Development of Placenta.pptx

The placenta is formed gradually during the first three months of pregnancy, while, after the fourth month, it grows parallel to the development of the uterus. Once completed, it resembles a spongy disc 20 cm in diameter and 3 cm thick.

1. Development of Placenta

2. Objectives Gross anatomy of placenta Development of placenta Classification of placenta Function of placenta Clinical correlates MCQ’s Clinical Vignettes References

3. Periods of embryology Length of human pregnancy 280 days or 40 weeks Gestation period is subdivided into two stages:- 1. Embryonic period ( first to eight week ) Germinal period Embryonic period 2. Foetal period ( third to termination of pregnancy )

4. Meiosis II complete Formation of male and female pronuclei Decondensation of male chromosomes Fusion of pronuclei Zygote Fertilization

5. Week 1: days 1-6 Fertilization, day 1 Cleavage, day 2-3 Compaction, day 3 Formation of blastocyst, day 4 Ends with implantation, day 6

6. Fertilized egg 2 polar bodies 2 pronuclei Day 1 0.1 mm Fertilized egg (zygote)

7. Cleavage Cleavage = cell division Goals: grow unicellular Zygote to multicellular embryo. Divisions are slow: 12 - 24h Divisions are not synchronous Cleavage begins about 24h after pronuclear fusion

8. 2 Cell Stage Individual cells = blastomeres Mitotic divisions maintain 2N (diploid) complement Cells become smaller Blastomeres are equivalent (aka totipotent ).

9. 4 cell; second cleavage 4 equivalent blastomeres Still in zona pellucida

10. 8 Cell; third cleavage Blastomeres still equivalent

11. Embryo undergoes compaction after 8-cell stage: first differentiation of embryonic lineages Caused by increased cell-cell adhesion Cells that are forced to the outside of the morula are destined to become trophoblast --cells that will form placenta The inner cells will form the embryo proper and are called the inner cell mass (ICM).

12. Formation of the blastocyst Sodium channels appear on the surface of the outer trophoblast cells; sodium and water are pumped into the forming blastocoele . Note that the embryo is still contained in the zona pellucida .

13. Early blastocyst Day 3 Later blastocyst Day 5 blastocoele inner cell mass

14. Monozygotic twinning typically occurs during cleavage/blastocyst stages

15. “Hatching” of the blastocyst: preparation for implantation Hatching of embryo from zona pellucida occurs just prior to implantation. Occasionally, inability to hatch results in infertility, and premature hatching can result in abnormal implantation in uterine tube.

16. Week 2: days 7-14 implantation Implanted embryo becomes more deeply embedded in endometrium Further development of trophoblast into placenta Development of a bi-laminar embryo, amniotic cavity, and yolk sac.

17. Development of Placenta

18. Implantation and placentation (day 8) Trophoblast further differentiates and invades maternal tissues Cytotrophoblast Syncytiotrophoblast Breaks maternal capillaries, trophoblastic lacunae fill with maternal blood Inner cell mass divides into epiblast and hypoblast:

19. Implantation and placentation (day 9)

20. Implantation and placentation (day 12) .

21. Implantation and placentation (day 13)

22. Stem villi

23.  Until beginning of 8 th week , entire chorionic sac is covered with villi. S ac grows, only part that is associated with Decidua basalis retain its villi. Villi of Decidua capsularis compressed by developing sac. Thus, two types of chorion are formed: Chorion frondosum (villous chorion) Chorion laeve – bare (smooth) chorion About 18 weeks old, it covers 15-30% of the decidua and weights about 1\ 6 of fetus 14

24. V illous chorion ( increase in number, enlarge and branch ) will form fetal part of placenta. D ecidua basalis will form maternal part of placenta. By end of 4 th month, decidua basalis is almost entirely replaced by fetal part of placenta.

25. All eutherian mammal consist of placenta Human placenta is Discoid Chorio - deciduate organ

26. Full term placenta is disc type Foetal surface Maternal surface Foetal surface Maternal surface

27. Foetal surface Smooth Covered with amnion Umblical cord attached close to it centre Umblical cord

28. Maternal surface Rough and irregular 15-30 polygonal area (cotyledons) C otyledons

29. Normal Placenta (At term) Diameter : 15 to 22 cm Thickness : 2.0 ~ 2.5 cm Weights : approximately 500 g (about 1 lb)

30. Placenta consist of

31. Placental Barrier Haemo-chorial

32. Classification of Placenta According to attachment of the umbilical cord Battle- dore placenta Velamentous placenta

33. According to site of implantation Placenta previa Accessory placenta

34. According to degree of adhesion and penetration

35. According to the shape of placenta Lobe placenta Placenta circumvallate

36. According to distribution of umbilical arteries Disperse type Magistral type

37. – Placental transfer – Hormone production – Haematopoietic – Immunological

38. RESPIRATORY-- Gaseous exchange [CO2, O2] Passive diffusion across a pressure gradient assisted by maternal hyperventilation [ progesterone effect] & fetal haemoglobin. Oxygen supply to the fetus @ 8ml/kg/min is achieved with cord blood flow of 165-330 ml/min.

