1 / 88

Lecture 2 DEVELOPMENT OF PLACENTA. PLACENTA’S MORPHOLOGY AND FUNCTIONS

Lecture 2 DEVELOPMENT OF PLACENTA. PLACENTA’S MORPHOLOGY AND FUNCTIONS. Prof. Vlad TICA, MD, PhD. FETAL TISSUES OF THE FETAL-MATERNAL COMMUNICATION SYSTEM. The extravillous and villous traphoblasts Placental arm The fetal membranes (the amnion-chorion leave) Paracrine arm

alexandriad
Download Presentation

Lecture 2 DEVELOPMENT OF PLACENTA. PLACENTA’S MORPHOLOGY AND FUNCTIONS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Lecture 2 DEVELOPMENT OF PLACENTA. PLACENTA’S MORPHOLOGY AND FUNCTIONS Prof. Vlad TICA, MD, PhD

  2. FETAL TISSUES OF THE FETAL-MATERNAL COMMUNICATIONSYSTEM • The extravillous and villous traphoblasts • Placental arm • The fetal membranes (the amnion-chorion leave) • Paracrine arm • Human placenta : hemochorioendothelial type

  3. EARLY HUMAN DEVELOPMENT • Zygote • Blastomeres • Morula • Blastocyst • Embryo • Fetus • Conceptus

  4. FERTILIZATION OF THE OVUM AND CLEAVAGE OF THE ZYGOTE

  5. 58-cell blastocyst • 107-cell blastocyst

  6. IMPLANTATION

  7. BIOLOGY OF TROPHOBLAST • Trophoblast is the most variable in structure, function and development • invasiveness provides for attatchment of blastocyst to decidua of uterine cavity • nutrition of the conceptus • function as endocrine organ in human pregnancy • essential to maternal physiological adaptations & maintenance of pregnancy

  8. Differentiation • Cellular, syncytial / uninuclear , multinuclear • Formation of the Syncytium

  9. Cytotrophoblasts are the cellular progenitorsof the syncytiotrophoblast

  10. after apposition & adherence, intrusion of cytotrophoblast between endometrial epithelial cells • this process is facilitated by degradation of the extracellula matrix of endometrium /decidua catalyzed by • urokinase-type plasminogen activator • urokinase plasminogen activator receptor • multiple metalloproteinase • These functions of cytotrophoblasts invading the endometrium are indistinguishable from those of metastasizing malignant cells

  11. IMMUNOLOGICAL ACCEPTANCE OF THE CONCEPTUS • Previous Theories: • antigenic immaturity of the embryo-fetus • diminished immunological responsiveness of the pregnant woman • Decidua: immunologically privileged tissue site • The acceptance and the survival of conceptus in the maternal uterus must be attributed to immunological peculiarity of the trophoblasts, not the decidua

  12. CURRENT STATUS OF RESEARCH • Expression of the HLA system in trophoblast unique set of lymphocytes • may provide explanation for immunological acceptance of the conceptus

  13. IMMUNOCOMPETENCY OF THE TROPHOBLASTS • Many researchers focused on the expression of the major histocompatibility complex (MHC) antigens in trophoblast • MHC class II antigens are absent from trophoblasts at all stages of gestation

  14. TROPHOBLAST HLA CLASS I EXPRESSION • Normal implantation is dependent upon controlled trophoblast invasion of maternal endometrium/decidua and the spiral arteries • a mechanism for permitting and then for limitting trophoblast invasion • Such a system involves the uterine large granular lymphocytes(LGSs) and the unique expression of specific nomomeric HLA class I antigensin the trophoblasts

  15. HLA-I GENE EXPRESSION • HLA genes • the products of multiple genetic loci of the MHC within short arm of chromosome 6 • 17 class I genes have been identified • three classical genes •  A, B, C  => major class I(a) transplantation antigens • three other class I(b) genes • E, F, G  => class I HLA antigen • HLA-G gene

  16. UTERINE LARGE GRANULAR LYMPHOCYTE (LGL) • Believed to be lymphoid and of bone marrow origin and natural killer cell lineage • Present in large numbers only at the midluteal phase of the cycle-at the expected time of implantation in the human endometrium • Near the end of luteal phase of nonfertile ovulatory cycles, the nuclei of LGLs begin to disintegrate • With blastocyst implantation, these cells persist in the decidua during the early weeks of pregnancy • Speculated that LGLs are involved in the regulation of trophoblast invasion

  17. HLA-G EXPRESSION IN HUMAN TROPHOBLASTS • HLA-G antigen • identified only in extravillous cytotrophoblast in decidua basails and chorion laeve • not present in villous trophoblast, either in syncytium or in cytotrophoblasts • expressed in cytotrophoblast that are contiguous with maternal tissue (decidual cell) • It is hopothesized that HLA-G is immunologically permissive of antigen mismatch between mother and fetus

  18. HLA EXPRESSION IN THE HUMAN EMBRYO • as gestation progresses, cells from inner cell mass of blastocyst gradually develop both class I and II HLA antigen • these tissue are not in direct contact with maternal tissue or blood

  19. IMPLANTATION AND INTEGRIN SWITCHING • Apposition, adherence, then intrusion and invasion of the endometrium/decidua by cytotrophoblast (implantation) appears to be dependent upon • trophoblast elaboration of specific proteinases • degrade selected extracellular matrix proteins of the endometrium/decidua • coordinated and alternating process referred to as "integrin switching“ • facilitates migration and then attachment of trophoblasts in the decidua

  20. INTEGRIN • one of four families of cell adhesion molecules (CAMs) • cell-surface receptors that mediate the adhesion of cells to extracellular matrix proteins

