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Fetal membranes , placenta and twins


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Mohamed El Fiky

Published in: Health & Medicine
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Fetal membranes , placenta and twins

  1. 1. Fetal membranes , placenta & twins Dr. Mohamed El fiky Professor of anatomy and embryology
  2. 2. Early Human Development Mohamed el fiky
  3. 3. Early Human Development Mohamed el fiky
  4. 4. Early Human Development Mohamed el fiky
  5. 5. Early Human Development Mohamed el fiky
  6. 6. Embryo after folding Head swelling Cardiac swelling Umbilical cord Y.S G U T Mohamed el fiky
  7. 7. • The term fetal membrane is applied to those structures derived from the blastocyst which do not contribute to the embryo. ØThe amnion, Øthe chorion, Øthe yolk sac ØAllantois ØUmbilical cord Mohamed el fiky
  8. 8. Amnion •Amniotic membrane : amniotic epi. + extraembryonic mesoderm •Amniotic fluid: Produce:1)amniotic cells 2) infusion of fluid from maternal blood 3) urine output from the fetus 4) pulmonary secretions Output: 1) absorbed by amniotic cells 2) fetus swallow Mohamed el fiky
  9. 9. Amniotic Fluid • Plays a major role in fetal growth and development. • Daily contribution of fluid from respiratory tract is 300-400 ml. • 500 ml of urine is added daily during the late pregnancy. • Amniotic fluid volume is 30 ml at 10 weeks, 350 ml at 20 weeks, 700-1000 ml at 37 weeks. Mohamed el fiky
  10. 10. Composition of Amniotic Fluid • 99 % is water • Desquamated fetal epithelial cells • Organic & inorganic salts • Protein, carbohydrates, fats, enzymes, hormones • Meconium & urine in the late stage Abnormalities of amniotic fluid • Oligo-hydramnios: the volume of the amniotic fluid is less than ½ litre. This may lead to adhesions between the embryo and the amnion. • Poly-hydramnios: the volume of the amniotic fluid is more than 2 litres. This may lead to premature rupture of the amnion. Mohamed el fiky
  11. 11. Significance of Amniotic Fluid • Permits symmetrical external growth of the embryo and fetus • Acts as a barrier to infection • During labor it help dilatation of the cervix of the uterus and It wash birth canal and protect the fetus against infections • Prevents adherence of amnion to fetus • Cushions & protects the embryo and fetus • Helps maintain the body temperature • Enables the fetus to move freely Mohamed el fiky
  12. 12. Yolk Sac • It is large at 32 days • Shrinks to 5mm pear shaped remnant by 10th week & connected to the midgut by a narrow yolk stalk • Becomes very small at 20 weeks • Usually not visible thereafter Primary yolk sac secondary yolk sac Mohamed el fiky
  13. 13. Significance of Yolk Sac • Has a role in transfer of nutrients during the 2nd and 3rd weeks • Blood development first occurs here • Incorporate into the endoderm of embryo as a primordial gut • Primordial germ cells appear in the endodermal lining of the wall of the yolk sac in the 3rd week Mohamed el fiky
  14. 14. Fate of Yolk Sac • At 10 weeks lies in the chorionic cavity between chorionic and amniotic sac • Atrophies as pregnancy advances • Sometimes it persists throughout the pregnancy but of no significance • In about 2% of adults the proximal intra-abdominal part of yolk stalk persists as an ileal diverticulum or Meckel diverticulum Mohamed el fiky
  15. 15. Allantois • In the 3rd week it appears as a sausagelike diverticulum from the caudal wall of yolk sac that extends into the connecting stalk • During the 2nd month, the extraembryonic part of the allantois degenerates Mohamed el fiky
  16. 16. Functions of Allantois • Blood formation occurs in the wall during the 3rd to 5th week • Its blood vessels persist as the umbilical vein and arteries • Becomes Urachus and after birth is transformed into median umbilical ligament extends from the apex of the bladder to the umbilicus Anomalies of allantois: • Urachal fistula: The urachus remains patent, urine discharges from the umbilicus. • Urachal sinus: The upper end of the urachus remains patent. • Urachal cyst :The middle part of the urachus remains patent. Mohamed el fiky
  17. 17. The Umbilical Cord Anatomy •Origin : It develops from the connecting stalk. •Length: At term, it measures about 50 cm. •Diameter: 2 cm. Mohamed el fiky
  18. 18. Structure: It consists of mesodermal connective tissue called Wharton's jelly, covered by amnion. It contains: 1. One umbilical vein carries oxygenated blood from the placenta to the foetus 2. Two umbilical arteries carry deoxygenated blood from the foetus to the placenta, 3. Remnants of the yolk sac and allantois. The Umbilical Cord Mohamed el fiky
