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Chapter 4

Chapter 4 - Tissues (1).docx

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Ryerson University
Tonya Davidson

Week 4 Anatomy – Tissue: The Living  Fabric Preparing Human Tissue for Microscopy 1. Specimen must be fixed (preserved) 2. Cut into sections (slices) thin enough to transmit light/electrons. 3. Stained to enhance contrast Light microscopy stains are organic & consist of -/+ charged molecules (acidic and basic stains) that bind within the tissue to macromolecules of the opposite charge. Transmission electron microscopy (TEM) stains are heavy metal salts that deflect electrons in the beam to different extents, providing contrast to the image. Scanning Electorn Microscopy (SEM) provides 3D pictures of an unsectioned tissue surface Preserved tissues we see under the microscope were altered and have minor distortions called artifacts. Epithelial Tissue • Epithelial tissue/epithelium - sheet of cell that covers a body surface/lines a body cavity o Covering and Lining Epithelium o Glandular Epithelium • Function: Protection, Absorption, Filtration, Excretion, Secretion & Sensory Reception Special Characteristics of Epithelium • Polarity- Apical Surface (Upper free surface exposed to body exterior or the cavity of an internal organ), and a lower attached Basal Surface. • Specialized Contacts o Except for glandular epithelia, epithelial cells fit closed to form continuous sheets. Adjacent cells are bound together at many points by lateral contacts, including tight junction and desmosomes. Tight junctions keep proteins in apical region of PM from diffusing into basal region, maintaining epithelial polarity • Supported by Connective Tissue o All epithelial sheets rest upon & are supported by connective tissue • Avascular but innervated o Epithelial cells nourished by substances diffusing from blood vessels in connective tissue • Regeneration o High regenerative capacity Classification of Epithelia - Each epithelium given two names: - 1) Number of cell layers o Simple epithelia – single layer found where absorption, secretion, filtration occur o Stratified epithelia – 2+ cell layers stacked. (High abrasion areas) - 2) Shape of its cells o In cross-section all cells have 6 sides; polyhedral shapes allows cells to be closely packed o Squamous cells – flattened and scale like o Cuboidal cells- box like (as tall as they are wide) o Columnar cells - tall and column shaped Simple Epithelia: Absorption, secretion & filtration. (Thin) Simple Squamous Epithelium - Thin and permeable; found where filtration/exchange of substances by rapid diffusion occurs Simple Cuboidal Epithelium - Forms walls of smallest ducts of glands and of many kidneys tubules Simple Columnar Epithelium - Absorption and secretion Pseudostratified Columnar Epithelium - Vary in height; all cells rest on basemet membrane, but only tallest reach free surface - Because nuclei lie at different levels, tissue gives false impression that several layers are present - Short cells unspecialized and give rise to taller cells - Secretes or absorbs substances tract Stratified Epithelia: 2+ cell layers Stratified Squamous Epithelium - Several layers; thick and well suited for protection - Found in areas subject to wear and tear Stratified Cuboidal and Columnar Epithelia Stratified - Rare in the body; found in ducts of some larger glands (sweat, mammary) - Typically has two layers of Cuboidal cells Stratified Columnar Epithelium - Limited distribution; small amounts in pharynx, male urethra, & lining some glandular ducts - Occurs at transition areas/junctions between two other types of epithelia Transitional Epithelium - Forms lining of hollow urinary organs - Basal layer cells are cuboidal/columnar. - Apical cells vary in appearance, depending on degree of distension of the organ - Ability of cells to change their shape allows greater volume of urine to flow through Glandular Epithelia Exocrine Glands • Secret products onto body surfaces (skin) or body cavities • Mucous, sweat, oil, and salivary glands, the liver (secretes bile), pancrease (enzymes), etc Unicellular Exocrine Glands - Important examples are mucous cells and goblet cells - In humans, all such glands produce mucin (glycoprotein that dissolves in water when secreted). Once dissolved, it forms mucus, a slimy coating that protects and lubricates surfaces. - In goblet cells, the cup-like accumulation of mucin distends the top of the cell, making it look like a glass with a stem. This doesn’t occur on mucous cells Multicellular Exocrine Glands - Structural Classification: Either simple or compound. Simple = unbranched duct, whereas Compound has a branched duct. Glands are further categorized by secretory units as tubular (if secretory cells form tubes), alveolar (form small flask like sacs), and tubuloalveolar (have both). The term acinar is used interchangeable with alveolar - Modes of Secretion: Most as merocrine glands which secrete products by exocytosis as they are produced. (Pancreas, most sweat glands, and salivary glands) Secretory cells of holocrine glands accumulate products within them until they rupture (sebaceous [oil] glands of the skin) Apocrine Glands accumulate their products, but only just beneath their free surface. Eventually the apex of the cell pinches off, releasing the secretory granules and small amount of cytoplasm. (Ex. Lipid droplets by mammary glands – not definite) Connective Tissue 1. Common Origin 2. Degrees of vascularity 3. Extracellular Matrix Structural Elements of Connective Tissue Three main elements: Ground substances, fibres, and cells. Together, they make up the extracellular matrix. Areolar Connective Tissue is used as the model for this group of tissues. Ground Substance - Unstructured material that fills the space between the cells and contains the fibers - Composed of interstitial (tissue) fluid, cell adhesion proteins & proteoglycans o CAP- tissue glue that cells use to attach themselves to matrix elements o Proteoglycans have protein core to which glycosaminoglycans (GAGs) are attached. o GAGs (Chondroitin sulphate and hyaluronic acid) are large, negative polysaccharides that make the ground substance viscous. Fibers - Collagen fibers – most abundant; Collagen molecules secreted into extracellular space, where they assemble into cross-linke fibrils, which are bundled together into thick collagen fibers o extremely tough and provide high resile strength - Elastic Fibers – long, thin fibers that form branching networks in extracellular matrix o Contain rubber-like protein, elastic, that allows them to stretch/recoil - Reticular Fibers – short, fine, collageneous fibers o Continuous with collagen fibers, and branch extensively, forming delicate networks that surround small blood vessels & support soft tissue of organs o Abundant where connective tissue abuts other tissue types. Cells • Blast cell types are (1) Connective Tissue Proper; fibroblast (2). Cartilage: chondroblast (3). Bone: osteoblast. The hematopoietic stem cell – undifferentiated blast cell that produces blood cells • Once synthesized in the matrix, blast cells assume their less active, mature mode (cyte) • Mature cells maintain the health of the matrix. If it is injured, they activate and repair • Connective tissue is also home to nutrient storing fat cells and mobile cells that m
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