Fetal Development

1. Fetal Development Developed by D. Ann Currie

2. Oogenesis • Ovary gives rise to oogonial cells. • Cells develop into oocytes. • Meiosis begins and stops before birth. • Cell division resumes at puberty. • Development of Graafian follicle.

3. Ovum • The female gamete are called Ovum. • The ovum are considered fertile for about 12-24 hours after ovulation.

4. Spermatogenesis • Production of sperm • First meiotic division: • Primary spermatocyte replicates and divides. • Second meiotic division: • Secondary spermatocytes replicate and divide. • Produce four spermatids.

5. Sperm • The male gamete are Sperm. • The sperm can survive in the female reproductive tract for 48-72 hours. • However they are believed to be healthy and highly fertile for only 24 hours. • In a single ejaculation the male deposits approximately 200-500 million sperm in the vagina. Only hundreds of sperm actually reach the ampulla. Only one sperm fertilizes the ovum.

7. FErtilization • Fertilization occurs: • when the sperm and ovum unite. • in the ampulla of the fallopian tube.

8. Changes to Sperm • Capacitation: • Removal of plasma membrane and glycoprotein coat • Loss of seminal plasma proteins • Acrosomal reaction: • Release of enzymes • Allows entry through corona radiata

9. Ferilization

10. After Sperm Entry • Zone pellucida blocks additional sperm from entering • Secondary oocyte completes second meiotic division • Forms nucleus of ovum • Nuclei of ovum and sperm unite • Membranes disappear • Chromosomes pair up

12. At the moment of fertilization the sex of the zygote is determined. Female have XX (sex chromosomes) Male have XY ( sex chromosomes)

13. Fertilization and cell division

14. Cell Division

16. Implantation(Nidation) • Zygote moves through the fallopian tube towards the cavity of the uterus. • Transportation takes 3 or more days. • Rapid mitotic divisions called cleavage is occurring. • 7-10days after fertilization the blastocyst implants. • Most frequent site of attachment is the upper part of the posterior uterine wall.

17. Primary Germ Layers About 10-14 days after conception • Primary germ layers: • Ectoderm • Mesoderm • Endoderm

18. Placenta Development • Chorionic villi form spaces in decidua basalis • Spaces fill with maternal blood. • Chorionic villi differentiate: • Syncytium: outer layer • Cytotrophoblast: inner layer • Anchoring villi form septa

19. Placenta

25. Placenta Function • Nutrition • Excretion • Fetal respiration • Production of fetal nutrients • Production of hormones • Large molecular compounds can not crossthe placenta • Other see text

26. Umbilical Cord • Body stalk fuses with embryonic portion of the placenta • Provides circulatory pathway from chorionic villa to the embryo • Delivers oxygenated blood to the fetus: • One Vein • Returns waste material to maternal circulation: • Two Arteries

28. Fetal Environment • Amnion: • Encloses the amniotic cavity • The inner membrane that forms about the • 2nd week of embryonic development • Forms a fluid-filled sac that surrounds the embryo and later the fetus. • Chorion: • Is the outer membrane • Becomes vascularized and forms the fetal portion of the placenta.

29. Amniotic Fluid • Consists of 800-1200 ml by the end the pregnancy • Surrounds, cushions, protects, the fetus and allows for fetal movement. • Maintains body temperature of the fetus. • Contains fetal urine and is a measurement of fetal kidney function. • The fetus modifies the amniotic fluid through the processes of swallowing, urinating, and movement trough respiratory tract. • Other see text.

30. Pre-embryonic • First 2 week after conception • Cleavage • Blastomeres form morula • Blastocyst: - develops into embryonic disc and amnion • Trophoblast: - develops into chorion

31. Embryonic Period • Beginning at Day 15 through approximately the 8th week after conception.

32. Fetal Period • Week 9 after conception to birth

33. Fetal Development Week 4 • Beginning development of GI tract • Heart is developing • Somites develop—beginning vertebrae • Heart is beating and circulating blood • Eyes and nose begin to form • Arm and leg buds are present

35. Fetal development Week 12 • Eyelids are closed • Tooth buds appear • Fetal heart tones can be heard • Genitals are well-differentiated • Urine is produced • Spontaneous movement occurs

36. Fetal development Week 16 • Lanugo begins to develop • Blood vessels are clearly developed • Active movements are present • Fetus makes sucking motions • Swallows amniotic fluid • Produces meconium

37. Fetal Development: Week 20 • Subcutaneous brown fat appears • Quickening is felt by mother • Nipples appear over mammary glands • Fetal heartbeat is heard by fetoscope

38. Fetal Development: Week 24 • Eyes are structurally complete • Vernix caseosa covers skin • Alveoli are beginning to form

39. Featl Development: Week 32 • Rhythmic breathing movements • Ability to partially control temperature • Bones are fully developed but soft and flexible • Variability seen on FHR monitor

40. Fetal Development: Week 36 • Increase in subcutaneous fat • Lanugo begins to disappear

41. Fetal Development: Week 38 • Skin appears polished • Lanugo has disappeared except in upper arms and shoulders • Hair is now coarse and approximately 1 inch in length • Fetus is flexed

42. Twins • Fraternal: two ova and two sperm • Identical: single fertilized ovum - Originate at different stages

43. Fetal Circulation • Umbilical Cord • Fetal Heart Rate-110-160 BPM • Ductus venosus • Ductus arteriosus • Foramen ovale

45. The end of this presentation but the beginning of a new life….