Fertilisation

Important facts :
1. From the time of ovulation it takes 3-4 days(or 18-19 days from the last menstrual cycle) --- for Fertilized Ovum in the Ampulla (Tube) to reach the Uterus.
2. From the time of ovulation it takes 7-9 days (or 21 – 22 days from the last menstrual cycle) --- for Implantation (During this time the Uterine milk /secretions provide nutrition for early dividing Ovum) – The predominant morphological feature is edema of the endometrial stroma.

3. Oogenesis begins in ovary – 6-8 weeks of gestation
4. Maximum number of oocytes (6-7 million) are attained at 20 weeks (5th Month) of gestation.
5. At birth total content of Both ovaries is 2 million primary oocytes.
6. At puberty number is decreased further and is – 300000 – 500000 of which only 500 are destined to mature during an Individual’s life !

7. All the primary oocyte in the ovary of a newborn till puberty – arrested in Late prophase

8. First polar body is released just prior to ovulation
9. Second division starts just after it and is -- arrested in metaphase
10. Thus second polar body release occurs only at the time of fertilization.

11. LH surge precedes ovulation by 34 – 36 hrs.
12. LH peak precedes ovulation by 10 – 16 hrs

13. Prior to ovulation :
a) Follicle reaches a size of 18 – 20 mm (KCET 2009)
b) Endometrium is 9 – 10 mm thick
c) Endometrium shows triple line on USG

14. Maximum action of Corpus Luteum is at 22 days of Menstruation
15. In the absence of fertilization – corpus Luteum persists for – 12–14 days
16. Maximum Growth of Corpus Luteum is at 8th week of Gestation and degenerates at 6th month of gestation

Extra points :
1. LH surge tends to occur at around 3 AM.
2. Ovulation occurs in morning between (midnight and 11 AM) in Spring
3. Ovulation occurs in evening between (4 PM and 7 PM ) in Autumn and winter .
4. Ovulation occurs more frequently from Right Ovary
5. Ovulation occurs alternatively between the two ovaries in younger women
6. In women more than 30 yrs age .. ovulation occurs frequently from the same ovary.

Remember :
1. The primitive germ cells takes origin from Yolk sac at 3rd week of gestation and migrate to the Genital ridge by 4th week of gestation .
2. 1st meiotic division – arrested in Prophase – completed just prior to Ovulation releasing the 1st polar body.
3. 2nd meiotic division – arrested in Metaphase – completed at the time of fertilization releasing the 2nd Polar body.

4. Also, Primary Oocyte – 44XX; Secondary Oocyte – 22X;
5. Primary Oocyte(44X) – undergoes 1st meotic division – Arrested in prophase – completed just prior to ovulation – releases First polar body (22X) + Secondary Oocyte (22X)
6. Secondary Oocyte (22X) – 2nd meiotic division – Arrested in Metaphase – At the time of fertilization – releases Second Polar Body (22X) + Ovum (22X)

7. In Males : Primary spermatocyte (44XX) – undergoes 1st meiotic division – forms secondary spermatocytes (2 in number)
8. Secondary spermatocytes (22X) (2 in number) – undergoes 2nd meiotic division – forms Spematids (22X)(4 in number)
9. Spermatids undergoes transformation as spermeiogenesis – forms Sperma (4 in number)
10. Developmental process from Spermatogoonia to Sperma takes 74 days (Some books 61days)and entire process till the transit to the ductal system takes 90 days (3 months)
11. So, in case of infertility of males the repeat sperm analysis is done after 3 months.

Age in days and development events :
1. 2 days – Embryo at 2 cell stage
2. 3 days – Morula is formed
3. 4 days – Blastocyst is formed
4. 8 days – Bilaminar disc is formed
5. 14 days – Prochordal plate & primitive streak seen
6. 16 days - Intra-embryonic mesoderm is formed / Disc is three germ layers