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Week 5 - Human Embryo Stages and Events (GA week 7) 
Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9
Pituitary - Week 5 elongation, contacts infundibulum, diverticulum of diencephalon

Heart - Week 5 septation starts, atrial and ventricular

Respire - Week 5 left and right lung buds push into the pericardioperitoneal canals (primordia of pleural cavity)

Respire - Week 5 to 17 lung histology - pseudoglandular

Hearing - Week 5 cochlear part of otic vesicle elongates (humans 2.5 turns)

Stage 14
Stage14 bf1c.jpg
Ectoderm - sensory placodes, lens pit, otocyst, nasal placode, primary/secondary vesicles, fourth ventricle of brain

Mesoderm - continued segmentation of paraxial mesoderm (somite pairs), heart prominence

Head - 1st, 2nd and 3rd pharyngeal arch, forebrain, site of lens placode, site of otic placode, stomodeum

Body - heart, liver, umbilical cord, mesonephric ridge visible externally as bulges.

Limb - upper and lower limb buds growing

Neural - first appearance of the future cerebral hemispheres. Cerebellar plate differentiated to an intermediate layer, and future rhombic lip identifiable[1]

Liver hepatic gland and its vascular channels enlarge, hematopoietic function appears[2]

Stage 15
Stage15 bf1.jpg

Neural - cranial nerves (except olfactory and optic) are identifiable in more advanced embryos[3]

  Eye - 35 to 37 days retinal pigment present
Note - the day timing of stages is only approximate, system names link to first page of that specific system, and events are based upon the literature cited below.
  1. <pubmed>3377191</pubmed>
  2. <pubmed>9407542</pubmed>
  3. <pubmed>3213956</pubmed>