Vol. 10, Issue 5, Part B (2025)

Author(s): J Bhagyalakshmi, K Balasundaram, VG Charitha and P Guru Vishnu

Abstract: The development of the spleen primordium in the sheep embryo was first observed at 37 days of gestation, appearing as an elongated cluster of mesenchymal cells located beneath the dorsal mesogastrium and adjacent to the developing rumen. By 56 to 60 days of gestation, a distinct splenic capsule had formed, completely enclosing the splenic parenchyma; however, trabecular structures were not yet evident. At 84 days of gestation, the capsule was well-developed, and trabeculae arising from the capsule began extending into the parenchyma. By 103 days of gestation, both the capsule and trabeculae exhibited advanced development, characterized by an increased deposition of collagen, elastic, and reticular fibers. At 126 days of gestation, further thickening of the capsule was noted, accompanied by a marked increase in the stromal components within the trabeculae. The outermost layer of the capsule was composed of loose connective tissue, covered externally by a mesothelial layer of flattened simple squamous epithelial cells. Histologically, the red pulp was composed of splenic sinuses and splenic cords containing numerous erythrocytes, reticular cells, lymphocytes, macrophages, and plasma cells. The splenic sinuses were lined by flattened endothelial cells, indicating progressive vascular organization within the red pulp.