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ANIMALS (VOCAB of Blastula (Blastopore→ opening of the central cavity…
ANIMALS
VOCAB of Blastula
blastula→ hollow ball of cells, END OF CLEAVAGE
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Blastocyst→ contains the inner cell mass that will form the embryo→ form definitive structures of the fetus
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trophoblast--< forming the outer layer of a blastocyst, they provide nutrients to the embryo and develop into a large part of the placenta. FIRST cells to differentiate from the ferti. Egg
Blastodisc→ embryo forming portion of an egg with meroblastic cleavage usually appearing as small disc on the upper surface of yolk.
SYNAPOMORPHIES
cell to cell junctions
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tight junctions--> take off stress, act as a barrier, holds together like a sheet of cells
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Gastrulation
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Frogs
yolk in displaced towards the vegetal pole (cleavage is slower at yolk rich areas), with a displaced blastocoel
asymmetrical yolk dist., since yolk cleaves slower, they are less numerous than yolk-free eggs
FIRST sperm entry moves the cytoplasm over morfing small crescent shape slit --> initiates formation of the blastopore
the animal pole INVOLUTES over the dorsal lip of the blastopore. which forms at the same location as the gray crescent
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The involuting cell layer eventually presses against the inner surface of the opposite side of the embryo, filling the blastocoel area with those germ layers, and producing an archenteron with a blastopore. In this case, however, the blastopore is filled with yolk-rich cells, forming the yolk plug.
the outer layer of cells resulting from these movements is the ectoderm, and the inner layer is the endoderm. Other cells that involute over the dorsal lip and ventral lip (the two lips of the blastopore that are separated by the yolk plug) migrate between the ectoderm and endoderm to form the third germ layer—the mesoderm. DELAMINITATION!!!!!!
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Birds
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epiblast cells migrate to midline, where they break away and INGRESS into the blastocoel cavity
tis furrow (analogous to an elongated blastopore) is called the primitive streak, there is a hensons nodeon the anteriot of the PS
some cell migrate through this, across the blastocoel cavity to displace cells in the lower layer forming the endoderm
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mammals
embryo develops from the ICM analogous to the blastodisc in birds( ICM is flattened despite yolk mass)
Placenta has made yolk dispensable, yet it still gastrulate as though sitting on top of a ball
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develops a yolk sac from extra embryonic cells the migrate away from lower blastoderm, and line the blastocoel cavity
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The extracellular matrix protein fibronectin and the corresponding integrin receptors of cells are essential molecules of gastrulation in many animals.
Germlayers
Endo derm
Lining of GI tracts and respiratory tracts, liver, pancreas, thymus, thyroid
<--mesoderm-->
notochords, bones, blood vessels, connective tissues, muscles and internal organs like kidneys and gonads, heart, skeleton
Ectoderm
Epidermis of skin, nervous system, sense organs
SYMPLESIOMORPHIES
eukaryotes, multicellular, locomotion, heterotrophic, internal digestion
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Cleavage
holoblastic
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frogs
yolk in displaced towards the vegetal pole (cleavage is slower at yolk rich areas), with a displaced blastocoel
mammals
little yolk, but lost blastomere dont have an effect on embryonic development
sea urchin
little yolk, but distributed evenly throughout the egg,
meroblastic
cleveage take place in the blastodisk, incomplete cleavage
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insects
yolk rich, blastoderm single layer of cell surrounding the central mass of the yolk
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