Embryogenesis and development 8 and 9 Flashcards
What is cleavage?
Cell division in early embryo
What is gastrulation?
Cell movements which produce gut and three primary germ layers
What is organogenesis?
Development of organs
Describe the features of sea urchin cleavage
Rapid divisions
Bastomeres all the same size
Holoblastic cleavage (division of whole cell)
Blastomeres become smaller with each division
What is unequal holoblastic division?
Blastomeres in animal pole are
smaller than blastomeres in
vegetal pole because of presence
of yolk in vegetal hemisphere.
When does unequal holoblastic division take place?
In amphibian cleavage
What is mesoblastic cleavage?
Cleavage plane does not direct yolk
What comes after the cleavage stage in chicks?
Blastula formation
What do we refer to cells as in embryogenesis?
Blastomeres
What is holoblastic division?
Cleavage plane divides the blastomere completely
What is a morula?
After several cleavage divisions, the small sold ball of blastomeres that form
Why are blastosomes the same size in sea urines?
There is no yolk in sea urine eggs
Does the amphibian egg contain lots of yolk?
Yes
What is the top pigmented half of the amphibian egg called?
Animal pole
Whats is the unpigmented bottom half of the amphibian egg called?
Vegetal hemisphere
What happens to the cytoplasm when the sperm enters the egg in amphibians?
Cytoplasm is rearranged and the cortex contracts towards the point of sperm entry revealing the grey crescent
What is the dorsal surface marked with in amphibians?
Grey crescent
What is the ventral surface marked with in amphibians?
Point of sperm entry
Who undergo meroblastic cleavage?
Chicks
What comes after blastula formation in chicks?
Gastrulation
Gastrulations forms which 3 germ layers in chicks?
Ectoderm
Mesoderm
Endoderm
What does the ectoderm include?
Epidermis of skin
Nervous system
Pituitary gland
Teeth
What does the mesoderm include?
Muscular system
Skeletal system
Reporductive system
Dermis of skin
What does the endoderm include?
Epithelial lining of gut, respiratory and excretory tracts
Describe the process of gastrulation in sea urchins.
Cells at the vegetal pole thicken to form the vegetal plate which fold inwards forming the archenteron which form the endoderm
Mesenchyme cells migrate into the blastocoel forming the mesoderm
Cells remaining on the surface form the ectoderm
Describe the process of gastrulation in chicks.
Straight invagination of the upper layer of cells of the blastoderm
Cells migrate through blastocoel displace the hydroblast cells and form the endoderm
Next cells migrate through the blastocoel to form the mesoderm
Remaining cells on top form the ectoderm
What is a primitive streak?
The line of invagionation in chick gastrulation
Describe the process of gastrulation in amphibians.
Tuck at a site where grey crescent is situated which is called the dorsal lip of the blastopore
The endoderm arises from cells lining the archenteron, the mesoderm arises from cells which were deep in the equator (marginal zone) and the ectoderm is derived from the cells remaining on the surface
What do the amnion and chorion develop from in chicks?
Folds of ectoderm and mesoderm which extend over the top of the embryo and fuse
What is the role of the amniotic sac in chicks?
Surround the embryo to protect it
What is the amniotic sac lined with?
Amnion
When is the first human cleavage?
24-30 hours after fertilisation
What is formed fro the first human cleavage?
2 blastomeres
When does the morula enter the uterus?
Day 4-5
When does a blastocyst form during human fertilisation?
32 cell stage
What does a blastocyst contain?
Inner cell mass
Blastocoel
Trophoblast
What happens on the 5th day after human fertilisation?
Hatching: The blastocyst digests a hole in the zone pellucida and emerges
What must occur before implantation in the uterus?
Hatching
What happens during implantation?
Day 6-7
Blastocyst secretes enzymes to burrow unto endometrium
Inner cell mass next to the endometrium
What happens 8 days after human fertilisation?
Bilaminar embryonic disc is formed where the inner cell mass has rearranged into two layers called the epiblast (upper) and the hypoblast (lower)
Describe the primitive streak in human gastrulation
Forms in dorsal epiblast
Defines anterior and posterior of the embryo
How does gastrulation in humans form the 3 germ layers?
It enables the production of a trilaminar embryonic disc which consists of all 3
What do cells form the primitive node produce?
notochord
How does neurulation in vertebrates occur?
Notochord develops from dorsal mesoderm
Induction of neural plate from ectoderm layer above the notochord
A neural groove and neural folds form from the dorsal ectoderm
The neural folds rise up, meet and fuse to form the neural tube
What does the neural tube become?
CNS
What are the first organs to develop in vertebrates?
Neural tube
Notochord
What 3 components in development comprised of?
Growth
Morphogenesis
Differentiation
WHAt happens in neurulation in amphibians?
Development of brain and spinal cord
What is induction?
The fate of one cell is influenced by another
What did the researchers do in the dorsal mesoderm experiment (1)?
Used two very early early newt embryos; unpigmented and pigmented. The dorsal lip of the blastopore from the unpigmented newt gastrula was transplanted
into the ventral side of the pigmented newt gastrula
What did the researchers find in the dorsal mesoderm experiment (1)?
Conjoined twins produced. Second embryo produced daily pigmented tissue.
How did the organiser alter cell fate?
BMP-4 is uniformly distributed in late blastula and causes VENTRAL development. Chordin and Noggin (secreted by organiser) stop action of BMP-4 and allow dorsal development e.g. muscle and notochord (dorsal mesoderm)
Describe the induction of the neural plate(2)
Signalling molecules from the notochord and surrounding cells cause the overlying ectoderm to take on a neural fate
