FERTILIZATION AND IMPLANTATION

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A presentation on physiological events of fertilization and implantation meant for undergraduate students. The images used are from the open access sources from the net.

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Presentation Transcript

Fertilization and implantation : 

1 Fertilization and implantation Dr. Fatima Zahra MD OBG

Learning objectives:: 

Learning objectives: Student should be able to tell the sequence of follicular maturation and timing of stages of meiosis of the ovum. Place of fertilization and enzymatic process involved. Timing and stages of zygote. Factors responsible for implantation. Early development (i.e 2 weeks) of the embryo and its terminology. 2

Lesson plan: 30 core slides, 9 revision slides; Total 1 Hr.: 

Lesson plan: 30 core slides, 9 revision slides; Total 1 Hr. Students’ pre-assessment done to know their understanding of ovarian and endometrial cycles and ovulation by showing them slides from no. 4 to 12; requires10 minutes approx. Thereafter fertilization and implantation is explained mainly through pictures. Important numerical data and highlights of the lesson are displayed on separate slides. 3

OVARIAN CYCLE: FOLLICULOGENESIS: 

4 OVARIAN CYCLE: FOLLICULOGENESIS

Slide 5: 

5

Slide 6: 

6

LAPAROSCOPIC VIEW OF STIGMA AT OVULATION: 

7 LAPAROSCOPIC VIEW OF STIGMA AT OVULATION

CORPUS LUTEUM AND ALBICANS: 

8 CORPUS LUTEUM AND ALBICANS

Slide 9: 

9

ENDOMETRIAL CYCLE: PROLIFERATIVE PHASE: 

10 ENDOMETRIAL CYCLE: PROLIFERATIVE PHASE

ENDOMETRIAL CYCLE: SECRETORY PHASE: 

11 ENDOMETRIAL CYCLE: SECRETORY PHASE

FIMBRIA AND HUMAN EGG: 

12 FIMBRIA AND HUMAN EGG

Slide 13: 

13 FERTILIZATION NORMALLY OCCURS IN THE FALLOPIAN TUBE 12-24 HOURS AFTER OVULATION EJACULATED SPERM CAN REMAIN VIABLE FOR ABOUT 48 HOURS AND A SECONDARY OOCYTE IS VIABLE FOR ABOUT 24 HOURS AFTER OVULATION

DAYS OF FERTILIZATION: 

14 DAYS OF FERTILIZATION

Slide 15: 

15 Sperm produce an enzyme (acrosin) that stimulates sperm motility and migration. Uterine contractions stimulated by the prostaglandins in semen aids sperm movement. Sperms undergo functional changes (capacitation) in the female reproductive tract: the membrane around the acrosome becomes fragile so that several destructive enzymes are released.

Human sperm: structure: 

16 Human sperm: structure

Slide 17: 

17 The enzymes help penetrate the ring of cells (corona radiata) that surround the oocyte One sperm penetrates and enters a secondary oocyte, this is called syngamy - syngamy causes depolarization, which triggers the release of calcium ions into the cell Calcium ions stimulate the release of granules, that in turn, promote change changes in the zona pelllucida to block entry of the other sperm

Slide 18: 

18 BINDING PROTEIN ON THE SPERM REACTS WITH BINDING RECEPTORS ON THE ENVELOPE. WHEN THESE PROTEINS RECOGNIZE EACH OTHER, THE EGG MEMBRANE SWALLOWS THE SPERM HEAD. THIS ALLOWS THE SPERM NUCLEUS TO ENTER THE EGG’S CYTOPLASM AND FUSE WITH THE EGG NUCLEUS

Slide 19: 

19

Slide 20: 

20

Slide 21: 

21

Sperm head penetrating the corona: 

22 Sperm head penetrating the corona

Days of fertilization: 

23 Days of fertilization

Slide 24: 

24 Oocyte completes equatorial division (meiosis ll) the nucleus from the sperms head and the nucleus from the ovum fuse to produce segmentation nucleus. The segmentation nucleus contains 23 chromosomes from the male pronucleus and 23 chromosomes from the female pronucleus. The fertilized ovum is now called a zygote

Slide 25: 

25

Slide 26: 

26 Rapid mitotic cell divisions of the zygote are called cleavage. Cleavage is completed 30 hours after fertilization. Successive cleavages produce a solid sphere of cells called morula. The morula is the same size as the original zygote. At 4 1/2 - 5 days, the dense cluster of cells has developed into a hollow ball of cells and enters the uterine cavity, it is now called a blastocyst

Slide 27: 

27

Slide 28: 

28 BLASTOCYST REMAINS FREE WITHIN THE UTERINE CAVITY FOR A SHORT PERIOD OF TIME BLASTOCYST ENLARGES AND RECEIVES NOURISHMENT FROM GLYCOGEN RICH SECRETIONS FROM THE UTERINE GLANDS

Breaking out of zona pellucida: 

29 Breaking out of zona pellucida

Attachment to the endometrium: 

30 Attachment to the endometrium

Sites of implantation: 

31 Sites of implantation

Slide 32: 

32 6 DAYS AFTER FERTILIZATION THE BLASTOCYST ATTACHES TO THE ENDOMETRIUM USUALLY IMPLANTS ON THE POSTERIOR WALL OF THE FUNDUS DEVELOPS TWO LAYERS IN THE REGION OF CONTACT BETWEEN THE BLASTOCYST AND ENDOMETRIUM, SYNCTIOTROPHOBLAST AND CYTOTROPHOBAST

Syncitiotrophoblast and cytotrophoblast: 

33 Syncitiotrophoblast and cytotrophoblast

Slide 34: 

34 Syncytiotrophoblast secretes enzymes that enables the blastocyst to penetrate the uterine lining, the enzymes digest and liquefy the endometrial cells. The trophoblast secretes hcg that rescues the corpus luteum from degeneration and sustains its secretions of progesterone and estrogens, thus menstruation does not begin.

Slide 35: 

35

Slide 36: 

36

Slide 37: 

37

Slide 38: 

38

Slide 39: 

39

Slide 40: 

40

Slide 41: 

41 Germinal disc Yolk sac Amniotic cavity Chorionic cavity Connecting stalk

Slide 42: 

42

Text book & Reference:: 

Text book & Reference: Holland &Brews Obstet. William’s Obstetrics Dutta; Obstetrics Images from various open access resources on the net. 43

Suggested reading for self-evaluation:: 

Suggested reading for self-evaluation: MCQ’s from PG entrance guides. Online assesment on some reproductive physiology sites. 44