BGDA Practical 7 - Week 5

From Embryology

Introduction

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Practical 6: Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8


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

By this week there are many different organs and tissues differentiating throughout the embryo, only a few select systems will be discussed.

Cardiovascular

See also Heart Development Timeline - Basic Cardiac Embryology

Respiratory

  • left and right lung buds push into the pericardioperitoneal canals (primordia of pleural cavity)

Neural

  • Central nervous system - secondary brain vesicles
  • Sensory - Hearing cochlear part of otic vesicle elongates (humans 2.5 turns)

Cardiovascular

Basic Heart Development Timeline.jpg

Heart Development Timeline (see Basic Cardiac Embryology)

Stage13-CVS-icon.jpg
 ‎‎Cardiovascular
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Week3 folding icon.jpg
 ‎‎Week 3
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Heart1 looping icon.jpg
 ‎‎Heart Looping
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Heart1 realign icon.jpg
 ‎‎Heart Realign
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Heart1 atrium icon.jpg
 ‎‎Atrial Septation
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Heart1 ventricle icon.jpg
 ‎‎Outflow Septation
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Respiratory

Stage13-GIT-icon.jpg
 ‎‎GIT Stage 13
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Week 4 - laryngotracheal groove forms on floor foregut.

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

Week 6 - descent of heart and lungs into thorax. Pleuroperitoneal foramen closes.

Week 7 - enlargement of liver stops descent of heart and lungs.

Month 3-6 - lungs appear glandular, end month 6 alveolar cells type 2 appear and begin to secrete surfactant.

Month 7 - respiratory bronchioles proliferate and end in alveolar ducts and alveolar sacs.

Neural

Stage13-CNS-icon.jpg
 ‎‎Stage 13 Neural
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Rapid growth folds the neural tube forming 3 brain flexures:
  1. cranial flexure (cephalic)- pushes mesencephalon upwards
  2. pontine flexure - generates 4th ventricle
  3. cervical flexure - between brain stem and spinal cord
Embryo stage13- brain flexures.jpg

Neural tube - brain flexures (stage 13)

CNS primary vesicles.jpg

Neural - 3 primary vesicles

CNS secondary vesicles.jpg

Neural - 5 secondary vesicles


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Practical 6: Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8



Embryo Stages and Events

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]

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

33
Stage 15 Stage15 bf1.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>



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Practical 6: Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8