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Early Embryology Simple Summary

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Embryology
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
Ovulation

* 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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