Vertebrate Development Flashcards
what are the early stages of development in frogs (4)
- cleavage
- blastula formation
- gastrulation
- neurulation
how do all vertebrates start life (2)
- as a single cell, which is a fertilized egg
- as a zygote
development
- when a single cell divides and differentiates into all of the cells which make up many different tissues and organs of an adult organism
what occurs during cleavage in frogs
- the zygote rapidly divides again and again to form the morula
zygote
- fertilized egg
morula
- a solid ball of 16-32 cells
animal pole (3)
- animal pole is located at the top of the egg
- has a lower concentration of yolk than the vegetal pole
- cells that divide near the animal pole are smaller than cells near the vegetal pole due to the lack of yolk
vegetal pole (3)
- vegetal pole is located at the bottom of the egg
- has a higher concentration of yolk than the animal pole
- cells that divide near the vegetal pole are larger than cells near the animal pole due to the abundance of yolk
how do the size of the cells within the egg and the egg itself change throughout early development (3)
- egg itself
- cells within the egg
- why
- sphere egg stays static in size
- individual cells get smaller in size
- this is because there is no time for growth of cells during rapid division that occurs during development
what happens during blastula formation in frogs
- morula continues to divide, forming a hollow ball of cells known as the blastula
blastula
- hollow ball of cells formed during blastula formation
blastocoel (3)
- defintion (2)
- function
- hollow space inside the blastula formed during blastula formation
- lined by undifferentiated/non-specialized cells
- no specific function, just a step that has to occur during development
what happens during gastrulation in frogs (3)
- major rearrangement of cells in the embryo: cells from the outer surface migrate inward through the blastopore
- specialization occurs and three embryonic germ layers are established: ectoderm, mesoderm, and endoderm
- gut formation
blastopore
- opening in the blastula outer surface
ectoderm (2)
- “outer skin”
- outer layer of cells
mesoderm (2)
- “middle skin”
- middle layer of cells, sandwiched between the ectoderm and the endoderm
endoderm (2)
- “inner skin”
- most inner layer of cells that line cavities within the egg
what occurs during gut formation of gastrulation in frogs (2)
- a new space forms within the embryo called the archenteron
- this new space completely displaces the blastocoel
archenteron (5)
- “early gut”
- new space formed within the embryo during gastrulation
- gives rise to the lumen of the digestive tract
- this space is lined by endoderm cells
- completely displaces the blastocoel
notochord (3)
- arises from the medial region of the mesoderm
- a flexible rod that provides structural support
- signalling centre that directs cells
what is the fate of the mesoderm in adult vertebrates (4)
gives rise to:
- many regions of the skeleton
- most muscles
- the notochord
- the circulatory system
what is the fate of the ectoderm in adult vertebrates (4)
gives rise to
- the epidermis
- many skin glands
- nervous system
- many sensory organs
what is the fate of the endoderm in adult vertebrates (8)
produces:
- lining of the digestive tract
- liver, pancreas, gall bladder, digestive glands
- lungs
- swim bladders
- urinary bladder
neural plate ectoderm
- thickened plate of ectoderm cells that lie on the dorsal side of the egg
- formed in early neurulation/late gastrulation
what happens during neurulation in frogs (3)
- the neural plate ectoderm bends along the dorsal midline forming a medial neural groove surrounded by neural folds on either side
- the neural folds fuse together to form the hollow neural tube
- some cells separate from the neural folds to form the neural crest
- differentiation of the mesoderm into 3 layers
neural crest (3)
- development
- function
- fate
- cells that separate from the neural folds during neurulation
- most ectoderm cells are organized into large sheets, but neural crest cells can migrate independently through the embryo
- highly mobile cells will give rise to wide variety of structures in the adult
neural tube (2)
- development
- fate
- formed when the neural folds fuse together to form a hollow tube during neurulation