  19. 19. Insertion: •The cord is inserted in the foetal surface of the placenta near the center "eccentric insertion" (70%) • Or at the center "central insertion" (30%). The Umbilical Cord Mohamed el fiky
  20. 20. Abnormalities Of The Umbilical Cord
  21. 21. (A) Abnormal cord insertion 1. Marginal insertion : in the placenta ( battledore insertion). 2. Velamentous insertion: in the membranes and vessels connect the cord to the edge of the placenta. • If these vessels pass at the region of the internal os , the condition is called " Vasa praevia". 1. Short cord which may lead to : i-Intrapartum haemorrhage due to premature separation of the placenta, ii-Delayed descent of the foetus druing labour, iii-Inversion of the uterus. 2. Long cord which may lead to i-Cord presentation and cord prolapse, ii-Coiling of the cord around the neck, iii-True knots of the cord. Mohamed el fiky Velamentous insertion(B) Abnormal cord length
  22. 22. Chorion Chorion 1- extraembryonic mesoderm 2- cytotrophoblast 3- Syncytiotrophoblast Chorion • Definition : Chorion is the name given to the trophoblast after the formation of the extraembryonic mesoderm from its inner surface. • The chorion is composed of : • Syncito-trophoblast (outer layer). • Cytotrophoblast (middle layer). • Extra-embryonic mesoderm (inner layer). Mohamed el fiky
  23. 23. CHORION FRONDOSUM AND DECIDUA BASALIS • In the early weeks of development, villi cover the entire surface of the chorion . As pregnancy advances, villi on the embryonic pole continue to grow and expand, giving rise to the chorion frondosum (bushy chorion). Villi on the abembryonic pole degenerate and by the third month this side of the chorion, now known as the chorion laeve, is smooth Mohamed el fiky
  24. 24. Chorion • Chorionic villi cover the entire chorionic sac until the beginning of 8th week • As this sac grows, the villi associated with decidua capsularis are compressed, reducing the blood supply to them • These villi soon degenerates producing an avascular bare area smooth chorion (chorion laeve) • As the villi disappear, those associated with the decidua basalis rapidly increase in number • Branch profusely and enlarge • This bushy part of the chorionic sac is villous chorion Mohamed el fiky
  25. 25. CHORIONIC VELLI • By the beginning of the third week, the trophoblast is characterized by primary villi that consist of a cytotrophoblastic core covered by a syncytial layer. During further development, mesodermal cells penetrate the core of primary villi and grow toward the decidua. The newly formed structure is known as a secondary villus . • By the end of the third week, mesodermal cells in the core of the villus begin to differentiate into blood cells and small blood vessels, forming the villous capillary system . The villus is now known as a tertiary villus or definitive placental villus. Mohamed el fiky
  26. 26. PRIMARY villous •Growth of these extensions are caused by underlying extraembryonic somatic mesoderm •The cellular projections form primary chorionic villi Mohamed el fiky
  27. 27. SECONDARY CHORIONIC VILLI Early in 3rd week, extraembryonic mesoderm extends inside the villi Mohamed el fiky
  28. 28. Tertiary villus During 3rd week, arterioles, venules & capillaries develop in the mesenchyme of villi & join umbilical vessels By the end of 3rd week, embryonic blood begins to flow slowly through capillaries in chorionic villi Mohamed el fiky
  29. 29. Decidua • The gravid endometrium is known as decidua • It is the functional layer of endometrium in a pregnant woman • This part of the endometrium separates from the rest of the uterus after parturition Mohamed el fiky
  30. 30. Parts of decidua • Decidua basalis: It is the part of decidua between blastocyst and myometrium. It forms the fetal part of placenta. • Decidua capsularis: It covers the blastocyst except embryonic pole and separates it from uterine cavity. • Decidua parietalis: It is the rest of endometrium that lines the rest of uterine cavity. Mohamed el fiky
  31. 31. Fate of decidua • Decidua basalis shares in the formation of placenta. • Decidua capsularis and parietalis fuse together and shedded with placenta after delivery. Decidua basalis Amniotic cavity Fused decidua paritalis , chorion laeve and amnion Mohamed el fiky
  32. 32. 32 PLACENTA • This is a fetomaternal organ. • It has two components: • Fetal part – develops from the chorion frondosum ) • Maternal part – derived from the decidua basalis ) Mohamed el fiky