  21. TROPHOBLAST ATTACHMENT IN DECIDUA: ONCOFETAL FIBRONECTIN • onfFN(oncofetalfibronectin) • unique glycopeptideof the trophouteronectin molecule • trophouteronectin or trophoblast glue • formed by extravilloustrophoblast, including those of chorionlaeve • Function: • a critical role for migration and attachment of the trophoblasts to maternal decidua • facilitates separation of extraembryonic tissuesfrom the uterus at delivery

  22. EMBRYONIC AND PLACENTAL DEVELOPMENT • Early Blastocyst • Trophoblast • hCG • Grow & expand

  23. EMBRYONIC DEVELOPMENT AFTER IMPLANTATION

  24. CYTOTROPHOBLASTINVASION OF DECIDUAL VESSELS • Capillary network • Arterioles • Spiral arteries

  25. SEVERAL CURIOUS FEATURES • trophoblasts in the vessels lumen do not appear to replicate • these cells are not readily dislodged by flow of blood • these cytotrophoblasts appear to migrate against arterial flow and pressure • no obvious adhesion of these cells one to the other • invasion of maternal vascular tissue bt trophoblasts involves only the decidual spiral arteries, not the veins

  26. ORGANIZATION OF PLACENTA

  27. ORGANIZATION OF PLACENTA • Trophoblast Ultrastructure • Prominent microvilli of the syncytial surface (brush border) • pinocytotic vacuoles and vesicles • absorptive and secretory placental function

  28. ORGANIZATION OF PLACENTA • Chorionic Villi • 12th day • Primary villi • proliferation of cytotrophoblast extend into syncytiotrophoblast • Secondary villi • mesenchymal cord, derived from cytotrophoblast, invade solid trophoblast column • Tertiary villi • after angiogenesis occurs from the mesenchymal cores in situ • 17th day - fetal blood vessels are functional & placental circulationestablished

  29. ORGANIZATION OF PLACENTA • Characteristic of development of H-mole • some villi, in which absence of angiogenesis results in a lack of circulation, may distended with fluid and form vesicles

  30. ORGANIZATION OF PLACENTA • Placental Cotyledons • Certain villi of the chorionfrondosum extend from chorionic plate to the decidua and serve as anchoring villi • Each of the main stem villi (truncal) and their ramifications (rami) constitute a placental cotyledon (lobe) • For each cotyledon, a 1:1:1 ratio of artery to vein to cotyledon

  31. ORGANIZATION OF PLACENTA • Breaks in the Placental "Barrier " • Numerous findings of passage of cells between mother and fetus in both directions • ex) erythroblastosis fetalis • A few fetal blood cells are found in the mother's blood • Fetal leukocytes may replicate in the mother and leukocytes bearing a Y chromosome have been identified in women for up to 5 years after giving birth to a son

  32. ORGANIZATION OF PLACENTA • Placetal Size and Weight • Total number of cotyledons remains the same throughout gestation • Individual cotyledones continue to grow • Placental weights vary considerably

  33. PLACENTAL AGING • As villi continue to branch and terminal ramifications become more numerous and smaller • > volume and prominence of cytotrophoblasts decrease • As syncytium thins and forms knots • > vessels become more prominent and lie closer to the surface • The stroma of the villi • in early pregnancy • branching connective ts. cells are seperated by abundant loose intercellular matrix • later • stroma becomes denser, and the cells more spindly and more closely packed

  34. PLACENTAL AGING • Histologic changes that accompany placental growth and aging are suggestive of increase in the efficiency of transport to and exchange to meet increasing fetal metabolic requirements • decrease in thickness of the syncytium • partial reduction of cytotropholastic cell • decrease in the stroma • increase in the number of capillaries and approximation of these vessels to the syncytial surface • By 4 months: • the apparent continuity of the cytotrophoblast is broken • the syncytium forms knots on the more numerous, smaller villi

  35. PLACENTAL AGING • At term: • Covering of villi may be focally reduced to a thin layer of syncytium with minimal connective tissue • Fetal capillaries seem to abut the tropohoblast • Villous stroma, Hofbauer cells, and cytotrophoblasts are markedly reduced • villi appear filled with thin-walled capillaries • Other changes suggestive of a decrease in the efficiency for placental exchange: • Thickening of the basement membrane of trophoblast capillaries • Obliteration of certain fetal vessels • Fibrin deposition on the surface of villi in basal and chorionic plates as well as elsewhere in the intervillous space

  36. BLOOD CIRCULATION IN THE MATURE PLACENTA • A section through the placenta in situ • amnion → chorion → chorionic villi → intervillous space → decidual plate → myometrium

  37. FETAL CIRCULATION • 2 umbilical arteries • deoxygenated, or "venous-like" blood flows to the placenta • 1 umbilical vein • with a significantly higher oxygen content • Hyrtl anastomosis • 2 umbilical a. separate at the chorionic plate to supply branches to the cotyledons

  38. MATERNAL CIRCULATION • Intervillous space -> chorionic plate -> vein • Spiral a., vein • Ut. Contraction • Intervillous space • Ramsey's concept

  39. THE PRINCIPLE FACTORS REGULATING THE FLOW OF BLOOD IN THE INTERVILLOUS SPACE • arterial blood pressure • intrauterine pressure • pattern of uterine contraction • factors that act specifically upon the arteriolar walls

  40. THE AMNION • Innermost fetal membrane and is contiguous with amnionic fluid • Avascular structure • Provide almost all of the tensile strength of the fetal membranes • protect against rupture or tearing

  41. STRUCTURE • single layer of cuboidal epithelial cells • basement membrane • acellular compact layer • fibroblast-like mesenchymal cells • zona spongiosa • Missing element of human amnion • smooth muscle cell, nerves, lymphatics, blood vessels

  42. DEVELOPMENT

More Related