Chambers of the Heart

The human heart consists of four chambers that work in a coordinated manner to circulate blood throughout the body. These chambers include two atria (right and left) and two ventricles (right and left). The atria receive blood returning to the heart, while the ventricles pump blood out of the heart. The chambers are separated by septa and regulated by valves that ensure unidirectional flow.

Overview of the Four Chambers

• Right Atrium: Receives deoxygenated blood from the systemic circulation via the superior and inferior vena cava
• Right Ventricle: Pumps deoxygenated blood to the lungs via the pulmonary trunk
• Left Atrium: Receives oxygenated blood from the lungs via the pulmonary veins
• Left Ventricle: Pumps oxygenated blood to the systemic circulation via the aorta

Right Atrium

Location and Borders

The right atrium forms the right border of the heart and is located anteriorly in the thorax. It receives blood from the systemic circulation and directs it into the right ventricle.

External Features

• Auricle: A muscular ear-like projection that overlaps the aorta
• Sulcus terminalis: A shallow groove on the external surface separating the smooth and rough parts of the atrium

Internal Anatomy

• Sinus venarum: Smooth-walled part receiving the venae cavae
• Musculi pectinati: Rough anterior wall composed of parallel ridges
• Crista terminalis: Internal vertical ridge separating the sinus venarum from the musculi pectinati
• Fossa ovalis: A depression in the interatrial septum marking the site of the fetal foramen ovale

Openings

• Superior vena cava
• Inferior vena cava
• Coronary sinus
• Right atrioventricular orifice (to right ventricle)

Right Ventricle

Location and Walls

The right ventricle forms most of the anterior surface of the heart and a portion of the diaphragmatic surface. It is crescent-shaped in cross-section and has thinner walls than the left ventricle.

Internal Anatomy

• Trabeculae carneae: Irregular muscular ridges on the inner surface
• Moderator band (septomarginal trabecula): A muscular band carrying part of the right bundle branch
• Conus arteriosus (infundibulum): Smooth-walled outflow tract leading to the pulmonary valve
• Papillary muscles: Anchor chordae tendineae attached to the tricuspid valve

Valves and Openings

• Tricuspid valve: Guards the right atrioventricular orifice
• Pulmonary valve: Located at the outflow tract leading to the pulmonary trunk

Left Atrium

Location and Borders

The left atrium is situated posteriorly and forms most of the base of the heart. It receives oxygenated blood from the lungs through four pulmonary veins.

External Features

• Left auricle: A muscular appendage overlapping the pulmonary trunk

Internal Anatomy

• The walls are mostly smooth, with musculi pectinati limited to the auricle
• The interatrial septum is continuous with that of the right atrium, where the fossa ovalis is seen from the opposite side

Openings

• Four pulmonary veins (two from each lung)
• Left atrioventricular orifice (to the left ventricle), guarded by the mitral valve

Left Ventricle

Location and Walls

The left ventricle forms the apex of the heart and most of its left and diaphragmatic surfaces. It has the thickest walls of any chamber due to the high pressures required to pump blood into systemic circulation.

Internal Anatomy

• Trabeculae carneae: More fine and delicate than in the right ventricle
• Aortic vestibule: Smooth-walled outflow tract leading to the aortic valve
• Papillary muscles: Typically two (anterior and posterior), larger than those in the right ventricle

Valves and Openings

• Mitral valve: Guards the left atrioventricular orifice
• Aortic valve: Located at the entrance to the ascending aorta

Interatrial and Interventricular Septa

Interatrial Septum

Separates the right and left atria. It is thin and contains the fossa ovalis in the right atrium, which corresponds to the floor of the closed foramen ovale.

Interventricular Septum

This is a thick, muscular wall separating the two ventricles. It has a small membranous part near the aortic valve and a larger muscular part. It is crucial for isolating the right and left sides of the heart's pumping systems.

Topographic Summary

• Right Atrium: Receives systemic venous blood
• Right Ventricle: Pumps blood into pulmonary circulation
• Left Atrium: Receives oxygenated blood from lungs
• Left Ventricle: Pumps blood into systemic circulation
• Septal Structures: Maintain directional separation of blood flow