The document discusses the placenta, fetal membranes, decidua, trophoblast, and amnion. It describes their structure, development, functions, and roles in implantation, fetal-maternal circulation and immunological acceptance of pregnancy. Key points include how the decidua and trophoblast interact for implantation, trophoblast invasion of maternal spiral arteries, establishment of maternal blood flow, and the metabolic and protective roles of the amnion and fetal membranes.

1. Placenta & Fetal Membranes Crisostomo S. O. Ordoño Jr. MD

2. Decidua Highly modified Specialized

3. Decidua Dependent on: Blastocyst Implantation Progesterone Estrogen

4. Decidua of Pregnancy Decidua Parietalis Decidua Capsularis Decidua Basalis Structure based on anatomical location:

5. Decidua 14 – 16 weeks AOG Decidua Vera

6. Decidua Zona Basalis Zona Spongiosa Zona Compacta Layers of the Decidua Parietalis & Basalis

7. Decidua Reaction Completed with Blastocyst Implantation Commences mid-luteal phase

8. Decidual Endometrial Stromal Cells Enlarge, polygonal Round & vesicular nuclei Clear & basophilic cytoplasm Pericellular membrane Decidual Reaction

9. Decidua Protection against proteases Attachment for the Trophoblast Pericellular Membrane provides:

10. Decidua Decidua Basalis Decidua Capsularis Decidua Parietalis Blood Supply:

11. Decidual Histology Bone Marrow Derived Cells Endometrial large granular lymphocytes Endometrial Stroma True Decidual Cells

12. Decidua Becoming cuboidal to flat in later pregnancy Large distended glands with hyperplasia minimal stroma Zona Spongiosa

13. Decidua Invaded by interstitial trophoblast & giant cells Spongy zone is mainly arteries & veins Decidua Basalis

14. Decidua Rohr Stria found at the bottom of the intervillous space & surrounding the anchoring villi Nitabuch’s Layer/ Fibrinoid Degeneration Histology

15. Decidua Different promoter to initiate transcription Identical amino acid sequence Produced by the same gene in the pituitary Prolactin production

16. Decidua Regulate angiogenesis Regulate immune function in the decidua Maintenance of AF volume Role of Prolactin

17. Fertilization & Implantation

18. 107 - cell Blastocyst Blastocyst directly influence the receptivity of the endometrium Due to proteases from the secretory endometrium Stage of release from the zona pellucida

19. Receptivity of the Endometrium Progesterone Estrogen Cytokines from the Blastocyst

20. Endometrial Response Effect: increase Protease secretion by Trophoblast to degrade the extracellular matrix Colony Stimulating Factor Leukemia Inhibiting Factor

21. Implantation Must be on Days 20 – 24 of the endometrial – ovarian cycle Apposition is the 1 st step of implantation Occurs within 6 – 7 days post fertilization

22. Biology of the Trophoblast

23. Trophoblast Differentiation Primitive mononuclear Cytotrophoblast Primitive Syncytiotrophoblast 8 th day Post Fertilization Trophoblast differentiates into:

24. Primitive Cytotrophoblast Can undergo DNA synthesis Well-demarcated cell border Germinal cells of the syncytium

25. Primitive Syncytiotrophoblast Lacks the ability for DNA synthesis No individual cells Multi-nucleated

26. Trophoblast Differentiation Extravillous Trophoblast Villous Trophoblast

27. Villous Trophoblast Function: Transport of oxygen & nutrients Gives rise to the chorionic villi

28. Extravillous Trophoblast Migrates to the decidua & myometrium Penetrates the maternal vasculature Interstitial trophoblast Endovascular trophoblast Gives rise to the primary villous stalk

29. Interstitial Trophoblast Surrounds the maternal spiral arteries Penetrates the maternal decidua & myometrium

30. Endovascular Trophoblast Penetrates the lumen of the spiral arteries

31. Trophoblast Invasion Similar invasion characteristic of metastatic cancer cells 10 th day the blastocyst is totally encased within the decidua

