Introduction to Embryology PDF

Introduction to Embryology Embryonic period: week 3 to 8 of gestation  Learning Outcomes: Describe the important events in embryonic period Identify the stages neurolation and formation of neural tube Describe the structures that derivatives from each embryonic germ layers  The e...

Introduction to Embryology Embryonic period: week 3 to 8 of gestation  Learning Outcomes: Describe the important events in embryonic period Identify the stages neurolation and formation of neural tube Describe the structures that derivatives from each embryonic germ layers  The embryonic period Extends from the third to the eighth weeks of development. Is the period during which each of the three germ layers, ectoderm, mesoderm, and endoderm, gives rise to the own tissues and organ systems. As a result of organ formation, major features of body shape are established Derivatives of the Ectodermal Germ Layer The ectodermal germ layer gives rise to the organs and structures that maintain contact with the outside world: Central nervous system (CNS); Peripheral nervous system (PNS); Sensory epithelium of ear, nose, and eye; Skin, including hair and nails; and Pituitary, mammary, and sweat glands and enamel of the teeth. Neurolation (video) Neurolation (video) Neurulation is the process whereby the neural plate forms the neural tube. As the neural plate lengthens, its lateral edges elevate to form neural folds, and the depressed mid-region forms the neural groove Gradually, the neural folds approach each other in the midline, where they fuse to form the neural tube Neurolation Neurolation Until fusion is complete, the cephalic and caudal ends of the neural tube communicate with the amniotic cavity by way of the anterior (cranial) and posterior (caudal) neuropores With closure of neuropores, Neurulation is complete, and the central nervous system is represented by a closed tubular structure  Neural tube defects (NTDs) Result when neural tube closure fails to occur. If the neural tube fails to close in the cranial region, then most of the brain fails to form, and the defect is called anencephaly. If closure fails anywhere from the cervical region caudally, then the defect is called spina bifida  Derivatives of the Mesodermal Germ Layer Important components of the mesodermal germ layer are: Paraxial mesoderm forms somitomeres, which give rise and organize into somites in occipital and caudal segments Intermediate mesoderm differentiates into urogenital structures lateral plate mesoderm splits into parietal (somatic) and visceral (splanchnic) layers Somites give rise to the myotome (muscle tissue), sclerotome (cartilage and bone), and dermatome (dermis of the skin), which are all supporting tissues of the body. Derivatives of the Endodermal Germ Layer The endodermal germ layer provides the epithelial lining of the: Gastrointestinal tract (including liver, and pancreas) Respiratory tract, (including thyroid, parathyroids) Urinary bladder It also forms the epithelial lining of the tympanic cavity and auditory tube. Derivatives of the Endodermal Germ Layer  Embryonic Folding As a result of formation of organ systems and rapid growth of the central nervous system, the initial flat embryonic disc begins to curve into the fetal position. As a result of this growth and folding, the amnion is pulled ventrally and the embryo lies within the amniotic cavity. Connection with the yolk sac and placenta is maintained through the vitelline duct and umbilical cord, respectively Any Questions?