Embryology

Embryology

1. Importance of embryology

   •  Birth defects lead to 270,000 neonatal deaths per year (2010 data)   Birth defects are a major contributor to morbidity, including physical and mental handicaps.  All women of childbearing age are at risk of having an infant with a birth defect. The incidence rate is 6/100 births.
   • Birth defects - major contributor to morbidity, including physical and mental handicaps
   • All women of childbearing age at risk of having an infant with birth defect
     • IIncidence rate = 6/100 births.
   • Before week 8 = embryo
     • after = foetus
   • Week 5 is peak time for birth defects to be induced
   • 20 weeks = gender scan

2. Early stages in an embryo’s development

   • 1st days 28 days in particular
   • 1st week
     • Release of follicle and wafted in by fimbria in uterine tube
     • Fertilisation usually occurs near ampulla
     • Corpus luteum maintained
     • Male and female pronuclei stage
     • Eventually implant in uterine wall
       • maintained thick - v vascular and lots of secretions as well
     • Morular stage
       • FIND OUT
     • 5-6 days - blastocyst formed
       • moves from ball of cells to with hole - SURROUNDING TROPHOBLASTS - FROM WHICH PLACENTAL TISSUES DERVIED -AND INTERNAL EMBRYOBLASTS- ALL EMBRYONIC TISSUES DERIVED - AT TIME OF IMPLANTATION
     • Ectopic pregnancy
       • COMPLETE THIS tubule pregnancy`?
       • wall of uterus
       • Cervix
       • Fallopean
       • Mesenteric
         • most common is rectal uterine pouch - due to gravitational pull
       • Sites
       • Can be fatal if ruptures - lots of blood
     • After 6 days - differentiation of trophoblast cells
     • Form sincitial trophoblasts
       • secret HCG
         • preg tests
         • influence corpus luteum to influence uterine wall
   • FOETUS
     • ROSTRAL - FRONT (BEAK) FACE CRANIAL - HEAD CAUDAL - BOTTOM VENTRAL ANS DORSAL
   • 2nd week
     • LOOK AT PPT TO COMPLETE
     • Day6-7.5
       • Further invasion and picks up blood supply as it goes
     • 9 days - fibrin and coagulin
     • End of week 2 - almost fully encirculated in lacunae of blood

3. Process of gastrulation

   • PPT DIAGRAMS  if wrong: too short - e.g. caudal diagenesis - mermaid syndrome too long - e.g. sacrococcygeal teratoma - within this find remnants of primitive streak
   • Define all your cell layers
     • 1layer - divide to have 3 cell layers migration of cells - primitive streaks
   • Process of forming 3 primary germ cell layers from the epiblast. Arises due to migration of cells through the primitive streak to form endoderm and mesoderm.
   • In epiblast groove starts to form at caudal end - primitive streaks
     • Epiblast cells move towards primitive streak - some migrate in and settle down at that layer different layers stay at top - ectoderm mesoderm - middle endoderm - bottom
   • At top of primitive streaks is primitive node which is known as the organiser
   • Transforms disc from bilaminar to trilaminar structure
   • Notochord
     • ORGANISER
     • umn of midline cells vital for induction of the neural plate, motor region of the brain & spinal cord and vertebral formation.
     • Formation

4. Derivatives of the germ layers

5. Process of neurulation

   • Process transforming the neural plate into the neural tube. From 3rd week-d.28.
     • if not formed by then, problems start to occur
   • Neural plate - induced cranially
   • Week 3 and 4
   • As this occurs, gastrulation and primitive streak continue caudally (at the same time)
   • Neural plate elevates above the epiblastic layer
   • Plate thickens and forms neural groove
     • Eventually seals off to neural tube
   • From surface ectoderm?
   • DIAGRAM
   • Closes starts at 23 - start to seal off at top and bottom
   • Neural Tube Defects
     • Due to lack of closure of different regions of the neural tube
     • Anencephaly
       • Abnormal cranial nerual tube closure
     • Spinal bifida
       • Can be cyst at base of spine

6. Formation of the CNS

7. Body folding results in foetal position