Prenatal D.

• How many phases is prenatal development divided into?

  Three phases
• What constitutes the embryonic stage of prenatal development?

  The first two phases combined
• What is the third phase of prenatal development called?

  Fetal stage
• How is the forming individual described during prenatal development?

  As an embryo or fetus
• When does the first phase of prenatal development begin?

  At fertilization
• How long does the first phase of prenatal development last?

  About 4 weeks
• What processes occur during the first phase of prenatal development?

  Cellular proliferation and migration
• What characterizes the second phase of prenatal development?

  Differentiation of major structures
• What is the term for the recognizable human form during development?

  Morphogenesis
• What happens from the end of the second phase to full term?

  Growth and maturation of the fetus
• What are homeobox genes known for?

  Regulating gene expression
• What do homeobox genes contain?

  A conserved region of 180 base pairs
• How do homeobox genes function?

  By producing transcription factors
• What is paracrine regulation?

  Growth factor acting on another cell
• What is autocrine regulation?

  Cell recapturing its own product
• What do growth factors require to have an effect?

  Cell surface receptors
• What are the three germ layers formed after fertilization?

  Zygote, morula, blastocyst
• What happens around day 8 of gestation?

  Embryoblast differentiates into a bilaminar disk
• What are the two layers of the bilaminar germ disk?

  Ectodermal and endodermal layers
• What does the ectodermal layer form during development?

  The amniotic cavity
• What does the endodermal layer form during development?

  The secondary yolk sac
• What is the prochordal plate?

  A region at the head end of the embryo
• What does the notochord provide?

  Axial support of the primitive embryo
• How is mesoderm formed during development?

  By ectodermal cells migrating toward the streak
• What do somites contribute to?

  Vertebrae, muscle, and skin connective tissue
• What does the lateral plate mesoderm give rise to?

  Connective tissue associated with muscle and viscera
• What does the neural tube give rise to?

  The spinal cord and brain
• What are rhombomeres?

  Segmentation in the hindbrain
• What is the stomatodeum?

  The primitive oral cavity
• What do neural crest cells differentiate into?

  Spinal sensory ganglia and connective tissue
• What is ectomesenchyme?

  Embryonic connective tissue in the head
• What happens in Treacher Collins syndrome?

  Neural crest cells fail to migrate properly
• What tissues are derived from neural crest cells?

  All tissues of the tooth except enamel
• What technologies help identify specific genes?

  Recombinant DNA technology and immunohistochemistry
• What role do trophoblast cells play?

  Implantation of the embryo and placenta formation
• What are the main stages of prenatal development?

  1. First phase: Fertilization to 4 weeks
  2. Second phase: 4 to 8 weeks
  3. Third phase: Fetal stage (9th week to 9th or 10th month)
• What are the key processes during the formation of the three-layered embryo?

  • Rapid proliferation and migration of cells
  • Formation of zygote, morula, and blastocyst
  • Differentiation into ectoderm, mesoderm, and endoderm
• What are the components of somites and their contributions?

  • Sclerotome: Vertebrae and disks
  • Myotome: Segmented muscle
  • Dermatome: Skin connective tissue
• What are the roles of the neural crest cells?

  • Form spinal sensory ganglia
  • Differentiate into sympathetic neurons
  • Contribute to connective tissue of the head
• What are the effects of neural crest cell depletion?

  • Impaired dental development
  • Malar and mandibular hypoplasia
  • Malformations in facial structures