Unit 2 - Tissues

Unit 2 - Tissues

1. Intercellular Junctions

   • Tight Junctions
     • Close space between cells by fusing cell membranes Ex. Cells that line the small intestine
   • Desmosomes
     • Bind cells by forming “spot welds” between cell membranes Ex. Cells of the outer skin layer
   • Gap Junctions
     • Form tubular channels between cells that allow the exchange of substances Ex. Muscle cells of the heart and digestive tract

2. Epithelial Tissue

   • protection, secretion, absorption, excretion
   • covers body surface, covers and lines internal organs & cavities, composes glands
   • **lacks blood vessels**, cells readily divide, cells are tightly packed together
   • basement membrane anchors epithelium to connective tissue
     • cancer cells secrete a substance that dissolves the basement membrane, enabling the cells to invade other tissue layers (metastasis)
       • cancer cells also produce fewer adhesion proteins (help cells to “stick” together) which allows them to spread into surrounding tissues.
   • classified according to cell shape and the number of cell layers
     • simple squamous
       • -one thin layer of flat cells (easily damaged) -diffusion (gas exchange in lungs), filtration (in kidney), secretion (glands) -alveoli of the lungs, kidney glomeruli, lining of the heart, blood vessels and lymphatic vessels, lining of the ventral body cavities.
     • stratified squamous
       • -several layers of cells, top layer is flattened (squamous), thickest layer of epithelial tissue, can be keratinized (contains the protein keratin) or nonkeratinized. -protection keratinized: epidermis -nonkeratinized: mouth, esophagus, tongue, vagina
     • simple cuboidal
       • -one layer of cube shaped cells (1 round nucleus) -secretion and absorption of substances (ex. to give urine its final composition, it moves substances in and out of the kidney tubule) -small glands, kidney tubules, ovary surface
     • simple columnar
       • -one layer of elongated cells (having one oval nucleus), ciliated or nonciliated (contains microvilli) -absorption & secretion -nonciliated: mainly in the lining of the digestive tract (absorption) and lining the ducts of some glands (secretions) -ciliated: small bronchi, the uterine tubes, part of the uterus (secretions)
     • glandular
     • stratified cuboidal
       • -several layers of cube shaped cells -protection -largest ducts of sweat glands, mammary glands, salivary glands
     • stratified columnar
       • -several layers, top layer contains elongated cells -protection and secretion -very rare in the body - it lines part of the urethra, large ducts of some glands, portion of the conjunctiva of the eye
     • simple psuedotratified (pseudostratified columnar)
       • -one layer of cells that are attached to the basement membrane, cells at different heights, nuclei at different heights, ciliated or nonciliated -secretion and movement of mucus -ciliated in respiratory tract (bronchi)
     • transitional
       • -several layers of cells that can be stretched. will look like a stratified squamous epithelium if it is stretched or a stratified cuboidal epithelium if it is unstretched -allows for distention of urinary organs -bladder, ureters, part of urethra

3. Connective Tissue

   • connects, supports, protects, provides frameworks, fills spaces, stores fat, produces blood cells, protects against infection, helps repair damaged tissues
   • usually have considerable extracellular matrix between them
     • consists of fibers and a ground substance (gel-like material)
   • major cell types
     • fibroblast
       • produce collagen and elastic fibers
       • macrophage
         • are phagocytes (“eat cells”)
         • mast cell
           • may release heparin and histamine
   • connective tissue fibers
     • collagen fibers
       • have a great tensile strength
       • elastic fibers
         • are composed of elastin and are stretchy
         • reticular fibers
           • are fine collagen fibers
   • CATEGORIES OF CONNECTIVE TISSUES
     • connective tissue proper
       • loose connective tissue
         • areolar
           • -forms thin membranes between organs and binds them together -found beneath the skin and surrounds organs
           • adipose
             • -stores fat, cushions, and insulates -found beneath the skin; in certain abdominal membranes; around the kidneys, heart, various joints
             • reticular
               • -thin branched reticular fibers -supports the walls of the liver and spleen
       • dense connective tissue
         • dense regular
           • strong collagen fibers that bind structures as parts of tendons and ligaments
           • dense irregular
             • thicker, randomly distributed collagen fibers and is found in the dermis
             • elastic
               • elastic fibers that make up hollow internal organs like the lungs and blood vessels
     • special connective tissues
       • cartiledge
         • -provides support -consists of fibers and a gel-like substances -lacks a direct blood supply, so it is slow to heal -found at the ends of various bones; in the ear; in the larynx; and in the pads between the bones of the spinal column, pelvic girdle, and knees
         • bone
           • -matrix consists of mineral salts and collagen -compact & spongy bones. -heals rapidly
           • blood
             • -composed of cells suspended in fluid -produced in the tissue of hollow parts of certain bones

4. Muscle Tissue

   • contracts, moving structure attached to it
   • AKA muscle fiber
   • skeletal muscle 40%, cardiac muscle 10%
   • 3 Types
     • Skeletal
       • Smooth
         • Cardiac

5. Nervous Tissue

   • found in brain, spinal cord, and **peripheral nerves
   • basic cells called neurons are highly specialized
     • coordinate, regulate, and integrate many body functions
   • neuroglia is the supporting cell of the nervous tissue

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