Summary
Highlights
The video introduces the interior anatomy of the heart, focusing on its four chambers: the right atrium, left atrium, right ventricle, and left ventricle. It sets the stage for a detailed discussion of each chamber's internal features.
The right atrium forms part of the sternocostal surface, right border, and upper border of the heart. It receives deoxygenated blood from the body via the superior vena cava and inferior vena cava. The upper anterior part forms the right auricle, which has a spongy interior. Externally, the sulcus terminalis extends from the superior to the inferior vena cava, corresponding to the crista terminalis internally. The sinoatrial (SA) node, the heart's pacemaker, is located in the upper part of the sulcus terminalis. The right atrium is separated from the right ventricle by the right atrioventricular groove.
Internally, the right atrium has a smooth posterior part (sinus venarum), developed from the absorbed right horn of the sinus venosus, and a rough anterior part (pectinate part or atrium proper), developed from the right half of the primitive atrium. These parts are separated by the crista terminalis. The sinus venarum features openings for the inferior vena cava, superior vena cava, and coronary sinus. A web-like network called the Thebesian network can sometimes be found between the inferior vena cava and coronary sinus openings. Small openings for the Thebesian veins are present in the posterior wall.
The rough anterior part of the right atrium is characterized by transverse muscular ridges known as musculi pectinati, which arise from the crista terminalis. The interatrial septum, separating the right and left atria, is developed from the septum primum and septum secundum. It features the fossa ovalis, a saucer-shaped depression formed from the septum primum, and its prominent margin, the limbus fossa ovalis or annulus ovalis, derived from the septum secundum. Remnants of the foramen ovale are sometimes present.
The left atrium is located posterior and left to the right atrium. It forms the left two-thirds of the base and upper border of the heart. Anteriorly and superiorly, it has a conical projection called the left auricle. It receives oxygenated blood from the lungs via four pulmonary veins. The interior of the left atrium is mostly smooth, developed from the absorbed pulmonary veins, except for the left auricle, which has a rough, musculi pectinati-lined interior developed from the primitive atrium. The interatrial septum in the left atrium shows the limbus fossa ovalis.
The right ventricle is triangular and forms the right two-thirds of the sternocostal surface, right one-third of the diaphragmatic surface, and part of the inferior border. Its interior is divided into a lower rough inflowing part and an upper smooth outflowing part. The rough inflowing part, developed from the proximal part of the bulbus cordis, contains muscular ridges called trabeculae carneae, categorized as ridges, bridges, and papillary muscles.
Papillary muscles (pillars) have one end attached to the ventricular wall and the other to the tricuspid valve cusps via thin string-like structures called chordae tendineae. The right ventricle typically has three papillary muscles: anterior (largest), posterior (smallest), and septal (numerous nipple-like projections). The anterior papillary muscle's base is connected to the interventricular septum by the septomarginal trabecula (moderator band), which prevents overdistension of the right ventricle.
The interventricular septum bulges into the right ventricle, giving its cavity a crescent shape. The right ventricular wall is thinner than the left, with a thickness ratio of 1:3. The smooth upper outflowing part, or infundibulum (conus arteriosus), is conical and leads to the pulmonary trunk. It is separated from the rough lower part by the supraventricular crest (infundibuloventricular crest), located between the pulmonary and right atrioventricular orifices.
The interventricular septum is positioned obliquely, with its lower part facing forward and right, and its upper surface facing backward and left. It separates the two ventricles, and its thin upper part separates the left ventricle from the right atrium. Its position on the heart's surface is indicated by the anterior and posterior interventricular grooves.
The left ventricle is conical and forms the left one-third of the sternocostal surface, left two-thirds of the diaphragmatic surface, the apex, and the left border. Like the right ventricle, it has a rough inflowing part with trabeculae carneae (ridges, bridges, and papillary muscles), developed from the primitive ventricle. A key difference from the right ventricle is that the left ventricle typically has only two papillary muscles (anterior and posterior), which attach to the mitral valve cusps via chordae tendineae. The smooth upper outflowing part, the aortic vestibule, leads into the aortic orifice and is guarded by the aortic valve. The aortic vestibule develops from the mid-portion of the bulbus cordis.
The video concludes by summarizing the main orifices and valves within the heart. The right atrium connects to the right ventricle via the right atrioventricular (tricuspid) orifice, guarded by the three-cusped tricuspid valve. Blood from the right ventricle enters the pulmonary trunk through the pulmonary orifice, guarded by the semilunar pulmonary valve. Oxygenated blood from the pulmonary veins enters the left atrium. The left atrium connects to the left ventricle through the left atrioventricular (mitral/bicuspid) orifice, guarded by the two-cusped mitral valve. Finally, blood from the left ventricle is pumped into the aorta through the aortic opening, protected by the three-cusped semilunar aortic valve.