Development of the Heart | The Heart Tube | Part 1/3 | Cardiac Looping | Cardiovascular Embryology
Summary
Highlights
The heart develops from the splanchnic layer of the lateral plate mesoderm. Cells in this layer differentiate into blood Islands, forming vessels through a process called vasculogenesis, which leads to the creation of paired heart tubes.
Embryonic folding, both lateral and cephalocaudal, causes the two paired heart tubes to fuse into a single heart tube. Cephalocaudal folding moves the heart from the cranial region into the thoracic region and into the pericardial cavity.
The heart tube consists of an endocardial lining, a myocardial layer formed from cardiac myoblasts, and an outer epicardial layer formed by migrating mesothelial cells. A cardiac jelly separates the endocardial and myocardial layers.
To understand heart development, it's essential to know the structures of the adult heart, including the four chambers (atria and ventricles), atrioventricular and semilunar valves, and their unique features like smooth posterior walls of atria, trabeculae carneae in ventricles, and smooth outflow tracts.
The heart tube has distinct segments: the truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and sinus venosus. Each segment is destined to form specific parts of the mature heart.
The truncus arteriosus forms the ascending aorta and pulmonary trunk. The bulbus cordis contributes to the smooth outflow tracts of the ventricles (infundibulum and aortic vestibule) and part of the right ventricle. The primitive ventricle forms the trabeculated part of the left ventricle, and the primitive atrium forms the rough parts of both atria.
Cardiac looping is a crucial process where the heart tube bends and reorients. The ventricular parts bend ventrally and shift downwards, while the atrial and sinus venosus parts shift dorsally and upwards, positioning them behind the ventricles. This complex rearrangement transforms the simple heart tube into a more heart-like structure, preparing it for the development of individual chambers.