Phagocytosis: Mechanism of uptaking the nutrition of the embryonic cells.
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Date
2012-01
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Abstract
Objective : To demonstrate the mechanisms of the embryonic cells, the epiblast, the mesoblast and the hypoblast of the chick embryo uptaking their nutrition by transmission electron microscopic (TEM) point of view.
Materials and Methods : The chick embryos of about 18-27 hours incubation were used, the primitive streak and the 7 somites stages of the embryo were processed for routinely transmission electron microscopic study at the region of primitive streak, where the mesoblast originates from the epiblast. These stages correspond to the 15 days and 20 days of the human embryos, respectively.
Results : The ultrastructural features of the epiblast, mesoblast and the hypoblast were observed. The epiblast cells arrange themselves as stratified columnar epithelium. The apical cells are columnar while the deeper cells are bottle-shaped and the deepest cells are round and separated to become the mesoblast. The superficial surfaces of the apical cells show many pseudopodia some of which curve to join with the adjacent. The clear materials are completely surrounded when the encompassing plasma membranes fuse and the membrane surround the engulfed material forms a vacuole, known as the phagosome, which detaches from the plasma membrane to float freely within the cytoplasm. The phagosome is then in some way recognized by one or more lysosomes which fuse with the phagosome to form the secondary lysosome. When the digestion is completed, the lysosomal membrane ruptures, discharging its contents into the cytoplasm. Undigested material remains within the membrane-bound vesicles called residual bodies, the contents of which later discharge at the cell surface by exocytosis. These processes also occur at the external surfaces of the hypoblast cells which arrange themselves as the simple squamous epithelium. The ventral plasma membrane shows many pseudopodia and also the series of phagocytotic process. The numerous clear vacuoles distribute in the cytoplasm of the epiblast and the hypoblast. These vacuoles are the nutritional uptake of the cell from the outside environment, the epiblast gets its nutrition from the albumin while the hypoblast from the egg yolk.
Concluison: TEM evident shows clearly that numerous clear and unclear vacuoles distribute throughout the cytoplasm of the epiblast and hypoblast. These vacuoles are the phagosomes of several stages of phagocytosis, and serve as the nutritions for the cells, as the cells are still young and also have no definitive organelles to produce their own materials. This findings also give another excellent model of explaining the series of the phagocytotic process.
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Keywords
Phagocytosis, Epiblast, Hypoblast, TEM
Citation
Roongruangchai Jantima, Roongruangchai Kosol, Kolaka Ratirat. Phagocytosis: Mechanism of uptaking the nutrition of the embryonic cells. Siriraj Medical Journal, 2012 Jan; 64(suppl): 65-67.