Body Plan 02: Week 3 (Gastrulation) Flashcards
Gastrulation
The formation of three primary germ layers
What are the four processes that occur in the third week of development?
Gastrulation, neurulation, notochord formation, and formation of the neural crest
What are the three germ layers that are formed in gastrulation?
Ectoderm, mesoderm, endoderm
Primitive Streak
The thickened linear band of epiblast that marks the beginning of gastrulation. This line becomes the long axis of the embryo
Primitive Groove
The groove located in the primitive streak
Primitive Pit
The proliferation of cells at the cranial end of the primitive streak
Primitive node
The node located at the primitive pit where cells dive below to become mesoblast and endoblast
Mesoblast
The layer of cells during gastrulation that settle between the epiblast and hypoblast
What are the two areas of the embryo that mesoblast does not settle in during gastrulation?
Oropharyngeal membrane (future mouth) and cloacal membrane (future anus)
Oropharyngeal membrane
A cranial membrane that becomes the mouth
Mesenchym
A connective tissue in which cells migrate
Cloacal membrane
A caudal membrane that becomes the anus
Ectoderm
The outermost germ layer. Forms the nervous system and skin
Mesoderm
The middle germ layer. Forms the muscles and red blood cells
Endoderm
The innermost germ layer. Forms the epithelia of many organs. Also forms the respiratory system, gastrointestinal system, and urinary system
Extraembryonic mesoderm
Mesoderm lying outside the embryo that lines the yolk sac and amniotic cavity
Somatic
Relates to outer body
Splanchnic
Relates to inner body
Chordamesoderm
Mesoderm cells that migrate rostally from the primitive pit, forming the notochord
Notochordal plate
The plate of chordamesoderm extending rostally to the oropharyngeal membrane
Neurenteric Canal
A temporary opening of the notochordal plate, allowing for communication and ion equalization between the aminotic cavity and the yolk sac
What cells line the yolk sac? What type of cells replace the roof lining of the yolk sack during gastrulation?
Hypoblast; endoblast
Intraembryonic mesoderm
Mesoderm that differentiates from embryonic mesoblast and contributes to fetal tissue
What are the three divisions of the intraembryonic mesoderm?
Paraxial, intermediate, and lateral
How is the lateral mesoderm split?
It is split dorsoventrally, creating a somatic layer and a splanchnic layer
What three things are formed with the split of the lateral mesoderm
A somatic layer, a splanchnic layer, and an intraembryonic celom
Intraembryonic celom
A product of lateral mesoderm splitting, it is a cavity in the emrbyo that gives rise to the peritoneal, pericardial, and pleural cavities
How is the paraxial mesoderm split?
Rostalcaudally, creating somites
Somite
The product of paraxial mesoderm splitting, it is a developmental structure that correlates to a section of the body
Neurulation
Formation of the neural tube
What induces neurulation?
The formation of the notochord
Neural plate
A differentiated section of the ectoblast that is induced by the notochord
How is the neural tube formed
The neural plate begins to fold into neural folds and neural grooves. The neural folds come together and pinch off the neural groove into forming the neural tube
Neural crest
Often called the 4th germ layer in vertebrates; cells that are pinched off of the neural plate during neurulation but do not remain as part of the nervous system
Neural tube
The product of neurulation and the precursor to the central nervous system (they become mesenchymal)
Secondary neurulation
The formation of a secondary neural tube in the caudial end of the embryo
Neuropore
The rolling up on the cranial and caudal ends of the embryo
What happens when rostal neuropore does not close?
Anencephaly
Spina Bifida
When the spinal cord does not close causally to the 4th somite
Skeletaginous septum
A septum that splits along the line of the notochord
Mesentery
An organ that attaches other organs to cell wall bodies. It double-wraps the gut tube dorsally and ventrally and is the primary communication method between the gut and the rest of the tube
