lab 3: embryology Flashcards
embryology
the study of the processes in the early development of an organism
fertilization
the initial event in development in sexual reproduction (sperm -> egg)
cleavage
-after fertilization, the period of rapid cell division without growth
-produces the morula (a solid ball of cells), then it forms blastula, a hollow sphere of many cells with a fluid-filled cavity (blastocoel), cells are called blastomeres
gastrulation
-rearranges the cells of a blastula into a 3-layered embryo (gastrula)
germ layers
-the three layers produced by gastrulation
ectoderm
-outer layer of the germ layers
endoderm
-lines the digestive tract
-layer of germ layer
mesoderm
-partly fills the space between the endoderm & ectoderm
organogenesis
-when various regions of the germ layers develop into organs
cell polarity
-refers to spatial differences in shape, structure & function within a cell
-polarity is defined by the heterogeneous distribution of substances like mRNA, proteins & yolk
-yolk is most concentrated at the vegetal pole & least at animal pole
fertilization in sea stars
-zygote divides to form 2 cells
-yolk is holoblastic (only a small amount of yolk is present)
-cleavage forms a ball of 16-32 cells called a morula, which forms a hollow sphere of many cells called blastula
-the fluid filled cavity within blastula is blastocoel, & the cells are called blastomeres
gastrulation in sea star
-occurs after blastula matures
-cells invaginate into blastocoel & form gastrula & new cavity called archenteron
-formation of germ layers [endoderm: digestive tract, ectoderm: skin & nervous system, mesoderm: muscular tissue & parts of reproductive & circulatory systems]
organogenesis
-formation of motile & feeding larval stage called the bipinnarial larva
-this stage is followed by the (brachiolaria larva: attach to the substrate & undergo metamorphosis)
-sea star arms grow -> juvenile sea star
in conclusion (reproduction & development of sea stars)
-first is meiosis where the adult male & female sea stars produce haploid gametes (sex cells)
-second is the sperm & egg fuse forming diploid zygote
-third is mitosis that produces a blastula
-fourth is continued mitosis & changes in shape to produce a gastrula
-fifth is the gastrula develops into a larva
-sixth is the larva undergoes metamorphosis & becomes an adult
-then the cycle repeats
fertilization in frogs
-cytoplasm becomes specialized in certain regions [animal pole: less yolk, more cytoplasm; vegetal pole: more yolk, less cytoplasm]
-eggs are telolecithal: vegetal pole contains significant amount of yolk, unevenly distributed
cleavage in frog
-holoblastic: small amount of yolk present resulting cells not equal in size, but total division
-morula -> blastula
-asymmetric blastula: vegetal pole cells of blastula have more yolk & divide slower than animal pole cells
gastrulation in frogs
-involution: layer on animal pole cells moves & grows down over vegetal cells. moves inward at blastopore
-yolk cells are enveloped, some produce a yolk plug through blastopore
-mesodermal layer develops
-formation of neural tube [neurulation: the process of formation of neural tube or nerve cord]
organogenesis
-producing functioning larva
in conclusion (development of frog)
-gametogenesis
-sperm & egg cells fertilize
-fertilized egg goes through cleavage which becomes the blastula
-gastrulation happens & the blastocoel & blastopore develops
-then the ectoderm, mesoderm & endoderm develop
-then the neurula & neural tube
-then organogenesis happens & produces functioning larva
fertilization in chicks
-occurs before hard shell is produced
-egg cell is large mass of yolk & small area of cytoplasm on its surface = germinal disk (contains egg nucleus)
-cells formed from germinal disk become the embryo
-albumen surrounds egg cell & supplies embryo w food & water
-albumen is surrounded by 2 shell membranes & a shell porous to gas
cleavage in chicks
-confined to germinal disc (abundance of yolk)
-blastodisc (blastoderm) consists of 2 layers: epiblast & hypoblast
-layers are separated by blastocoel; epiblast forms endoderm & mesoderm
-cells on surface of embryo form ectoderm
gastrulation in chicks
-cells migrate across surface of blastodisc & into the primitive streak (becomes midline of developing chicks)
-embryo is surrounded by a network of arteries & veins -> to extra-embryonic membranes
-[amnion: surrounds embryo; yolk sac: surrounds yolk; allantois: waste disposal sac; chorion: surrounds the entire embryo or yolk]
summary (starfish)
-amount of yolk: holoblastic
-distribution of yolk: isolecithal
-blastulation: holoblastic
-gastrulation: ectoderm, endoderm, mesoderm
-larval stage: motile, free floating
-egg size: microscopic
summary (frog)
-amount of yolk: holoblastic
-distribution of yolk: telolecithal
-blastulation: holoblastic
-gastrulation: nerurulation, open cavity
-larval stage: tadpole, motile
-egg size: small but visible to naked eye but clearer beneath microscope
summary (chick)
-amount of yolk: meroblastic
-distribution of yolk: partial merblastic
-blastulation: meroblastic
-gastrulation: primitive streak
-larval stage: nonmotile, inside egg, surrounded by yellow yolk
-egg size: very large, no need for microscope
meroblastic
partial cleavage of the zygote in chicks; produces a flat blastodisc of developing cells lying atop the bulky yolk
holoblastic
cleavage of the zygote: only a small amount of yolk is present, divides evenly in the sea star. in frog zygote, the resulting cells are not equal in size
telolecithal
vegetal pole contains significant amount of yolk, unevenly distributed
isolecithical
yolk is distributed evenly
