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Anatomy of the Heart: Difference between revisions
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[[Image:Figure 3.jpg|300px|right | [[Image:Figure 3.jpg|thumb|300px|right|Figure 3.<br> | ||
'''A.''' Viewed from the front, the right atrium and right ventricle overlaps the left atrium and left ventricle. The atrial chambers are to the right of their respective ventricular chambers. | |||
<br>'''B.''' The four cardiac valves are at different levels and different planes with the pulmonary(P) valve situated the most cephalad. The aortic(A) valve is wedged between the tricuspid(T) and mitral(M) valves.]] | |||
<br>'''B.''' The four cardiac valves are at different levels and different planes with the pulmonary(P) valve situated the most cephalad. The aortic(A) valve is wedged between the tricuspid(T) and mitral(M) valves. | |||
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The cardiac silhouette is generally taken to be trapezoidal in shape. The rib cage provides good markers for charting the cardiac silhouette. The normal position of the cardiac apex is generally taken to be in the fifth intercostal space in the mid-clavicular line. The lower border is a nearly horizontal line in the area of the left sixth rib to the right sixth costal cartilage (Figure 2). The upper border is hidden behind the sternum at the level of the second and third cartilages. The right margin of the heart peeps out behind the right border of the sternum between the right third and sixth cartilages. In the infant, the upper part of the cardiac shadow is broad owing to the prominence of the overlying thymus gland. | The cardiac silhouette is generally taken to be trapezoidal in shape. The rib cage provides good markers for charting the cardiac silhouette. The normal position of the cardiac apex is generally taken to be in the fifth intercostal space in the mid-clavicular line. The lower border is a nearly horizontal line in the area of the left sixth rib to the right sixth costal cartilage (Figure 2). The upper border is hidden behind the sternum at the level of the second and third cartilages. The right margin of the heart peeps out behind the right border of the sternum between the right third and sixth cartilages. In the infant, the upper part of the cardiac shadow is broad owing to the prominence of the overlying thymus gland. | ||
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When the pericardium is removed, the major part of the heart visible from the front is the ventricular mass. Here, the morphologically right ventricle occupies the greater part (Figure 3). The left ventricle appears only as a narrow slip along the left cardiac border. The shape of the heart is generally likened to a pyramid. The apex points downwards, forwards and to the left while the base faces posteriorly and to the right. While the cardiac apex is usually represented by the vortex of the left ventricle, the cardiac base is less well defined owing to differences in definition. | When the pericardium is removed, the major part of the heart visible from the front is the ventricular mass. Here, the morphologically right ventricle occupies the greater part (Figure 3). The left ventricle appears only as a narrow slip along the left cardiac border. The shape of the heart is generally likened to a pyramid. The apex points downwards, forwards and to the left while the base faces posteriorly and to the right. While the cardiac apex is usually represented by the vortex of the left ventricle, the cardiac base is less well defined owing to differences in definition. | ||
[[Image:Figure 4.jpg|300px| | [[Image:Figure 4.jpg|thumb|300px|center|'''A.''' This frontal view shows the right and left surfaces of the heart. The left anterior descending coronary artery buried in epicardial fat marks the plane of the ventricular septum. | ||
<br>'''B.''' The obtuse and acute margins of the ventricles are demonstrated in this apical view.]] | |||
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<br>'''B.''' The obtuse and acute margins of the ventricles are demonstrated in this apical view. | |||
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The anatomical base is formed mainly by the left atrium receiving the pulmonary veins and to a small extent by the posterior part of the right atrium. The base in clinical practice, however, refers to the portion of the heart near the parasternal parts of the second intercostal spaces. The cardiac long axis, therefore, lies in a line drawn from the left hypochondrium towards the right shoulder. This orientation deviates considerably from the long axis of the body. Furthermore, the position of the cardiac septum at about 45º to the median brings the ‘right heart’ structures anterior to the ‘left heart’ structures (Figure 3A). The ventricles are situated inferior and leftward relative to their corresponding atria. | The anatomical base is formed mainly by the left atrium receiving the pulmonary veins and to a small extent by the posterior part of the right atrium. The base in clinical practice, however, refers to the portion of the heart near the parasternal parts of the second intercostal spaces. The cardiac long axis, therefore, lies in a line drawn from the left hypochondrium towards the right shoulder. This orientation deviates considerably from the long axis of the body. Furthermore, the position of the cardiac septum at about 45º to the median brings the ‘right heart’ structures anterior to the ‘left heart’ structures (Figure 3A). The ventricles are situated inferior and leftward relative to their corresponding atria. | ||
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==The morphologically left atrium== | ==The morphologically left atrium== | ||
[[Image:Figure 6.jpg|300px| | [[Image:Figure 6.jpg|thumb|300px|center|'''A.''' This view from the left-lateral aspect shows the finger-like left atrial appendage with the left atrium situated posteriorly. The left ventricle tapers to a rounded apex. | ||
<br>'''B.''' This section through the aortic root and mitral valve displays the left atrial aspect of the septum enface. The crescentic edge (arrow) of the fossa valve has not sealed completely resulting in a PFO. The asterisk marks the location of the transverse pericardial sinus.]] | |||
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<br>'''B.''' This section through the aortic root and mitral valve displays the left atrial aspect of the septum enface. The crescentic edge (arrow) of the fossa valve has not sealed completely resulting in a PFO. The asterisk marks the location of the transverse pericardial sinus. | |||
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The left atrium also has a venous component, a characteristic appendage, a septal component and a vestibule that leads to the mitral orifice. Other than the appendage, the main chamber of the left atrium is relatively smooth-walled. The appendage is hook-shaped with a crenelated external appearance and a narrow junction with the venous component (Figure 6). The junction is not marked by any structure comparable to the terminal crest although in many hearts there is a prominent infolding of the atrial wall between the orifice of the atrial appendage and the orifices of the left pulmonary veins. The venous portion is anchored by the pulmonary veins which drain directly into its superior and posterior parts. There are usually four pulmonary venous orifices but variations are not uncommon. The coronary sinus runs inferiorly behind the posterior wall to open into the right atrium. The flap valve of the oval fossa on the septal aspect has a small crescent marking the free edge of the valve at the fossa opening (the site of the PFO) whereas the rest of the valve blends into the atrial wall (Figure 6). | The left atrium also has a venous component, a characteristic appendage, a septal component and a vestibule that leads to the mitral orifice. Other than the appendage, the main chamber of the left atrium is relatively smooth-walled. The appendage is hook-shaped with a crenelated external appearance and a narrow junction with the venous component (Figure 6). The junction is not marked by any structure comparable to the terminal crest although in many hearts there is a prominent infolding of the atrial wall between the orifice of the atrial appendage and the orifices of the left pulmonary veins. The venous portion is anchored by the pulmonary veins which drain directly into its superior and posterior parts. There are usually four pulmonary venous orifices but variations are not uncommon. The coronary sinus runs inferiorly behind the posterior wall to open into the right atrium. The flap valve of the oval fossa on the septal aspect has a small crescent marking the free edge of the valve at the fossa opening (the site of the PFO) whereas the rest of the valve blends into the atrial wall (Figure 6). | ||