Histology of the Testis and Spermatogenesis
Spermatogenesis in the human can be divided into cycles based on the six stages of spermatid maturation from round spermatid to the elongated sperm with a tail (Figs. 6.1, 6.2, 6.3, and 6.4). There are six distinct cellular associations of spermatogonia and spermatocytes in each of these stages of the cycle of spermatogenesis. In mice and rats and most animals, these stages pass like a wave along the seminiferous tubule, and at any given point along the tubule at any time, you only see one of these stages, meaning there may be no sperm or elongated spermatids seen, even though spermatogenesis is normal, and you are seeing only one stage at any given point [1–10]. However, in the human there is no such obvious wave, and the cellular associations of various stages or all stages of spermatogenesis may very well be in any location of the tubule you biopsy (Figs. 6.5a, b and 6.6). At any point in the human seminiferous tubules, you do not have to look for a specific wave to find sperm. This chaotic distribution of the stages of spermatogenesis in the human is very important for clinical performance of TESE as will be explained in Part II of this book.
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