The provisionality of endocrine part of cattle’s pancreas in embryogenesis

By histological, morphometrical and histochemical methods were investigated endocrine part of the pancreas of cattle in embryonic, early postnatal development and in adult animals. After fixation in 10% neutral formalin solution, Carnoy’s fluid and acetone, whole embryos or parts of their pancreas were embedded in paraffin. The sections obtained on a rotary microtome were stained with hematoxylin and eosin, chrome hematoxylin sensu Bargmann, aldehyde fuchsin sensu Gaba, sensu Dominici-Kedrovsky; glycogen was detected sensu Shabadash, acide and alkaline phosphatase - sensu Gomory methods. The area of endocrine islets and insulocytes B was measured. The results of measurement were processed statistically. The work was performed in the morpho- logical laboratory of Institute of Veterinary Medicine and Biotechnology of Omsk State Agrarian University. It was found that the first endocrinocytes were detected in pancreatic primordium of embryos of 30 days age. Morphological and tinctorial properties of these endocrinocytes are similar to pancreocytes A of definitive islets. The appearance and specific differentiation of endocrine pancreocytes A occurs before the formation of the tem of ducts and acini of pancreatic exocrine part and after the begining of its formation these cells are situated in epithelial layer of exocrine structures. These cells give rise to islets buds and, subsequently, endocrine islets. Endocrine pancreocytes B in pancreatic islets appear at the end of the second month of embryogenesis. In the development of the endocrine part of the pancreas there was a change of two generations of pancreatic islets. The islets of first generation developed between lobules of exocrine pancreas or at its edges. This place provides a better vascularisation and contact with the nerve ganglia. The greatest development of these islets occured in the last trimester of pregnancy, when done the most intensive growth of the fetus. At the end of pregnancy began involution of these islets, which culminated in the postnatal period. Islets of second generation are the precursors of definitive islets. They are formed inside the lobules and distinct from first generation islet by smaller area and features of low functional activity. During the period of embryonic development and in adult animals endocrine islets do not lose morphological relationship with small ducts and acini of exocrine pancreas. The islets of the first generation are provisional structure. Consisting mainly of endocrine pancreocytes B, they produce large amounts of insulin, ensure the supply intensively growing tissues and organs of the fetus by glucose, and after the birth, when the growth rate is reduced, these islets regress.