Chapter 19: Cardiac Anatomy and Physiology

Heart Wall Structure

The heart is a muscular organ with distinct structural differences between its chambers. The left ventricular wall is notably thicker than the right ventricular wall.

• Left Ventricular Wall Thickness: The left ventricle pumps blood to the entire body through the systemic circuit, requiring greater force and pressure. Therefore, its wall is thicker to generate this higher pressure.

• Right Ventricular Wall: The right ventricle pumps blood only to the lungs via the pulmonary circuit, which is a shorter, lower-pressure pathway, so its wall is thinner.

• Example: The left ventricle must overcome systemic vascular resistance, while the right ventricle only overcomes pulmonary resistance.

Blood Flow Through the Heart

Understanding the flow of blood through the heart is essential for distinguishing between oxygenated and deoxygenated blood and the vessels involved.

• Pulmonary Arteries: Carry deoxygenated blood from the right ventricle to the lungs.

• Pulmonary Veins: Carry oxygenated blood from the lungs to the left atrium.

• Ventricular Circuit: When leaving the ventricle, blood enters either the pulmonary arteries (right ventricle) or the aorta (left ventricle).

• Oxygenation Status: Blood is deoxygenated in the right side of the heart and pulmonary arteries; it becomes oxygenated in the lungs and returns via pulmonary veins to the left side of the heart.

• Example: Blood entering the right atrium from the body is deoxygenated; after passing through the lungs, it returns to the left atrium oxygenated.

Location of the Heart: The Mediastinum

The heart is located in a central thoracic region known as the mediastinum.

• Mediastinum: The space in the thoracic cavity between the lungs, containing the heart, great vessels, trachea, and esophagus.

• Example: The heart sits in the middle mediastinum, surrounded by the pericardial cavity.

Foramen Ovale

The foramen ovale is an important fetal cardiac structure.

• Definition: An opening in the interatrial septum of the fetal heart that allows blood to bypass the non-functioning fetal lungs by flowing directly from the right atrium to the left atrium.

• Postnatal Change: After birth, the foramen ovale closes and becomes the fossa ovalis.

• Example: Failure of the foramen ovale to close can result in an atrial septal defect.

Pericardium and Pericardial Cavity

The heart is enclosed by a double-walled sac called the pericardium, which contains the pericardial cavity.

• Pericardium: Consists of two layers: the fibrous pericardium (outer) and the serous pericardium (inner).

• Pericardial Cavity: The space between the parietal layer (outer serous pericardium) and the visceral layer (epicardium) of the serous pericardium, filled with pericardial fluid to reduce friction.

• Pleura: The pleura are membranes surrounding the lungs, distinct from the pericardium.

• Example: Pericarditis is inflammation of the pericardium, which can affect the pericardial cavity.

Coronary Circulation: Blood Supply to the Myocardium

The myocardium (heart muscle) receives its blood supply from specialized vessels known as the coronary arteries.

• Coronary Arteries: Branches from the ascending aorta that supply oxygenated blood to the heart muscle.

• Coronary Veins: Collect deoxygenated blood from the myocardium and drain into the coronary sinus, which empties into the right atrium.

• Example: Blockage of a coronary artery can lead to myocardial infarction (heart attack).

Summary Table: Oxygenation Status of Blood in Heart Chambers and Major Vessels

This table summarizes where blood is oxygenated and deoxygenated in the heart and major vessels.

Additional info: Some terms were clarified and expanded for academic completeness, such as the structure and function of the pericardium, the foramen ovale, and the coronary circulation.