BGDA Practical 7 - Week 5

From Embryology


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 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.

Later week 5 development (Stage 15) showing a sagittal section upper half of human embryo.
Stage 15 - Ventral View

Stage15 bf2.jpg

 ‎‎Mobile | Desktop | Original

Stage 15 | Embryo Slides


See also Heart Development Timeline - Basic Cardiac Embryology


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


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


Basic Heart Development Timeline.jpg

Heart Development Timeline (see Basic Cardiac Embryology)

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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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Atrial Septation

Stage 13 image 067.jpg Stage 13 image 068.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.

The trachea can be see making its initial branching into the lung bud mesenchyme.

Stage 13 image 070.jpg Gray0961.jpg
Bifurcation of the trachea into the main or primary bronchi, the left and right bronchus. Adult bronchial tree.


During week 5 the five secondary brain vesicles form from the original primary vesicles formed in week 4 and the cranial end of the neural tube now has 3 flexures (bends).

(see also Additional Information).

CNS secondary vesicles.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)

Week 5 Interactive Component

Attempt the Quiz - Week 5  

Here are a few simple Quiz questions that relate to Week 5 (GA week 7) from the lecture and practical.

See your Quiz Result - Answer all the questions, then click "submit" to complete. The page will reload and you can then reopen this table to see your result and feedback.


1 The important human cardiogenic event commencing during week 5 is

  heart tube fusion
  heart looping
  heart septation
  heart valve development

2 The 5 secondary brain vesicles listed in rostrocaudal order are:

  myelencephalon - metencephalon - mesencephalon - diencephalon - telencephalon
  telencephalon - diencephalon - mesencephalon - metencephalon - myelencephalon
  prosencephalon - diencephalon - mesencephalon - metencephalon - rhombencephalon
  telencephalon - diencephalon - mesencephalon - myelencephalon - metencephalon
  None of the above.

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

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

Additional Information

Additional Information - Content shown under this heading is not part of the material covered in this class. It is provided for those students who would like to know about some concepts or current research in topics related to the current class page.


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

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

respiratory - 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]

  vision - 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. Müller F & O'Rahilly R. (1988). The first appearance of the future cerebral hemispheres in the human embryo at stage 14. Anat. Embryol. , 177, 495-511. PMID: 3377191
  2. Godlewski G, Gaubert-Cristol R, Rouy S & Prudhomme M. (1997). Liver development in the rat and in man during the embryonic period (Carnegie stages 11-23). Microsc. Res. Tech. , 39, 314-27. PMID: 9407542 <314::AID-JEMT2>3.0.CO;2-H DOI.
  3. Müller F & O'Rahilly R. (1988). The development of the human brain, including the longitudinal zoning in the diencephalon at stage 15. Anat. Embryol. , 179, 55-71. PMID: 3213956

Neural Development

Embryonic Central Nervous System
Stage 13 Stage 14 Stage 16 Stage 21
Human Stage13 sagittal upper half01.jpg

scale bar = 1 mm

Human Stage14 neural01.jpg Human Stage16 neural03.jpg Human Stage21 neural01.jpg
Week 4 Week 5 Week 6 Week 8

Neural Tube Development
Neural Tube Primary Vesicles Secondary Vesicles Adult Structures
week 3 week 4 week 5 adult
neural plate
neural groove
neural tube

prosencephalon (forebrain) telencephalon Rhinencephalon, Amygdala, hippocampus, cerebrum (cortex), hypothalamus‎, pituitary | Basal Ganglia, lateral ventricles
diencephalon epithalamus, thalamus, Subthalamus, pineal, posterior commissure, pretectum, third ventricle
mesencephalon (midbrain) mesencephalon tectum, Cerebral peduncle, cerebral aqueduct, pons
rhombencephalon (hindbrain) metencephalon cerebellum
myelencephalon medulla oblongata, isthmus
spinal cord, pyramidal decussation, central canal


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