Embryology 2 Flashcards
What happens during week 3?
- Formation of germ layers – GASTRULATION
- Formation of neural tube – NEURULATION
- Development of somites
- Early development of cardiovascular system
How is the primitive streak formed?
Formed in midline of epiblast by dipping in of cells (invagination)
What is formed after the primitve streak is formed?
Axis of embryo is formed
Where do epiblast layers migrate to?
Space between epiblast and the hypoblast layers
Cells displace the hypoblast
From the original epiblast, what three layers are formed?
- Ectoderm
- Mesoderm
- Endoderm
Trilaminar disk
What is gastrulation?
Formation of three germ layers
What layer does the primitive streak form from?
Ectoderm
What is the name given to the solid tube of cells formed from the ectoderm called?
The notochord
What is does the notochord do?
Induces ectodermal cells on midline to form neural tube
What is the precursor for the neural tube?
The neural plate
What is neurulation?
What is the effect of the neural tube on the mesoderm?
Causes the mesoderm to thicken
What happens after the mesoderm thickens?
It splits into three parts
What is the name of the three parts of the mesoderm?
- Paraxial mesoderm
- Intermediate plate mesoderm
- Lateral plate mesoderm
What happens to the lateral plate of the mesoderm?
Lateral plate mesoderm splits to form a somatic and splanchnic mesoderm
Space formed in between: intraembryonic coelom
What does the paraxial mesoderm form?
Somites
What does the intermediate plate mesoderm form?
Urogenital system (kidneys + repro)
What does the lateral plate form
Body cavity and coverings. Peritoneum, pleura, and body cavities
Segmentation of paraxial mesoderm forms?
Somites
What does each paraxial mesoderm divide into?
- Dermatome
- Myotome
- Sclerotome
What is the function of each of these divisions of the somites?
What happens during 4th – 8th weeks – Embryonic period / Organogenetic period?
- Folding into a tube (lateral folds) which started in 3rd week completes
- Neural tube – forebrain, midbrain, hindbrain and spinal cord development
- Heart starts to beat on Day 24
- Gut formation from endoderm
- Urogenital system formation from intermediate mesoderm
- Body cavities from lateral plate mesoderm
- 43 pairs of somites form in the paraxial mesoderm and differentiate further
- Limb buds form
- Neck development – pharyngeal arches
Which lateral plate is on the inside when the lateral folding of the embryo has been completed?
The splanchnic
What do the somatic mesoderm and the splanchnic mesoderm form?
Pleura:
Somatic = Parietal
Splanchnic = Visceral
Look
Summary of the three germ layers
Label the above structures
What are teratogens?
Environmental factors that cause abnormal development.
What is congenital rubella caused by?
Contraction of german measles when pregnant
What are the environmetnal teratogens?
Drugs – prescription / other
Alcohol/ tobacco
Infectious agents: ToRCH (Toxoplasma, Rubella, Cytomegalovirus, Herpes ) can transfer through placenta and affect developing embryo
Others – eg: radiation
What are the genetic factors?
Too many/too few chromosomes:
- Turner’s syndrome – 45 chromosomes single X
- Down’s syndrome – 47 chromosomes trisomy 21
Structural changes – deletions of genes, segments of chromosomes
Causes:
- Increased maternal age
- Damage from environmental factors such as radiation (eg: X-rays)
Which weeks have a high risk of death, low risk of teratogens?
Weeks 1 and 2
Which weeks whow a eriod of the greatest sensitivity to teratogens?
Weeks 3-8
Which weeks show a decreasing sensitivity to teratogens?
Weeks 9 - 38
What does the risk of a teratogen depend on?
- Exposure during critical periods of development
- Dosage of drug/chemical/factor
- Genetic constitution of embryo i.e. some more susceptible than others at equivalent doses etc
How are prenatal diagnosis of malformations made?
Blood - AFP
Ultrasound scan – 12 week anomaly scan
Invasive tests - chorionic villus sampling and amniocentesis
How are postnatal diagnosis of malformations made?
- Hip stability
- Testes (descent)
- Fingers and toes
- Hearing
