Week 5

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

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

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

30
   
31
   
32
Stage 14
Stage14 human.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 PMID: 3377191

GIT - Liver hepatic gland and its vascular channels enlarge, hematopoietic function appears PMID: 9407542

33
Stage 15 File:CST15.gif

Neural cranial nerves (except olfactory and optic) are identifiable in more advanced embryos PMID: 3213956

34
 
35
  Sense - Eye 35 to 37 days retinal pigment present


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Dr Mark Hill 2009, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G