Formation of the Body Plan (Gastrulation/Neurulation) Flashcards
What is gastrulation?
- process that converts the single epithelial layer of the epiblast into multiple layers of the fetus
- coordinated series of cell movements placing mesoderm and endoderm within embryo, give rise to internal organs
Tissues formed by ectoderm
- epidermis (skin, nails, hair follicle, glands…)
- nervous system (neurons, glia)
- bone/cartilage (frontal bones, facial bones, auditory ossicles, teeth, hyoid catilages)
Tissues formed by mesoderm
- axial mesoderm (some cranial mesoderm, notochord and later intervertebral discs)
- paraxial mesoderm (bone/cart of ribs/vertebrae, connective tissue - skin, skeletal muscle)
- intermediate mesoderm (kidney, gonad, reproductive tract)
- lateral plate mesoderm (bone/cart of limbs, connective tissue - skin, digestive tract, smooth muscle tendons/vasculature of heart
Tissues formed by endoderm
- digestive tract
- organs (most cells - liver, pancreas, gall bladder)
- respiratory tract
What are the future positions of mouth and anus?
- future mouth: buccopharyngeal membrane
- future anus: cloacal membrane
- formed by closely apposed epiblast and hypoblast
What do cells ingressing from the node form?
notochord and prechordal mesoderm (=axial mesoderm)
How are the mesodermal bands formed on either side of the axial mesoderm?
paraxial, intermediate and lateral plate mesoderm are specified by morphogen gradiant created by the axial mesoderm
What is neurulation?
-process that generates CNS in embryo
(usually contiguous with gastrulation)
-neural tube formed from dorsal ectoderm
-involves coordinated series of cell movements
and cell shape changes
-formation of glia and neurons of CNS and PNS
How does the neural plate arise?
-neural induction: node, notochord and prechordal mesoderm secrete proteins/signals
=induce neural plate + induce/inhibit epidermis
Describe process by which neural tube is placed within embryo
-neural plate folds along midline
-lateral edges rise
-hinge points form (folds)
-lateral edges of neural plate move towards each other
-edges fuse to form neural tube
+epidermis also fuses= neural tube within embryo
When does neural tube formation occur?
- 4th week of dev
- day 21: edges initially only meet at boundary of hindbrain and spinal cord (+midbrain and anterior boundary in some mammals)
- tube closes like a zipper from these sites
- rostral neuropore closes on day 24
- caudal neuropore closes at the very end, day 26
What are NTDs?
- neural tube defects caused by failure of neural tube closure during 4th week of dev
- 1 of most common congenital defects
- most pregnancies terminated
- adding Folic Acid = Vitamin B9 to diet may decrease chances of NTDs by 70%
What is anencephaly?
NTD: cranial neuropore fails to close, brain underdeveloped
embryos may be miscarried in early dev = rarest form of NTD to survive birth, fetus usually stillborn
What is spina bifada?
NTD: caudal neuropore fails to close, spinal chord + meninges protrude from spinal opening
(permanent nerve damage, paralysis/bowel bladder problems often remain, most common form of NTD)
What are Neural Crest cells?
- multipotent stem cells
- originate from margin of neural plate and epidermis
- during neural folding, NCCs break away from ectoderm and migrate (to different locations, forming different cell-types determined by interactions with cells in new location)
