The human heart, a muscular organ located centrally in the chest, tirelessly pumps blood throughout the body. This intricate network of chambers and vessels ensures that oxygen and nutrients reach every cell while removing waste products. Understanding the heart’s complex anatomy, including its less prominent features, provides insight into its overall function and how certain structures can influence health.
The Auricles
The “flaps on the front of the atria” are known as auricles, a term from the Latin “auricula” meaning “little ear.” Each of the heart’s two upper chambers, the atria, possesses one of these small, ear-like pouches. While “auricle” once referred to the entire atrium, it now specifically denotes these distinct appendages, also called atrial appendages, with one on the right atrium and one on the left.
Structure and Location
These structures are on the front surface of both the right and left atria. They have a wrinkled appearance due to muscular ridges called pectinate muscles lining their inner walls. While physically connected to the main atrial chambers, auricles are somewhat separate, pouch-like extensions. The right auricle is a broad, triangular pouch that can overlap the ascending aorta, while the left auricle is more tubular and trabeculated.
Their Purpose in Circulation
Auricles primarily function as expandable reservoirs, allowing for increased atrial capacity to accommodate additional blood volume, such as during increased venous return or high atrial pressure. The left atrial appendage also acts as a decompression chamber during left ventricular contraction or when left atrial pressure rises. It can also release natriuretic peptides, proteins that help regulate blood volume and pressure by encouraging the kidneys to excrete more salt and water. In healthy adults, however, their precise function remains debated, and they are considered remnants of embryonic development.
Medical Importance
Despite their debated role in normal circulation, auricles, particularly the left atrial appendage (LAA), hold significant medical importance. Their complex, ridged internal structure, formed by the pectinate muscles, can lead to stagnant blood flow, especially in atrial fibrillation (AFib). In AFib, the irregular and rapid beating of the atria causes blood to pool within the LAA, making it a common site for blood clot formation. These clots pose a substantial risk because they can dislodge and travel through the bloodstream, potentially blocking an artery in the brain and causing an ischemic stroke. Over 90% of stroke-causing clots in individuals with non-valvular AFib originate in the LAA, with certain LAA morphologies and low blood flow velocity increasing this risk.