Plate 90 Corpus Luteum

After the oocyte and its immediately surrounding cells (i.e., the cells of the cumulus oophorus) are discharged from the mature ovarian follicle (ovulation), the remaining follicle cells (membrana granulosa) and the adjacent theca interna cells differentiate into a new functional unit, the corpus luteum.

The cells of the corpus luteum, luteal cells, rapidly increase in size and become filled with lipid droplets. A lipid-soluble pigment in the cytoplasm of the cells, lipochrome, gives them their yellow appearance in fresh tissue. Electron micrographs of the luteal cells demonstrate that they have features typical of steroid-secreting cells, namely, abundant smooth endoplasmic reticulum and mitochondria with tubular cristae. Two types of luteal cells are identified: Large, centrally located granulosa lutein cells are derived from the granulosa cells; smaller, peripherally located theca lutein cells are derived from the theca interna. A rich vascular network is established in the corpus luteum into which progesterone and estrogen are secreted by the lutein cells. These hormones stimulate growth and differentiation of the uterine endometrium to prepare it for implantation of a fertilized ovum.

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