32. Chorion Trophoblast with an underlying mesenchyme

33. Villi Tertiary Villi Secondary Villi Primary Villi

34. Placental Organization Chorio: Chorion Placenta Hemo: maternal Blood bathing the Syncytiotrophoblast Hemochorial Placentation

35. Langhan’s Cells Inner layer of cytotrophoblast in a chorionic villi

36. Anchoring Villi Proliferation of trophoblast at the tip that is anchored to the decidua

37. Chorionic Plate Hemomonochorial Hemodichorial When amnion & mesenchyme of chorion fuse together Formed by 8 – 10 weeks

38. Placental Development

39. Development of the Chorion & Decidua Inner pole forms the placenta Outer pole expands towards the endometrial cavity Blastocyst

40. Inner Pole Chorionic villi proliferate to form the chorionic frondosum Composed of the villous trophoblast & anchoring cytotrophoblast

41. Outer Pole Composed of cytotrophoblast and mesenchyme More translucent than the amnion Due to the degeneration of the villi in contact with the decidua capsularis Forms the chorion laeve

42. Amniochorion Paracrine Arm of the Fetal-Maternal Communication System Site of molecular transfer & metabolic activity Formed by the union of the amnion and chorion

43. Trophoblast Invasion And activate proteinases already present in the endometrium Due to its ability to secrete proteolytic enzymes to digest the extracellular matrix

44. Trophoblast Invasion Endometrial Factors Autocrine & Paracrine Trophoblastic Ability to invade in the 1 st trimester and limited Invasiveness in the last trimester is controlled by:

45. Trophoblast Invasion Promotes invasion into the endometrium Acts in an autocrine manner Insulin – like growth Factor Trophoblast

46. Trophoblast Invasion HENCE: controlled invasiveness Blocks the autocrine loop Insulin like growth factor binding protein type 4 Decidual Cells

47. Trophoblast Invasion A Trophoblastic Glue Oncofetal Fibronectin or Fetal-Specific Fibronectin Secured by Fetal Fibronectin

48. Decidual Spiral Artery Invasion Endovascular Trophoblast Interstitial Trophoblast Carried out by two populations of Extravillous Trophoblast:

49. Decidual Spiral Artery Invasion Prepares the arteries to facilitate invasion Aggregates around the maternal spiral arteries Interstitial Trophoblast

50. Decidual Spiral Artery Invasion Destroys the endothelium Fibrinoid material replaces muscle and connective tissue Initially forming cellular plugs Enters the lumen of the spiral arteries Endovascular Trophoblast

51. Decidual Spiral Artery Invasion Decidual Veins are not invaded Does not involve the Decidua Parietalis

52. Decidual Spiral Artery Invasion 1 st Stage Before 12 weeks AOG Invasion & Modification of Spiral Arteries Stages of Uteroplacental Vessel Development

53. Decidual Spiral Artery Invasion 2 nd Stage Between 12 – 16 weeks Invasion of intramyometrial parts of the spiral arteries Producing low-resistance vessels Stages of Uteroplacental Vessel Development

54. Establishment of Maternal Blood Flow Occurs approximately 4 weeks post fertilization

55. Villus Branching Each lobule has one artery and vein Each truncal villi and ramification is one lobule/ cotyledon Majority would arborize and end freely in the intervillous space Some become anchoring villi

56. Placental Growth & Maturation

57. Placental Growth At Term, placenta is 1/6 of the fetal weight 17 th week AOG placenta & fetal weights are approximately equal

58. Placental Dimensions Weight 508 grams Volume 497 Thickness 23 mm Diameter 185 mm

59. Placental Maturation Infiltration of Hofbauer cells Later becomes dense and cells more spindly and closely packed Abundant and loose intracellular matrix early in gestation Stroma of the Villi

60. Placental Maturation Capable of paracrine regulation of Trophoblast Function Increase in number and maturation as pregnancy progress Fetal Macrophages Hofbauer Cells

