EMBRYOLOGY EDIT The Placenta: Its Development and Function TABLE OF CONTENTS: Formation of placenta 3 Full term placenta 4 Structure of a Cotyledon 5 Fetal Placental circulation / Maternal 6 Placental Circulation Placental membrane 7 Function of the Placenta 8 Anomalies of Placenta 9 2 When it is formed? Formed by the beginning of the 4th month. What is it? What is the function of it? It is a Fetomaternal structure It is the primary site for (Part from the fetus and exchange of gases and part from the mother) nutrients between the mother and the fetus. Placenta #Formation of placenta Fetal part: Villous Chorion. Decidua (Gravid Endometrium) : It is the functional layer of the It is the bushy area at the embryonic pole. endometrium during pregnancy which Its villi are more in number, enlarged and branch profusely. is shed after parturition. Maternal Part: 3 Decidua Basalis (part of the decidua deep to the conceptus). #Full term placenta Discoid in shape. Fetal surface Maternal surface Weighs: (500 – 600)g. Has two surfaces: • Smooth because it is covered • Rough. 1. Fetal with the amnion. • Formed of (15 –20) irregular 2. Maternal • The umbilical cord is attached to convex areas (Cotyledons): its center. -which are separated by grooves • The chorionic vessels are (placental septa). radiating from the umbilical cord. -Each cotyledon is covered by a thin layer of decidua basalis. 4 #Structure of a Cotyledon It consists of two or more Stem Villi with their many branch villi. It receives (80-100) maternal spiral arteries that enter the #intervillous spaces at regular intervals. #Intervillous spaces Large blood filled spaces which are freely communicating They receive spiral arteries from the lacunae in the syncytiotrophoblast. The spaces are drained through endometrial veins. 5 #Fetal Placental circulation / Maternal Placental Circulation Fetal Placental Maternal Placental Circulation Circulation - 80–100 spiral endometrial arteries discharge into the intervillous spaces. -The blood is propelled in jet like fountains by the Two Umbilical Arteries: maternal blood pressure. Carry poorly oxygenated blood from the fetus to the -The pressure of this entering blood is higher than placenta. that in the intervillous space. -It forms a roof of the space. -As the pressure dissipates, the blood flows slowly around the branch villi. within the branch chorionic villi, they form: Arterio-capillary venous network: -It brings the fetal blood extremely close to the maternal - Exchange of metabolites and gases with the fetal blood. blood. -The well oxygenated fetal blood in the capillaries passes - As the pressure decreases, the blood flows back into veins accompanying the chorionic arteries. from the chorionic plate and enter the endometrial -At the umbilical cord, they form the One Umbilical Vein. veins to the maternal circulation. 6 #Placental membrane It is a composite thin membrane of extra fetal tissues which separates the fetal and maternal bloods. Up to (20) weeks, it is composed of (4) layers: Cytotrophoblast Endothelium of Connective tissue Syncytiotrophoblast (Disappear later) fetal capillaries. of the villus. At some sites, the syncytio comes in direct contact with the endothelium of the At full term It becomes thinner and composed of (3) layers only: capillaries and forms Vasculosyncytial placental membrane. Endothelium of Connective tissue Syncytiotrophoblast Cytotrophoblast fetal capillaries. of the villus. 7 Fetal drug addiction can be due to some drugs as Heroin. All sedatives and analgesics can affect the fetus to some degree. #Function of the Placenta Drugs used for management of labor can cause respiratory distress to the newborn. 8 Table from embryology team 433 #Anomalies of Placenta 1. Placenta Accreta: Abnormal absence of chorionic villi with partial or complete absence of the decidua basalis. 2. Placenta Percreta: • Chorionic villi penetrate the myometrium to the perimetrium. • The most common presenting sign of these two anomalies is trimester bleeding. 3. Placenta Previa: #Fate of the placenta • The blastocyst is implanted close to or overlying the The strong uterine contractions that continue internal uterine os. after birth compress uterine blood vessels to • It is associated with late pregnancy bleeding. limit bleeding & cause the placenta to detach • Delivery is through Cesarean section. from the uterine wall (within 15 minutes after birth of the infant). 9 1.The placenta will detach from the uterine wall 5. Which of the following is true regarding within____after birth of the infant: (Placenta previa): a. 15min. a. No associated bleeding b. 15 hours. b. Abnormal absence of chorionic villi c. 24 hours. c. Delivery is through Cesarean section d. 1 week. d. A & B. 2. Criteria of Maternal Surface are: 6. Which of the following layers disappear at a. Rough. full term placenta: b. The umbilical cord. c. Decidua basalis. a. Endothelium of fetal capillaries. d. A & C. b. Connective tissue of the villus. MCQs c. Syncytiotrophoblast d. Cytotrophoblast 3. The placenta is formed at: 1. A sh a. 1 Week 2. D th b. 4 Week 3. C th c. 4 month 4. C th 11 d. 5 month. 5. D Done by: Embryology team 434 Thank you for checking our team For any questions or suggestions please email us: [email protected] 12 .