M01.05.013 The Chambers of the Heart

The heart consists of four chambers – two atria and two ventricles – that work together to circulate blood through the body. Understanding the anatomy of these chambers, their internal structures, and their clinical relevance is essential for medical students.

Structure and Function of the Heart Chambers

1. Right Atrium

• Function: Receives deoxygenated blood from the superior and inferior vena cavae, and coronary veins, pumping it into the right ventricle through the tricuspid valve.
• Location: Forms the right border of the heart.
• Internal Structure:
  • Sinus Venarum: Receives blood from the vena cavae and has smooth walls, derived from the sinus venosus.
  • Atrium Proper: Contains the right auricle, has rough muscular walls formed by pectinate muscles.

2. Interatrial Septum

• Function: Separates the right and left atria.
• Notable Feature: Contains the fossa ovalis, a remnant of the foramen ovale, which allows right-to-left blood shunting in fetal circulation.

3. Left Atrium

• Function: Receives oxygenated blood from the four pulmonary veins and pumps it into the left ventricle through the mitral valve.
• Location: Forms the posterior border (base) of the heart.
• Internal Structure:
  • Inflow Portion: Receives blood from the pulmonary veins, smooth internal surface.
  • Outflow Portion: Includes the left auricle, lined by pectinate muscles.

4. Right Ventricle

• Function: Pumps deoxygenated blood through the pulmonary valve into the pulmonary artery for pulmonary circulation.
• Location: Forms the majority of the anterior border of the heart.
• Internal Structure:
  • Inflow Portion: Lined with trabeculae carnae (muscular ridges).
  • Outflow Portion: Known as conus arteriosus, leading to the pulmonary artery, with smooth walls.

5. Left Ventricle

• Function: Pumps oxygenated blood through the aortic valve into the aorta for systemic circulation.
• Location: Forms the apex and left and diaphragmatic borders of the heart.
• Internal Structure:
  • Inflow Portion: Lined with trabeculae carnae, two papillary muscles attached to the mitral valve.
  • Outflow Portion: Known as aortic vestibule, smooth-walled, derived from the bulbus cordis.

Clinical Relevance

Atrial Septal Defect (ASD)

• Definition: An abnormal opening in the interatrial septum, often persisting from a patent foramen ovale.
• Complications: Can lead to right ventricular overload, pulmonary hypertension, right heart failure.
• Treatment: Surgical or transcatheter closure.

Tetralogy of Fallot

• Definition: A congenital heart defect comprising four abnormalities:
  1. Ventricular septal defect (VSD)
  2. Overriding aorta
  3. Pulmonary valve stenosis
  4. Right ventricular hypertrophy
• Mechanism: Pulmonary stenosis increases right ventricular pressure, causing right-to-left shunting of blood through the VSD.
• Treatment: Surgical correction, usually in the first few months of life.

Key Points to Remember

• The heart consists of four chambers: two atria and two ventricles, with distinct functions in pumping blood to the lungs and systemic circulation.
• Right Atrium: Receives deoxygenated blood from the body.
• Left Atrium: Receives oxygenated blood from the lungs.
• Right Ventricle: Pumps deoxygenated blood to the lungs.
• Left Ventricle: Pumps oxygenated blood to the body.
• Septal Defects: Atrial and ventricular septal defects can cause significant circulatory problems and require surgical intervention.
• Understanding the anatomical and functional characteristics of these chambers is crucial for diagnosing and treating cardiovascular conditions.