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Chapter 47. Cleavage A period of rapid cell division after fertilization –Skips the G1 and G2 phases –No growth during this period, just division Includes.

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Presentation on theme: "Chapter 47. Cleavage A period of rapid cell division after fertilization –Skips the G1 and G2 phases –No growth during this period, just division Includes."— Presentation transcript:

1 Chapter 47

2 Cleavage A period of rapid cell division after fertilization –Skips the G1 and G2 phases –No growth during this period, just division Includes the following developmental stages –Zygote –Blastomeres –Morula –Blastula (with blastocoel) IVF AnimationAnimation

3 Gastrulation Rearrangement of blastula cells to form a gastrula with three distinct germ layers Accomplished by change in: –Cell motility –Cell shape –Cell adhesion to other cells & extracellular matrix

4 Germ Layers Ectoderm –Outer layer Endoderm –Lines embryonic digestive tract Mesoderm –Partly fills the space between the endoderm & ectoderm

5 Organogenesis The germ layers work together to develop into the rudimentary organs Can be seen by folds, splits, and clustering of cells in localized tissues By 8 weeks in humans the fetus has all the basic versions of their organs

6 First Organs in Chordates Notochord –Formed from mesoderm –Future position of the vertebral column Neural tube –Becomes the central nervous system –Neural crest is formed along the border which becomes the peripheral nerves, teeth, skull, and more (aka: 4 th germ layer) Somites –Lateral strips along notochords, in pairs –Forms vertebrae –Associated with axial muscle development

7 Adaptation in Amniotes A moist environment is needed for the developing embryo Amniotic fluid is the solution: –Shelled eggs for birds, reptiles, and monotremes –Uterus for marsupial and eutherian mammals

8 Adaptations in Mammals Internal fertilizition Small eggs with little amounts of stored nutrients –Reliant on a uterus to provide nutrients from the mother Slow cleavage (first division done after ~36 hours)

9 Human Embryo Development 1.Blastocyst has reached the uterus 2.The trophoblast begins to implant into the endometrium by secreting catabolic enzymes 3.Trophoblast expands into maternal tissues via mitosis to gain nutrients from her blood supply 4.Implantation in completed and gastrulation begins 5.The end of gastrulation has arrived and the embryo is now surrounded by extraembryonic membranes

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11 Extraembryonic Membrane in Humans Chorion: surrounds all extraembryonic membranes & provides gas exchange Amnion: provides the protective layer around the amniotic fluid Yolk sac: found below the embryo this cavity is where blood cells are formed which travel to the embryo Allantonis: part of the umbilical cord in the form of blood vessels to move nutrients and waste

12 The Fate of Embryonic Cells This is dependent on the movement of cells to allow for changes in cell shape & function –Cells move by using the cytoskeleton to crawl from one location in the embryo to another –This movement is regulated by ECM and secreted glycoproteins Fibronectin: which provides anchorage Cell adhesion molecules: bind to the CAM’s on other cells for tissue building Cadherins: helps with tight junctions

13 Formation of the Neural Tube

14 The Fate of Embryonic Cells Induction: A group of embryonic cells has the ability to influence the formation of another group resulting in specialized cells (by expressing only specific genes) Fate Mapping: Embryonic cells have a specific fate before gastrulation occurs (as cells mature they are limited in what they can become) Cellular Asymmetry: position of the nuclei in the sperm & egg may play in role in determining developmental axes

15 The Fate of Embryonic Cells Restriction to cell potency: in humans embryonic cells are totipotent until the 16 cell stage when they are determined to be either blastocyst or trophoblast based on location Inductive signals: embryonic cells will be influenced by other about their final fate through gastrula organizers –Ex: dorsal lip is an organizer the controls the development of notochord, neural tube, and more Brain Pop: Stem Cells


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