Atrium 1 and 2

Overview of the Atria

  • Definition: Atria are the upper chambers of the heart that receive blood.

  • Structure:

    • Composed of three layers: epicardium, myocardium, and endocardium.

    • Notably thin compared to ventricles.

Functions of the Atria

  • Receiving Chambers:

    • Both right and left atria serve to receive blood returning to the heart.

    • Right atrium receives deoxygenated blood from the body; left atrium receives oxygenated blood from the lungs.

Right Atrium

  • Receiving Veins:

    • Major Veins Draining into Right Atrium:

      • Superior Vena Cava: Carries blood from the upper body.

      • Inferior Vena Cava: Carries blood from the lower body.

      • Coronary Sinus: Drains blood from the heart muscle itself.

  • Anatomy and Location:

    • Located at the upper right portion of the heart.

    • The posterior wall is formed mostly by the opening of these large veins.

  • Coronary Sinus Location:

    • Situated within the coronary sulcus (atrioventricular sulcus).

  • Size:

    • Relatively small chamber, necessitating extensions for capacity known as auricles.

  • Auricle of the Right Atrium:

    • An extension that increases the volume capacity of the right atrium.

Left Atrium

  • Receiving Veins:

    • Major Veins Draining into Left Atrium:

      • Pulmonary Veins (4 total): Bring oxygenated blood from the lungs.

  • Anatomy and Location:

    • Located at the upper left portion of the heart.

    • The auricle extends from the left atrium just as in the right atrium.

  • Auricle of the Left Atrium:

    • An extension similar in function to that of the right atrium.

Blood Characteristics

  • Deoxygenated Blood:

    • Blood that enters the right atrium is low in oxygen and high in carbon dioxide.

    • Importance in the circulatory process as it prepares for oxygenation in the lungs.

Wall Structure of the Atria

  • Right Atrial Wall:

    • Comprised of two areas:

      • Posterior Portion: Contains pectinate muscles with ridged structures.

      • Anterior Portion: Features a smooth wall.

Visual Identification**

  • Heart Model:

    • Identifying features include:

      • Right atrium receiving blood through the superior vena cava, inferior vena cava, and coronary sinus.

      • Left atrium receiving blood via the pulmonary veins.

      • Distinguishing auricles on both atria which extend outward.