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Embryology

Elly Scanlon English

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Embryology

Fertilisation
- Gametes fuse
  - Sperm + oocyte -> Zygote
    - 2x 23 = 46 chromosomes
      - = fertilization
    - 1. Sperm penetration
      - Divided into three phases
        Penetration of corona radiata
        Penetration of zona pellucida + acrosome reaction
        Fusion of the oocyte and sperm cell membranes
    - Oocyte
      - Develops in follicles
        Extruded onto surface of ovary
        Swept up into fallopian tube by fimbriae
        Moves down tube - peristaltic contractions
        Enters uterus
    - Block to polyspermy
      - Electrical block
        Fast, change in membrane potential
      - Cortical reaction
        Slow
        Calcium wave -> granules -> membrane -> lysosomal enzymes -> alter zona pellucida
    - 2. Nuclear combination
      - Male pronucleus forms
        Pronuclei fuse
        Division of genetic material
  - Known as gametogenosis
- Cleavage
  - 1. Zygote --> blastomeres
    - Still has ZP
      - Division not accompanied with growth
    - 1 --> 14
  - Implantation
    - Placenta formation
      - Embryo = almost completely embedded in uterine wall
      - Gastrulation
        Neurulation
        Ectoderm forms
        Neural tube
        Neural crest
        Notochord = mesoderm
        1. N -Induces the ectoderm to form the neural plate
        2. Neural plate folds
        3. Neural crest bought together
        medial hinge point
        Dorso-lateral
        4. Neural crest meets and fuses
        5. Neural tube folds
        6.Neural crest cells detach and migrate
        7. ectoderm fuses
        8. Neural tube incorporated into body
        Neural tube defects
        See FC
        Mesoderm
        Somitogenesis
        Body folding
        Lateral
        Right and left edges of amniotic cavity move towards yolk sac
        Constricts the neck of the yolk sac
        Each layer fuses with the same layer on the otherside
        Sphlanchnic mesoderm is pinched off and forms a tube
        Covers visceral organs
        Ectoderm covers surface
        Somatic mesoderm forms the body wall
        Gut is formed
        Cephalocaudal
        Growth of brain vesicles causes this
        Larger proportion of endeoderm --> body proper
        Endoderm gives rise to digestive and respiratory tube
        Two gut regions established
        Occurs progressively from anterior to posterior
        From paraxial mesoderm
        balls of cells that are made either side of NT
        Hox genes control identity of somites
        Paraxial mesoderm
        Forms axial skeleton
        And limb and axial muscles
        Forms Somites
        Lateral plate mesoderm
        Extraembryonic mesoderm
        Cavities develop
        Seperates mesoderm
        Somatic mesoderm
        Splanchnic mesoderm
        Limb skeleton
        Mesenteries
        Blood, heart and circulatory system
        Intermediate mesoderm
        Forms urogenital system
        Chorda mesoderm
        Embryoblast = pluripotent
        1. Differentiates
        Bilaminar embryonic disk
        Epiblast
        2. A cavity forms
        Epiblast cells lining the cavity = amnioblasts
        Cavity = amniotic cavity
        10. Gastrulation begins
        11. Formation of primitive streak @ CAUDAL END
        12. Primitive node develops @ CEPHALIC END
        13. Epiblast cells migrate to the streak
        14. Change morphology and detach
        15. Cells invaginate
        Displace the hypoblast
        Embryonic ENDODERM
        Gut tube
        Lie between Epi and Hypo
        Embryonic MESODERM
        Muscle bone urogenital system
        or don't invaginate
        Embryonic ECTODERM
        Nervous system
        Where cells invaginate changes fates
        Primitive node
        Notochord
        Paraxial mesoderm
        Primitive streak
        Paraxial mesoderm
        Lateral mesoderm
        Extraembryonic mesoderm
        Epiblast cell
        Bottle cell
        Mesenchymal
        Hypoblast
        3. Some of these cells migrate
        to line blastocoele
        4. Cell flatten --> extracoelomic membrane
        Space between EM and cytotrophoblast becomes
        5. Extraembryonic mesoderm
        Expand to surround entire amnion
        6. Cavities appear in the Extra Meso
        7. Fuse --> Chorionic cavity
        8. Chorionic cavity expands
        9. Connecting stalk left
        Twinning - see flashcards
      - 1. Vacuoles appear in syncytiotrophoblast
        2. Vacuoles fuse --> Lacunae
      - 3. Syncytiotrophoblast erodes endothelial lining of maternal capillaries
        4. Blood vessels form sinusoids
        5. Lacunae and sinusoids fuse
        Blood enters lacunae system
      - 6. Cytotrophoblast proliferates --> primary villi
        Will contain capilarries --> embryonic circulatory system
      - 7. Primary villi --> secondary --> tertiary
    - 1. Blastocyst attaches to uterine wall
      - Uterine wall
        Perimetrium
        Myometrium
        Endometrium
        This is where the blastocyst implants
        Developing oocyte --> Oestrogen --> builds up uterine wall
        Progesterone --> lining matures
      - 2. Penetration of endometrium
        3. Syncytiotrophoblast envelops embryo
        Trophoblast differentiates
        Cytotrophoblast
        Syncytiotrophoblast
        Sends projections through endometrial cells
        Allowing embryo to bury deeper into the endometrium
      - Endometrium posesses adhesion molecules
      - Moolecular velcro on trophoblast cells of blastocyst
      - Attachememnt occurrs above embryoblast cells
    - Abnormal implantation
      - See flashcards
  - 2. Compaction at 8 cell stage
    - Tight Junctions form between outside cells
  - 3. 16 cell stage - Morula
  - 5. Morula develops a blastocoele
    - Uptake of fluid increases hydrostatic pressure
      - Leads to fluid filled chamber (blastocoele)
        Seperates embryoblast from trophoblast
  - 6.. Morula --> blastocyst
    - Hatching occurrs
      - Zygote bores out of ZP
  - 4. Get differentiation of cells on the inside and the outside
    - Embryoblast
    - Trophobplast

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Description: Mind Map on Embryology, created by Elly Scanlon on 28/03/2017.
Created by: Elly Scanlon
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Embryology

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