Summary
The ultrastructural aspect of ovular and follicular atresia were studied in 6–60 days old white rats. In pre-antrum folliculi two types of follicular cells were encountered, one, the more numerous, is a round clear cell, the other is dark and elongated. In antrum folliculi, vacuolization of the cytoplasm and nuclear pyknosis are seen.
The disappearance of the prolongations of the follicular cells and ovular microvilli occur in all ages.
The oocytes of atretic follicles may present the following changes: 1. lamellar alteration of the cytoplasmic matrix. It consists of clear zones devoid of cytoplasmic organelles (initial aspect) in which the disordered fibrous matrix organizes gradually in parallel lamella. Each lamella shows a regularly spaced longitudinal striation. 2. Changes in the distribution of the oocyte organelles; mitochondria, Golgi bodies, multivesicular bodies and clumps of vesicles which in the normal growing oocytes form a cortical and perinuclear layers are distributed at random in the cytoplasm like it occur in fertilized eggs. 3. Anomalous segmentation. Many oocytes undergo a process of segmentation. The segments are of unequal size, some of them are nucleated, others are devoid of a nucleus, Nuclei in an apparent process of amitotic division are frequently found, mitotic divisions are rare.
Final stages of atresia are characterized by loss of contact of the oocytes with the corona cells, increase of the density of the cytoplasm in some cases or decrease in others. In the oocyte cytoplasm vacuolization and increase in density of the mitochondria are very intense. The oocyte outline changes as a consequence of a general shrinking of the oocyte. The last remnant of the follicle and oocyte within the ovary is the zona pellucida.
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Vazquez-Nin, G.H., Sotelo, J.R. Electron microscope study of the atretic oocytes of the rat. Z. Zellforsch. 80, 518–533 (1967). https://doi.org/10.1007/BF00330720
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DOI: https://doi.org/10.1007/BF00330720