UNSW Embryology

Week 2

© Dr Mark Hill (2011)

Acknowledgements

Introduction

Implantation begins first with attachment (adplantation) of the blastocyst through the outer trophopoblast cells to the uterine lining. Following adplantation, trophoblast cells on the outside differentiate into syncitiotrophoblasts which invade the uterine endometrium. The blastocyst then moves moves into the endometrium, initially partially buried, and on completion of implantation, is fully buried in the endometrium. The site of implantation is marked on the surface by a "plug".

• Normal sites of implantation in the uterus
  • uterine wall
  • posterior, lateral
  • cervix, superior
• Abnormal
  • Tubal or Ectopic (not in uterus)
• Abnormal Implantation
  • often occurs if zona pellucida is lost too early allowing premature implantion
  • Tubal pregnancy 94%
  • embryo may develop through early stages.
  • can erode through the uterine horn
  • reattach within the peritoneal cavity
• Ectopic Pregnancy
  • external surface of uterus
  • bowel
  • gastrointestinal tract, mesentry
  • peritoneal wall
  • If not spontaneous then, embryo has to be removed surgically
• Normal Implantation- Endometrium
  • consists of 3 layers in secretatory phase of menstral cycle
    • compact
      • implantation odccurs in this layer
      • dense stromal cells, uterine gland necks, capillaries of spiral arteries
    • spongy
      • swollen stromal cells, uterine gland bodies, spiral arteries
    • basal
      • not lost during menstruation or childbirth, own blood supply
  • Myometrium
    • muscular layer outside endometrium
    • contracts in parturition

Quick Links

Week 2 Pages:

Introduction | Timeline Week 2 | Carnegie stages 5 to 7 | Abnormalities | Blastocyst Implantation | Sites of Implantation | Bilaminar Embryo | Embryonic Cavitites | Early Placentation | Molecular | Stem Cells | References | Text only | WWW Links | Movies - Week 2

Development Notes ----------------- Menstrual Cycle Week 1 Week 2 Week 3 Week 4 Placenta Serial Images Molecular Dev Abnormal Dev Postnatal Dev Notes Index

System Notes ----------------- All Systems Heart/Cardiovascular Respiratory Coelomic cavity Gastrointestinal Tract Head and Neck Neural Neural Crest Eye Ear Nose Endocrine Renal Genital Musculoskeletal Integumentary

Movies ----------------- Movies Quicktime Flash Audio Week 1 Week 2 Week 3 Stage 13 Stage 22 Neural Heart Gastrointestinal Renal Genital Other Embryos

Other Embryos ----------------- All Animals Chicken Fly Frog Mouse Rabbit Rat Worm Zebrafish Guinea Pig

UNSW Embryology ISBN: 978 0 7334 2609 4

UNSW CRICOS Provider Code No. 00098G