H/E Lecture 3 Flashcards
(28 cards)
What happens to the epiblast during gastrulation?
epiblast cells proliferate and migrate to form 3 germ layers:
Endoderm (inside towards hypoblast)
Mesoderm (middle)
Ectoderm (outside towards endometirum)
What three main events take place during week 3?
Gastrulation: formation of tri laminar disc
Neurulation: formation of neural tube
Body folding: embryonic disc becomes cylindrical
Name the structures caused by epiblast invagination.
Primitive node
Primitive streak
What are the names for the head and tail ends of the embryo?
Head=cephalic
Tail=caudal
What happens at the primitive streak and node?
through epithelial-mesenchymal transformation, undifferentiated migratory mesenchymal cells are formed from epiblast cells
These also induce cell migration and starts organization of the germ layers.
What is the end result of gastrulation?
establishment of the body axes:
Cephalocaudal (head-tail)
Ventral-dorsal (front-back)
Right-left
In which direction does mesenchymal migration take place?
migration is from caudal to cephalic
or tail to head
In which direction does maturation take place?
maturation cephalic to caudal or head to tail
Which membranes are the future mouth and anus?
oropharyngeal membrane= mouth
cloacal membrane= anus
What happens to the primitive node and streak after gastrulation?
at the end of week 4, they degenerate when gastrulation completes
What happens during neurulation?
The notochord forms and induces formation of the neural tube (future brain, spinal cord)
How does the notochord form?
Cells migrate along the midline and stop at the prechordal plate
How does the neural tube form?
The notochord induces a portion of the overlying ectoderm to fold and form the neural tube.
What problems can arise from the ends of the neural tube not closing?
Anencephaly: the rostral (head) neuropore doesn’t close
Spina Bifida: caudal neuropore doesn’t close
Spina Bifida Cystica: presents a fluid filled cist that can contain meningocele (tissue around spinal cord) or myomeningocele (spinal cord tissue)
What are somites and what do they do?
Somites are part of the mesoderm and they grow and drive the lateral body folding.
What major structures are formed by lateral body folding?
Lateral folding is around the neural tube axis. This forms the gut tube from the endoderm and mesoderm around the SYS. The amniotic cavity engulfs all, and the intraembryonic cavity is formed (future thoracic and abdominopelvic cavities)
What drives cephalocaudal body folding, and what does it do?
Driven by longitudinal growth of the neural tube.
Relocates mouth and heart to adult position.
What major events occur during the last 4 weeks of embryonic period? (Weeks 4-8)
Tail regresses Limbs elongate and rotate Digits appear Face develops Organs form
When do most birth defects appear?
Week 5
What structures are eventually formed by the endoderm?
Gametes
Epithelial cells lining digestive organs, respiratory airways, and some urogenital passages.
What structures are eventually formed by the ectoderm?
Surface ectoderm becomes epidermis and its derivatives (hair, nails, glands)
Neuroectoderm forms the brain and the spinal cord
What does the mesoderm differentiate into?
Paraxial Mesoderm: dermis, skeletal muscle, vertebrae & ribs
Intermediate Mesoderm: urogenital system
Lateral Plate Mesoderm: parietal layer and visceral layer
What do the parietal layer and visceral layer become?
Parietal: CT of body wall & limbs
Visceral: GI/respiratory organs except the epithelial lining
Where do Somites come from and what do they become?
Paraxial mesoderm differentiates into somites (somitomeres in head region) Somites become: Sclerotome Myotome Dermatome
