A quantitative evaluation of the development and anatomy of the ovine spleen and the hematology and histopathology of the ovine spleen exposed to hypoxia

The spleen is an important hematological and immunological organ; however, results of studies are not available on the spleen of the sheep. Therefore, this experiment was designed to study the normal development and structure of the sheep spleen and the effect of hypobaric hypoxia on splenic volume and cellular structure, and blood elements. The normal development and microanatomy of the spleen of the sheep were studied in 8-age-groups: prenatal; 1- day; 1-, 3-, and 6-weeks; 4- and 5-months; and 2-years of age. Morphometrical data were gathered and tested by statistical analysis of variance. The effects of exposure to hypoxia for 15 days on the spleen and peripheral blood were evaluated in 4-month-old sheep. The morphology of the spleen and the changes in the peripheral blood after exposure to hypoxia were studied and compared with the spleen of sheep kept at normal atmospheric pressure. The developmental findings in the 8-age-groups were: 1) splenic-weight per body-weight ratio increased from prenatal to 3-weeks of age, then declined; 2) germinal centers were observed after 3-weeks of age; 3) white pulp increased with age and reached its maximum development by 4-months of age; 4) capsule and trabeculae increased in thickness with age; and 5) no megakaryocytes were observed in any age groups. Histological findings in the spleen of hypoxic sheep were: 1) a significant increase in red pulp volume; 2) multiple nuclei in reticular cells; and 3) an increased thickness of the capsule of the spleen. The hematopoietic results after exposure to hypoxia were: 1) a decrease in platelet sizes; 2) an increase in red blood cell numbers and packed cell volumes; and 3) an initial increase followed by a decrease in platelet numbers. The effects of hypoxia on body growth and splenic weight were. 1) decreased body weight and 2) splenic weight. The increase in white pulp compartments reflects an increase in the immunity of the animal until the fourth month of life. Hypoxia studies lead to the conclusion that stem cell competition between the megakaryocytic and erythroid cell lines is responsible for the decrease in platelet numbers.