Placenta and Fetal Membranes PDF

Placenta and Fetal Membranes Prof. Dr. Aylin YABA UÇAR Department of Histology and Embryology Learning objectives Describe to structure and function of the placenta, umblical membranes. cord and fetal Placenta and Fetal Membranes Amnion - Epiblast / Extraembryonic Mesoderm Yolk Sac - Hypoblast / Ext...

Placenta and Fetal Membranes Prof. Dr. Aylin YABA UÇAR Department of Histology and Embryology Learning objectives Describe to structure and function of the placenta, umblical membranes. cord and fetal Placenta and Fetal Membranes Amnion - Epiblast / Extraembryonic Mesoderm Yolk Sac - Hypoblast / Extraembryonic Mesoderm Allantois - Embryonic Hindgut Chorion - Trophoblasts / Extraembryonic Mesoderm Placenta - Chorion / Maternal Decidua FORMATION OF AMNIOTIC CAVITY, EMBRYONIC DISC, AND UMBILICAL VESICLE 8. Day 9. Day The fluid in the lacunae—embryotroph—passes to the embryonic disc by diffusion. The 10-day conceptus (embryo and extraembryonic membrane) is completely embedded in the endometrium 10. Day The communication of the eroded uterine vessels with the lacunae represents the beginning of the primordial uteroplacental circulation. Decidualization The endometrial connective tissue cells undergo a transformation—the decidual reaction—resulting from cyclic adenosine monophosphate and progesterone signaling. The cells swell because of the accumulation of glycogen and lipid in their cytoplasm, and they are then called secretory decidual cells. The primary function of the decidual reaction is to provide an immunologically privileged site for the conceptus. DEVELOPMENT OF CHORIONIC SAC The end characterized of by the second week is the appearance of primary chorionic villi. The extraembryonic somatic mesoderm and the two layers of trophoblast form the chorion. 13. Day The embryo, amniotic sac, and umbilical vesicle are suspended in the chorionic cavity by the connecting stalk. 14. Day Illustrations of the development of the secondary chorionic villi into the tertiary chorionic villi. A, Sagittal section of an embryo (at approximately 16 days). B, Section of a secondary chorionic villus. C, Section of an embryo (at approximately 21 days). D, Section of a tertiary chorionic villus. By the end of the third week, a primordial uteroplacental circulation has developed. The chorion / maternal endometrium =placenta Chorion forms stem villi Yolk Sac Hypoblast - the primary yolk sac or Heuser's membrane. Day 12 - Second wave of cell migration - forms definitive yolk sac composed of extrembryonic endoderm Early nutrition (2-3 weeks) for the embryo - later shrinking - nonfunctional – Meckels (outpocketing of small intestine) Connects to midgut via the yolk sac stalk diverticulum Yolk Sac Derivatives: Early blood cells forms from blood islands Primordial germ cells The early gut Epithelium of the respiratory and digestive tracts Allantois Endodermal origin – caudal outpocketing of the yolk sac Invades the connecting stalk (extraembryonic mesoderm) that suspends the embryo in the chorionic cavity Blood cell formation occurs during the third to fifth development. in its wall weeks of Allantois The allantois blood vessels - artery and vein becomes the umbilical vessels Remnants of Allantois becomes the urachus ligament that connects the belly button to the bladder. Placenta The placenta is a fetomaternal organ that has two components: A fetal part that develops from part of the chorionic sac A maternal part that is derived from the endometrium, the mucous membrane comprising the inner layer of the uterine wall Functions and Activities: Protection, Nutrition, Respiration, Excretion of waste products, Hormone production. Decidua Decidua basalis—the part of the decidua deep to the conceptus (embryo and membranes) that forms the maternal part of the placenta Decidua capsularis—the superficial part of the decidua overlying the conceptus Decidua parietalis—the remaining intervening parts of the decidua Amniochorionic Membrane The amniotic sac enlarges faster than the chorionic sac. As a result, the amnion and smooth chorion soon fuse to form the amniochorionic membrane. It is the amniochorionic membrane that ruptures during labor. Preterm rupture of this membrane is the most common event leading to premature labor. When the amniochorionic membrane ruptures, the amniotic fluid escapes through the cervix and vagina. Placental Circulation Fetoplacental Circulation Maternal-Placental Circulation Placental Membrane Until about 20 weeks, the placental membrane consists of four layers: 1. syncytiotrophoblast, 2. cytotrophoblast, 3. Connective tissue of the villus, 4. Endothelium of the fetal capillaries Functions of Placenta Metabolism - glycogen, cholesterol, and fatty acids Transport of gases and nutrients as well as drugs and infecious agents - simple diffusion, facilitated diffusion, active transport, and pinocytosis. Cytomegalovirus, rubella, and coxsackieviruses, as well as viruses associated with variola, varicella, measles, and poliomyelitis, may pass through the placental membrane and cause fetal infection. Protection by maternal antibodies - Only immunoglobulin G is transferred across the placenta (receptor-mediated transcytosis). - Maternal antibodies confer fetal immunity for diseases such as diphtheria, smallpox, and measles; however, no immunity is acquired to pertussis (whooping cough) or varicella (chickenpox). Excretion of waste products urea, uric acid, conjugated bilirubin Placental Endocrine Synthesis and Secretion 1. Human chorionic gonadotropin (hCG) 2. Human chorionic somatomammotropin placental lactogen) 3. Human chorionic thyrotropin 4. Human chorionic corticotropin (human Placenta and Fetal Membranes after Birth Umbilical Cord Significance of Amniotic Fluid Permits uniform external growth of the embryo Acts as a barrier to infection Permits fetal lung development Prevents adherence of the amnion to the embryo Cushions the embryo against injuries by distributing impacts that the mother may receive Significance of Amniotic Fluid Helps to control embryonic body temperature by maintaining a relatively constant temperature Enables the fetus to move freely, thereby aiding muscular development (e.g., in the limbs) Assists in maintaining homeostasis of fluid and electrolytes PARTURITION Dilation Expulsion Placental separation MULTIPLE PREGNANCIES two zygotes dizygotic (DZ) twinsfraternal twins one zygote monozygotic (MZ) twinsidentical twins Dizygotic Twins DZ twins always have two amnions and two chorions, but the chorions and placentas may be fused. Monozygotic Twins Because they result from the fertilization of one oocyte and develop from one zygote, MZ twins are of the same sex, are genetically identical, and are similar in physical appearance. Other Types of Multiple Births Triplets may be derived from: One zygote and be identical Two zygotes and consist of identical twins and a singleton Three zygotes and be of the same sex or of different sexes, in which case the infants are no more similar than infants from three separate pregnancies Twin-to-twin transfusion syndrome (TTTS) is the result of an intrauterine blood transfusion from one twin (donor) to another twin (recipient).