Development: Amphibians and Birds (LP.2) Flashcards
What environment do Ambhibians develop from?
-From eggs w/ a moderate amount of yolk
What environment do birds develop from?
-Develop from eggs w/ large amounts of yolk
What does the amount of yolk in an egg influence?
-It influences the way development occurs w/ respect to cleavage patterns & morphogenesis
What are the key characteristics of amphibian eggs?
- They have more yolk in them than echinoderms
- The yolk is more dense & concentrated in animal pole= animal-vegetal polarity
What occurs after the fertilization of an Amphibian egg?
-There is a shift in animal-hemisphere pigment which forms the grey crescent= the dorsal region of the embryo
How does cleavage begin in Amphibian eggs?
- It is vertical= begins are animal pole & works its way down to the vegetal pole
- But the Cleavage Furrow is slow as it gets to the vegetal pole bc there’s more yolk there
What is the 2nd cleavage like in Amphibian eggs?
-It’s Vertical & starts before the first one even completes
What is the 3rd cleavage like in Amphibian eggs?
-It is Horizontal BUT it doesn’t cut the blastomeres into equal animal/ vegetal sets bc the plane is offset towards animal pole= upper tier of blastomeres is smaller than the lower one
Why do the animal hemisphere blastomeres get cleaved quicker in Amphibian eggs?
-Bc theres less yolk than in the vegetal pole
What is the Blastoceol like in Amphibian eggs?
-It is formed normally but it is restricted to the animal-hemisphere
Why isn’t the Blastoceol formed in the Vegetal Hemisphere of Amphibian Eggs?
-Bc its solid w/ large yolk-packed cells
What are the beginning stages of Gastrulation like in Amphibian eggs?
- The cells in the ventral margin of where the grey crescent was migrate to the interior of the embyro which produces a blastopore & archenteron on the side of the blastula
- (DOES NOT BEGIN IN VEGETAL POLE)
What occurs as Gastrulation proceeds in Amphibian eggs?
- The blastocoel reduces in volume by the Invaginating Mesoderm & Endoderm cells
- Then the 3 germ layers are formed
What are the 3 germ layers in Amphibian Gastrulation?
- The Endoderm (inside)= Lungs, &digestive organs like the Gut, pancreas, liver
- The Mesoderm (middle)=bone, muscle, blood, kidneys, gonads
- Ectoderm (outside)= outer layer of the skin, nervous system
What is the Archenteron Roof?
- In amphibians
- The upper layer of cells of the archenteron
How does the Central Nervous system of Amphibians develop?
- Begins when the thickening of the Archenteron Roof
- The neural plate folds into neural tube that becomes brain & spinal cord
What are the steps in Amphibian development?
1) Egg/zygote
2) 2 cell
3) early cleavage
4) blastula
5) early gastrula
6) Gastrula
7) Neural Plate
8) Neural Groove
9) Neural tube
What does the Blastula stage of Amphibian development consist of?
-The Blastula formation at the animal pole
What does the Early Gastural stage of the Amphibian Development consist of?
- Blastocoel at animal pole
- Arhenteron starting to form
- The blastopore (dorsal lip) starting to form from that archenteron forming
What does the Gastrula stage of Amphibian development consist of?
- The blastopore still in the animal-hempishere
- The dorsal lip forming around the
- Yolk plug in the middle
What does the Neural Plate stage of Amphibian development consist of?
- Notochord starting to form on top of the archenteron
- The archenteron takes on an upsidedown “U” shape
- The mesoderm starts to form
What does the Neural Groove stage of Amphibian development consist of?
- The notochord is fully formed on top of archenteron
- Archenteron has same upsidedown “U” shape but its thicker
- Neural fold starts to form at the animal-hempishere
- Somites take place in the “empty” space
What does the Neural Tube stage of Amphibian development consist of?
- The neural tube is now pinching off
- The notochord is till on top of “archenteron”
- The archenteron has now formed into a gut
- Somite is everything else inside
What are Bird eggs like?
- They have hella yolk
- BUT the blastodisc at animal pole has a little less yolk to allow for cleavage
- Has very distinct animal-vegetal polarity
How are the first cleavages like in Bird eggs?
-They are vertical but extend only a short distance downward
How is the 3rd cleavage of Bird eggs like?
-It is horizontal= gives rise to several layers of blastomeres that make up the disc cells at the top of the yolk
How does Gastrulation start in Bird eggs?
-It starts by the separation of cells from the lower surface of the blastoderm which forms the hypoblast below the Epiblast
What is the Hypoblast?
- Only in Bird eggs
- Flimsy layer of endoderm
What is an Epiblast?
- Only in birds
- It is a layer of cells above the hypoblast
What’s in the Middle of the Epiblast and Hypoblast?
-The blastocoel
What happens as Gastrulation in Bird eggs continues?
- The hypoblast expands to form complete layer
- Cells of the Epiblast migrate toward posterior & central region to form a thickened region of the epiblast= Primitive Streak
What do some cells in the Primitive Streak do?
-Migrate to a space between the Epiblast and Hypolast = forms middle layer of cells (notochord in midline & lateral mesoderm flanking it)
When does the Primitive Streak regress & what is the consequence of this?
- When the middle layer of cells begin to move inward
- It leaves the notochord & lateral mesoderm in its wake
When does the Neural Plate of Bird eggs form?
-When the ectoderm above the notochord thickens
Where does the Neural Tube form in Bird eggs?
-It forms the brain on the broad anterior end & the spinal cord at the narrower posterior end
What are the 6 general stages of development like in Birds?
1) develops optic vesicles
2) then the cerebral vesicles
3) these cerebral vesicles turn into cerebral hemispheres
4) Lateral to neural tube=blocks of mesoderm=Somites
5) Structures like vertebrate, dermis, muscles, develop from the somites
6) Heart develops from tube that forms lateral mesoderm
What developed in the 16-18 hours of incubation in Birds?
-The primitive streak
What develops in the 33 hour of incubation in birds?
-The brain, optic vesicles, spinal cord, somites, heart
What develops in the 48 hour of incubation in birds?
-Brain, optic cups, spinal cord, lenses, somites, heart, limb buds, pharyngeal slits, somites
What develops in the 72 hour of incubation in birds?
-Everything in 48 hour plus cerebral vesicles
