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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

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fetal membranes 2

Fetal Membranes 2

Dr Rania Gabr


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
  • SHAPE: circular disc
  • WEIGHT: about one-sixth that of fetus (500-600 gm)
  • DIAMETER: 15-20 cm
  • THICKNESS: 2-3 cm

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)

  • 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
Functions of the Placenta
  • Exchange of metabolic & gaseous productsbetween 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
anomalies of placenta
  • Normally chorionic villi persist only at site of decidualbasalis:
  • 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
anomalies of placenta1
  • Placenta previa: when blastocyst implants close to or overlying internal os of uterus late pregnancy bleeding
  • Placenta accreta: chorionic villi extend to the myometrium
  • Placenta percreta: chorionic villi penetrate the whole thickness of myometrium & extend to perimetrium
anomalies of placenta2
  • 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
Battledore placenta

Velamentous insertion of cord

umbilical 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
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
  • Theumbilical 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
Umbilical Cord: Formation cont’d
  • Initial contents:
    • Connecting stalk
    • Umbilical vessels
    • Allantois
    • Yolk sac
    • Extraembryoniccelome
    • Intestinal loop (during 6-10 weeks)
umbilical cord at term
Umbilical Cord: At Term

At term, the typical umbilical cord:

  • Is 55-60 cm in length,with adiameter of 2-2.5 cm
  • Hasknottyappearance
  • Usually contains two arteriesandone vein
  • Issurrounded by a jelly like substance called the Wharton's jelly
  • Is enclosed in amnion


umbilical cord placental attachment
Umbilical Cord: Placental Attachment

May attach to the placenta near its margin- Marginal attachment

Typically attaches to the placenta near its center- Eccentric attachment


May attach to the membranes around the placenta- Membranous (Velamentous ) attachment

umbilical cord cont d
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
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