Somites and Embryonic Folding Flashcards
Describe the intraembryonic coelom formation
Describe the shape formed by the intraembryonic coelom and the cavities it forms (in adults)
Pericardial Cavity (Cavity surrounding heart) Pleural Cavity (Lung formation) Peritoneal Cavity (Guts, Liver, Organs in abdomen)
What are the 3 longitudinal columns of intraembryonic mesoderm in an embryo (approx week 3)
What forms at either side of the neural tube at the paraxial mesoderm and what are the specialisations
Somites
The medial part forms sclerotome (skeleton) that forms vertibrae of spine around neural tube
The intermediate part becomes myotome (muscle)
The lateral part of the paraxial mesoderm becomes dermotome (skin - dermis)
(Think deep to superficial)
What happens to the intermediate mesoderm
Becomes nephrotome (forms genitourinary system)
What happens to the lateral mesoderm
Becomes either parietal (body wall) or visceral (lining of gut) tissue
Describe structure of embryo once somites begin to form
(Note that somites begin forming from rostral end backwards; can be used to age an embryo)
What happens to somites and nerves as embryo ages
The spinal nerves that somites form with the neural tube stay with it, even as the embryo grows and they separate
Describe the numbers of somites per body part
3 Occipital (near head, forms tongue musculature)
8 Cervical (neck region)
12 Thoracic
5 Lumbar
5 Sacral
1-5 Coccygeal
Mostly correspond to vertebrae
How does the neural tube look like when closing and roughly how many days does it take
Anterior and Posterior Neuropores
How does the intraembryonic coelom look relative to the prochordal plate
How does the intraembryonic coelom look relative to the neural tube and notochord when somites haven’t reached that far back
What are the somatopleuric and splanchonopleuric mesoderm
Where do the septum transversum and pericardial cavity form relative to the neural tube
Here is an electron micrograph of the neural tube and stuff. That is all. No memorisation, just see it a couple times
How do the somites correspond to spinal nerves
Each part of the skin (dermatome) and also muscle (myotome) is connected to a single spinal nerve connected to a somite as such
Each somite receives a segmental spinal nerve
Allows identification of spinal nerve malfunction
How do we see the neural tube in a longitudinal direction
What does the septum transversum form
Diaphragm
What happens to this structure in terms of the numbers (and endo/ectodermal cavities) as the embryo develops
Neural part (especially brain) expands and the edges of the amniotic cavity swing around; 5 goes above 2 and pericardial cavity is more underneath the embryo and yolk sack is more pinched
What happens after this stage of the embryo
Amniotic cavity swings around even further to envelope the embryo and yolk sac; pericardial cavity swings around and numbers reverse (process named reversal)
We have brain, mouth then heart so more in order of normal human
Gut will be lined by endoderm from mouth (prochordal plate) to anus (cloacal plate)
What is the reversal process of embryo development
Longitudinal folding (brain development and pinching out of yolk sac/enveloping of embryo by ectoderm)
How do the notochord and neural tube look from a lateral view of an embryo
-
What happens to the embryo during lateral folding
Edges of amnion move around so mesoderm becomes trapped by amnion
Yolk sac elongates and moves downwards
What happens to the neural tube from this point onwards
Neural tube pinches off and is separate
Eventually no continuity between gut part and yolk sac (pinches off/shed) part of indederm (small opening - vitello-intestinal duct)
Still connection between intra and extra-embryonic mesoderm
What is the last step of lateral folding (looking through gut tube)
Amniotic Cavity entirely surrounds embryo and embryo is suspended within it
Gut is pinched off from yolk sac; held by mesoderm
Enclosed cavity (intra-embryonic coelom) on either side of gut surrounding by parietal mesoderm
Gut surrounded by visceral mesoderm
