Fetal Membranes 2 Dr Rania Gabr

Objectives By the end of this lecture, the student should be able to: Describe the structure, functions, anomalies of the placenta Describe the structure, functions, anomalies of the umbilical cord

PLACENTA SHAPE: circular disc WEIGHT: about one-sixth that of fetus (500-600 gm) DIAMETER: 15-20 cm THICKNESS: 2-3 cm SURFACES: 1. Fetal surface: smooth, transparent, covered by amnion with umbilical cord attached near its center & umbilical vessels radiating from it 2. Maternal surface: irregular, divided into convex areas (cotyledons)

Each cotyledon contains 2 or more stem villi with their branch villi PLACENTA The fetal part of placenta is divided into cotyledons by projections from decidua basalis (placental septa) Each cotyledon contains 2 or more stem villi with their branch villi By the end of 4th month, decidua basalis is almost entirely replaced by cotyledons

PLACENTAL CIRCULATION Poorly oxygenated blood leaves the fetus & passes through the 2 umbilical arteries to the placenta Umbilical arteries divide into several chorionic arteries that enter chorionic villi An arterio-capillary-venous network is formed in chorionic villi Exchange of materials between fetal & maternal blood (in intervillous spaces) occurs across placental membrane (barrier) Oxygenated blood returns to fetus by umbilical vein

Functions of the Placenta Exchange of metabolic & gaseous products between maternal & fetal bloodstreams Respiratory function: Exchange of gases – Nutritive function: Exchange of nutrients & electrolytes – Transmission of maternal antibodies – Excretory function: Co2 and other stuff Barrier function: prevents passage of some bacteria and some drugs from maternal to fetal blood.

Endocrine function: Production of hormones Protein hormones: Human chorionic gonadotropin (early pregnancy tests) Human placental lactogen Human chorionic thyrotropin Human chorionic corticotropin Relaxin Steroid hormones: Progesterone Estrogen

Normally chorionic villi persist only at site of decidual basalis: ANOMALIES OF PLACENTA ANOMALIES IN SIZE & SHAPE: Normally chorionic villi persist only at site of decidual basalis: Placenta membranacea: a large thin membranous placenta due to persistence of functioning villi on the entire surface of chorionic sac Accessory placenta: a patch of chorionic villi persisted a short distance from main placenta

ACCESSORY PLACENTA

PLACENTA PREVIA, ACCRETA & PERCRETA

ANOMALIES OF PLACENTA ANOMALIES IN POSITION: Placenta previa: when blastocyst implants close to or overlying internal os of uterus late pregnancy bleeding ANOMALIES IN EXTENSION: Placenta accreta: chorionic villi extend to the myometrium Placenta percreta: chorionic villi penetrate the whole thickness of myometrium & extend to perimetrium

ANOMALIES OF PLACENTA ANOMALIES IN ATTACHMENT OF UMBILICAL CORD: Battledore placenta: the cord is attached to the margin of placenta Velamentous insertion of cord: the cord is attached to the membranes surrounding placenta, umbilical vessels are liable to be ruptured

Velamentous insertion of cord Battledore placenta Velamentous insertion of cord

Umbilical Cord Cord like structure Connects fetus to the placenta Attached to the ventral surface of the fetal body and to the smooth chorionic plate of the placenta

Umbilical Cord: Formation Develops from the connecting stalk The connecting stalk initially attached to the caudal end of the embryonic disc, after folding, becomes attached to the ventral surface of the curved embryonic disc, at the umbilical region The umbilical region wider initially, becomes narrower as the folding progresses The underlying structures are compressed together and form a cord like structure, the umbilical cord

Umbilical Cord: Formation cont’d Initial contents: Connecting stalk Umbilical vessels Allantois Yolk sac Extraembryonic celome Intestinal loop (during 6-10 weeks)

Umbilical Cord: At Term At term, the typical umbilical cord: Is 55-60 cm in length, with a diameter of 2-2.5 cm Has knotty appearance Usually contains two arteries and one vein Is surrounded by a jelly like substance called the Wharton's jelly Is enclosed in amnion amnion

Umbilical Cord: Placental Attachment May attach to the placenta near its margin- Marginal attachment Typically attaches to the placenta near its center- Eccentric attachment placenta May attach to the membranes around the placenta- Membranous (Velamentous ) attachment

Umbilical Cord cont’d After delivery of the placenta the umbilical cord is usually clamped and severed The site of its attachment leaves a scar, the navel (belly button), on the anterior wall of the abdomen

Abnormalities Related to Umbilical Cord Omphalocele: Failure of returning of intestinal loops back into the abdominal cavity Long cord may prolapse or coil around the fetus thus cause difficulty in labour Short cord may result in premature pull and separation of placenta causing severe bleeding during birth True knots True knot Prolapsed cord

Thank You & Good Luck