The Embryology of Ventricular Flow Pathways in Man

Abstract

From measurements of certain distances in the fetal human heart (using material of the Carnegie Institution of Washington in Baltimore from fetal age 3 wks. to 3 mos.) differences between fibroblastic and myo-blastic growth rates are identified. It is concluded that the shape changes of the heart during the first 6 weeks are relatable to the fact that fibroblastic portions of the primary heart tube have much shorter growth history than myoblastic portions. Indeed, when fibroblastic structures such as the A-V cushions and the truncal ridges complete invasive growth which partitions the primary heart tube in the fifth fetal week, they cease further growth, and subsequent increases in the size and shape of the heart are nearly entirely attributable to growth of myoblastic regions. These fibroplastic structures (the A-V cushions, the right bulbar ridge, and the truncal ridges) form a cytological continuum on the inner concave surface of the coiled heart tube. The implications of these findings for the morphogenesis of the normal heart and the congenitally abnormal heart are discussed.