Development Of Placenta And Fetal Membranes - Part 1 PDF

DEVELOPMENT OF THE PLACENTA AND FETAL MEMBRANES-PART 1 & 2 MOHD ASIM KHAN...

DEVELOPMENT OF THE PLACENTA AND FETAL MEMBRANES-PART 1 & 2 MOHD ASIM KHAN [email protected] LEARNING OBJECTIVES ▪ At the end of this lecture, the students should be able to: 1. Explain briefly the development of the placenta and fetal membranes 2. List the functions of placenta, amniotic fluid and yolk sac 3. Describe the placental abnormalities 4. Define parturition and describe the stages of labor 5. Explain the embryological basis of the Dizygotic and Monozygotic twins References (Contents): 1. Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  PLACENTA 1. Primary site of nutrient and gas exchange between the mother and fetus 2. Fetomaternal organ that has two components: ▪ A fetal part that develops from the part of the chorionic sac ▪ A maternal part that is derived from the endometrium (inner layer of uterine wall) 3. The placenta and umbilical cord function as a transport system for substances passing between the mother and the fetus some 4. ▪ Nutrients and oxygen pass from the maternal blood through the placenta to the fetal blood ▪ Waste materials and carbon dioxide pass from the fetal blood through the placenta to the maternal blood Reference: Wheater’s Functional Histology-A Text & Colour Atlas By Young, 6th Edition n F Reference: Human Embryology and Developmental Biology, By Carlson, 3rd Edition Circulation of amniotic fluid to and from the fetus Structure of placental villi  PLACENTA 5. The placenta and fetal membranes perform the following functions and activities: 1. Protection 2. Nutrition 3. Respiration 4. Excretion 5. Hormone production 6. Shortly after birth, the placenta and fetal membranes are expelled from the uterus as the afterbirth Reference: Human Embryology and Developmental Biology, By Carlson, 3rd Edition Placentas and fetal membranes after birth A: Maternal surface B: Fetal surface Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition Circulation of amniotic fluid to and from the fetus  DECIDUA The term decidua means “falling off,” “shed,” or “sloughed off” 1. Decidua refers to the gravid endometrium, the functional layer of the endometrium in a pregnant woman 2. Decidua separates from the remainder of the uterus after parturition (childbirth) 3. The three regions of the decidua are named according to their relation to the implantation site: 3A. DECIDUA BASALIS ▪ Part of the decidua deep to the conceptus that forms the maternal part of the placenta 3B. DECIDUA CAPSULARIS ▪ Superficial part of the decidua overlying the conceptus 3C. DECIDUA PARIETALIS ▪ All the remaining parts of the decidua 4. The decidua basalis and decidua parietalis shed as part of the afterbirth 5. E Eat The decidua capsularis attenuates and degenerates at week 22 of development because of a reduced blood supply Development of placenta and fetal membranes Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  DEVELOPMENT OF PLACENTA 1. Early placental development is characterized by the rapid proliferation of the trophoblast & development of the chorionic sac & chorionic villi 2. By the end of the 3rd week, the anatomic arrangements necessary for physiologic exchanges between the mother and the embryo have been established 3. By the end of the 4th week, a complex vascular network develops in the placenta, allowing maternal- embryonic exchanges of gases, nutrients, & metabolic waste products 5 Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition Reference: Essentials of Human Embryology by Moore Section of an embryo (at approximately 21 days) Drawings of embryo during the fourth week of development  DEVELOPMENT OF PLACENTA 4. - Chorionic villi cover the entire chorionic sac until the beginning of the eighth week 5. - Growth of chorionic sac results in compression of the villi associated with the decidua capsularis 6. - The blood supply to the villi is reduced due to compression and the villi degenerate producing a relatively avascular bare area, the smooth chorion or chorionic laeve (Laeve: Latin levis, smooth) 7. - The villi associated with the decidua basalis rapidly increase in number, branch profusely, and enlarge - This bushy part of the chorionic sac is the villous chorion or chorionic frondosum (Frondosum: Latin, full of leaves) Development of placenta and fetal membranes Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition  