1. Spermatogenisis and Oogensis

2. 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

3. 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

4. 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.

5. 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

7. 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

8. 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.

10. Spermatogenesis
Sertoli Cells – influence/nurture developing sperm

12. Video Representation Spermatogenesis: Oogenesis
Oogenesis

13. 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