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Zoology, lecture 16
Vertebrates: Embryology
| Question | Answer |
|---|---|
| What are the two traits indicating common ancestry between echinodermates and chordates? | Deuterostomia and pharyngeal gill slits. |
| Embryogenesis | Embryonic development, development of the embryo. |
| Ontogenesis | Process of development of the individual development that starts with fertilization and ends at maturity. |
| Phylogenesis | Transformation of the structures of the entire group through evolution. |
| Haeckel's Law of Biogenetics | During embryonic development the individual goes back over all of the phylogenetic processes of the entire group. (Recapitulation theory) |
| Examples of recapitulation in the skeleton | Notochord comes before cartilage, cartilage comes before bone. |
| Examples of recapitulation in the nervous system | The simple hollow dorsal nerve cord comes before the development of brains. |
| Examples of recapitulation in the excretory system | Appearance of a frontal kidney followed by middle and rear. |
| Examples of recapitulation in the respiratory system | Appearance of pharyngeal gill slits in all vertebrate embryos |
| Examples of recapitulation in the circulatory system | Development of arterial arches to the gills. |
| Stages of embryonic development: | Gametogenesis, fertilization, cleavage, gastrulation, neurulation, organogenesis |
| Gametogenesis | Production of haploid cells from diploid cells through the process of meiosis. |
| Fertilization | Meeting between the two haploid gametes (sperm and egg) to form a diploid zygote |
| Cleavage | Dividing of the zygote to produce a multicellular embryo. |
| Gastrulation | Cell migration resulting in the production of three germ layers in the developing embryo (ectoderm, endoderm, mesoderm). The first stage that changes the embryo's orientation and shape. |
| Neurulation | Production of the nerve cord |
| Organogenesis | Production of the tissues and organs |
| Growth and Differentiation | Growth and differentiation continues until maturity. |
| Gametogenesis details | Sperm in the testis and eggs in the ovaries are haploid cells produced from diploid cells that have gone through the stages of meiosis. |
| Meiosis | Each diploid cell produces four haploid cells. The resulting sperm are all equal and function but that's not true of the egg cells where one takes all of the nutrients and the rest are small/disappear. |
| Sperm cell structure | They look a lot like certain unicellular organisms--nucleus in the head with a flagellum tail. |
| Acrosome | The frontal organelle on the sperm cell that produces enzymes that can eat through the egg cell wall. |
| Sperm flagellum structure | Very similar to cilia/flagella structure in certain invertebrate cells. |
| Egg structure | A round cell with yolk (amount varying with egg size) covered in two membranes (external-vitelline, internal-plasma) with a narrow space between them. Mostly filled with yolk concentrated in the bottom. Cortical granules inside. |
| Vegetal pole | Bottom pole of the egg filled with yolk making it heavier. |
| Animal pole | Top pole of the egg where more cytoplasm is concentrated (nucleus also at the top) |
| Cortical granules | Granules made of polysaccharide substance called mucopolysaccharide that can absorb a large amount of water and expand. (name cause of location like cortex) |
| Mucopolysaccharide substance | Found in the cortical granules that line the inside of the plasma membrane in an egg cell. It can absorb an incredible amount of liquid. |
| Egg protection | The egg is covered with a protective coat (can be acellular--mucopolysaccharide, or can be filled with cells like in humans) We have a number of layers that protect our eggs. |
| How does the sperm get through the protective layers of the egg? | They have the acrosome at their tip and when it reaches the egg cell it releases its enzymatic contents digesting the layers to allow access for the sperm cell. |
| Egg-receptor proteins | Proteins on the surface of the sperm that allow it to recognize the egg and start acrosomal enzymatic activity. |
| Fusion | The vitelline membrane of the egg fuses with the sperm membrane forming a fertilization cone. |
| Cortical reaction | As soon as the sperm membrane fuses with the vitelline producing the fertilization cone, the cortical granules release their contents into the space between the plasma and vitelline taking up water producing a fertilization membrane |
| Fertilization ring | Ring of inflated mucopolysaccharides that fill the space between the vitelline and plasma membranes after the sperm has entered. |
| What is the purpose of the fertilization ring? | Originally they thought it was meant to prevent polyspermy but it takes to long to finish but they now believe that it is there to hold together the blastomeres until the 16-cell stage when there are junctions. |
| Stages of cleavage | First divides top to bottom producing 2 equal blastomeres, the second produces 4 (at 90 degrees to the first) |
| Blastomere | The cells produced during cleavage of the embryo. In deuterostomes with indeterminate reproduction each blastomere (until a certain stage) can produce an entire embryo if separated. |
| Upon what is the complete/incomplete cleavage based? | It is determined by the egg size. If it's a few microns (as opposed to a bird egg cell) |
| Oligolecithal | A small egg with only a little yolk. |
| Holoblastic cleavage | Complete cleavage that takes place in oligolecithal eggs (cause they are little with just a little yolk) |
| Telolecithal | Big egg with a lot of yolk. |
| Meroblastic cleavage | Incomplete cleavage (cause there's too much yolk) it takes place telolecithal eggs and all of the divisions take place only in the upper disk of the animal pole. |
| Cleavage process in meroblastic division | The first division stops above the yolk, the second is 90 degrees to the first, the third is horizontal and because most of the yolk is at the bottom the division is not in the middle, its up above the yolk producing 8 non equal blastomeres. |
