PLACENTATION Associate Professor IolandaElena BLIDARU MD Ph D

PLACENTATION Associate Professor Iolanda-Elena BLIDARU MD, Ph. D

The macroscopic anatomy of the placenta ♦ fleshy organ - the form of a disc or an ellipsis ♦ diameter: 18 -20 cm ♦ central thickness = 3 -4 cm; peripheral = 5 -6 mm ♦ weight at term = 500 -600 g (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

PLACENTA The basal plate The intervillous space The villous massif The chorionic plate

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

CP: Chorionic plate IVS: The intervillous space

Architectural study of the placenta 2. The villous massif vit develops together with the intervillous space vmesenchimal villi represent the starting point for the growth and differentiation of all types of villi vthe process of differentiation leads to the extension of the villous tree and to its maturation vthe terminal villi growing form the vasculosyncytial membranes → facilitates relationships between the maternal and fetal circulation.

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 -800 ml/min.

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

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.

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

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 as the outer layer of cells of the blastocyst.

PLACENTA Trophoblast → syncytiotrophoblast → cytotrophoblast

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.

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

PLACENTA The basal plate The intervillous space The villous massif The chorionic plate

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

DECIDUA

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

The decidua consists of three layers: 1. The superficial compact layer, 2. The intermediate spongy layer,

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

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.

The decidua 1. 2. 3. 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.

The decidua

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.

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

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.

PLACENTATION 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.

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.

PLACENTATION The 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.

PLACENTA Placental - 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) → truncal arteries → capillary network → truncal veins (in the chorionic plate) → the single umbilical vein (carry arterial-like blood). Each truncal artery supplies one cotyledon.

1 Umbilical arteries 2 Umbilical vein 3 Fetal capillaries

PLACENTA Utero-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).

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

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

PLACENTA The microscopic study of the chorionic villous Structure – 2 nd month syncitiotrophoblast (ST) superficially cytotrophoblast (CT) = Langhans layer → forms ST 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.

PLACENTA The 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, TH 1 cytokines production

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

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. 2. 3. 4. Decidua SC CT islands Septum

PLACENTA The 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.