61. Placental Maturation Increase Vascularity Decrease Stroma Decrease in thickness of the syncytium Histological Changes that provides an increased efficiency of transport & exchange

62. Fetal & Maternal Blood Circulation in Mature Placenta

63. Fetal Circulation Blood with a higher O2 content passes thru the umbilical vein Umbilical vessels branch repeatedly beneath the amnion and diving villi Deoxygenated Blood flows through two umbilical arteries

64. Fetal Circulation Arteries always cross over the veins Responsive to vasoactive substances Umbilical vessels along the fetal surface of the chorionic plate Placental Surface / Chorionic vessels

65. Fetal Circulation Decrease amount of smooth muscle but has increase in caliber Each supply one cotyledon Perforating branches of the surface arteries Truncal Arteries

66. Maternal Circulation Maternal blood drains back to the venous orifices Blood flows back down as it baths the microvillous surface Maternal blood thru the basal plate and driven high up to the chorionic plate Physiological Maternal-Placental Circulation

67. Maternal – Placental Circulation Arterial Blood Pressure Factors acting on the arterial wall Pattern of Uterine Contractions Intrauterine Pressure Factors Regulating Blood Flow

68. Immunological Considerations Immunological peculiarity of the Trophoblast The acceptance and survival of the conceptus in the maternal uterus must be attributed to:

69. Immunogenicity of the Trophoblast But invasive cytotrophoblast express MHC class I molecules Making it appear immunologically Inert Major Histocompatibility complex (MHC) class I and II antigens are absent from villous trophoblast

70. Trophoblast HLA (MHC) Class I Expression “ normal implantation is dependent on controlled trophoblastic invasion of maternal endometrium-decidua and spiral arteries” Moffett-King (2002)

71. Trophoblast HLA (MHC) Class I Expression Non – Classical HLA - G Non Classical HLA - E Classical HLA - C Human Leukocyte Antigens Express by the Trophoblasts

72. Amnion Provides almost all of the tensile strength of the fetal membranes

73. Amnion Structure Single layer of epithelial cells-ectoderm derived Acellular zona spongiosa Fibroblast-like mesenchymal cells Acellular Compact Layer composed of interstitial collagen Basement membrane

74. Amnion Development End of the 1 st trimester – apposition of the mesoblast of the chorion and amnion Growth of the amnion eventually engulfs the embryo and prolapses into the cavity Amniogenic cells – precursor of amnionic epithelium

75. Amnion Epithelial Cells Metabolically Active Major site of transfer between AF and amnion

76. Metabolic Activity of the Amnion Synthesis of vasoactive peptides Site of Prostaglandin production Produce PGE2 & Fetal Fibronectin Inhibits metalloprotinase-1 synthesis

77. Vasoactive peptides produced by the Amnion Corticotrophin – Releasing Hormone – smooth muscle relaxant Brain natriuretic peptide – smooth muscle relaxant Parathyroid – related protein - vasodilator Endothelin - vasoconstrictor

78. Importance of the Metabolic Activity of the Amnion Availability to the fetus of the bioactive agents Modulates chorionic vessel tone and blood flow

79. Amnion Anatomy Umbilical Cord Amnion Placental Amnion

80. Amnion Tensile Strength Composed of x-linked collagens I & III Exclusively resides in the compact layer

81. Metabolic Function Sensitive to mechanical stretching: Triggers autocrine & paracrine responses Production of bioactive agents Maintain AF homeostasis

82. Amnionic Fluid Average Volume : 1,000 ml at term Continuously increase amount until 34 weeks Clear fluid

83. Umbilical Cord & Related Structures

84. Cord Structure & Function Covered by amnion Moist Dull white Extends from the fetal umbilicus to the fetal surface of the placenta

85. Cord Structure & Function Contains : 2 arteries 1 vein Wharton jelly : extracellular matrix Average Length: 55 cm Diameter: 0.8 – 2.0 cm

86. Thank You!