- gives rise to the central nervous system, including the brain, spinal cord and parts of the eyes
neurocoel (2)
- development
- fate
- hollow cavity in the neural tube that is formed during neurulation
- becomes the ventricles of the brain and the central canal of the spinal cord
in folic acid deficiency, the neural folds do not fuse together
- what is most likely to occur in the case of severe deficiency of folic acid? (3)
- neural tube will not be formed properly
- embryo will not have a functional brain or spinal cord
- embryo will most likely not survive
describe the differentiation of the mesoderm in frogs
- after gastrulation, the mesoderm differentiates into epimere, mesomere, and hypomere
epimere mesoderm (3)
- “on top middle skin”: the mesoderm that is located near the dorsal portion of the embryo
- forms somites in the trunk region
- further differentiates into dermatome (dermis and connective tissue), myotome (skeletal muscle), and sclerotome (vertebrae and ribs)
mesomere mesoderm
- “middle middle skin”: the mesoderm that is located in the mid-section of the embryo
hypomere mesoderm (2)
- “bottom middle skin”: mesoderm located near the ventral portion of the embryo
- solid sheet of hypomere mesoderm splints into two layers: somatic hypomere and splanchnic hypomere
coelom (2)
- development
- fate
- hollow space that forms between the two hypomere mesoderm layers
- gives rise to major body cavities of the adult
vertebrate egg types (3)
- mesolecithal
- microlecithal
- macrolecithal
mesolecithal (4)
- yolk size
- vertebrate type
- blastocoel and cell size (2)
- vertebrate egg type with a moderate amount of yolk
- embryo formed in amphibians
- large yolk causes blastocoel to be small and unevenly distributed (lies closer to the animal pole where there is less yolk)
- uneven cell size: larger cells near the vegetal pole where there is more yolk and smaller cells near the animal pole where there is less yolk
microlecithal (4)
- yolk size
- vertebrate type
- blastocoel and cell size (2)
- vertebrate egg type with little yolk
- embryo formed in amphioxus or eutherian mammals
- due to small egg size, blastocoel takes up even distribution in the blastula
- more even cell sizes across the blastula
macrolecithal (3)
- yolk size
- vertebrate type
- blastocoel and cell size
- vertebrate egg type with large yolk
- embryo formed in birds and many fish
- embryo initially develops as a flattened yolk disk sitting on top of the enormous yolk (yolk is not incorporated into the cell)
how does cleavage and blastula formation occur in birds (4)
- cleavage (1)
- blastula formation (3)
- cleavage is restricted to a small region at the animal pole of the zygote
- produces a blastodisc
- cells of blastodisc form two layers: the epiblast and the hypoblast
- hollow space between two layers forms the blastocoel
blastodisc (3)
- flat disc of cells that forms on top of the yolk in bird embryos during cleavage
- cells of the blastodisk form two layers: the epiblast and the hypoblast
- the space between these two layers forms the blastocoel
epiblast
- the top layer/dorsal layer of the blastodisc
hypoblast (3)
- the bottom/ventral layer of the blastodisc
- hypoblast cells help guide the migration of epiblast cells during gastrulation; act as a scaffold/guide
- at the end of gastrulation, hypoblast cells are displaced and lost
how does gastrulation occur in birds (3)
- primitive streak forms from the anterior to the posterior of the blastodisc
- migration of epiblasts cells inward through the primitive streak
- during the migration, there is formation and differentiation of the 3 embryonic germ layers: ectoderm, mesoderm, and endoderm
describe the migration of cells inward through the primitive streak during gastrulation in birds and its connection to the three germ layers (3)
- some epiblast cells come inward and displace the hypoblast cells, eventually forming the endoderm
- some epiblast cells come inward and fill blastocoel space, eventually forming the mesoderm
- some epiblast cells remain on the outside dorsal surface, eventually becoming the ectoderm
during gastrulation, what embryonic structure in the frog has a similar function to the primitive streak in the chick? (2)
- the blastopore
- cells migrate inward in both the primitive streak and in the blastopore
what is one major difference in gastrulation between the chick and the frog?
