricles (diaphragmatic), Right atrium (right pulmonary), Left ventricle (left pulmonary) | Cardiac muscle fibers with intercalated discs, Dense connective tissue skeleton | Valve cusps attached to chordae tendineae, anchored by papillary muscles |
| Function | External relationships and spatial orientation of the heart | Contractile tissue enabling synchronized contraction; structural support | Ensure unidirectional blood flow; prevent backflow during systole and diastole |
| Author/Key Concept | Details |
|---|---|
| Surface Anatomy | Know the borders and surface features as described in the surface anatomy section. |
| Heart Wall Layers | Know SMITH's definition of epicardium, myocardium, endocardium. |
| Intercalated Discs | Facilitate synchronized contraction via desmosomes and gap junctions. |
| Fibrous Skeleton | Provides structural support and electrical insulation. |
| Valve Mechanics | Chordae tendineae and papillary muscles prevent prolapse; semilunar valves prevent backflow. |
Teste dein Wissen zu Heart Anatomy and Function mit 7 Multiple-Choice-Fragen mit detaillierten Korrekturen.
1. How does the location of the apex beat differ from the position of the base of the heart?
2. Who is credited with discovering the sinoatrial node as the heart's natural pacemaker?
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Heart location — mediastinum?
Heart resides in the mediastinum of the thoracic cavity.
Apex beat — position?
Located in the left 5th intercostal space at the midclavicular line.
Base of the Heart — formed by?
Primarily by the left atrium.
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