Germ Layers Flashcards
(35 cards)
What induces the formation of the neural plate?
the notochord induces overlying ectodermal tissue to form the neural plate
*this is the result of specific signaling molecules from the notochord altering the gene expression patterns in the adjacent ectoderm
How does the neural plate increase in surface area?
through a combination of cell proliferation and cell movements
The neural plate increases in surface area through a combination of cell proliferation and cell movements. The plate sinks down into the underlying mesoderm while rolling into a tube. The edges or crests of the neural plate are called what?
the neural folds
Fusion of the neural folds into a tube first occurs in the ____ of the embryo (about the region of the 4th somite) and then proceeds both ____ and _____.
Fusion of the neural folds into a tube first occurs in the MIDDLE of the embryo (about the region of the 4th somite) and then proceeds both CRANIALLY and CAUDALLY.
Failure of the neural tube to fuse correctly results in birth defects. What are two resulting birth defects?
- Anencephaly (failure of fusion at the cranial end)
- Spina Bifida (failure to fuse at the caudal end)
What might neural tube defects be due to?
folic acid deficiency (a B group vitamin), although the molecular basis for the effect is unknown
- supplementing folic acid levels in diet of pregnant women have led to a decrease in neural tube birth defects
- folic acid is only found in animals, for vegans we have put this in food items
What is Anencephaly?
neural tube defect: failure of fusion at the cranial end
What is Spina Bifida?
neural tube defect: failure of fusion at the caudal end
At about the same time that the neural tube closes, during the third week, the first signs of the developing eyes and ears become visible.
What is the optic placode?
The optic placode is a thickening of ectodermal tissue that will later invaginate and develop into the lens of the eye.
At about the same time that the neural tube closes, during the third week, the first signs of the developing eyes and ears become visible.
What is the otic vesicle?
the otic vesicle will invaginate to form the inner ear and the balance organs
What are neural crest cells primarily responsible for?
the face
Where are neural crest cells located?
neural crest cells are initially located at the crests of the neural plate that form the neural folds. this is also the lateral extreme of the developing neural tissues
At approximately the time of neural tube closure, neural crest cells become mobile and migrate away from the developing neural tube. Depending on their final destination, neural crest cells develop into a remarkable array of different cell types. Neural crest derivatives include, but are not limited to:
- the dorsal root ganglia
- the peripheral nervous system
- most of the bones and cartilage of the face
- pigment cells
- tooth papillae
- CT of aortic arch arteries and especially the septum separating the aorta and pulmonary vessel
What is believes to determine the fate of neural crest cells?
it is believed to be primarily determined by signals from adjacent tissues at their final location, not by an intrinsic property of the cells prior to migration
What are three clinical consequences of neural crest defects?
- Treacher-Collins syndrome (insufficient neural crest contribution to face)
- Waardenberg’s syndrome (facial and pigmentation defects and digestive system problems)
- Neurofibromatosis (autosomal dominant disease; mostly benign tumors of neural crest cells including melanocytes and Schwann cells; due to mutation in a tumor suppressor gene)
What is Treacher-Collins syndrome?
insufficient neural crest contribution to face
What is Waardenberg’s syndrome?
facial and pigmentation defects and digestive system problems
What is neurofibromatosis?
- autosomal dominant disease affecting about 1 in 4000
- mostly benign tumors of neural crest cells including melanocytes and Schwann cells
- due to mutation in a tumor suppressor gene
The embryonic ectoderm develops into what specialized tissue types?
(primarily those that come in contact with the outside environment)
- epidermis, including hair and nails
- sensory epithelium of the ear and nose and the lens of the eye
- sweat glands, mammary glands, pituitary gland
- enamel of the teeth
Mesoderm lateral to the notochord is divided into what three subsections?
- paraxial mesoderm
- intermediate mesoderm
- lateral mesoderm
- respectively at increasing distances from the midline
Which subsection of the mesoderm forms the somites? What are somites?
- paraxial mesoderm (closest to midline)
- somites are repeating structures that serve as the primitive musculature of the embryo
What does the intermediate mesoderm form?
it will form mesodermal structures of the urinary system and the reproductive system
The lateral mesoderm will split into what two layers separated by the embryonic coelem?
- SOMATIC mesoderm (parietal mesoderm; the outer layer in contact with the ectoderm)
- SPLANCHNIC mesoderm (visceral mesoderm; inner layer in contact with the endoderm)
What is the somatic mesoderm?
- aka parietal mesoderm
- the outer (initially dorsal (upper, back)) layer in contact with the ectoderm
- goes on to form tissues that line the outer body wall, including CT, bone, fat and tendons
