Embryonic Period Flashcards
What is the embryonic period
Period of organogenesis
From third to the eighth week
What is folding of the embryo
Conversion of flat trimlaminar to cylindrical
Begins by end of third week and completed by 4th week
Types of folding
Cephalocoaual folding
Lateral folding
What is cephalocaudal folding
Caused by rapid longitudinal growth of CNS
Head fold:structures lie ventral to embryo: a)oral membrane b)cariogenic plate c)septum transversum
Tail fold: allantois and cloacal membrane shift to embryo
Forms hind gut
What is lateral folding
Due to rapid growth of somite
Lateral folding leads to formation of mid gut
Leads to wide communication between extra embryonic ceolom and mid gut called yolk stalk
What are the results of folding
1-gives embryo its cylindrical form
2-formation of gut
3-crainocaudal arrangement of mouth heart and diaghram
4-cloacal membrane and allantois become ventral in position
5-umbilical cord is formed and the connecting stalk is shifted ventrally
What are the layers of secondary mesoderm
Paraxial
Intermediate
Lateral
What is the paraxial mesoderm
Medial part that lies on either side of the notochord
Divided by transverse grooves in to body blocks called somites (4 occipital,8 cervical,12 thoracic,5 lumbar, 8-10 coccygeal)
Give axial skeleton its vertebral muscles and covering skin
What is the intermediate cell mass
Gives rise to urinary and genital systems
What is the lateral plate of mesoderm
Cavity appears in lateral plate of mesoderm called embryonic coelom
Splits mesoderm in to
Somatic: gives muscles of body wall
Splanchnic: next to endoderm and gives smooth or involuntary muscles
What are endodermal derivatives
Provides epithelial lining of GIT, respiratory tract, and urinary bladder
Also forms parenchyma of thyroid,parathyroids, liver and pancreas
What are ectodermal derivatives
Ectoderm gives rise to organs and structures that maintain contact with outside world
CNS, PNS, sensory epithelium of nose,ear and eye, skin including hair and nails
Pituitary,mammary and sweat gland, enamel of teeth
What is neurulation
Neural plate appears as thick as embryonic ectoderm induced by developing of notochord
Describe neurulation
A longitudinal neural groove develops in neural plate, which is flanked by neural folds
Fusion of folds forms the neural tube
As neural folds fuse to form neural tube, neuroectodermal cells form a neural crest between surface of ectoderm and neural tube
