Gastrulation PDF

GASTRULATION It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.“ – Wolpert (1986) AZO 422 – DEVELOPMENTAL ZOOLOGY What is Gastrulation?  Coined by Ernst Hackel (1872)  Most characteristic evet occurs during 3rd week of...

GASTRULATION It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life.“ – Wolpert (1986) AZO 422 – DEVELOPMENTAL ZOOLOGY What is Gastrulation?  Coined by Ernst Hackel (1872)  Most characteristic evet occurs during 3rd week of gestation is gastrulation  process whereby cells undergo morphogenetic movements  formation of 3 germ layers Character of Gastrulation Stage  First stage of cellular differentiation  Embryonic cells begin to follow specific layer thru morphogenetic movements  Three embryonic layer  Cellular division lose synchronization  Coordination becomes dominant over metabolic changes  Nucleus has more impact than before in the process of control of development and shows chromosome gemes Morphogenetic processes invagination involution ingression Morphogenetic processes delamination epiboly Morphogenetic processes Fig. 32.7a Cells NOT totipotent Cells totipotent Protostomes- the first opening in the embryo becomes the mouth Deuterostomes- the first opening in the embryo becomes the anus Fig. 47.6 Early cleavage stages Fig. 47.9 Gastrulation in the Sea urchin Axis Formation Fish Gastrulation  epiboly of the blastoderm cells over the yolk  deep cells move outwardly to intercalate with superficial cells  YSL  EVL  Germ ring Fish Gastrulation Fish Gastrulation Fish Gastrulation Fish Gastrulation Amphibian Gastrulation Amphibian Gastrulation Amphibian Gastrulation Amphibian Gastrulation  Gastrulation in the frog Fig. 47.10 Fig. 47.16 Changes in cell shape during morphogenesis Avian Gastrulation  area pellucida forms the epiblast and primary hypoblast (by delamination)  posterior cell sheets migrate anteriorly to form secondary hypoblast Avian Gastrulation Avian Gastrulation  Primitive streak  thickening of the epiblast  anterior to Koller’s sickle  migration of cells from lateral to the center Avian Gastrulation Primitive groove  depression within the streak  homologous to blastopore of amphibian Hensen’s node  anterior end of primitive streak  homologous to dorsal lip of blastopore Avian Gastrulation Primitive pit  funnel shaped depression where cells can pass  center of the node Avian Gastrulation Avian Gastrulation Avian Gastrulation Avian Gastrulation Avian Gastrulation Avian Gastrulation Mammalian Gastrulation  similar to avian gastrulation  involves formation of extraembryonic membranes and the embryo Implantation Implantation  First week  formation of blastocyst when fluid secreted within the morula forms a cavity  trophoblast – part of placenta (chorion)  ICM – embryoblast – embryo and associated yolk sac, allantois and amnion Implantation  ZP must degenerate  Blastocyst implants within the posterior wall of uterus  Trophoblast contain integrins & collagenase, stromelysin and plasminogen activator  Trophoblast develops into cytotrophoblast and syncytiotrophoblast Implantation  Second Week  bilaminar embryo  embryoblast differentiates into epiblast and hypoblast Mammalian Gastrulation Abnormal Implantation Abnormal Implantation Human Gastrulation Mammalian Gastrulation Mammalian Gastrulation Umbilical cord  narrow stalk of extraembryonic mesoderm that links the embryo to the trophoblast Mammalian Gastrulation Clinical Correlation Sirenomelia (caudal dysgenesis) loss of mesoderm Clinical Correlation Sacrococcygeal teratoma – remnant of primitive streak END