lab 3: embryology Flashcards
(29 cards)
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
