Tubular heart

The tubular heart or primitive heart tube is the earliest stage of heart development. The heart is the first organ to develop during human embryonic development.

From the inflow to the outflow, the tubular heart consists of sinus venosus, primitive atrium, the primitive ventricle, the bulbus cordis, and truncus arteriosus. The sinus venosus will become part of the right atrium and contain the primary cardiac pacemaker. The primitive atrium and primitive ventricle will develop into the upper and lower chambers of the heart. The bulbus cordis will form part of the right ventricle, while the truncus arteriosis split into pulmonary and aortic vessels that carry blood away from the heart. Blood flow is driven by contractions and is different compared to that of an adult heart.

The tubular heart forms primarily from splanchnic mesoderm, an embryonic tissue that develops into several key structures in the body. It consists of three layers essential for proper heart function, corresponding to those in the adult human heart: the endothelial lining, the muscular bulk, and the external surface. The endothelial lining acts as a barrier between the blood and surrounding tissues, the muscular bulk contains cardiac muscle that contracts to pump blood, and the external surface provides a protective covering for the heart.