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Foetal membranes

Foetal membranes. Fertilization & Implantation. Implantation. Formation of lacunae. Radial arrangement of lacunae. Primary villi. Secondary villi. Tertiary villi. Cytotrophoblastic shell. Maternal surface. Free villi. Term Pacenta. Maternal Cotyledons. Formation of Umbilical Cord.

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Foetal membranes

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  1. Foetal membranes

  2. Fertilization & Implantation

  3. Implantation

  4. Formation of lacunae

  5. Radial arrangement of lacunae

  6. Primary villi

  7. Secondary villi

  8. Tertiary villi

  9. Cytotrophoblastic shell

  10. Maternal surface

  11. Free villi

  12. Term Pacenta

  13. Maternal Cotyledons

  14. Formation of Umbilical Cord

  15. Foetal membranes & Placenta • Structures that are developed from Zygote but do not form the parts of the embryo or foetus • Exception: parts such as yolk sac and allantois • Responsible for protection and nourishment of the embryo and foetus • Includes yolk sac, allantois, amnion and chorion

  16. Foetal membranes • Yolk sac • Development of primitive yolk sac – 2nd week (early part) • Development of secondary yolk sac – 2nd week (Late part) • Covered by extra embryonic splanchnopleuric mesoderm • Lined by endodermal cells • Incorporation into the body of the embryo • Formation of foregut, mid gut and hindgut

  17. Foetal membranes • Yolk sac (contd) • Development of the vitelline duct - disappears • If persists - Meckel’s diverticulum • Vitelline vessels develop in the mesoderm covering the yolk sac • Plays important role in the transfer of nutrients

  18. Foetal membranes • Allantois • 2nd week of IUL • Arises as diverticulum from the caudal end of the yolk sac • Grows into the body stalk • Umbilical vessels develop in close association • Becomes a fibrous cord called urachus • Related to the development of the urinary bladder

  19. Foetal membranes • Formation of primitive Umbilical cord • Fusion of the mesoderm of the connecting stalk and yolk sac • Covered by the epithelium of the amnion • Primitive umbilical ring - meeting point of the amnion and ectoderm • Attachments • Center of the foetal surface of the placenta • Center of the anterior abdominal wall

  20. Foetal membranes • Structure passing through the umbilical ring • Connecting stalk • 2 umbilical arteries • 1 umbilical vein • Yolksac with vitelline vessels

  21. Foetal membranes-Umbilical cord • When fully developed • Length - 18 inches • Thickness – 1 inch • Cord is twisted presenting false knots • Rarely presents true knots – may tighten – causing fetal death due to anoxia • Long cord may occasionally encircle the neck • Contents of the cord • Whaton’s jelly – Mucoid connective tissue • Urachus • Umbilical vein – one • Umbilical arteries – two • Vessels are longer then the cord

  22. Amnion and amniotic cavity • Amnion is formed by amnioblasts • They are derived from epiblasts • Lines the cavity called amniotic cavity • Filled with clear, watery fluid produced by amniotic cells • Embryo is suspended during the early months of pregnancy • The fluid absorb jolts, prevents the adherence of the embryo to the amnion

  23. Amnion and amniotic cavity • Allows foetal movements • The water in the cavity change every three hours • By 5th month foetus swallows fluid • At the end of the pregnancy urine is added to the fluid • The aquatic habitat provided uniform hydrostatic support for the delicate body of the embryo and prevents asymmetrical development • 800 to 1000 ml at 37 weeks

  24. Amnion and amniotic cavity • Hydramnios – Excess of amniotic fluid (1500-2000 ml) • Oligohydramnios – decreased amount of amniotic fluid (less than 400 ml) • Premature rupture of the amniochorionic membrane

  25. Amniotic bands • Tears in amnion – amniotic bands • Bands encircles the parts of the fetus, particularly the limbs and digits • Results in amputations, ring constrictions, and craniofacial abnormalities

  26. Placenta • Human placenta is discoid in shape • Connects foetus to the uterine wall through umbilical cord • Developed from two sources • Decidua basalis • Chorionic frondosum

  27. Placenta • Development of decidua basalis • Endometrial stromal cells are modified during pregnancy – decidual cells • Contain abundant amount of lipids and glycogen • Decidual basalis, parietalis and capsularis • Development of decidual septa – 4th month • Formation of 15 – 20 cotyledons ( Compartments)

  28. Placenta • Development of chorionic frondosum • 2nd week – uteroplacental circulation • 3rd week – tertiary villi formation • 4th week – heart begins to beat • Rapid growth chorionic villi • Formation of outer cytotrophoblastic shell • Villi are anchored by chorionic plate and cytotrophoblastic shell • Rapid expansion of size and complexity opposite to the decidua basalis

  29. Placental barrier

  30. Placental barrier • Maternal hormones do not cross • Hormones that cross the placenta • Thyroxine • Synthetic oestrogen (diethylstilbestrol) • Viruses • Rubella virus • Measles • Poliomyelitis virus • Drugs and drug metabolites

  31. Placenta • Full term placenta • Discoid in shape • Diameter 15 – 25 cms • Thickness – 3 cm • Weight – 500 – 600 grams • Surface • Foetal surface • Amnion • Chorionic vessels • Attachment of umbilical cord

  32. Full term placenta

  33. Placenta • Maternal surface • Show cotyledons • Decidua basalis • Placental barrier is of haemochorial type • Dividing membrane between maternal and foetal circulation

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