Spermatogenisis and Oogensis

Oogenesis Begins in the female embryo with production of oogonia from primordial germ cells Oogonia divide by mitosis to form primary oocytes They are developmentally arrested cells (stopped at prophase I before birth) Reside in a small follicle At puberty, FSH periodically stimulates small group of follicles to resume growth and development

Typically only one follicle fully matures each month. That primary oocyte completes meiosis I Second meiotic division begins, but stops at metaphase The secondary oocyte is arrested in meiosis II until released at ovulation. Only if a sperm cell penetrates the oocyte does meiosis II resume

Each of the meiotic division results in unequal cytokinesis. The smaller cells become polar bodies that eventually degenerate (**the first polar body may or may not divide a second time) The ruptured follicle left from ovulation becomes the corpus luteum If the released oocyte does not complete oogenesis (fertilization), that corpus luteum degenerates.

FSH – stimulates follicle development Estrogen – produced by growing follicles (and corpus luteum), high amounts signal ovulation LH – stimulates corpus luteum growth and maintenance Progesterone – produced by corpus luteum. Inhibits further ovulation, maintains uterine lining during pregnancy

Spermatogenesis Initial germ cells of the embryonic testes divide and differentiate into stem cells which divide mitotically into spermatogonia Spermatogonia generate spermatocytes (by mitosis) Each spermatocyte gives rise to 4 spermatids meiotic cell division to reduce chromosome number from diploid (2n = 46) to haploid (n =23) Spermatids differentiate into sperm

Spermatogenesis Stem cells situated near outter edge of seminiferous tubules As spermatogenesis proceeds, cells move steadily inwards, as they pass through the stages In the last step, the mature sperm are released into the lumen of the tubule, which they travel through to reach the epididymis.

Spermatogenesis Sertoli Cells – influence/nurture developing sperm

Video Representation Spermatogenesis: Oogenesis http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__spermatogenesis__quiz_1_.html Oogenesis http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__maturation_of_the_follicle_and_oocyte.html

Spermatogenesis vs. Oogenesis All 4 products of meiosis develop into mature gametes 1 mature gamete (ovum), 3 polar bodies that degenerate Occurs throughout adolescence and adulthood Mitotic divisions complete before birth, and production of mature gametes ceases around age 50 Produces mature sperm from percursor cells in continuous sequence Had long interruptions during the development of mature gamete