Tissues: The Living Fabric

• Tissues: The Living Fabric• To optimize functions, body cells are organized into tissues• Four basic tissue types exist in humans– Epithelial tissue– Connective tissue– Muscle tissue– Nervous tissue• Epithelial tissue– Lining and covering epithelium• Cover internal or external surfaces (all exposed body surfaces)• Located on the skin, GIT, respiratory tract– Glandular epithelium– Functions• Specialized secretory structures• Protection, absorption, filtration, excretion and secretion• Special Characteristics of Epithelium• Specialized contacts• Polarity– Cells are held closely together forming continuous sheets– Adjacent cells are tightly bound to each other via specialized contacts (desmosomes andtight junctions)– An apical surface and a basal surface is present in all epithelia– The apical surface is exposed to the body exterior or cavity of an internal organ• Bears cilia or microvilli– The basal surface is attached to the underlying tissue• Supported by connective tissue– Epithelial tissue sheets rest on an underlying layer of connective tissue that also providessupport

– The basal lamina of the epithelial tissue and the reticular lamina of the connective tissuejoin together to form a basement membrane– The basement membrane is the interface between the epithelial tissue and the connectivetissue– Special Characteristics of Epithelium• Avascularity• Regeneration• Epithelia do not contain blood vessels but is innervated• Nutrients are obtained from the exposed or underlying surface• Epithelial cells are exposed to damage• They have the ability to regenerate and replace the cells that slough off thesurfaceClassification of Epithelia• Shape– Squamous– Cuboidal– Columnar• Degree of layering– Simple– Stratified• Simple epithelia– Consist of a single cell layer– Line surfaces used for exchange– Located in the GIT, respiratory tract, inner surface of blood vessels and heart chambers– Classification of Epithelia• Stratified epithelia– Several layer of cells (additional protection)

• Absorption, secretion• Location• GIT (from stomach to anal canal)• Pseudostratified Columnar Epithelium• Description• Single layer of cell with differing heights (false stratification)• May contain goblet cells and bear cilia• Function• Secretion (primarily mucus)• Mucus propulsion by ciliary action• Location• Nasal cavity, trachea and bronchi• Stratified Squamous Epithelia• Description• Several call layers• Basal cells are cuboidal or columnar• Surface cells are squamous• Keratinized type has the protein keratin that helps in preventing water loss• Function• Provides protection to underlying areas subject to abrasion• LocationNonkeratinized typeEsophageal lining, mouth, vaginaKeratinizedEpidermis of the skinTransitional Epithelium• Description

• Function• Location– Basal cells are cuboidal or columnar– Surface cells are dome-shaped or squamouslike depending on the degree of stretch of theorgan– Allows distention of urinary organs– Ureters, bladder and parts of urethra• Glandular Epithelia• Glands make and secrete watery substances referred to as secretions• Two types exist– Endocrine (ductless) glands• Release secretions directly into the blood stream or lymph– Exocrine glands (glands have ducts)• Release secretions onto body surface or into body cavities• Classification of Exocrine Glands• Unicellular– Goblet cell• Multicellular– Have a secretory portion (acinus) and duct• Structurally classified as simple (straight duct) or compound (branchedduct)• Classified based on secretory units as tubular (tube-shaped acinus), alveolar(flasklike acinus), and tubuloalveolar if both are present.– Figure 4.4b Goblet cell (unicellular exocrine gland).• Multicellular– Classified based on secretory mode as:• Merocrine – secretes by exocytosis• Holocrine - secretory cells rupture to release secretion• Apocrine – apical portion of secretory cell ruptures to release secretion

• Connective Tissue• Most abundant and widely distributed tissue type.– Four classes exist.• Common characteristics– Common origin• Develop from embryonic tissue called mesenchyme– Degree of vascularity• May be avascular, mildly vascularized or richly vascularized– Extracellular matrix• Non-living material surrounding cells• Composed of ground substance (IF, cell adhesion molecules, and proteoglycans)and fibers• Connective Tissue Cells• Adipocytes – Store fat• Macrophages – Phagocytes• Fibroblasts - Produce fiber– “-blast” = actively mitotic immature cell– “-cyte” = mature cell• WBCs – Immune cells– Plasma cells – Produce antibodies• Mast cells – Produce histamine and heparin• Connective Tissue Fibers• Three types of fibers exist– Collagen fibers (white fibers)• Most abundant and provides high tensile strength– Reticular fibers– Found in tendons and ligaments• Network of short, highly branched, collagenous fibers

• Used to support organs– Elastic fibers• Long, thin, elastin fibers that stretch• Types of Connective Tissue• Connective tissue proper (excludes bone, cartilage and blood)• Two subclasses exist• Lose connective tissue– (Areolar tissue)• Found throughout the body acting as packing material between tissues– Adipose tissue• Stores fat– Reticular tissue• Found in the lymphatic system where it provides support to the cells of theimmune system• Dense connective tissue– Dense regular• Includes tendons and ligaments– Dense irregular• Found in skin, joint capsule and surrounding various organs• Cartilage– Properties are intermediate between dense connective tissue and bone– Primary cells are chondrocytes• Hyaline cartilage– Most common– Matrix has closely packed collagen fibers for strength and flexibility

– Found between ribs and the sternum, trachea and articular surfaces of most joints• Elastic cartilage– Contains lots of elastic fibers– Found in the outer ear, epiglottis and larynx• Fibrocartilage– Densely packed with collagen– Very tough– Found between the vertebrae (intervertebral discs) and between the pubic bones (pubicsymphysis)– Covering and Lining Membranes• Membranes are formed by epithelial and connective tissues– Cutaneous membranes• Skin– Mucous membranes (mucosae)• GIT, respiratory, reproductive, urinary tracts– Serous membranes• Pleura, peritoneum and pericardium– Synovial membranes• Joints• Tissue Repair– Note that synovial membranes are NOT epithelial membranes and aresolely made up of connective tissue• Tissue injury results in body damage and increased susceptibility to pathogenic invasion• Tissue injury stimulates two major body responses– Inflammatory response– Immune response• Tissue Response• Inflammatory response

– Remove harmful agents– Prevent further injury– Restore tissue health• Immune response– Specific and deadly attacks against invading pathogens• Steps of tissue repair– Inflammation• Chemicals (histamines) are released from damaged tissue and they causecapillaries to dilate and leak• Fluid enters injury site with more chemicals (clotting factors and antibodies)• WBCs enter site of injury– Organization• New capillaries proliferate and restore proper blood flow to injured tissue• Clot is replaced by granulation tissue• Debris is phagocytized• Fibroblasts produce collagen fibers to help strengthen injured tissue• Epithelia regenerate• Regeneration and fibrosis– Scab detaches– Regeneration is replacement of damaged tissue with new tissue– Fibrosis is the proliferation of connective tissue to form scar• Fibrosis may occur depending on the type and severity of the injury• Epithelial tissue and bone tissue are good at regenerating without fibrosis• Dense regular connective tissue and cartilage have considerably less regenerativeproperties• Cardiac tissue and nervous tissue have essentially no functional regenerativecapacity• Name the tissue– Amorphous matrix that appears glassy

– Multiple layers of cells stacked in layers with the topmost layer consisting of flat cell– Allow stretching of the organ in which it is found– Can resist tensile strain or stress from multiple directions– Posses cilia and goblet cells• How does the structure of each tissue relate to its function?– Simple squamous epithelium– Dense regular connective tissue– Stratified squamous epithelium (keratinized type)– Simple columnar epithelium– Fibrocartilage• What is the level of structural organization?– Collagen– Elastin– Lymphocytes– Adipocytes– Chondroblast– Fibrocyte