PLACENTATION

1. PLACENTATION Associate Professor Iolanda-Elena BLIDARU MD,PhD

2. The macroscopic anatomy of the placenta ♦fleshy organ - the form of a disc or an ellipsis ♦ diameter:18-20cm ♦ central thickness = 3-4cm; peripheral = 5-6mm ♦ weight at term = 500-600g (1/6 of the fetus) ♦ two surfaces * fetal surface (smooth, glossy) umbilical cord insertion * maternal surface - the cotyledons separated by ditches ♦the placental edge – membrane insertion + caduca (decidua) junction

5. PLACENTA • The basal plate • The intervillous space • The villous massif • The chorionic plate

6. Architectural study of the placenta 1. The chorionic plate • Fetal surface of the placenta with a flat, gray surface • Umbilical cord inserts into the chorionic plate (usually central or paracentral) • 2 layers – a gelly-like (acelular) one, covered by amniotic epithelium; contains fetal arteries and veins – a fibrous one, covered by ST and Langhans fibrinoid

7. CP: Chorionic plate • IVS: The intervillous space

8. Architectural study of the placenta2. The villous massif • it develops together with the intervillous space • mesenchimal villi represent the starting point for the growth and differentiation of all types of villi • the process of differentiation leads to the extension of the villous tree and to its maturation • the terminal villi growing form the vasculosyncytial membranes → facilitates relationships between the maternal and fetal circulation.

9. Architectural study of the placenta 3. The intervillous space • the maternal blood vessels of the endometrium open into the spaces of the trophoblastic network → filled with maternal blood = the intervillous space from which the fetus gains nutrition. • fibrinoid deposits at the periphery Langhans fibrinoid on the chorionic plate Rohr fibrinoid on the basal plate • 120 utero-placental arteries perpendicular to the uterine wall • the uterine veins parallel to the uterine wall • maternal blood flow – 600-800ml/min.

10. Maternal arteries and veins directly enter the intervillous space after 8 weeks gestation, and the intervillous space will contain about an unitof blood (400-500 mL). A. Primary chorionic villi. B. Secondary chorionic villi.

11. Architectural study of the placenta 4. The basal plate • corresponds to the maternal and fetal tissue junction • is formed by the fusion of the chorion with decidua basalis. Structures of the basal plate (at term): => ST (lining the intervillous space); => Rohr fibrinoid; => remnants of cytotrophoblastic shell; => Nitabuch fibrinoid (which separates the maternal tissues from the fetal ones); => remnants of the decidua basalis.

12. A Subchorial Langhans' layer • B Rohr's layer • C Nitabuch's layer – a continous fibrin layer between cytotrophoblastic shell and decidua basalis

13. PLACENTA - site of the maternal-fetal exchanges - is hemochorioendothelial • Placentation – first 4 months • The precursor cells of the human placenta–the trophoblasts–first appear 4 days after fertilization asthe outer layer of cells of the blastocyst.

14. PLACENTA Trophoblast → syncytiotrophoblast → cytotrophoblast

15. PLACENTA Primary villi - week 2, first stage of chorionic villi development, trophoblastic shell cells form finger-like extensions into maternal decidua. Secondary villi - week 3, second stage of chorionic villi development, extraembryonic mesoderm grows into villi, covers entire surface of chorionic sac. Tertiary villi - third stage of chorionic villi development, mesenchyme differentiates into blood vessels and cells, forms arteriocapillary network, fuse with placental vessels, developing in connecting stalk.

16. PLACENTA Primary to secondary to tertiary villi by end of 3rd week of gestation

17. PLACENTA • The basal plate • The intervillous space • The villous massif • The chorionic plate

18. Stem villi - or anchoring villi, cytotrophoblast cells attached to maternal tissue. Branched villi - or terminal villi, grow from sides of stem villi, region of main exchange, surrounded by maternal blood in intervillous spaces

19. DECIDUA

20. The decidua • It is the thickened vascular endometrium of the pregnant uterus. • The glands become enlarged, tortuous and filled with secretion. • The stromal cells become large with small nuclei and clear cytoplasm, these are called decidual cells.

21. The decidua The decidua consists of three layers: • The superficial compact layer, • The intermediate spongy layer, • The thin basal layer.

22. The decidua • The separation of placenta occurs through the spongy layer • While the endometrium regenerates again from the basal layer.

23. The decidua The trophoblast of the blastocyst invades the decidua to be implanted in: -The posterior surface of the upper uterine segment in about 2/3 of cases, -The anterior surface of the upper uterine segment in about 1/3 of cases.

