Embryology Flashcards
2 differences of chick gastrulation vs. frog (other than being flat)
- endoderm displaces hypoblast
2. Hensen’s node closes primitive streak to end gastrulation
What does the blastocoel form in the adult?
Nothing (gets filled up)
Compare blastula cells in mesolecithal
Asymmetric/different because yolk slows cleavage
Describe steps of neurulation
Thick dorsal ectoderm = neural plate
Invaginates, neural groove w/folds on sides
Folds fuse, enclosing neural tube
Epidermal ectoderm grows over top
Germ layer origin of chorion
Ectoderm, somatic hypomere mesoderm
Name the 4 major extra-embryonic membranes
- Yolk sac
- Amnion
- Chorion
- Allantois
Blastula formation events
Form hollow ball of cells; hole = blastocoel
Which organisms have a chorioallantoic placenta?
Most eutherian mammals
Morula (def)
symmetric ball of cells
Germ layer origin of allantois
Endoderm, splanchnic hypomere mesoderm (from hindgut region)
Events of cleavage
Short/no growth phase between cell divisions (division while overall embryo maintains size)
Major events of organogenesis
- embryo grows, lengthens
- germ layers further differentiate, work in concert to form complex organs
Which direction does Koller’s sickle move?
posterior to anterior
How do extra-embryonic membranes form?
Lateral germ layers (ectoderm, hypomere mesoderm, endoderm) form folds, grow around embryo
Describe blastodisk of macrolecithal egg from dorsal to ventral
epiblast (dorsal, formed first, forms embryo), blastocoel (middle), hypoblast (ventral, forms after, guides cell migration in gastrulation)
Where do neural crest cells originate?
In neural folds (during neurulation)
Animal pole (def)
thinner, yolk-less end of blastula/gastrula (top in most diagrams, made of ectoderm)
Germ layer origin of notochord?
Mesoderm
Homoplasty (def)
Structures with a similar appearance
What does the archenteron become in the adult?
Gut (blastopore = anus in deuterostomes)
What does the posterior marginal zone in the chick embryo become?
Koller’s sickle, then primitive streak
Shape of macrolecithal-egg embryo
disk
What does the neural tube become in adults?
Brain: ventricles
Spinal cord: cerebrospinal fluid canal
Function of the yolk sac
extra-embryonic membrane surrounding yolk, forming vitelline vessels to transport nutrients from yolk to embryo
Which vertebrates have a yolk sac placenta?
Most methatherian mammals
Function of allantois/allantoic membrane
Sequester nitrogenous wastes away from the embryo so it doesn’t poison itself
Describe epiblast from anterior to posterior
Area opaca -> area pellucida (most of the epiblast) -> posterior marginal zone (thicker, becomes Koller’s sickle, then primitive streak)
What does the coelomic fold become in the adult?
Muscular diaphragm (mammals only)
Mesoderm differentiates into…
Notochord, Epimere, Mesomere, Hypomere
What happens to the hypoblast in the chick embryo?
Displaced by endoderm during gastrulation
Hypoblast: lower layer of blastula, directly dorsal to yolk
Cells migrate into the blastopore through which analogous structures in the frog and chick embryo?
frog: blastopore
chick: primitive streak
What does the coelom divide into in all vertebrates? What separates them?
Pericardial & pleuroperitoneal cavities; transverse septum
Vegetal pole (def)
Thicker, yolk-filled end of blastula/gastrula (bottom in most diagrams, made of endoderm)
Which direction does Hensen’s node move?
anterior to posterior
How do metatherian mammals form the embryonic placenta?
From yolk sac
What is Hensen’s node?
Anterior end of the primitive streak
Germ layer origin of yolk sac
Endoderm, splanchnic hypomere mesoderm
How do complex organs form in the embryo?
Several germ layers work together
Which organisms do/don’t have an allantois & why?
Anamniotes: no, wastes diffuse into water
Mammals: no, wastes removed by placenta
Sauropsids: yes, can’t get rid of wastes
Germ layer origin of amnion
Ectoderm, somatic hypomere mesoderm
Ectoderm differentiates into…
Neural crest cells, neural plate cells, Epidermal
Epimere mesoderm forms… In the 24-hour chick embryo (overall structure name, plus differentiated layers)
somites (little balls); dermatome, myotome, sclerotome
What does the pleuroperitoneal cavity divide into in mammals, and what separates it?
Pleural cavity, peritoneal cavity; coelomic fold (becomes muscular -> diaphragm)
What is contained in the amnion?
Embryo, amniotic fluid
Who has protostome development?
Invertebrates: arthropods, molluscs, insects, etc.
How do eutherian mammals form the placenta?
From chorioallantoic membrane
3 main events of gastrulation
- archenteron formation by cell migration into blastocoel
- germ layer differentiation
- committed anterior/posterior
Function of amnion
Cushion embryo in amniotic fluid, prevent dessication (b/c waterproof)
What is the transverse septum & what does it do?
Fold that divides coelom into pericardial & pleuroperitoneal cavities
Function of placenta
Exchange gases, nutrients, wastes between mother & embryo
Where is the coelom located?
Between the somatic and splanchnic hypomere mesoderm
3 differences between deuterostomes & protostomes
- Cleavage pattern (spiral in protostomes, radial in deuterostomes)
- End function of blastopore (mouth in protostomes, anus in deuterostomes)
- Origin of skeleton (protostomes: ectoderm mostly, deuterostomes: mesoderm mostly)
How is the primitive streak formed?
Migration of Koller’s sickle from posterior to anterior (mnemonic: sickle cuts up to form streak)
Describe structure & function of chorion
Membrane fuses w/allantois to form chorioallantoic membrane; allows gas exchange through egg shell via many blood vessels
What is the coelomic fold and what does it do?
Divides pleuroperitoneal cavity in mammals into pleural and peritoneal cavities by fusing with transverse septum