- in chicks: cells of the hypoblast act as a scaffold to guide migrating cells during gastrulation
- in frogs: there is no transient structure like the hypoblast to guide the migrating cells
neurulation in birds (4)
- neural plate ectoderm bends along midline, sinking ventrally into embryo and forming a neural groove with neural folds on each side
- neural crest cells separate from neural folds
- neural folds fuse to form the hollow neural tube
- occurs in a wave, from anterior to posterior
neurocoel (2)
- hollow cavity in neural tube
- becomes ventricles of the brain and central canal of the spinal cord
post neurulation: development of central nervous system (2)
- after neurulation is complete in the anterior of the embryo, the neural tube in the head region swells and expands to produce the brain
- posterior to the head, the neural tube gives rise to the spinal cord
post neurulation: differentiation of mesoderm into 3 regions (3)
- mesoderm differentiates into: epimere, mesomere, and hypomere
- epimere mesoderm forms somites in the trunk region
- somites differentiate into myotome, dermatome, and sclerotome
post neurulation: formation of coelom in the chick (3)
- solid sheet of hypomere mesoderm splints into two layers: somatic and splanchnic hypomere
- creates a space called the coelom
- cells of mesoderm will be organized into continuous sheets
coelom (2)
- space between somatic and splanchnic hypomere
- gives rise to major body cavities in adult
post-neurulation events (3)
- development of CNS
- differentiation of mesoderm into 3 layers
- formation of coelom in chicks
mesenchyme (3)
- loosely associated accumulation of undifferentiated mesodermal cells
- can easily and independently migrate throughout body
- can shed from different mesoderm regions at various times during development and gives rise to variety of structures
how does formation of the digestive system differ between chick and frog embryos (2)
- frog: during gastrulation, before neurulation
- chick: after neurulation
neurulation and gastrulation in birds (2)
- can be occurring at the same time
- neurulation in the anterior regions while gastrulation in the posterior region (posterior to the Hensen’s node)
organogenesis (3)
- embryo continues to grow and each embryonic germ layer continues to differentiate
- interactions between germ layers stimulate tissue and organ formation
- every cell contains genetic material necessary to become any cell type, but differentiation into specific cell types is a function of gene regulation
extra-embryonic membranes (4)
- membranes (4)
- production
- amnion
- chorion
- allantois
- yolk sac
- produced by embryo and grow outward
which extra-embryonic membranes do amniotes have
- amnion
- chorion
- allantois
somatopleure (2)
- extra-embryonic ectoderm and somatic hypomere mesoderm
- form amnion and chorion
splanchnopleure (2)
- extra-embryonic endoderm and splanchnic hypomere mesoderm
- form yolk sac and allantois
allantois (2)
- sequesters nitrogenous metabolic wastes away from the embryo
- removes toxic wastes away from fragile embryo to prevent disruption to development
yolk sac
- grows ventrally to surround yolk and forms vitelline blood vessels
vitelline vessels (2)
- transport nutrients from yolk to the embryo
- simple diffusion is not sufficient enough to support embryo growth
chorion (4)
- fuses with outer section of allantois to form chorioallantoic membrane (respiratory membrane)
- splanchnic hypomere mesoderm within this membrane forms many allantoic vessels
- vascular membrane used to exchange gases with the environment (through the shell)
- transports calcium from the shell to the embryo
amnion (2)
- water-proof membrane that surrounds embryo in a capsule filled with amniotic fluid
- protects the embryo
how does the amnion protect the embryo (3)
- shock absorption and cushioning
- prevents fluid loss/desiccation
- provides support and structure against gravity
extra-embryonic membranes in mammals (2)
- chorioallantoic membrane or yolk sac produces the umbilical cord and the embryonic region of the placenta
- amnion surrounds embryo in a fluid-filled capsule
