Corpus Luteum

The collapsed follicle undergoes reorganization into the corpus luteum after ovulation

At ovulation, the follicular wall, composed of the remaining granulosa and thecal cells, is thrown into deep folds as the follicle collapses and is transformed into the corpus luteum (yellow body), or luteal gland (Fig. 22.11a). At first, bleeding from the capillaries in the theca interna into the follicular lumen leads to formation of the corpus bemorrbagicum with a central clot. Connective tissue from the stroma then invades the former follicular cavity. Cells of the granulosa and theca interna layers then undergo dramatic morphologic changes. These luteal cells increase in size and become filled with lipid droplets (Fig. 22.11b). A lipid-soluble pigment, lipochrome, in the cytoplasm of the cells gives them a yellow appearance in fresh preparations. At the ultrastructural level, the cells demonstrate features associated with steroid-secreting cells, namely, abundant sER and mitochondria with tubular cristae (Fig. 22.12). Two types of luteal cells are identified:

• Granulosa lutein cells, large (about 30 ¡xm in diameter), centrally located cells derived from the granulosa cells

• Theca lutein cells, smaller (about 15 /xm), more deeply staining, peripherally located cells derived from the cells of the theca interna layer

As the corpus luteum begins to form, blood and lymphatic vessels from the theca interna rapidly grow into the granulosa layer. A rich vascular network is established within the corpus luteum. This highly vascularized structure located in the cortex of the ovary secretes proges-

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