The functional significance of human notochord in the development of vertebral column. An electron microscopic study

Twenty-one human embryos or fetuses from four to twenty-one weeks in gestation age were submitted to light and electron microscopic observations of the notochord and its related structures. The notochord cells were found to have densely developed rER and Golgi areas, which were correlated with an activity to secrete into their surroundings specific ground substance probably containing proteoglycan. The highest differentiation of this cell as estimated by the peak secretory activity was reached at about ten weeks, while signs of degeneration emerged shortly thereafter and became increasingly apparent with the advancing gestation. The synthesis and secretion of matrices were likely to be taken over by the fibrocartilage cells surrounding the notochord by about 20 weeks when the notochord cells had undergone severe degenerative changes. Another characteristic feature of the notochord cells at their fully differentiated stage was abundance in intracytoplasmic glycogen that coexisted with striking paucity of mitochondria. This was interpreted as suggesting the metabolic dependence of these cells upon anaerobic glycolysis even at the peak of their secretory performance.