Heart General characteristics
The apex of the heart is the blunt rounded extremity of the heart formed by the left ventricle and lies in the left fifth intercostal space slightly medial to the midclavicular (or nipple) line, about 9 cm from the midline. This location is useful clinically for determining the left border of the heart and for auscultating the mitral valve.
- Its posterior aspect, called the base, is formed primarily by the left atrium and only partly by the posterior right atrium.
- Its right (acute) border is formed by the SVC, right atrium, and IVC, and its left (obtuse) border is formed by the left ventricle. (In radiology, the left border consists of the aortic arch, pulmonary trunk, left auricle, and left ventricle.)
- The heart wall consists of three layers: inner endocardium, middle myocardium and outer epicardium.
- The sulcus terminalis, a groove on the external surface of the right atrium, marks the junction of the primitive sinus venosus with the atrium in the embryo and corresponds to a ridge on the internal heart surface, the crista terminalis.
- The coronary sulcus, a groove on the external surface of the heart, marks the division between the atria and the ventricles. The crux is the point at which the interventricular and interatrial sulci cross the coronary sulcus.
- The cardiovascular silhouette , or cardiac shadow, is the contour of the heart and great vessels seen on chest radiographs. Its right border is formed by the SVC, the right atrium, and the IVC. Its left border is formed by the aortic arch (which produces the aortic knob ), the pulmonary trunk, the left auricle, and the left ventricle. Its inferior border is formed by the right ventricle, and the left atrium shows no border.
Internal anatomy of the heartRight atrium
- Has an anteriorly situated rough-walled atrium proper and the auricle lined with pectinate muscles and a posteriorly situated smooth-walled sinus venarum , into which the two venae cavae open.
- Is larger than the left atrium but has a thinner wall, and its sinus venarum between two venae cavae is separated from the atrium proper by the crista terminalis.
- Has a right atrial pressure that is normally slightly lower than left atrial pressure.
- Contains the valve (eustachian) of the IVC and the valve (thebesian) of the coronary sinus.
- Right auricle
- Is the conical muscular pouch of the upper anterior portion of the right atrium, which covers the first part of the right coronary artery.
- Sinus venarum (sinus venarum cavarum)
- Is a posteriorly situated, smooth-walled area that is separated from the more muscular atrium proper by the crista terminalis.
- Develops from the embryonic sinus venosus and receives the SVC, IVC, coronary sinus, andanterior cardiac veins.
- Pectinate muscles
- Are prominent ridges of atrial myocardium located in the interior of both auricles and the right atrium.
- Crista terminalis
- Is a vertical muscular ridge running anteriorly along the right atrial wall from the opening of the SVC to the opening of the IVC, providing the origin of the pectinate muscles.
- Represents the junction between the primitive sinus venarum (a smooth-walled region) and the right atrium proper and is indicated externally by the sulcus terminalis .
- Venae cordis minimae
- Are the smallest cardiac veins, which begin in the substance of the heart (endocardium and innermost layer of the myocardium) and end chiefly in the atria at the foramina venarum minimarum cordis.
- Fossa ovalis
- Is an oval-shaped depression in the interatrial septum and represents the site of the foramen ovale , through which blood runs from the right atrium to the left atrium before birth. The upper rounded margin of the fossa is called the limbus fossa ovale
- Is smaller and has thicker walls than the right atrium, but its walls are smooth, except for a few pectinate muscles in the auricle.
- Is the most posterior of the four chambers lying posterior to the right atrium but anterior to the esophagus and shows no structural borders on a posteroanterior radiograph.
- Receives oxygenated blood through four pulmonary veins.
- Makes up the major portion of the anterior (sternocostal) surface of the heart.
Contains the following structures:
- Trabeculae carneae cordis
- Are anastomosing muscular ridges of myocardium in the ventricles.
- Papillary muscles
- Are cone-shaped muscles enveloped by endocardium.
- Extend from the anterior and posterior ventricular walls and the septum, and their apices are attached to the chordae tendineae.
- Contract to tighten the chordae tendineae, preventing the cusps of the tricuspid valve from being everted into the atrium by the pressure developed by the pumping action of the heart. This prevents regurgitation of ventricular blood into the right atrium.
- Chordae tendineae
- Extend from one papillary muscle to more than one cusp of the tricuspid valve.
- Prevent eversion of the valve cusps into the atrium during ventricular contractions.
- Conus arteriosus (infundibulum)
- Is the upper smooth-walled portion of the right ventricle, which leads to the pulmonary trunk
- Septomarginal trabecula (moderator band)
- Is an isolated band of trabeculae carneae that forms a bridge between the intraventricular (IV)
septum and the base of the anterior papillary muscle of the anterior wall of the right ventricle.
- Is called the moderator band for its ability to prevent overdistention of the ventricle and carries
the right limb (Purkinje fibers) of the atrioventricular (AV) bundle from the septum to the
sternocostal wall of the ventricle.
- Is the place of origin of the septal papillary muscle.
- Is mostly muscular but has a small membranous upper part, which is a common site of ventricular septal defects
- Lies at the back of the heart, and its apex is directed downward, forward, and to the left.
- Is divided into the left ventricle proper and the aortic vestibule , which is the upper anterior part of the left ventricle and leads into the aorta.
- Contains two papillary muscles (anterior and posterior) with their chordae tendineae and a meshwork of muscular ridges, the trabeculae carneae cordis.
- Performs harder work , has a thicker (two to three times as thick) wall, and is longer, narrower, and more conical-shaped than the right ventricle.
Heart valvesPulmonary valve
- Lies behind the medial end of the left third costal cartilage and adjoining part of the sternum.
- Is most audible over the left second intercostal space just lateral to the sternum.
- Is opened by the ventricular systole and shut slightly after closure of the aortic valve.
Tricuspid (right AV) valve
- Lies behind the left half of the sternum opposite the third intercostal space.
- Is closed during the ventricular diastole; its closure at the beginning of ventricular diastole causes the second heart sound .
- Is most audible over the right second intercostal space just lateral to the sternum.
Bicuspid (left AV) valve
- Lies between the right atrium and ventricle, behind the right half of the sternum opposite the fourth intercostal space, and is covered by endocardium.
- Is most audible over the right lower part of the body of the sternum.
- Has anterior, posterior, and septal cusps, which are attached by the chordae tendineae to three papillary muscles that keep the valve closed against the pressure developed by the pumping action of the heart.
- Is closed during the ventricular systole (contraction). Its closure contributes to the first heart sound.
- Is called the mitral valve because it is shaped like a bishop's miter.
- Lies between the left atrium and ventricle, behind the left half of the sternum at the fourth costal cartilage, and has two cusps: a larger anterior and a smaller posterior.
- Is closed slightly before the tricuspid valve by the ventricular contraction (systole); its closure at the onset of ventricular systole causes the first heart sound.
- Is most audible over the apical region of the heart in the left fifth intercostal space at the midclavicular line.
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