ECR L28/9
FEMALE REPRODUCTIVE TRACT & OOGENESIS
20/01/2000
PROF FRASER

NB: in spermatogenesis, there are stem cells. The whole process takes 64 days.
1) proliferation (spermatogonia ==> spermatocytes)
2) meiosis (spermatocytes ==> spermatids) haploid
3) spermiogenesis (spermatids ==> spermatozoon)

LH from the Leydig cells produces testosterone
FSH from the sertoli cells produces inhibin and androgen binding protein (ABP)

Knockout mice for FSH: the females are sterile, but the males are still fertile, although their testes are half the size and there is a decreased sperm production.

You not only need hormone, but androgen receptors as well. Tfm - testicular feminization - no receptors - have testes but look female in appearance.

One spermatocyte produces 4 speramtozoa in the end.

The cortical area of the gonads have the most concentration of primordial germ cells when it is going to become female.

Myometrium has a lot of gap junctions, so they contract as a syncitium
Endometrium into which embryo implant and forms the placenta - responds to hormones of the cycle. Oestrogen (glands), progesterone and oestrogen (function - fluid)
Cervix - has lots of in-pocketings, and has a lot of cervical mucous.

Some women can have a bifurcated uterus. The uterine tube is not smooth, but is very folded, and sperm can get stuck and lost. Therefore they change the way they swim to combat this.

Fimbrae expand and embrace ovary at ovulation
Myometrium is really quite thick
Normal implantation occurs at the fundal region
Fertilisation usually occurs at the ampulla

Kartagener’s syndrome - a genetic defect where there is defective dynein (an ATPase in cilia and flagella) required for movement. If the cilia in the lungs don’t work, you get bronchitis. In men you get immotile sperm. In women the cilia are not obligatory for reproduction.

OVARY:
Somatic cells - gonadal ridge
Germ cells - primordial germ cells (migrate to gonadal ridge)
You need both of the above components. In Turner’s syndrome (45, XO) there are no primordial germ cells, therefore they only develop "streak" ovaries. They are in the right place, but there is no follicle development. They are probably actually mosaic, and have a mixture of 46, XX and 45, XO.

OOGENESIS

In the foetal ovary, germ cells undergo a massive proliferation. At about 20 weeks, there are the maximum number of oogonia that there ever will be (approximately 6-7 x 106). Women have no stem cell populations, therefore the oogonia are just lost by atresia. By birth there are about 1 x 106, by puberty there are about 500,000 and at menopause there is effectively 0.

OOGONIA:
Between late foetal to early post natal all the oogonia enter meiosis I and become primary oocytes. They then proceed to undergo DNA synthesis, pairing and crossing over. They then STOP. The earliest time that they restart is at puberty (10-12 years), and the latest is at about 50 years old. This is why chromosome abnormalities increase with the age of the mother - they have been suspended at the same stage for nearly 40 years.

The signal for restarting is LH, and the response is to complete meiosis I and enter metaphase of meiosis II forming the secondary oocyte. It then STOPS again. The secondary oocyte is then ovulated, and the process is restarted when there is fusion of the sperm with the oocyte membrane. It then goes on to complete meiosis.

The first polar body usually degenerates before being able to produce the third polar body. There is the same amount of genetic information in the secondary oocyte and the first polar body, but there is an uneven distribution of cytoplasm. The haploid female gamete/zygote (ootid) never really exists.

This is not a continuous process - errors are more likely to occur. Also, the longer the oocyte spends in before being fertilised with sperm, the more likely it is for errors to occur.

If there are 1, 3 or 4 pronuclei, there’s something wrong, either with the uterus or more likely, with the oocytes. The quality of oocytes decreases considerably with age.