In longitudinal section how do the walls of atria and ventricles differ?
In a longitudinal section, the walls of the atria and ventricles of the heart exhibit distinct differences in their structure:
1. Thickness: The ventricular walls are generally thicker than the atrial walls. This difference in thickness is primarily due to the greater workload and pressure demands placed on the ventricles during their contraction to pump blood out of the heart.
2. Musculature: The myocardial fibers (muscle fibers) in the ventricular walls are arranged in a more complex and interwoven manner compared to the atrial walls. This intricate arrangement allows the ventricles to generate stronger and more coordinated contractions necessary for efficient blood ejection.
3. Papillary Muscles and Trabeculae Carneae: The ventricular walls, particularly in the right ventricle, contain prominent muscular ridges called trabeculae carneae and projections called papillary muscles. These structures aid in preventing the inward bulging (ballooning) of the ventricular walls during ventricular contraction.
4. Endocardial Cushions and Valves: The atrioventricular junctions, where the atria connect to the ventricles, are equipped with specialized structures known as endocardial cushions. During embryonic development, these cushions contribute to the formation of heart valves (mitral/bicuspid and tricuspid valves) that control the flow of blood between the atria and ventricles.
5. Purkinje Fibers: The ventricular walls contain specialized cardiac muscle cells called Purkinje fibers. These fibers are responsible for conducting electrical impulses rapidly and precisely throughout the ventricles, ensuring coordinated and efficient ventricular contraction.
Overall, the structural differences between the atrial and ventricular walls reflect their respective functions in the cardiac cycle. The thicker ventricular walls and complex myocardial arrangement facilitate the powerful contractions necessary for pumping blood into the circulation.