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
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
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
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
57. Placental Growth At Term, placenta is 1/6 of the fetal weight 17 th week AOG placenta & fetal weights are approximately equal
58.
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
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
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
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
76. Metabolic Activity of the Amnion Synthesis of vasoactive peptides Site of Prostaglandin production Produce PGE2 & Fetal Fibronectin Inhibits metalloprotinase-1 synthesis
77.
78. Importance of the Metabolic Activity of the Amnion Availability to the fetus of the bioactive agents Modulates chorionic vessel tone and blood flow
Decidua is a specialized, highly modified endometrium of pregnancy and is a function of the hemochorial placentation
Transformation is dependent on: Estrogen, Progesterone & factors secreted by the blastocyst during trophoblast invasion
The decidua of pregnancy is anatomically composed of three parts: Decidua Basalis, Decidua Capsularis, Decidua Parietalis
Decidua vera is the point where decidua parietalis and capsularis are joined
The decidua basalis & parietalis are composed of three layers
Predecidual reaction starts during the mid luteal phase of the endometrial cycle
Protection against proteases of the cytotrophoblast
Decidua Parietalis = retain a smooth muscle wall and endothelium and remain responsive to vasoactive agents Decidua Capsularis = blood supply is lost as the embryo grows Decidua Basalis = spiral arteries are invaded by the trophoblast and a vascular shell is left behind, not responsive to vasoactive agents
The primary cell components of the true decidual cells are from endometrial stromal cells & numerous bone marrow derived Cells
Initially with large distended glands with abundant secreatory activity for nourishment of the bastocyst
Decidua Basalis contributes to the formation of the basal plate of the placenta It differs from the decidua parietalis in two important respects: D. Basalis consist mainly of arteries and veins D. Basalis s invaded by large numbers of interstitial trophoblast cells & giant cells
Where the invading trophoblast meet the decidua there is a zone of fibrinoid degeneration/ Nitabuch’s layer
Decidua is the source of the prolactin that is present in enormous amounts in amnionic fluid during human pregnancy
Role in solute and water transport across the amniochorion Act on human T cells in an autocrine & paracrine manner Regulate angiogenesis during implantation
Fertilization must occur within a few hours Almost all pregnancies occur during the 2 days preceding or on the day of ovulation Zygote undergoes slow cleavage for 3 days while still in the fallopian tube Morula enters the uterine cavity about 3 days after fertilization 58 cell blastula differentiates into 5 cell inner cell mass & 53 outer cell mass 107 cell blastocyst = 8 inner cell mass & 99 trophoblastic cells.
