BGDA Practical 7 - Week 5
Introduction
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
- Heart - septation starts, atrial septation and ventricular septation
- Vascular - 3 vascular systems (systemic, placental, vitelline) extensively remodelled
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
Heart Development Timeline (see Basic Cardiac Embryology)
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Respiratory
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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
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Rapid growth folds the neural tube forming 3 brain flexures:
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Neural tube - brain flexures (stage 13) |
Neural - 3 primary vesicles |
Neural - 5 secondary vesicles |
Practical 6: Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 |
Embryo Stages and Events
Event | ||
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 | 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 |
Neural - cranial nerves (except olfactory and optic) are identifiable in more advanced embryos[3] | |
Eye - 35 to 37 days retinal pigment present |
References
Practical 6: Week 3 | Week 4 | Week 5 | Week 6 | Week 7 | Week 8 |