39. EXCRETORY Waste products from fetus such as urea, uric acid & creatinine are excreted in maternal blood by simple diffusion. NUTRITIVE Glucose - facilitated diffusion Lipids - triglycerides & fatty acids directly transported from mother to fetus. Amino acids - active transport (amino acid concentration is higher in fetal blood than in maternal blood)

40.  Water and Electrolytes Na, K, Cl - simple diffusion Ca, P, Fe - active transport Water soluble vitamins - active transport Fat soluble vitamins - slow transfer (remains at low level in fetal blood)

41.  HORMONES Insulin Adrenal steroids Thyro xine Chorionic gonadotrophin cross placenta at a very slow rate to keep the fetal plasma concentration low. Parathormone Calcitonin does not cross the placenta.

42. Some Substances and virus easily crosses placenta Hormone Synthetic progestins Synthetics estrogen diethylstilbestrol (DES) Virus Rubella Cytomegalo virus Coxsackie Variola Varicella Measles and poliomyelitis

43. Protein [polypeptides] Hormones 1. Human Chorionic Gonadotrophin – rises in 1st-early 2nd trimester, low levels after ~16 wks responsible for fetal adrenal cortex development 2. Human Chorionic Somatotrophin – - fosters embryonic development by increasing fetal cell glucose absorption and stimulating lipid and CHO metabolism.

44. 3 . Human Placental Lactogen – - R ises progressively from ~12 wks upt o term P ossibly useful in preparation for lactation C ontributes to diabetogenic effects of pregnancy 4. TSH , Melanocyte Stimulating Hormone, Relaxin, Oxytocin, Vasopressin – All isolated from placental tissue but most likely are of maternal or fetal origin.

45. All rise progressively to plateau at term 1. Progesterone – Maintains pregnancy Maintains uterine quiesence ↑ mammary growth Antialdosterone effect Oestrogens (oestriol) – ↑ uterine growth & vascular supply to decidua & myometrium - ↑ metabolism & placental enzyme systems. Androgens Corticosteroids STEROID HORMONE

46. Placenta takes up Fe, Vit. B12 & Folic acid  tendency towards anaemia in pregnancy. Fetal erythropoietin may cross placenta to mother since maternal reticulocyte counts are elevated in presence of fetal anaemia.

47. Feto-placental unit is an allograft that defies foreign body tissue reaction. [ Type IV cell-mediated reaction] Fetus not antigenically mature.

48. Clinical Correlates

49. Causes : Trophoblast aging or impairment of uteroplacental circulation with infarction. Deposition of calcium salts is heaviest on maternal surface in basal plate – → further deposition occurs along septa and both increase as pregnancy progresses. Diagnosis : Sonography

50. Placental Infarctions Maternal Floor Infarction Placental Vessel Thrombosis

51. Erythroblastosis fetalis & Fetal Hydrops Fetal blood escape placenta barrier Elicit antibody response by mother’s immune system If maternal response is sufficient, anitbodies will attack and hemolyze fetal red blood

52. Gestational Trophoblastic Disease Chorioangioma (hemangioma) Tumours metastatic to Placenta Embolic Fetal Brain Tissue

53. MCQ’s Q1 Which of the hormone is secrete by women in the urine used as an indicator of pregnancy? Pregestrone Estriol Human chorionic gonadotropin ( hCG ) Somatomammotropin Human chorionic gonadotropin ( hCG ) langmans-medical-embryology-12th-ed , pg no -107)

54. Q2 which of the hormone, cross placental barrier? Parathormone Calcitonin Heparine Thyroxine Thyroxine (langmans-medical-embryology-12th-ed , pg no -107)

55. Clinical Vignettes Q A foetus of age 23 rd week and 4 day born dead with edema and effusion into the body as shown in image below , mother diagnosis with D( Rh )negative body and she says her first delivery is completely normal . What would be probable diagnosis and condition on basis of above sign ? Fetal hydrops and Isoimmunization (langmans-medical-embryology-12th-ed , pg no -106)

56. Q2) A 32 year old 10 weeks pregnant women visit gynae clinic for her routine check-up, during (USG) physician found abnormality in placental position which produce serious haemorrhage before parturition and would be a life threatening to mother. Name the condition in which blastocyst implanted over internal os of cervix ? Ans Placenta previa (A.K Datta medical-embryology-7th-ed , pg no -67 )