24. The decidua According to the topography the decidua becomes differentiated into: • Decidua basalis - under the site of implantation. • Decidua capsularis - covering the ovum. • Decidua parietalis or vera - lining the rest of the uterine cavity.

25. The decidua

26. The decidua • As the conceptus enlarges and fills the uterine cavity the decidua capsularis fuses with the decidua parietalis. • This occurs nearly at the end of 12 weeks.

27. Sectional plan of the pregnant uterus in the third and fourth month

28. The decidua The decidua has the following functions: 1.It is the site of implantation. 2.It resists more invasion of the trophoblast. 3.It nourishes the early implanted ovum by its glycogen and lipid contents. 4.It shares in the formation of the placenta.

29. PLACENTATIONThe Chorion • The Chorion frondosum- arborescent villi disposed towards the decidua basalis → the fetal component of the placenta. • The Chorion laeve- the villi in contact with the decidua capsularis; almost complete degenerated(2-nd month). • The amnion → in direct contact with the chorionic vessels and the chorionic plate on the fetal surface of the placenta. • The decidua basalis →the maternal component of the placenta. The compact layer of the decidua basalis develops = the basal or decidual plate.

30. PLACENTATION • Cytotrophoblast cells migrate from anchoring villi + the cytotrophoblast shell into the decidua and myometrium → a key role in the development of the maternal blood supply to the placenta. • In humans, the chorion laeve and amnion form amniochorion (fetal membranes) → an important site of transfer and of metabolic activity.

31. PLACENTATIONThe placenton (cotyledon) • From the chorionic plate → about 15-30 villi trunk grade I → several trunks grade II → 20-40 trunks grade III → numerous ramifications = a complex named placenton. • Each placenton (cotyledon) has a corresponding intervillous space centrifugally perfused. • The villous tree ends into terminal villi with diameters of 30-80 millimicrons with capillaries.

33. PLACENTAPlacental - fetal circulation • Includes the umbilical cord blood vessels and the placental blood vessels that carry fetal blood. • The 2 umbilical arteries (carry venous-like blood) → 16-24 chorionic arteries (at the juncture of the umbilical cord with the placenta) →truncalarteries → capillary network → truncalveins (in the chorionic plate) → the single umbilical vein(carry arterial-like blood). • Each truncal artery supplies one cotyledon.

34. 1 Umbilical arteries • 2 Umbilical vein • 3 Fetal capillaries

35. PLACENTAUtero-placental circulation • The uterine arteries → 5-14 branches → helicoidal arteries → radial arteries → basal arteries + spiral arteries( in the spongy layer). • At term, placenta is irrigated by about 120-150 spiral arteries, ending at the level of the basal plate in the form of an ostium widely opened into the intervillous space. • The blood leaves the intervillous spaces via the uterine veins (in the periphery of the intervillous space).

36. 1 Spiral arteries 2 Uterine veins 3 Intervillous spaces A Basal plate

37. PLACENTAMaternal-placental circulation control • The uterine circulation constantly adapts to the growing metabolic needs of the embryo. • Placenta → an organ without any innervation.

38. PLACENTAThe microscopic study of the chorionic villous Structure– 2nd month • syncitiotrophoblast (ST) superficially • cytotrophoblast (CT) = Langhans layer → formsST • stroma (lax connective tissue) + 1 artery and 1 vein (branches of umbilical vessels) + a rich capillary network. • Hofbauer cells (in the stroma) – roles: endocrine, fetal nutrition, modeling of the stromal components, transfer of intercellular information, phagocytosis, immunologic.

39. PLACENTAThe microscopic study of the chorionic villous Structure– 5-th month • ST becomes thinner • CT becomes discontinuous • stroma becomes denser, capillaries multiply, Hofbauer cells ↓ in number • the macrophages (inside the basal plate) roles: local immunological protection, enzymatic activity, TH1 cytokines production

40. PLACENTAThe microscopic study of the chorionic villous Structure– at term: • thin villi • thin ST • disrupted CT (vasculosyncytial membranes) • reduced stroma with enlarged capillaries

41. The cytotrophoblast disappears from the walls of the tertiary villi and from the chorionic plate. • The decidua + fibrin deposits → inter-cotyledon septa → project into the intervillous space, dividing it into cotyledons =placentons (about 30). 1. Decidua 2. SC 3. CT islands 4. Septum

43. PLACENTAThe ultramicroscopic study of the chorionic villous • ST → a "brush border" made of microvilli. On this level there are transport vesicles, lisosomes, enzymes, receptors, small channels, junctional elements. • The microvillositary surface → the interface between the maternal and the fetal blood. • ST and CT lie on a basal lamina which delimits them from the stromal core.