MDDE 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
What do malformations in the cleavage, implantation, and gastrulation result in?
→death
What is involved in organogenesis?
→Differentiation of somitic derivatives →Development of sensory organs →Limb formation →Formation of face structures →Formation of genital structures
