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The Human Heart Development

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The Human Heart Development

The Human heart is the first organ to develop in a human's body, in fact, it is the first organ to develop in any vertebrate's body. There are five main stages of heart development in the human body. First there is specification of cardiac precursor cells. In this phase, the lateral plate mesoderm breaks apart to form two layers: the parietal mesoderm and the visceral mesoderm. The heart precursor cells come from the two regions of the mesoderm called the cardiogenic mesoderm. These cells can differentiate into endocardium which lines the heart chamber and valves and the myocardium which forms the muscles of the ventricles and the atria.

The heart cells are specified in the mesoderm by proteins such as Dickkopf-1, Nodal, and Cerberus secreted by the anterior endoderm. Whether Dickkopf-1 and Nodal act directly on the cardiac mesoderm is debated. Regardless, it is neccesary that the anterior endoderm is removed, or the heart will be hindered in its formation. Anterior endoderm is also sufficient to stimulate heart differientation since it can cause non-cardiogenic mesoderm from more posterior positions in the embryo to form the heart.

The secretion of proteins such as Cerberus, Dickkopf and Crescent by the anterior endoderm also prevents other materials secreted by the neural tube from hindering heart formation. The notochord secretes Chordin and Noggin to prevent formation of cardiac mesoderm in the wrong places.

Next there is migration of cardiac precursor cells and fusion of the primordia. The cardiac precursor cells migrate anteriorly towards the midline and fuse into a single heart tube. If this migration event is blocked, cardia bifida results where the two heart primordia remain separated. During fusion, the heart tube is patterned along the anterior/posterior axis for the various regions and chambers of the heart.

Next, the heart structure undergoes a phase called heart looping. Heart looping is where the heart undergoes a change where the structure curls to the right, to change the polarity to right/left polarity. How the heart does this is unknown to scientists right now.

After the heart looping, the heart chambers form, and then the septum, which is a wall between the two chambers, and the valves form.



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