Early Embryology Simple Summary

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Week 1
Ovarian cycle:
GnRH from hypothalamus FSH and LH from pituitary cyclic changes in the ovary.
Follicular phase: * 15-20 preantral follicles start to grow due to FSH * 1 reaches full maturity released * Others undrgo atresia * Estrogens are released which; 1. Proliferate endometrium 2. Thin the cervical mucus 3. Stimulate pituitary to release LH * The LH; 1. Elevate concentrations of maturation promoting factor (oocytes complete meiosis one and begin meiosis II, stopped at metaphase) 2. Stimulate progesterone production by follicular stromal cells (luteinisation) 3. Cause follicular rupture

* High concentration of LH makes the collagenase
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Week 4 * Folded disc * Neural plate closing to become neural groove * Neuropores are open * Heart bulge * Big paraxial mesoderm * Beginning of Guts * Pharyngeal arches start to emerge

Week 5 * Forebrain * pharyngeal arches (each one has all 3 germ layers) * upper limb bud * liver bulge * placodes present * Late in the week = lower limb bud, bigger first pharyngeal arch. * Begin to see stomach

Week 6 * Cranial flexure * Cervical flexure * Vertebral discs forming from somites * Dermis is spreading out * 3rd and fouther arch are buried under the skin with the Otic placode * Upper limb bud has fan structure
Week 7 * Arches are merging * Mesonephric swelling * Ossification occurs
Week 8 * Elbow and shoulders are evident * Later can see wrist and knee * Vascular plexus on skull * All of inner ear structures are formed
Week 9
Mesenchyme around membranous labyrinth chondrifies
Week 12 – 16
Capsule adjacent to membranous labyrinth undergoes vacuolisation to form cavity around membranous labyrinth and fills with perilymph
Week 16-24
Centres of ossification appear in remaining cartilage of otic capsule petrous part of temporal bone.
Face and Neck * Each arch consists of the 3 germ layers + neural crest cells that will form the skeletal components. * Mesoderm muscles of the face and neck
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