As indicated above, the cycle of the seminiferous epithelium describes changes that occur with time at any given site in the tubule. In addition, the ivave of the seminiferous epithelium describes the distribution of patterns of cellular association (stages) along the length of the tubule. In rodents and other mammals that have been studied, including subhuman primates, each stage occupies a significant length of the seminiferous tubule, and the stages appear to occur sequentially along the length of the tubule. In the rat, there are approximately 12 waves in each tubule. A transverse section through the tubule usually reveals only one pattern of cell associations. There are no waves in the human seminiferous epithelium. Each pattern of cellular associations (stage of the cycle) has a patch-like distribution in the human seminiferous tubule (Fig. 21.14). Patches do not extend around the circumference of the tubule, nor are they in sequence. Therefore, a transverse section through a human seminiferous tubule may reveal as many as six different stages of the cycle arranged in a pie-wedge fashion around the circumference of the tubule.
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