PART 2 Basic Embryology

Changes in the Embryo Figure 3.7a, b Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Changes in the Embryo Figure 3.7c, d Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Week 4 – The Body Takes Shape Folding of embryo laterally and at the head and tail Embryonic disc bulges; growing faster than yolk sac “Tadpole shape” by day 24 after conception Primitive gut – encloses tubular part of the yolk sac Site of future digestive tube and respiratory structures Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Week 4 – The Body Takes Shape Figure 3.8 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Week 4 – The Body Takes Shape Derivatives of the germ layers Ectoderm forms Brain, spinal cord, and epidermis Endoderm forms Inner epithelial lining of the gut tube Respiratory tubes, digestive organs, and urinary bladder Notochord (where vertebrae are) – gives rise to nucleus pulposus within intervertebral discs Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Week 4 – The Body Takes Shape Mesoderm – forms Muscle Bone Dermis Connective tissues (all) Mesoderm differentiates further and is more complex than the other two layers Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Derivatives of Germ Layers Splancnic Mesoderm gives rise to: Heart and blood vessels Figure 3.10 Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Week 4 – The Body Takes Shape Mesoderm (continued) Somites divides into Sclerotome Dermatome Myotome Intermediate mesoderm forms Kidneys and gonads Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Week 4 – The Body Takes Shape Mesoderm (continued) Splanchnic mesoderm Forms musculature, connective tissues, and serosa of the digestive and respiratory structures Forms heart and most blood vessels Somatic mesoderm – forms Dermis of skin Bones Ligaments Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

3. dorsal hollow nerve cord 4. notocord and vertebrae 5.segmentation What do I need to know? Which structures originate from ectoderm, mesoderm and endoderm – Slide 8 List 6 unique features found in all vertebrates at some stage of their life: 1. tube within a tube 2.bilateral symmetry 3. dorsal hollow nerve cord 4. notocord and vertebrae 5.segmentation 6. pharyngeal pounches Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings

Distinguish between the types of tissues that make up th eendoderm, ectoderm and mesoderm and explain how these tissues relate to their developmental processes. Both endoderm and ectoderm are epithelial tissues. These cells are joined together in sheets that form external or internal linings of the body. The mesoderm consists of mesenchyme tissue whose cells don’t stick together. Instead, the cells and groups of cells are free to migrate within the embryo to eventually give rise to muscles, bones and viscera.(organs) Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings