Embryology Flashcards
What 4 main things does the endoderm (internal layer) develop into?
- Epithelial lining of GI, respiratory tracts & bladder
- Epithelia of tympanic cavity and auditory tube
- Parenchyma of thyroid, parathyroid, liver, pancreas
- Notochord
What 7 main things does the mesoderm (middle layer) develop into?
- Circulatory system
- Skeletal muscle cells, myotomes
- Kidneys and their ducts
- Red blood cells
- Cartilage and bone
- Dermis of skin
- Muscle, connective tissue, peritoneal compartments of gut wall
What 6 main things does the ectoderm (external layer) develop into?
- Epidermis of skin, hair, nails
- CNS & PNS
- Sensory epithelia - nose, eye, ear
- Pituitary, mammary and sweat glands
- Enamel of teeth
- Lens of eye and parts of middle ear
At how many cells is a morula?
16
When is a blastocyst formed?
Further cell division results in cavity at one end of morula
What are the 2 different cell masses the blastocyst develops into?
Embryoblast, inner
Trophoblast, outer
What develops into the placenta?
Trophoblast
What 2 layers does the embryoblast differentiate into & what cells are these made up of?
Epiblast (columnar cells)
Hypoblast (cuboidal cells)
What do these 2 layers of the embryoblast form?
Bilaminar disc
What do the epiblasts migrate to?
Line the newly formed cavity (between epiblast and trophoblast)
Becomes amniotic cavity
What do the hypoblasts migrate to?
Line inner surface of trophoblast
Enclose blastocyst cavity, which becomes primitive yolk sac
When does the trophoblast develop extensions to invade the endometrium?
When the blastocyst has formed
What are the initial 2 layers of the trophoblast?
Syncytiotrophoblast (lies against endometrium)
Cytotrophoblast (surrounds embryoblast)
How does the embryo develop freedom from he trophoblast?
New layer of cells form, the extra-embryonic mesoderm
Between the cytotrophoblast and the hypoblast cells lining the primative yolk sac
Eventually a thick layer separating the embryoblast and the trophoblast
How does the embryo receive its primitive blood supply?
Trophoblastic lacunae
What is the hypoblast replaced by?
Cells from ectoderm to form endoderm
Migrate to line primitive yolk sac, making it the secondary yolk sac
What occurs during the 1st week of development?
Fertilization, formation of the morula and blastocyst
What occurs during the 2nd week of development?
Implantation of the blastocyst and formation of bilaminar embryonic discand early placenta
What occurs during the 3rd week of development?
Further differentiation of cell layers to form the tri-laminar embryonic disc
What occurs during the 4th week of development?
Folding of embryo
What occurs from the 5th-8th weeks of development?
Development of all organs
What is the primitive streak?
Folding occurs along caudal midline as ectoderm grows
What forms the mesoderm?
Cells from the base of the primitive streak break off and migrate to lie between the layers of the ectoderm and endoderm
What are the 3 germ layers?
Ectoderm
Mesoderm
Endoderm (lines yolk sac)
What does the notochord develop from?
Tube from pit at end of primitive streak
Endoderm
