DEVELOPMENT OF THE VENTRICULOARTERIAL SEGMENT OF THE HUMAN EMBRYONIC HEART - A MORPHOMETRICS STUDY

In the literature, discussions continue on the question whether the di stal portion of the cardiac outlet segment (ventriculoarterial portion , outflow tract of the embryonic heart) is subject to a shortening (ab sorption, retraction) during development. In 28 human embryos ranging from 4-42 mm crown-rump length, stereological estimates of volume frac tions and surface densities were used to calculate the diameter and th e length of the distal outlet segment and their changes during develop ment. A significant increase was found in the wall thickness of this s egment, whereas its length remained about the same. An actual shorteni ng was not found. It is concluded that the relative change in proporti ons is the cause of the disagreements. It is further concluded that th ere is still a mechanical role for the aorticopulmonary septum in main taining the length of the outlet segment during growth of this region. (C) 1993 Wiley-Liss, Inc.