| Micromeres | Small blastomeres produced from the third cleavage in meroblastic division. They are at the top above the yolk where its easy to cut. |
| Macromeres | Large blastomeres produced from the 3rd cleavage in meroblastic division. They are at the bottom where the yolk is concentrated. |
| What type of cleavage is typical of Amphioxus? | Meroblastic cleavage. |
| What happens after the third division in meroblastic cleavage? | The cells continue to divide and start to move away from each other leaving a space open to the outside producing the morula |
| Morula | Stage of the embryo when the cleavage produces cells that move away from each other leaving a space open to the outside that later closes on itself leaving a cavity in the middle. |
| Blastula | The final result of the cleavage stage--a hollow mass of cells equal in size to the original zygote. |
| What is the mechanism of cleavage in amphibians | They are in between oligo and telolecithal eggs in that they have a lot of yolk but it doesn't stop the division so the result is holoblastic division. |
| Mesolecithal eggs | Eggs with a medium amount of yolk like in amphibians. The yolk doesn't hinder division so its holoblastic still. |
| What is the connection between phylogenesis and cleavage? | There is none. Birds and fish are telolecithal with meroblastic cleavage while we and echinodermates are oligolecithal with holoblastic cleavage. |
| Fate map | Map of the determined purpose of every area of the blastula. The upper will be ectoderm, the bottom third (macromeres) will be endoderm and the belt in the middle will be mesoderm. |
| Process of gastrulation | The migration of cells and alteration of the shape of the embryo. It starts as a sinking of the blastula wall into the blastocoel. |
| Which cells sink into the blastocoel during gastrulation? | The macromeres cause the micromeres are smaller and are dividing faster forcing the macromeres inwards and actively as a result of the components liquid in the blastocoel that can direct the movement. |
| What happens as the blastula wall sinks inwards? | The blastocoel starts to disappear and the gastrocoel is formed. |
| Gastrocoel | Becomes the primary gut (gut in invertebrates) |
| Blastopore | The primary oral opening that results from invagination during gastrulation. Mouth in protostomes. Becomes the anus in deuterostomes. |
| Which animals are deuterostomes? | Echinodermates and chordates. |
| What is the shape and orientation of the embryo after gastrulation? | Because of the change in weight distribution he lies on his side at an angle of 90 degrees and then starts to elongate becoming oval shaped with the animal pole pointing sideways (mouth) |
| Whats the difference between deuterostomia in echinodermates and chordates? | In echinodermates the blastopore is the anus, in chordates, the blastopore closes and the anus opens next to it. |
| What is the end result of gastrulation? | Three germ layers with ectoderm on the outside, endoderm lining the bottom and the mesoderm lining the dorsal side. |
| Archenteron | Another word for gastrocoel--it is a primitive gut with a mesodermal roof. |
| Neurulation characteristics | Development of the nervous system that results from the invagination of the ectoderm on the dorsal side that then closes forming a tube that extends for the whole length of the embryo. |
| What happens to the central part of the mesoderm in the developing embryo? | It develops into the notochord that extends for the entire length of the body. |
| Lateral mesoderm | Right and left hand chunks of mesoderm that side on either side of the mesoderm that becomes the notochord. |
| What happens to the lateral mesoderm during organogenesis? | Each invaginates upwards and closes forming a hollow pocket. The pocket is called the enterocoel cause the cavity originated in the archenteron. |
| Enterocoel | Cavity produced by the closing of the lateral mesodermal pockets (originated as the archenteron) |
| In which organisms is there enterocoelic development? | Echinodermates but not other invertebrates. Also exists in lower chordates. |
| What is the next step after the formation of the enterocoel? | The enterocoel is two cavities that extend along the body length that are then divided into segments resulting in a pair of somites in each segment. |
| What is the cavity inside the somites? | Enterocoel |
| What connects amphioxus to echinodermates? | Enterocoel. But if you look at all its segments the frontal ones have enterocoel but the rear ones are schizocoel. |
| How does coelomic development happen in vertebrates? | It's schizocoelic. It detaches as a chunk from the bottom of the endoderm and then rises and splits forming the cavities of the somites. |
| What is the cavity called in schizocoelic animals? | Its not enterocoelic cause it doesn't originate from the archenteron! It's called schizocoel! |
| What in the embryogenesis of amphioxus shows our phylogenetic origin? | The frontal segments are enterocoelic (like echinodermates) and the rear segments are schizocoelic (like chordates) |
| Splanchnopleura | Leaf of the coelom that lies against the endoderm develops smooth muscles of the digestive system, connective tissue, blood vessels making up most of the thickness of the digestive system. |
| Somatopleura | Leaf of the coelom that lies against the ectoderm. It gives connective tissue (NOT BLOOD VESSELS which develop from the splanchnopleura). It is essentially an extension of the dermatome. |
| Sclerotome | In vertebrates the notochord affects this area of the mesoderm right next to it forcing it to make the cartilaginous cover (cyclostoma..) The cartilage closes over the notochord and each segment is a vertebra. |
| Myotome | Part of the mesoderm that forms muscle |
| Dermatome | Part of the mesoderm that forms the connective tissues |
Created by:
YaelNoa
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