  33. 33. Mohamed el fiky
  34. 34. • During the 4th and 5th month, the decidua forms a number of decidual septa, which project into the intervillous space. • As a result of this septum formation, the placenta is divided into a number of compartments (cotyledons). Mohamed el fiky
  35. 35. PLACENTAL MEMBRANE (placental barrier) • This is a composite structure that separating the fetal blood from the maternal blood. • Early placental barrier : (It has four layers): • Syncytiotrophoblast • Cytotrophoblast • Connective tissue of villus • Endothelium of fetal capillaries • Late placental barrier : After the 20th week, the cytotrophoblastic cells disappear and the placental membrane consists only of 2 layer : • Syncytiotrophoblast • Endothelium of fetal capillaries 35Mohamed el fiky
  36. 36. 36 It separates fetal from maternal blood. It prevents mixing of them. It is an incomplete barrier as it only prevents large molecules to pass ( heparin & bacteria) But cannot prevents passage of viruses(e.g. rubella), micro- organisms(toxoplama, treponema pallidum) drugs and hormones. Mohamed el fiky
  37. 37. is discoid in shape. n Diameter = 15-25 cm, n 2-3 cm thick, n Weight = 0.5 kg. n Umbilical cord is attached to its center. nPosition : in the upper uterine segment (99.5%), either in the posterior surface (2/3) or the anterior surface (1/3). The full term placenta Mohamed el fiky
  38. 38. 1- Fetal surface: which is smooth and shinny because it is covered by an amniotic membrane. The umbilical cord is attached centrally to this surface. 2- Maternal surface: which is rough, reddish, and has 15 – 20 elevated areas called cotyledons with deep grooves in between made by the decidual septa. Surfaces Mohamed el fiky
  39. 39. Function of placenta:- 1. Respiratory function 2. Excretory function 3. Nutritional function 4. Endocrine function:- placenta acts as endocrine gland 5. Barrier function:- prevents transfer of maternal infection. 6. Enzymatic action- 7. Immunological function:- ig G. Mohamed el fiky
  40. 40. Abnormalities Of The Placenta (A) Abnormal Shape (B) Abnormal Diameter (C) Abnormal Weight (D) Abnormal Position (E) Abnormal Adhesion Mohamed el fiky
  41. 41. Abnormalities of placenta 1- Abnormal position: Placenta Previa the placenta is attached to the lower uterine segment (due to low level of implantation of the blastocyst). It causes severe antepartum haemorrhage. There are three types: Mohamed el fiky Marginalis Lateralis (parietalis) Centralis the placenta does not reach the internal os of the cervix. the margin of the placenta overlies the internal os of the cervix. the center of the placenta overlies the internal os of the cervix .
  42. 42. 2- Abnormal adhesion: 1- Placenta accreta: due to abnormal adhesion between the chorionic villi and the uterine wall. 2- Placenta percreta: The chorionic villi penetrate the myometrium all the way to the perimetrium. - the placenta fails to separate from the uterus after birth and may cause severe postpartum hemorrhage. Mohamed el fiky
  43. 43. 3- Abnormal attachment of umbilical cord: a- Velamentous attachment: The cord does not reach the placenta itself but is attached to amniotic membrane over the fetal surface of placenta. The umbilical vessels pass in the membrane to reach the placenta. It is easly torn. Mohamed el fiky
  44. 44. (4) Abnormal Shape A- Accessory placenta: one or two lobes are completely separated from the main placenta. Bilobate , Bipartite B- Placenta Fenestrate (5) Abnormal Diameter : Placenta membranacea : The placenta is large, thin and may measure 30-40 cm in diameter. may encroach on the lower uterine segment Mohamed el fiky
  45. 45. Twins Mohamed el fiky
  46. 46. Twins • Di-zygotic twins • Incidece : more common (70%). • Mechanism of development : results from fertilization of 2 ova (from 2 ovaries ) during an overian cycle by 2 separate sperms. • Placenta : 2 separate placentae. • Chorion : 2 separate chorionic sacs. • Sex : may be of the same or different sex. • Features : different fetures. Mohamed el fiky
  47. 47. Twins •zygotic -Mono • Incidece : less common. results from fertilization of one ova by one sperms. • Mechanism of development : results from division of a single fertilized ovum during one of the following stages of development: • Two cell stage. • Stage of blastocyst, where the inner cell mass divides into 2 masses. • Placenta : single common placenta. • Chorion : single common chorionic sac. • Sex : always of the same sex. • Features : exactly identical. Mohamed el fiky