DEVELOPMENT OF PLACENTA 8. The placenta has two parts: 11A: The fetal part of the placenta 11B: The maternal part of the placenta 8A. The fetal part of the placenta ▪ Formed by the villous chorion ▪ The chorionic villi that arise from villious chorion project into the intervillous space containing maternal blood Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition Illustration of a transverse section through a full-term placenta, showing 1. the relation of the villous chorion (fetal part of placenta) to the decidua basalis (maternal part of placenta) 2. the fetal placental circulation 3. the maternal placental circulation  DEVELOPMENT OF PLACENTA 8B. The maternal part of the placenta ▪ Formed by the decidua basalis, the part of the decidua related to the fetal component of the placenta at ▪ By the end of the fourth month, the decidua basalis is almost entirely replaced by the fetal part of the placenta Illustration of a transverse section through a full-term placenta, showing Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition 1. the relation of the villous chorion (fetal part of placenta) to the decidua basalis (maternal part of placenta) 2. the fetal placental circulation 3. the maternal placental circulation The maternal placental bed (the area below the fetal placenta resembles an egg carton  FETOMATERNAL JUNCTION IN 1. The fetal part of the placenta (villous chorion) is attached to the maternal part of the placenta (decidua basalis) by the cytotrophoblastic shell SIN 2. The cytotrophoblastic IN shell is the external layer of trophoblastic cells on the maternal surface of the placenta 3. The chorionic villi attach firmly to the decidua basalis through the cytotrophoblastic shell & anchor the chorionic sac to the decidua basalis a 4. Endometrial arteries and veins pass freely through gaps in the cytotrophoblastic shell and open into the intervillous space Reference: Wheater’s Functional Histology-A Text & Colour Atlas By Young, 6th Edition Reference: Netter’s Atlas of Human Embryology, By Cochard, 1st edition Development of the placenta: chorionic villi 0 Structure of placental villi  FETOMATERNAL JUNCTION 5. - The shape of the placenta is determined by the shape of the persistent area of chorionic villi - Usually this is a circular area, giving the placenta a discoid shape inte they Reference: Medical Embryology By Langman, 13th Edition Reference: Essentials of Human Embryology by Moore A full-term placenta A: Fetal side: The chorionic plate & umbilical cord are covered by amnion B: Maternal side showing the cotyledons Section of full-term placenta Discoid: Having the form of a discus or disk  FETOMATERNAL JUNCTION Cotyledon: Greek, Any cup-shaped hollow 5 6. The placental septa divide the fetal part of the placenta into irregular convex areas, cotyledons 7. Each cotyledon consists of two or more stem villi and their many branch villi 8. By the end of the fourth month, the decidua basalis is almost entirely replaced by the cotyledons Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition Reference: Netter’s Atlas of Human Embryology, By Cochard, 1st edition Maternal part of placenta Illustration of a transverse section through a full-term placenta  INTERVILLOUS SPACE 1. The intervillous space of the placenta contains maternal blood which is derived from the lacunae that developed in the syncytiotrophoblast during the second week of development sin 2. The intervillous space which is large blood-filled space results from the coalescence enlargement of the lacunar networks 3. The intervillous space of the placenta is divided into compartments by the placental septa; however, there is free communication between the compartments because the septa do not reach the chorionic plate, the part of the chorion associated with placenta Illustration of a transverse section through a full-term placenta Placental anatomy and blood flow Reference: Lippincott Illustrated Reviews: Physiology by Preston, 2nd Edition Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition nWN É  INTERVILLOUS SPACE 4. Maternal blood enters the intervillous space from the spiral endometrial arteries in the decidua basalis 5. The spiral arteries pass through gaps in the cytotrophoblastic shell and discharge blood into the intervillous space 6. The intervillous space is drained by endometrial veins that also penetrate the cytotrophoblastic shell 7. Endometrial veins are found over the entire