Читать книгу Bovine Reproduction - Группа авторов - Страница 49

The final stage of development results in the release of the spermatozoa into the lumen of the seminiferous tubules by a process referred to as spermiation [33]. As the final stages of spermiogenesis are completed, the spermatozoa emerge from the adluminal compartment of the seminiferous tubules tail toward the apex of the Sertoli cells and the tubule lumen. During the process of migration from the rete testis through the epididymis and ejaculate, the spermatozoa shed their cytoplasmic droplets, but not all emerge as normal spermatozoa in the ejaculate (Figure 2.5). Before spermatozoa are capable of fertilization they must undergo additional maturation in the epididymis. Capacitation, the final stage of maturation where spermatozoa gain the ability to penetrate the zona pellucida (the outer membrane of the oocyte), occurs in the female reproductive tract. For more specific descriptions of the process of spermatogenesis in the bull the reader is referred to a series of articles by Amann [152], Berndtson and Desjardins [153], and Johnson et al. [154].

Figure 2.5 Schematic representation of spermatozoa reflecting visible changes as they migrate from the rete testis through the caput (head), corpus (body), and cauda (tail) regions of the epididymis to the ejaculate. Sperm found in the rete testis, efferent ducts, and caput epididymis are identified by the proximal nature of the protoplasmic droplet, while in sperm in the distal caput through to the corpus epididymis the protoplasmic droplet has translocated to the bend of the flagellum; by the time the spermatozoa reach the cauda epididymis the droplet has located at the distal portion of the middle piece of the flagellum (a). Schematic representations of ejaculated normal and autolysis spermatozoa are shown in (b). Normal sperm show an intact acrosome in the form of the apical ridge along the apical edge of the spermatozoan head, while the spermatozoan head images to the right show examples of false or premature acrosomal reactions typically associated with dead or dying spermatozoa. The paddle‐shaped nature of the bovine spermatozoon is shown in (c).

Source:[151], © 2003, Germinal Dimensions Incorporated.