Week 5

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Key Events of Human Development during the fifth week (week 5) following fertilization or Clinical week 7 (LMP).

Carnegie Stages: 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23
Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9

Timeline

Day
Stage
Event
29
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)

30
   
31
   
32
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]

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

33
Stage 15 Stage15 bf1c.jpg

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

34
 
35
  Eye - 35 to 37 days retinal pigment present

References

  1. <pubmed>3377191</pubmed>
  2. <pubmed>9407542</pubmed>
  3. <pubmed>3213956</pubmed>



Embryo Week: Week 1 | Week 2 | Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 | Week 9

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Cite this page: Hill, M.A. (2024, March 28) Embryology Week 5. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Week_5

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G