surface of the decidua basalis Illustration of a transverse section through a full-term placenta Placental anatomy and blood flow Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition Reference: Lippincott Illustrated Reviews: Physiology by Preston, 2nd Edition  INTERVILLOUS SPACE 8. The numerous branch villi arising from stem villi are continuously showered (bathed) with maternal blood that circulates through the intervillous space 9. The blood in intervillous space carries oxygen & nutritional materials that are necessary for fetal growth & development 10. The maternal blood also contains fetal waste products such as carbon dioxide, salts, and products of protein metabolism o Illustration of a transverse section through a full-term placenta Placental anatomy and blood flow Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition Reference: Lippincott Illustrated Reviews: Physiology by Preston, 2nd Edition  PLACENTAL CIRCULATION 1. The many branch chorionic villi of the placenta provide a large surface area where materials may be exchanged across the very thin placental membrane ("barrier") interposed between the fetal and maternal circulations 2. It is through the numerous branch villi that arise from the stem villi that the main exchange of material between the mother and fetus takes place www.s an im io 3. The circulations of the fetus and the mother are separated by the placental membrane consisting of extrafetal tissues A: Illustration of a stem chorionic villus showing its arteriocapillary-venous system Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition B: Section through a branch villus at 10 weeks gestation C: Section through a branch villus at full term The placental membrane, composed of extrafetal tissues, separates the maternal blood in the intervillious space from the fetal blood in the capillaries in the villi ………………………………………………………………………………. The placental membrane becomes very thin at full term B ………………………………………………………………………………. Hofbauer cells are believed to be phagocytic cells ………………………………………………………………………………. mains fifths A C  FETOPLACENTAL CIRCULATION (FETAL PLACENTAL CIRCULATION) 1. Poorly oxygenated blood leaves the fetus and passes through the umbilical arteries to the placenta 2. The umbilical arteries divide into several radially disposed chorionic arteries at the site of attachment of the umbilical cord to the placenta 3. The chorionic arteries branch freely in the chorionic plate before entering the chorionic villi 4. The blood vessels form an extensive arteriocapillary-venous system within the chorionic villi which brings the fetal blood extremely close to the maternal blood Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition Reference: Medical Embryology By Langman, 13th Edition 0 The placenta in the second half of pregnancy Illustration of a stem chorionic villus showing its arteriocapillary-venous system The cotyledons are partially separated by the decidual (maternal) septa  MATERNAL-PLACENTAL CIRCULATION 1. The maternal blood in the intervillous space is temporarily outside the maternal circulatory system 2. The maternal blood enters the intervillous space through 80 to 100 spiral endometrial arteries in the decidua basalis 3. The spiral endometrial vessels discharge into the intervillous space through gaps in the cytotrophoblastic shell 4. The blood flow from the spiral arteries is pulsatile and is propelled in jetlike fountains by the maternal blood pressure Reference: Lippincott Illustrated Reviews: Physiology by Preston, 2nd Edition Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition Placental anatomy and blood flow Illustration of a transverse section through a full-term placenta  MATERNAL-PLACENTAL CIRCULATION 5. The entering blood is at a considerably higher pressure than that in the intervillous space and spurts toward the chorionic plate forming the "roof" of the intervillous space 6. The blood flows slowly around the branch villi as the pressure dissipates and allows exchange of metabolic and gaseous products with the fetal blood I am 36 095 won did e 7. The blood eventually returns through the endometrial veins to the maternal circulation Reference: Before we are Born- Essentials of Embryology and Birth Defects, By Moore, 8th Edition Reference: Lippincott Illustrated Reviews: Physiology by Preston, 2nd Edition i n Illustration of a transverse section through a full-term placenta Placental anatomy and blood flow