Lecture 08.pdf Placenta Development PDF

DEVELOPMENT OF PLACENTA AND MEMBRANES PART I: PLACENTA RUQAIYA AL JABRI Development of trophoblast: Formation of primary villi 3rd week  Syncytiotrophoblastcells are highly invasive  Blood lacunae ( spaces) are being formed in endometrium( maternal blood)  Proliferating cytotrophoblasts in...

DEVELOPMENT OF PLACENTA AND MEMBRANES PART I: PLACENTA RUQAIYA AL JABRI Development of trophoblast: Formation of primary villi 3rd week  Syncytiotrophoblastcells are highly invasive  Blood lacunae ( spaces) are being formed in endometrium( maternal blood)  Proliferating cytotrophoblasts invaginate into syncytiotrophoblasts  Primary chorionic villi have formed  DEVELOPMENT OF SECONDARY AND TERTIARY VILLI  Primary villi are being invaded by extraembryonic mesoderm to form secondary villi  Foetal blood vessels from chorionic plate and connecting stalk have penetrated the EEM forming definitive placental villi (tertiary villi)  Capillaries in the tertiary villi connect with capillaries in the chorionic plate and in the connecting stalk  These vessels establish contact with the intraembryonic developing vessels and heart  Initially villi develop all around the chorion EMBRYO AND THE TROPHOBLAST AT THE END OF THE THIRD WEEK: THE CYTOTROPHOBLAST SHELL  Cytotrophoblast cells penetrate the syncytiotrophoblast and surround the trophoblast  They form a thin cytotrophoblast shell:  Are in direct contact with the endometrium  Attaches the chorion firmly to the maternal endometrium  Intervillous spaces,  are found throughout the trophoblast  are between the chorionic villi  The embryo is suspended in the chorionic cavity by means of the connecting stalk.  At the embryonic pole, villi are numerous and well formed. This part of the chorion is known as chorion frondosum  At the abembryonic ( opposite) pole, they are few in number and poorly developed.  The rest of the chorion is known as chorion laevae (smooth)(As villi slowly disappear here) FOETAL PART OF PLACENTA : STRUCTURE  Chorionic plate composed of  Extra embryonic somatic mesoderm containing foetal blood vessels  Cytotrophoblast  Syncytiotrophoblast  Tertiary Chorionic villi MATERNAL PART OF PLACENTA: DECIDUA BASALIS  Functional layer of endometrium at site of implantation:  Decidual reaction: -consists of a compact layer of large decidual cells derived from endometrial stroma.  Cells filled with abundant lipids and glycogen (source of early nutrition)  Maternal blood vessels-open into lacunae, intervillous spaces  Endometrial glands  Incomplete septa grow into intervillous spaces DECIDUA BASALIS & PLACENTAL CIRCULATION  Incomplete decidual septa or partitions grow out of the decidual plate  They do not reach chorionic plate  These divide the maternal side of placenta into 15-20 placental lobules or cotyledons PLACENTAL MEMBRANE/BARRIER : SITE OF EXCHANGE: A SELECTIVE SEMI PERMEABLE MEMBRANE  Formed by  Endothelial cells of fetal blood vessels  Extraembryonic Mesoderm  Cytotrophoblast cells  Syncytiotrophoblast cells  Maternal and foetal blood does NOT mix PLACENTAL CIRCULATION  Spiral arteries---branches of endometrial ( uterine) arteries deliver blood to placenta  Enters intervillous spaces  Cytotrophoblastcells ( from the shell) invade the terminal portions of spiral arteries  Transform into endothelial cells lining maternal spiral arteries (epithelial –to-endothelial transformation)  This invasion transforms these small diameter, high resistance vessels into large diameter, low resistance vessels-more blood can be delivered into intervillous spaces PLACENTAL CIRCULATION  Blood enters intervillous spaces  Bathes chorionic villi  Exchange of nutrients, gases and metabolites occurs at placental membrane of free villi  More free villi grow out into the intervillous spaces  Endometrial veins carry waste products and CO 2 back into maternal circulation PLACENTA FUNCTIONS  Facilitates nutrient, electrolyte and gas exchange by diffusion across placental membrane  Exchange of metabolites  Transmission of maternal antibodies-IgG (Immunity to fetus)  Hormone production  Progesterone, oestrogen, HCG, somatomammotropin (a growth-hormone-like substance)  A semipermeable barrier-allows some bacteria, viruses, drugs to cross into foetal circulation BEYOND 4 MONTHS IUL  Placental barrier begins to thin due to thinning of cytotrophoblastic layer to facilitate greater exchange  Some mesoderm connective tissue also degenerates  The barrier is only formed by syncytiotrophoblast sand capillary endothelium in some areas.  Few remaining cytotrophoblasts do not participate in exchange  Full term placenta:  Diameter: 15-25 cms.  Thickness: 3 cms.  Weight: 500-600 gms.  Attachment of umbilical cord is usually eccentric on Foetal side Foetal side of the placenta  PLACENTAL CHANGES AT THE END OF PREGNANCY  At the end of pregnancy, a number of changes that occur in the placenta  reduced exchange between the two circulations.  These changes include  an increase in fibrous tissue in the core of the villus,  thickening of basement membranes in fetal capillaries  obliteration of small capillaries of the villi,  deposition of fibrinoid on the surface of the villi in the junctional zone and in the chorionic plate.  Excessive fibrinoid formation frequently causes infarction of an intervillous lake or an entire cotyledon. The cotyledon then assumes a whitish appearance. NORMAL POSITION OF PLACENTA ABNORMAL ATTACHMENT AND PENETRATION OF PLACENTA  Placenta accreta:  Anchoring placental villi attach to the myometrium rather than the decidua resulting in abnormally adherent placenta.  Placenta increta  Chorionic villi penetrate into the myometrium.  Placenta percreta  Chorionic villi penetrate through the myometrium to the uterine serosa or adjacent organs. CLINICAL APPLICATION: RH INCOMPATIBILITY  Placental barrier is semipermeable  allows harmful viruses like rubella, measles, polio and AIDS , some drugs, antigens etc. to enter foetal circulation  If Rh–ve mother:  Foetal RBCS of an Rh +ve (D or Rh antigen) foetus can enter maternal blood during delivery/trauma etc. stimulate anti-Rh antibodies (isoimmunisation) in mother.  If antibody production is sufficient, antibodies attack and destroy fetal RBCs in next pregnancy :  hemolytic disease of the newborn:  Erythroblastosis foetalis  The severe anaemia can cause tissue fluid accumulation and oedema  Fetal hydrops Slide courtesy of Dr. Sadhana