7. Somites and embryonic folding Flashcards
the intraembryonic mesoderm
becomes divided into three columns- paraxial, intermediate and lateral plate mesoderm
how does the intraembryonic coelom arise
cavities develop in the mesoderm of the lateral plate and the cardiogenic area (region of septum transversum) to form intraembryonic coelom- this is initially isolated from extraembryonic coelom
What happens to the intraembryonic coelom eventually?
a horse shoe shaped cavity is formed which becomes continuous with the extraembryonic coelom
What will the intrambryonic coelom form?
pericardial cavity
pleural cavity
peritoneal cavity
What does the paraxial column form?
somites:
the medial part forms sclerotome (vertebral column, ribs, sternum)
the intermediate part forms myotome (muscles)
the lateral part forms dermatome (dermis)
What does the intermediate column form
nephrotome, genitourinary system
what does the lateral plate mesoderm become and what is it continuous with
muscles of the parietal (ventral body wall) or muscles of visceral wall (wall of gut)
it is continuous with extra-embryonic mesoderm
What happens at the beginning of the fourth week
paraxial mesoderm forms paired cuboidal bodies in a cranio-caudal sequence- SOMITES each receiving spinal nerves that follows tissue wherever it migrates
eventually there are:
3 occipital
8 cercival
12 thoracic
5 lumbar
1-5 coccygeal
occipital-> tongue musculature
where does the neural tube close from
the middle
How can somites be used to tell the age of embryo
at 4 weeks all of the somites would have formed
when is risk of the first congential abnormality
when the neural tube starts to close
What are the types of mesoderm the lateral plate will split to
somatopleuric mesoderm: continuos with mesoderm of the amniotic cavity- forms striated muscle
- somatic and parietal
splanchnopleuric mesoderm (continuous with mesoderm of yolk sac) forms smooth muscle of gut
- splanchnic (relating to viscera) and visceral (gut wall)
what is unique regarding the lower limb nerve supply?
there is twisting of the lower limb nerve supply
Longitudinal folding 1
reversal folding
- initially the embryo forms a flat oval disc
Longitudinal folding 2
Expansion of neural tube starts to change the shape of the embryo
the prospective heart and diaphragm (1,2,3) lie in front of the prospective mouth (3-4) and the prospective brain (5) lies behind it
Longitudinal folding 3
Differential growth of the embryo causes it to fold both cranio-caudally and laterally.
The previously flat trilaminar disc comes up to take the general body shape.
Rapid growth of neural tube is important in producing reversal.
Longitudinal folding 5
After reversal the amnion is only attached to the embru over a small region- the UMBILICUS
A constriction of produced at the junction of embryo and yolk sac.
part of the yolk sac has become incorporated into the gut tube.
yolk sac is pinched off with connecting stalk forming the umbilical cord
Lateral folding 1
the edges of amnion grow towards yolk sac
Lateral folding 2
The folding is greatly reducing the communication between intra and extra embryonic coelom.
In the region of the umbilicus a connection between the gut tube and yolk sac remains- the VITELLO INTESTINAL DUCT
Lateral folding 3
