CHAPTER 4LECTURE OUTLINEI. INTRODUCTION1. A tissue is a group of similar cells that usually have a similar embryological origin and are specialized for a particular function.a. The nature of the extracellular material that surrounds the connections between the cells that compose the tissue influence the structure and properties of a specific tissue.b. The science that deals with the study of tissues is called histology.2. Pathologists, physicians who specialize in laboratory studies of cells and tissues,aid other physicians in making diagnoses; they also perform autopsies. Analysis of biopsies, samples of living tissue removed for microscopic examination, is a chief responsibility of a pathologist.II. TYPES OF TISSUES AND THEIR ORIGINS1. Depending on their function and structure, the various tissues of the body are classified into four principal types.a. Epithelial tissue covers body surfaces, lines hollow organs, body cavities, and ducts; and forms glands.b. Connective tissue protects and supports the body and its organs, binds organs together, stores energy reserves as fat, and provides immunity.c. Muscle tissue is responsible for movement and generation of force.d. Nervous tissue initiates and transmits action potentials (nerve impulses) that help coordinate body activities.e. Clinical connection: biopsyIII. CELL JUNCTIONS 1. Cell junctions are points of contact between adjacent plasma membranes.2. Depending on their structure, cell junctions may serve one of three functions.a. Some cell junctions form fluid-tight seals between cells.b. Other cell junctions anchor cells together or to extracellular material.c. Still others act as channels, which allow ions and molecules to pass from cell to cell within a tissue.3. The five most important kinds of cell junctions are tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions.a. Tight junctions form fluid-tight seals between cells and are common among epithelial cells that line the stomach, intestines, and urinary bladder (Figure 4.2a).b. Adherens junctions are made of plaque and anchor cells together (Figure 4.2.b).4. Transmembrane glycoproteins called cadherins join the cellsa. Desmosomes are composed of plaque and are linked by transmembrane glycoproteins that extend across a gap between adjacent cell membranes and link the cytoskeletons of cells together (Figure 4.2c).b. Hemidesmosomes connect cells to extracellular material such as the basement membrane (Figure 4.2d).c. Gap junctions allow cells in a tissue to rapidly communicate through connexins, transmembrane protein channels that connect cells together (Figure 4.2e).IV. COMPARISON BETWEEN EPITHELIAL AND CONNECTIVE TISSUES1. Major structural differences between an epithelial tissue and a connective tissue (Figure 4.3)a. The number of cells in relation to the extracellular matrix1. epithelial tissue many cells are tightly packed together with little or no extracellular matrix2. in a connective tissue a large amount of extracellular material separates cells b. blood vessels1. epithelial tissue has no blood vessels2. most connective tissues have significant networks of blood vesselsc. epithelial tissues almost always form surface layers and are not covered by another tissueV. EPITHELIAL TISSUESI. General Features of Epithelial Tissues1. Epithelial cells are arranged in sheets, in either single or multiplelayers (Figure 4.4)2. Epithelium consists mostly of packer cells with little extracellular material.3. Many cell junctions are present, providing secure attachments among cells.4. An epithelial cell has an apical surface and a basal surface attached to a base membrane (Figure 4.4). 5. Epithelia adhere firmly to nearby connective tissue via a thin extracellular layer, the basement membrane (Figure 4.4).6. Epithelial tissue is avascular; exchange of materials between epithelium and adjacent connective tissue is by diffusion.7. Epithelia have a nerve supply.8. Epithelia have a high capacity for renewal (a high mitotic rate).9. Clinical connection: Basement membranes have a role in some diseasesII. Classification1. The eight types of covering and lining epithelial tissue are classified according to the way the cells are arranged in layers (Figure 4.5)2. Epithelial tissue is also classified by the characteristic shape of cell (Figure 4.5)3. Layers are arranged as simple (one layer), stratified (several layers), and pseudostratified (one layer that appears as several).4. Cell shapes include squamous (flat), cuboidal (cube-like), columnar (rectangular), and transitional (variable). III. Covering and lining epithelia 1. may be classified as a combination of arrangement of layers and shape of the cells. The name of the specific type of stratified epithelium depends on the shape of the surface cells. Each of the epithelial tissues described in the following sections is illustratedin Table 4.1. 2. Clinical connection: Papanicolaou TestIV. Simple Epitheliuma. Simple squamous epithelium consists of a single layer of flat, scalelike cells (Table 4.1A)1. It is adapted for diffusion and filtration and is found in lungs and kidneys.2. It is found in parts of the body that are subject to little wear and tear.3. Endothelium lines the heart and blood vessels.4. Mesothelium lines the thoracic and abdominopelvic cavities and covers the organs within them.b. Simple cuboidal epithelium consists of a simple layer of cube-shaped cells and performs the functions of secretion and absorption (Table 4.1B).c. Simple columnar epithelium consists of a single layer of rectangular cellsand can exist in two forms: nonciliated simple columnar epithelium and ciliated simple columnar epithelium.1. Nonciliated simple columnar epithelium contains microvilli (Figure 3.2) to increase surface are and the rate of absorption and goblet cells that secrete mucus (Table 4.1C).2. Ciliated simple columnar epithelium (Table 4.1D) contains cells with cilia, motile, hair-like processes that help to move fluids or particles along a surface.d. Pseudostratified epithelium (Table 4.1E) has only one layer but gives the appearance of many.1. All cells are attached to the basement membrane but some do not reach the apical surface.2. In pseudostratified ciliated columnar epithelium, the cells that reach the surface either secrete mucus (goblet cells) or bear cilia that sweep away mucus and trapped foreign particles.3. Pseudostratified nonciliated columnar epithelium contains no cilia or goblet cells.e.