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The Living Body 7 - Morphogenesis.docx

5 Pages

Natural Science
Course Code
NATS 1610
Barbara Czaban

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NATS 1610 WINTER TERM L26 – The Embryonic Period: Morphogenesis Embryonic Period rd th • Extends from the 3 to the 8 week • Pre-embryo now called an Embryo • Period of morphogenesis − Development of the body form − Tissues and organs form • By the end of the embryonic period distinct human appearance − All organs have formed Major events during Embryonic Period 1. Gastrulation • Movement of cells within the inner cell mass • Forming primary germ layers – ectoderm, mesoderm, endoderm • Embryo during this period is called a gastrula 2. All the tissues develop from the primary germ layers – the organs develop 3. A notochord develops from the mesoderm • Providing the long axis of the embryo • The vertebral column later forms in this region 4. Neurulation follows • To form the central nervous system • Embryo during this period is called a neurula 5. Organs and anatomical features form Gastrulation begins the process by which the developing embryo’s (gastrula) body takes shape and becomes organized • During implantation, inner cell moves from surface of blastocyst • Inner cell mass flattens – plate like structure – embryonic disk – becomes embryo • Amniotic cavity forms – lined by amnion – filled with amniotic fluid Cells of embryonic disk differentiate (change & specialize) & migrate inward • Forming 3 primary germ layers – ectoderm, mesoderm, endoderm − Day 4 – Morula: Solid ball of cells formed as the zygote undergoes cleavage − Day 6 – Early blastocyst: Hollow ball of cells with a fluid-filled cavity − Day 10 – Late blastocyst: Pre-embryo, with the embryonic disk, two layers of cells that become the embryo proper − Day 16 – Gastrula: Embryo with three primary germ layers (ectoderm, mesoderm, and endoderm) Totipotent • Cell that can divide & produce all of the differentiated cells in an organism, including extraembryonic tissues • Is capable of developing into any cell type • Only morula cells are totipotent Pluripotent • Cell that has the potential to differentiate into any of the 3 germ layers & give rise to any fetal or adult cell type • Cannot develop into an organism because cannot contribute to extraembryonic tissue Multipotent • Cell that can give rise to cells from multiple but limited cell lineages – i.e., hematopoietic cells are blood cells that can develop into any type of blood cell only Unipotent • Can differentiate into only one cell type The development of organs can be related to the three germ layers • Different sets of cells within each layer develop differently • Some groups of cells migrate to localized regions of embryo • Organs are communities of tissues – work co-operatively Organ Origins • Ectoderm – outer layer − Nervous system, spinal cord, brain, epidermis of skin, hair, nails, oil glands, sweat glands, mammary glands, portions of eyes & teeth, and epithelial lining of mouth & rectum & digestive tract • Mesoderm – middle layer − All connective tissues including muscle, bone, blood, dermis of skin, heart, kidneys, ovaries or testes, all reproductive ducts, lymphatic vessels • Endoderm – inner layer − Lining of digest
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