Lab 7 - chicken whole mounts are organogenesis of the heart Flashcards
What is the egg type and cleavage type of chickens?
egg type = extreme teloelicthal
cleavage type = discoidal meroblastic
Where is the egg cytoplasm located in a chicken egg?
Confined to a blastodisc on top of the yolk
Describe the steps of chick cleavage
- Blastodisc and its nucleus divide to form a disc-like layer of cells (blastoderm)
- Blastoderm is several cells thick and is separated by a space = subgerminal cavity from the underlying yolk
- From the blastoderm, a lower group of cells (1o hypoblast) separates from the upper cell layer (epiblast) in groups of cells called polyinvagination islands, and a space is formed between them = blastocoele (where the embryo develops)
- Delamination (but actually ingression)
- Note, separation does not occur at the periphery/margins of the blastoderm - Deep cells at the posterior marginal zone migrate anteriorly in a sheet and combine with 1o hypoblasts and forms 2o hypoblast
- Epiblast gives rise to all three germ layers
Describe gastrulation of chick embryos
- Begins when one quadrant of the blastoderm thickens and elongates
- 1st thickening = future posterior end
- Cell migration + convergence → thickened area = primitive streak
- Primitive streak = where the axial structure of the embryo will develop - Primitive streak → central depression = primitive groove + primitive ridges
- Migration of cells between the layers of the embryo →primitive groove
- Piling up of cells → ridges
- Migrating cells from part of the endoderm and all of the mesoderm - Primitive streak ends anteriorly in a thickened region called Hensen’s node
- Dorsal organizer
- Region where proliferation + migration of presumptive notochord cells into the interior occur - Embryo develops anterior to the primitive streak, which regresses as development occurs and comes to occupy the tail region of older embryos
What does Hensen’s node correlate to in other model organisms?
- Dorsal lip of the blastopore in frog
- Vegetal plate in sea urchins
- Embryonic shield in zebrafish
What germ tissue does the heart develop from?
the lateral plate mesoderm, specifically the splanchnopleure
What is the fusion order of heart structures? Which structure will become the pacemaker?
- truncus
- future ventricle
- future atrium
- sinus venous (stays separate)
- pacemaker
What are the brain structures of the 33-36 hour chick embryo and what brain structures do they differentiate into?
- prosencephalon (forebrain)
- telencephalon
- diencephalon - mesencephalon (midbrain)
- mesencephalon - rhombencephalon (hindbrain)
- metenceophalon
- myelncephalon
When looking at cross sections through the heart of chicken whole mounts, how can you identify the ventricle, atrium and truncus arterioles?
ventricle is always furthest away from the notochord, atrium appears as the longest vesicle, truncus is the smallest vesicle
If you are looking at a chicken whole mount at the heart is pointing out to the right, what view are you looking at the embryo from?
dorsal view
How can you identify the diencephalon from whole mount cross sections?
the eyes are located in the diencephalon
Why does the embryonic movement torsion occur?
allows brain growth - go from laying on your head to on your side
How is the heart mesodermal tissue brought together during development?
brought close together by closing of the gut
How does the neural tube close in chicks?
occurs both anteriorly and posteriorly from the midbrain of the embryo
How does the gut close in chicks?
A–>P
