Embryology 2 Flashcards
What happens during week 3?
Formation of germ layers (gastrulation)
Formation of neural tube (neurulatrion)
Development of somites
Early development of cardiovascular system
What are germ layers?
Layers that can germinate (grow into something)
What is the first thing that happens during week 3?
Formation of the primitive streak

Where is the primitive streak formed?
In the midline of the epiblast by the dipping in of cells (invagination)
What is the structure of the cells of the epiblast?
Columnar

What is formed once the primitive streak is formed?
Axis of the embryo
What does the axis of the embryo allow cells to know?
Where they are, at the head or the feet
What happens during gastruation?
Epiblast cells migrate into the space between the epiblast and hypoblast layers

What do the cells that migrate from the epiblast during gastrulation do, and cause the hypoblast to do?
Displaces the hypblast and forms 3 layers
What 3 layers do migrated cells from the epiblast during gastrulation form?
Ectoderm
Mesoderm
Endoderm

What do the migrated cells from the epiblast during gastrulation form?
Trilaminar disk

What is the trilaminar disk composed of?
Ectoderm
Mesoderm
Endoderm

What is 1?

Ectoderm
What is 2?

Mesoderm
What is 3?

Endoderm
What does the ectoderm, mesoderm and endoderm originate?
Epiblast
What happens to the cells during the formation of the trilaminar disk?
They become specialised, so can only go on to form certain things
What is formed after the trilaminar disk?
Notochord

What is the notochord?
Solid tube of cells

What does the notochord induce?
Ectodermal cells in the midline to form a neural tube (neurulation)

What does the neural tube and notochord originate from?
Ectoderm

What is A?

Paraxial mesoderm
What does the neural tube induce?
Mesoderm to thicken

What happens after the mesoderm thickens?
Seperates into 3 parts:
Paraxial mesoderm
Intermediate plate mesoderm
Lateral plate mesoderm

What does the thickened mesoderm seperate into?
Paraxial mesoderm
Intermediate plate mesoderm
Lateral plate mesoderm

What is B?

Intermediate plate mesoderm
What is C?

Lateral plate mesoderm
What are the paraxial mesoderm, intermediate plate mesoderm and lateral plate mesoderm formed from?
Mesoderm

What happens after the mesoderm splits into the paraxial, intermediate and lateral plate mesoderm?
Lateral plate mesoderm splits to form:
Somatic mesoderm
Splanchnic mesoderm
Space between the 2 called intraembryonic coelom
What does the lateral plate mesoderm split into?
Somatic mesoderm
Splanchnic mesoderm

What is the space between the somatic and splanchnic mesoderms known as?
Intraembryonic coelom

What does each part of the mesoderm go on to do?
Form different things

What does the paraxial mesoderm go onto form?
Somites

What does the intermediate plate mesoderm go onto form?
Urogenital system (kidneys and reproductive systems)

What does the lateral plate mesoderm go onto form?
Body cavity and coverings

What are somites formed from?
Paraxial mesoderm

What are kidneys and reproductive system formed from?
Intermediate plate mesoderm

What are body cavitys and coverings formed from?
Lateral plate mesoderm

What is a somite?
Each of a number of body segments containing the same internal structures
What does each somite (paraxial mesoderm) divide into?
3 structures:
Dermatome
Myotome
Sclerotome

What are dermatomes, myotomes and sclerotomes formed from?
Somites

What does dermatome form?
Dermis of skin

What does sclerotome form?
Bones

What does myotome form?
Muscles

What do dermatomes and myotomes go onto do?
Migrate, with the nerve supply following them
What is the 4th to the 8th week known as?
Embryonic or organogenetic period
When is the embryonic organogenetic period?
4th to 8th week
What happens during the embryonic period?
Folding into a tube (lateral folds)
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)
When does lateral folding start and finish?
Starts in 3rd week and finishes between the 4th and 8th week
When does the heart start to beat?
Day 24
What is the gut formed from?
Endoderm
How many pairs of somites are there?
43
Why does lateral folding of the embryo occur?
Weight of cell growth causes it to bend until each end comes together

What is A?

Neural tube
What is B?

Somite (paraxial mesoderm)
What is C?

Intermediate plate mesoderm
What is D?

Endoderm (gut)
What is E?

Ectoderm
What is F?

Somatic mesoderm
What is G?

Splanchnic mesoderm
What is H?

Intra-embryonic coelom
How does head and tail folding affect the amniotic cavity and yolk sac?
Causes the amniotic cavity to cover the entire embryo, with the yolk sac in the middle

What does the endoderm go onto form?
Gut and respiratory systems
What is A?

Neural tube
What is B?

Somites
What is C?

Gut
What is D?

Yolk sac
What is E?

Limb bud
When is the embryo formed?
After head to tail folding
What is teratology?
Study of when things go wrong during development
What is the study of when things go wrong during development called?
Teratology
What are teratogens?
Environmental factors that cause abnormal development
What are examples of teratogens?
Congenital rebulla syndromes caused by contraction of German measles when pregnant
Malformed limbs due to maternal use of Thalidomide
What drug causes malformed limbs?
Thalidomide
What does thalidomide cause?
Malformed limbs
What causes congenetial rebulla syndromes?
Contraction of German measles when pregnant
What does contraction of German measles when pregnant cause?
Congenital rebulla syndromes
What are the causes of abnormal development?
Most are unknown (60%)
Multifactorial (20%)
Genetic (10%)
Environmental (10%)
What are examples of environmental teratogens?
Drugs
Alcohol
Tobacco
Infectious agent (can transfer through placenta and affect the developing embryo)
Radiation
What are some examples of infectious agents that can be teratogens?
Toxoplasma
Rebella
Cytomegalovirus
Herpes
What are some genetic factors that may impact development?
Too many/few chromosomes
Structural changes (deletion of genes or segments of chromosomes)
What can cause genetic factors that impact development?
Maternal age
Damage from environmental factors such as radiation
When is embryogenesis from?
Weeks 3 to 8

When is fetogenesis?
Weeks 9 to 38

When is the greatest sensitivity to teratogenesis?
Embryonic period (weeks 3 to 8)
What is the main risk during weeks 1 and 2?
High risk of death
What does the rick posed by a teratogen depend on?
Exposure during critical periods of development
Dosage of drug/chemical/factor
Genetic constitution of embryo, such as some more susceptible than others at equilvalent doses
When is the foetal period from?
Week 9 to 38
What do teratogens generally cause during the embryonic and foetal periods?
During embryonic period causes major congenital anomalies
During foetal period causes functional and minor anomalies

How are malformations diagnosed prenatal?
Blood (AFP, alpha-feto protein)
Ultrasound scan (12 week anomoly scan)
Invasive tests (chorionic villus sampling and amniocentesis)
What is an example of an ultrasound scan?
12 week anomaly scan
What are examples of invasive tests?
Chorionic villus sampling
Amniocentesis
How are malformations diagnosed postnatal?
Hip stability
Testes
Fingers and toes
Hearing