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					                                      Chapter 4 Tissues

Human tissues are collections of cells and cell products that

Four types of tissues: Epithelial, Connective, Muscular, Nervous

I. Epithelial
       • "covering" and “lining”
       • form glands

       Characteristics of Epithelial Tissue:
       • Cellularity: formed of closely joined cells – in sheets

       • polarity – 2 different surfaces
               Apical (exposed)
               Basal (attached) surface of cells

       • attachment – attached to connective tissue via basal lamina (basement membrane).

       • avascular –

       • regeneration-

       Functions of Epithelial Tissue:
       1.) Provide physical protection

       2.) Control Permeability (absorption/secretion)

       3.) Sensation

       4.) Produce secretions
              Glandular epithelium

       Specializations of Epithelial Cells

              Microvilli: extensions of cell membrane

              Cilia: hair like structures which beat

       Maintaining the Integrity of Epithelia
       1.) intercellular connections
       2.) attachment to basal lamina
       3.) epithelial maintenance & repair

       1. Intercellular Connections: anchor cell membranes
              cell adhesion molecules (CAMs)
              intercellular cement: glycosaminoglycans – hyaluronan

       Cell Junctions – specialized areas in cell membrane
              a. Tight (occluding) junctions: impermeable

                      Lining of intestinal tract – lumen

              b. Gap junctions: cells held together by connexons (channel proteins)

              c. Desmosomes (macula adherens): in areas subject to mechanical stress
                     Held with CAMs and proteoglycans

2. Attachment to basal lamina
       Two layers:
              1.) lamina lucida

              2.) lamina densa

3. Epithelial Maintenance and Repair
       • cells often only live for days and die/shed

       • stem cells (germinative cells) deep and have rapid mitotic rate

       • damaged cells quickly replaced

Classified by the number of layers and the shape of cells
        A. Layers:

       B. Shape of Cells:

       1. Simple Squamous: one layer

              -good for
              -found in the linings of

              -also known as mesothelium and endothelium

       2. Stratified Squamous:
              -most widespread

              -found in areas subject to friction: mouth, vagina, anus

       3. Simple Cuboidal: one layer

              -have large spherical central nucleus
              -found in glands: thyroid & nephron

       4. Transitional:
             - stretches & recoils without damage
             - appearance changes as it stretches
             -found in urinary bladder

       5. Simple Columnar:
             - function for absorption, secretion, protection
             -found in lining of

       6. Psuedostratified Ciliated Columnar:
              -looks striated but it isn’t
              - cilia function for?

              -found in

Glandular Epithelium
Exocrine vs. Endocrine Glands
       Endocrine glands: secrete directly into blood
              Secretions termed:

       Exocrine glands: secrete through ducts

              modes of secretion
              1.) Merocrine: exocytosis of secretions
                     Salivary glands secrete (mucin) or mucus
                     Merocrine sweat glands

              2.) Apocrine: apical portion of cell shed with secretions
                     Mammary glands

              3.) Holocrine: entire cell ruptures to release secretions
                     Sebaceous glands

              Types of secretions:
              1.) serous glands

              2.) mucous glands

              glands can be simple or compound in structure

II. Connective
              1. binds               &              together & supports structure
              2. framework for                      cells
              3. protects
              4. storage sites for

              5. forms rigid skeletal framework of body
              6. limits ROM

              7. transports                         fights                (defense of body)

       Connective tissue consists of few cells with a lot of intercellular matrix (ground

       Classification of Connective Tissues
       1.) Connective tissue proper
       2.) Fluid connective tissues
       3.) Supporting connective tissues

       1.) Connective Tissue Proper
              • contains fibers, ground substance & cells

       Cells associated with connective tissue proper
               1. fibroblast:
                      Secreted hyaluronan and protein fibers
                      Important for tissue growth & repair

              2. macrophages: phagocytes:

