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Sunday, October 14, 2007

Physiology -Chap 4- Outline2

Chapter 4 (Pgs. 108-111)

Types of Tissues and their Origins

  • Epithelial tissue:
covers body surfaces and lines hollow organs, body cavities, and ducts; it also forms glands
  • Connective tissue: protects and supports the body and its organs; binds organs together, stores energy reserves as fat, and helps provide immunity to disease-causing organisms
  • Muscular tissue: generates the physical force needed to make body structures move
  • Nervous tissue: detects changes in a variety of conditions inside and outside the body and response by generating nerve impulses that help maintain homeostasis
  • Tissues of the body develop from three primary germ layers

  • ~Epithelial tissues develop from all three primary germ layers
    ~The first tissues formed in the human embryo are called:
    --nervous tissue develops from ectoderm
    --all connective tissue and most muscle tissues derive from mesoderm
    • Normally, most cells within a tissue remain anchored to other cells or structures

    Cell Junctions

    • Cell Junctions: contact points between the plasma membranes of tissue cells

    ~5 types

    -tight junctions
    -adherens junctions
    -gap junctions

    Tight Junctions

    • Tight Junctions: consist of web-like strands of transmembrane proteins that fuse the outer surfaces of adjacent plasma membranes together

    ~Ex: Cells of epithelial tissues that line the stomach, intestines, and urinary bladders

    Adherens Junctions

    • Adherens Junctions:
    contain plaque, a dense layer of proteins on the inside of the plasma membrane that attaches to both membrane proteins and to microfilaments of the cytoskeleton
  • Cadherins: transmembrane glycoproteins that join the cells
  • In epithelial cells, adherens junctions often form extensive zones called adhesion belts
  • Help epithelial surfaces resist separation during various contractile activities (Ex: when food moves through the intestines)
  • Desmosomes

    • Desmosomes: contain plaque and have transmembrane glycoproteins (cadherins) that extend into the intracellular space between adjacent cell membranes and attach cells to one another
    • Unlike adherens junctions, the plaque of desmosomes does not attach to microfilaments; it attaches to the intermediate filaments that consist of the protein keratin
    • Desmosomes prevent epidermal cells from separating under tension and cardiac muscle cells from pulling apart during contraction


    • Hemisesmosomes: resemble desmosomes but they do not link adjacent cells
    • The transmembrane glycoproteins in hemidesmosomes are integrins rather than cadherins
    ~On the inside of the plasma membrane, the integrins attach to intermediate filaments made of the protein keratin
    ~On the outside of the plasma membrane, the integrins attach to the protein laminin
    • Hemidesmosomes anchor cells not to each other, but to the basement membrane

    Gap Junctions

    • Gap Junctions:
    membrane proteins called connexins form tiny fluid-filled tunnels called connexons that connect neighboring cells
  • The plasma membranes of gap junctions are not fused together as in tight junctions but are separated by very narrow intercellular gap
  • The transfer of nutrients, and perhaps wastes, takes place through gap junctions in avascular tissues
  • Gap junctions allow the cells in a tissue to communicate with one another
  • Enable nerve or muscle impulses to spread rapidly among cells, a process that is crucial for the normal operation of some parts of the nervous system
  • Epithelial Tissue

    • Epithelial Tissue (a.k.a. Epithelium): consists of cells arranged in continuous sheets, in either single or multiple layers

    ~Little intercellular space between adjacent plasma membranes

    • Apical (free) Surface:
    most superficial layer of cells
  • Lateral Surfaces: face the adjacent cells on either side
  • Basal Surface: deepest layer of cells
  • Basement Membrane: a thin extra cellular layer that commonly consists of two layers, the basal lamina and reticular lamina
  • ~Basal lamina: is close to and secreted by the epithelial cells

    • The basement membrane functions as a point of attachment and support for the overlying epithelial tissue

    Basement Membranes and Disease

    • Become markedly thickened, due to increased production of callagen and laminin
    • Epithelial tissue is avascular (lacks its own blood supply)
    • Exchange of substances between epithelium and connective tissue occurs by diffusion
    • Epithelial tissue constantly has to renew and repair itself by sloughing off dead or injured cells
    • Epithelial tissue performs the roles of: protection, filtration, secretion, absorption, and excretion
    • Epithelial tissue combines with nervous tissue to form special organs for smell, hearing, vision, and touch
    • 2 types of epithelial tissue:
    ~Covering and lining epithelium: forms the outer covering of the skin and some internal organs
    ~Glandular epithelium: makes up the secreting portion of glands such as the thyroid gland, adrenal glands, and sweat glands

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