Flashcards
Cleavage to gastrulation
Cards in this deck (41)
- 1Define cleavage?CLEAVAGE: immediately follows fertilisation. Series of rapid
cell divisions, without growth, that divides the embryo up into
numerous small cells - 2Define cleavage?CLEAVAGE: immediately follows fertilisation. Series of rapid cell divisions, without growth, that divides the embryo up into numerous small cells
- 3There are two types of cleavage, what are they?- Holoblastic (complete) - takes place in mammals, flatworms, nematodes, amphibians
- Meroblastic (incomplete) - takes place in fish, reptiles, birds, insects - 4What is holoblastic cleavage?- Seen in the absence of a large conc of yolk
- Cleavage panes pass all the way through the zygotes during cytokinesis
- First cleavage always occurs along vegetal-animal axis of egg
- Second cleavage always perpendicular to first
- Thereafter, due to diff panes of cleavage in diff organisms, spatial arrangement of the blastomeres then proceeds in various patterns - 5There are different types/shapes of holoblastic cleavage based on the different patterns of cleavage that proceed in different organisms, what are they?
- 6There are two types of meroblastic cleavage, what are they?- Discoidal (zebrafish, chick)
- Superficial (drosophila) - 7What is discoidal meroblastic cleavage?- Cleavage furrows do not penetrate the yolk
- Embryo forms disc of cells (blastodisc) on top of yolk
- Commonly found in birds, reptiles, and fish - as they have egg cells w/yolk conc at one end - 8What is superficial meroblastic cleavage?- Mitosis occurs but not cytokinesis -> results in polynuclear cell
- Yolk positioned in centre of egg cell -> nuclei migrate to periphery of cell
- Plasma membrane then grows inwards, partitioning the nuclei into indiv cells
- Occurs in arthropods as they have yolk in the centre of the egg cell - 9What defines the vegetal (heavy) pole?- That is where the yolk is concentrated, at least initially
- 10What is the zona pellucida?- The thick transparent membrane surrounding a mammalian ovum before implantation
- 11What is a morula?- An early-stage embryo consisting of 16 cells (called blastomeres) in a solid ball contained within the zona pellucida
- 12What is the trophoblast?- Cells that form the outer layer of a blastocyst
- Present four days post-fertilization in humans
- Provide nutrients to the embryo and develop into a large part of the placenta - 13What is the blastocoel/blastocyst cavity?- A fluid-filled cavity that forms in the blastula of early amphibian and echinoderm embryos, or between the epiblast and hypoblast of avian, reptilian, and mammalian blastoderm-stage embryos
- 14What is the inner cell mass/embryoblast?- A mass of cells inside the primordial embryo that will eventually give rise to the definitive structures of the foetus (In most eutherian animals)
- 15Diagram of human embryogenesis - fill in the blanks
- 16When does cleavage start in humans?- When the fertilised egg passes from the ovary into the oviduct
- 17What does meroblastic cleavage look like in the fish?
- 18What is the syncytium?- A single cell or cytoplasmic mass containing several nuclei, formed by division of nuclei
- 19What is the area pellucida and the area opaca?- Area pellucida = the pellucid (transparent, clear) central area that immediately surrounds a vertebrate embryo (as of a bird) formed by discoidal cleavage
- Area opaca = the peripheral opaque area that surrounds the area pellucida of a vertebrate embryo (as of a bird) formed by discoidal cleavage. - 20What does meroblastic discoidal cleavage look like in the chick?- Slide one of cleavage PP!
- 21What is the blastula?- A hollow sphere of cells (blastomeres) surrounding an inner fluid-filled cavity (the blastocoel)
- 22What is gastrulation?- Process by which the cells forming the
endoderm and mesoderm move from the outer surface of the embryo to the inside where they are going to form the
inner organs
- Formation of the trilaminar embryo
- When the three germ layers, ectoderm, mesoderm, endoderm, emerge via the blastula folding in on itself - 23What happens at the end of the cleavage stage in xenopus and fish?- Some cell specification has
occurred such that three cell types are defined (ectoderm, mesoderm, endoderm) - 24What are maternal determinants?- Maternally supplied resources
- mRNAs and proteins that are
synthesized and laid down in the egg by the mother (transcription factors, signalling molecules, and signalling regulators) - 25What is the syncytial blastoderm?- Comprises a superficial layer of nuclei and cytoplasm
- Surrounds a central mass of yolky cytoplasm
- The syncytial blastoderm is equivalent to the blastula stage in embryos such as Xenopus - 26How early is cell lineage restricted in the worm and how is this done?- Cell lineage restriction by maternal determinant from first cleavage onwards in the worm
- 27In mammals, the fate of cells is not initially specified in the zygote so how IS it specified?- Cell fate in mammals depends on relative position w/in the embryo
- Occurs after 32-cell stage - 28What are the two types of maternal signalling?- Intrinsic -> those that affect the cell they are
located in
- Extrinsic -> those that influence the fate of another cell - 29What is involution?- Movement of a SHEET of cells towards the inside of the embryo, by rolling in under itself
- 30What is epiboly?- The expansion of one cell sheet over other cells
- 31What is the archenteron?- The cavity of a gastrula forming a primitive gut
- Gastrocoel - 32What is the blastopore?- The opening of the archenteron - formed by invagination of cells on the embryo surface
- 33What is epiboly in fish specifically?- General movement of “migration” of
the embryonic mass around the yolk mass. - 34What is convergence/extension?- Movements of cells towards the dorsal side of the gastrula, during which cells
intercalate and therefore induce elongation of the tissue they form. - 35What is intercalation>- Rows of cells move between one another, creating an array of cells that is longer (in one or more dimensions) but thinner
- 36What is ingression?- Movement of INDIVIDUAL cells from the epiblast towards the inside of the embryo.
- 37What is the epiblast?- The outermost layer of an embryo before it differentiates into ectoderm and mesoderm
- 38What is the primitive streak?- The groove formed by the involuting and ingressing mesendodermal cells (seen in chick embryos)
- 39What is Henson's node?- A node, or primitive knot, is an enlarged group of cells located in the anterior portion of the primitive streak in a developing gastrula
- The node is the site where gastrulation, the formation of the three germ layers, first begins - 40Which model organisms do humans gastrulate similarly to?- The chick!
- We have a primitive node, primitive streak, etc - 41In which animals does gastrulation begin at the primitive streak?- Chicks
- Humans
- Mice
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- Undergrad Essentials of Embryology Flashcards on Cleavage to gastrulation , created by Liberty Grisman-Hughes on 25/04/2022.
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