Morfogénesis Cardíaca

Heart Morphogenesis

The development of the embryonic heart is a complex process, involving several stages from initial formation to the mature four-chambered structure found in adult mammals. Here, we will explore this journey through the lens of heart morphogenesis.

Early Stages: Heart Tube Formation

In the early stages of embryonic development, around five weeks into pregnancy, the heart begins to form from two layers of cells called mesoderm and endoderm. Mesoderm gives rise to three primary germ layers: somites (which contribute to skeletal muscles), splanchnic mesoderm (contributing to the gastrointestinal tract among other tissues), and lateral plate mesoderm – which becomes the source of the circulatory system, including the heart.

The heart tube forms when these layers fuse together in the midline, with the outer layer forming the epicardium and inner layer contributing to the primitive myocardium. This fusion occurs first at the ventral aspect and then extends dorsally, forming the heart tube along its entire length.

Cardiogenic Fields

Cardiac precursors arise within specialized regions called cardiogenic fields that give rise to specific parts of the heart. In mice, there are distinct anterior and posterior regions contributing to different chambers of the heart; while in humans, there are two cardiac crescent regions. These fields are marked by the presence of crucial proteins such as Nkx2.5 and Tbx5, which regulate the specification of commitment to the cardiac lineage.

Looping and Maturation of Chambers

As the heart tube grows, it undergoes looping, which causes the chambers to assume their characteristic shape. Initially, the tube loops in the craniocaudal direction, generating leftward bends and creating a 'Y' shape, with the upper chamber being the right atrium and the lower chamber becoming the left ventricle. At the same time, the outflow tracts develop from the tips of the 'Y', with the aorta budding off from the left side and the pulmonary artery from the right.

During this period, endocardial cushions appear near the junction between the atria and ventricles, eventually developing into cardiac valves. Additionally, the interatrial septum forms, dividing the right and left atria, and the bulbus cordis divides to become the interventricular septum, separating the left and right ventricles.

Concurrently, the myocardium thickens and gains contractile properties, while the coronary vasculature begins to develop. Finally, the pericardial sac envelopes the fully formed heart.

Conclusion

Heart morphogenesis is a complex process involving multiple steps and interactions between various cell types and signaling molecules. Understanding this process is crucial for studying congenital heart defects and potentially improving heart disease treatment strategies.