Anatomy of the Pericardium

Pericardium

• The pericardium is a double-walled fibrous membrane that encloses the heart and the roots of great vessels.
• It lies posterior to the body of the sternum and the second to sixth costal cartilages.
• The fibrous pericardium is the tough, outermost layer that prevents the heart from expanding too much.
• The internal surface of the fibrous pericardium is lined with serous pericardium.
• The fibrous pericardium is fused with the tunica adventitia of great vessels, attached to the posterior surface of the sternum by sternopericardial ligaments, and fused with the central tendon of the diaphragm.

Serous Pericardium

• The serous pericardium is the inner layer of the pericardium, made up of two layers: parietal and visceral layers.
• The parietal layer is the outer layer, firmly attached to the fibrous pericardium.
• The visceral layer is the innermost layer, directly covering the heart and roots of great vessels.
• The pericardial cavity is the space between the two layers of the serous pericardium, holding the pericardial fluid.

Pericarditis and Pericardial Effusion

• Normally, the layers of serous pericardium make no detectable sound during auscultation.
• Pericarditis makes the surfaces rough, resulting in a pericardial friction rub, which sounds like the rustle of silk when listening with a stethoscope.
• Certain inflammatory diseases may produce pericardial effusion.

Heart Wall

• The wall of the heart consists of three layers: epicardium, myocardium, and endocardium.
• The epicardium is a thin external layer formed by the visceral layer of serous pericardium.
• The myocardium is a thick middle layer composed of cardiac muscle.
• The endocardium is a thin internal layer, or lining membrane of the heart, that also covers its valves.

Heart Chambers

• The heart is divided into four chambers: right atrium, left atrium, right ventricle, and left ventricle.
• The atria are separated by the atrial septum, and the ventricles are separated by the ventricular septum.
• The ventricles have thicker walls and pump blood to the lungs and body.

Right Atrium

• The right atrium forms the right border of the heart and receives venous blood from the superior vena cava, inferior vena cava, and coronary sinus.
• The ear-like right auricle is a small, conical muscular pouch that projects from the right atrium and overlaps the ascending aorta.

Left Atrium

• The left atrium forms most of the base of the heart, where the pairs of valveless right and left pulmonary veins enter.
• The interior of the left atrium has a smooth-walled part, a smaller muscular auricle containing pectinate muscles, four pulmonary veins entering its posterior wall, a slightly thicker wall than that of the right atrium, and an interatrial septum that slopes posteriorly and to the right.

Left Ventricle

• The left ventricle forms the apex of the heart, nearly all of its left (pulmonary) surface and border, and most of the diaphragmatic surface.
• Because arterial pressure is much higher in the systemic than in the pulmonary circulation, the left ventricle performs more work than the right ventricle.
• The interior of the left ventricle has a double-leaflet mitral valve, walls that are two to three times as thick as those of the right ventricle, a conical cavity, and walls covered with thick muscular ridges, trabeculae carneae.

Fibrous Skeleton of the Heart

• The fibrous heart skeleton is located between the atria and ventricles and is formed from dense irregular connective tissue.
• It separates the atria and ventricles, anchors heart valves by forming supportive rings at their attachment points, provides electrical insulation between atria and ventricles, and provides a rigid framework for the attachment of cardiac muscle tissue.

Valves of the Heart

• There are two types of valves in the heart: atrioventricular valves and semilunar valves.
• Atrioventricular valves separate the atria from the ventricles, and semilunar valves separate the ventricles from the output large vessels (aorta and pulmonary arteries).

Right Atrioventricular Valve

• The right atrioventricular valve, also called the tricuspid valve, separates the right atrium from the right ventricle and has three triangular flaps.
• Venous blood flows from the right atrium, through the valve into the right ventricle, and is forced closed when the right ventricle begins to contract, preventing blood backflow into the right atrium.

Left Atrioventricular Valve

• The left atrioventricular valve, also called the bicuspid valve or mitral valve, separates the left atrium from the left ventricle and has chordae tendineae.
• Oxygenated blood flows from the left atrium into the left ventricle, and is forced closed when the left ventricle begins to contract, preventing blood backflow into the left atrium.

Semilunar Valves

• The pulmonary valve, located at the apex of the conus arteriosus, is at the level of the left third costal cartilage.
• The aortic valve, obliquely placed, is located between the left ventricle and the root of the aorta.

Pulmonary and Systemic Circulation

• Systemic circulation: oxygenated blood from the left ventricle is pumped into the aorta and then into smaller systemic arteries; gas exchange in tissues occurs from capillaries; systemic veins then carry deoxygenated blood and waste products.
• Pulmonary circulation: deoxygenated blood from the right ventricle is pumped into the pulmonary artery and then into smaller pulmonary arteries; gas exchange in lungs occurs from capillaries; pulmonary veins then carry oxygenated blood and return it to the left atrium.