DevelopmentW2010.Lecture7notes

DevelopmentW2010.Lecture7notes - Development BIO 120 Winter...

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BIO 120 Winter 2010 Jeremy Lee Patrick Yuh Eva Murdock Lecture 7 Gastrulation I. Process of Gastrulation a. Gastrulation marks the beginning of morphogenesis , and involves cellular movements that generate the rudiments of the embryo's organs and determine an overall body plan. b. The gastrulation process is highly variable between animals of different phyla. c. Gastrulation in all animals involves cell movements into the embryo. In most animals, this leads to the formation of three primary cell layers (Fig. #1): the outer ectoderm , the inner endoderm , and the mesoderm between them. Each of these layers will form specific kinds of tissue. 1. In vertebrates, the tissues derived from ectoderm include epidermis; sweat glands; mammary glands; cornea and lens of eye; the nervous system; tooth enamel; and the epithelium of mouth and rectum. (Fig. #2) 2. In vertebrates, the tissues derived from mesoderm include the notochord (see below); muscle; circulatory and lymphatic systems; the heart; reproductive organs (except germ cells); dermis of skin; lining of the body cavity; the kidney; and the axial skeleton. 3. In vertebrates, the tissues derived from endoderm include epithelium of the digestive tract (except the mouth and rectum); the lungs; the liver; the pancreas; the thyroid; the parathyoroid; the thymus; and the urinary bladder II. Types of Cell Movements in Gastrulation (Fig. #3) a. Invagination : infolding or buckling of cells inward. b. Involution : inward movement of an outer layer of cells around a point or points, so that the inner cell layer folds back and spreads over the inner surface of the outer cell layer. c. Convergent extension : extension of a cell layer in one direction, with simultaneous shortening of the layer in another direction. May be due to changes in shell shape (elongation) or due to movement of cells into a layer by intercalation (movement between cells), causing cell layer to lengthen. d. Epiboly : movement of epithelial cells as sheets that spread. Epithelial sheets often spread around the embryo as units of cells; this also generally involves elongation of the cells. e. Delamination : splitting of a layer of cells into two parallel layers. f. Ingression: movement of an individual cell from an epithelium into a cavity. III. Other Cell Behaviors Important in Morphogenesis, including Gastrulation
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DevelopmentW2010.Lecture7notes - Development BIO 120 Winter...

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