Somites and embryonic folding Flashcards
What is the intra-embryonic mesoderm divided into
- paraxial
- intermediate
- lateral
columns
What happens to the trilaminar disk in the fourth week
Folds
Where is the paraxial column of the intraembryonic mesoderm
Nearest to the neural tube
Where is the intermediate column of the intraembryonic mesoderm
IN the little fold in the middle of the neural tube and the extra embryonic mesoderm
Where is the lateral column of the intraembryonic mesoderm
-What is it continuous with
Nearest to the outside
-continous with the extra-embryonic mesoderm
In the beginning of the fourth week, what does the paraxial mesoderm do
Begins to form somites
What does the medial part of the paraxial mesoderm become
Sclerotome (skeleton)
What does the intermediate part of the paraxial mesoderm become
Myotome (muscle)
What does the lateral part of the paraxial mesoderm become
Dermatome (skin)
What does the intermediate mesoderm become
Nephrotome
What does the nephrotome form
Genitourinary system
What does the lateral mesoderm become
Either parietal (body wall) or visceral (wall of gut)
In the fourth week, what do somites form
In a crania-caudal sequence
Numberings of the somites and what they become
3 occipital 8 cervical 12 thoracic 5 lumbar 5 sacral 1-5 coccygeal
remain
What is the occipital
Tongue musculature
What does each somite receive
Each receive a segmental spinal nerve which follows that tissue wherever it goes
What is the lateral plate split into
- somatopleuric mesoderm
- splanchnopleuric mesoderm
What is the somatopleuric mesoderm continuous with
Mesoderm of the amniotic cavity
What will the somatopleuric mesoderm eventually form
Striated (voluntary) muscle
What is the splanchnopleuric mesoderm continuous with
Mesoderm of the yolk sac
What will the splanchnopleuric mesoderm eventually form
Smooth muscle of the gut
What will the intraembryonic coelom eventually form
- pericardial cavity
- pleural cavity
- peritoneal cavity
What happens in longitudinal folding
Reversal
What does the differential growth of the embryo cause it to do
Fold both cranio-caudally and laterally
What is important in producing reversal
Rapid growth of the neural tube
After reversal, how is the amnion attached to the embryo
Only attached via the ubmilicus
In reversal, which part is enlarging quickly
Amniotic cavity
What happens to part of the yolk sac after reversal
HAs become incorporated into the gut tube
What does folding do
reduce communication between intra and extra embryonic coelom
What happens in lateral folding
The edges of the amnion grow downwards towards the yolk sac
What is the Vitelli-intestinal duct
In the region of the umbilicus a connection between the gut tube and the yolk sac remains
