Cell Biology And Molecular Actions

A. Hormonal Aspects of Fertilization

1. Capacitation

Within 5-15 min after sperm are deposited in the vagina, motile spermatozoa are present in the fallopian tubes. Estrogen, secreted late in the follicular phase, causes the endocervical glands to secrete a mucus that favors sperm transport and motility. The process of fertilization is initiated by the union of a competent spermatozoon with an ovum of the same species.

Capacitation of a spermatozoon is required before a successful union with an ovum can be achieved. Capacitation involves the removal of an outer coating from the surface of the spermatozoon; this is followed by the removal of the acrosome or tip of the spermatozoon (see Figure 14-13 and also Figure 12-4). This latter process, which has been termed the acrosome reaction, allows the acrosomal hyaluronidase enzymes to come into contact with the substances surrounding the ovum, so that the spermatozoon may penetrate and unite. While estrogens do not have an effect on the capacitation process, progesterone can inhibit capacitation from occurring in the uterus.

figure 14-13 Capacitation of a spermatozoon before (A), during (B), and after (C) acrosomal reaction. Abbreviations: acp, acrosomal cap region; acr, acrosomal collar region; ia, inner acrosomal membrane; oa, outer acrosomal membrane; pc, postnuclear cap region; sp, plasma membrane of the spermatozoon. Modified from Yanagimachi, R., and Noda, Y. (1970). Electron microscope studies of sperm incorporation into the golden hamster egg. Am. J. Anat. 128, 429-462.

figure 14-13 Capacitation of a spermatozoon before (A), during (B), and after (C) acrosomal reaction. Abbreviations: acp, acrosomal cap region; acr, acrosomal collar region; ia, inner acrosomal membrane; oa, outer acrosomal membrane; pc, postnuclear cap region; sp, plasma membrane of the spermatozoon. Modified from Yanagimachi, R., and Noda, Y. (1970). Electron microscope studies of sperm incorporation into the golden hamster egg. Am. J. Anat. 128, 429-462.

TABLE 14-4 Chromosomal Karotypes Related to Human Disorders

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