L4: Mechanism Of Disease During Embryogenesis Flashcards
What is compaction?
→ change in shape of the embryo
What is a morula?
→ blastomeres begin to form tight junctions with one another, leading to deformation of their round shape and formation
How old is a morula?
→ 12-16 days
How is the site of implantation sealed?
→ by a fibrin plug
What does the bilaminar germ disk consist of?
→ epiblast
→ hypoblast
When is the amniotic cavity formed?
→ 9 days
What displaces the hypoblast?
→ by involuting cells that become definitive endoderm, and mesoderm
When does gastrulation occur?
→ 3rd week
What does gastrulation allow?
→ the two cell layers become three germ cell layers,
→ the bodily axes observed in the mature adult are created
What lies in the primitive streak?
→ a primitive node at the cranial end, and within the primitive node lies the primitive pit.
What happens to cells of the epiblast?
→ epiblast layer break off and migrate toward the primitive pit
→ detach and penetrate through the epiblast layer to form three new germ cell layers
How is the endoderm formed?
→ by epiblast cells that migrate through the primitive pit and displace the hypoblast cells
How is the mesoderm formed?
→ formed by epiblast cells that migrate through the primitive pit and lie between the epiblast layer and the newly created endoderm.
How is the ectoderm formed?
→ formed by the epiblast cells that remain in position
What does the endoderm give rise to?
→ Epithelial lining of digestive and respiratory tracts,
→ Lining of urethra, bladder and reproductive System
→ Liver and pancreas
What does the mesoderm give rise to?
→ Notochord
→ Musculoskeletal system
→ Muscular layer of stomach, intestine etc
→ Circulatory system
What does the ectoderm give rise to?
→ Epidermis of skin
→ Cornea and lens of eye
→ Nervous system
Describe the neurulation process?
→ectoderm differentiate to form a neural plate
→neural plate then bends dorsally, folding inwards to form a groove flanked by a neural crest
→infolded groove closes off and separates from the neural crest to form the neural tube
What does the neural tube elongate into?
→form the central nervous system (brain and spinal cord)
What do the the cells of the neural crest differentiate into?
→peripheral nervous system
How does the neural tube close?
starts at hindbrain and then progresses anteriorly and posteriorly
Describe the cloth purse model of folding
→ septum and heart move from margin to centre
→yolk sac, allantois and stalk make umbilical cord
→prochordal and cloacal plates delimit gut tube
What happens during folding?
→Heart and other structures move from margin of embryo to the centre
Describe the folding process
→amnion and embryonic disc grow vigorously but the yolk sac does not.
→ the expanding disk balloons into a 3D, cylindrical shape.
→The dorsal structures of notochord, brain and somites stiffen this axis
such that the flexion takes place at the thin, flexible outer rim of the disc