              3. adipocytes: store fat

              4. mesenchymal cells: stem cells

              5. melanocytes: produce melanin

              6. mast cells: release histamine & heparin

              7. lymphocytes: WBC

              8. microphages: neutrophils and eosinophils

       Connective Tissue Fibers

              A. Collagenous: most abundant – “white fibers”

      B. Reticular: short, thin

      C. Elastic:

Types of Connective Tissue Proper:
1. Loose Connective Tissues – “packing peanuts”
       Areolar, Adipose, Reticular

      A. Areolar: most abundant
            •consists mostly of collagenous fibers

             •large spaces between cells:

             •unorganized fiber arrangement

             •functions:    1.attach skin
                            2. fill spaces

                            3. surround & support

      B. Adipose Tissue:

             • white vs. brown fat
                    Brown fat very metabolically active

             • visceral vs. subcutaneous fat:
                    Subcutaneous fat found below skin
                    Visceral found in abdomen (belly fat)

                    Waist: hip ratio

      C. Reticular Connective Tissue:
             •similar to loose connective tissue, contains ground substance in network
             of interlacing fibers
             •make up the inner framework in

      2. Dense Connective Tissues – Connective tissues proper, tightly packed with
      high numbers of collagen or elastic fibers

      A. Dense Regular Connective Tissue:
            •tightly packed bundles of collagenous fibers

             many fibroblasts

             1. tendons

             2. ligaments

             3. fascia

             4. aponeuroses

      B. Dense Irregular Connective Tissue:

             •fibers oriented randomly:

             •found in:     1. dermis
                            2. fibrous coverings: (perichondrium), (periosteum), &

                            3. capsules of many organs

      C. Elastic Connective Tissue:
             •contains more elastic than collagenous fibers
             •good for
             •found in walls of

2. Fluid Connective Tissues –
       A. Blood: watery mix of dissolved proteins
             contains formed elements (cells) and plasma
             Formed elements: RBC, WBC, platelets

      B. Lymph: fluid contains protein, lymphocytes, fats
            Similar to interstitial fluid
            Circulates via lymphatics

3.) Supporting Connective Tissues: Support soft tissues & body weight

         • Gel-type ground substance
         • For shock absorption and protection
         • Calcified (made rigid by calcium salts, minerals)
         • For weight support

      A. Cartilage
            •numerous collagen fibers in a firm matrix contains:
            1.) Proteoglycans derived from chondroitin sulfates
            2.) Ground substance proteins
            3.) Chondrocytes (cartilage cells) surrounded by lacunae (chambers)

             •fibers/matrix formed by cells:



             •avascular: due to secretion of antiangiogenesis factor

                     - surrounded by perichondrium
                            Outer fibrous layer
                            Inner cellular layer

      Cartilage growth (both stop in adults)
              1.) interstitial growth: chondrocyte undergoes mitosis
                      growth from within cartilage
                      mainly during embryonic development - adolescence

             2.) appositional growth: new layers of cartilage added to surface

                     -does not occur in adults

      Types of cartilage
             1. Hyaline:
                     -most abundant
                     -provides support & reduces friction

                     -precursor to bone (fetal skeleton), costal cartilage
                     -also found in

             2. Fibrocartilage (fibrous)
                    -collagen fibers in thick bundles
                    -slightly compressible
                    -found in regions that

                     -intervertebral discs, knee joint: meniscii
                     and pubic symphysis

             3. Elastic -contains collagen but
                    -found in

8. Bone or osseous tissue:
      • strong mineralized matrix
             Calcium & phosphate salts
             Resist shattering


      • osteocyte:
             Inside lacunae
             Lacunae interconnected with canaliculi

              • 2 differences between bone and cartilage:
                      1. bone well supplied by
                      2. canaliculi

              • surrounded by periosteum

Membranes: physical barriers that line
     Consist of: an epithelium supported by

       1.) mucous membranes: secrete mucus (sticky)
             Found in

       2.) serous membranes: line ventral body cavities


       3.) cutaneous membrane: skin

       4.) synovial membranes

III. Muscular
      •specialized for

       • contains actin & myosin: proteins which produce all body movements

       •3 types of muscle tissue:
              1. skeletal: largest cells & striated

                      Appearance: long

                      Specializations: myosatellite cells (satellite cells) – stem cells for skeletal

              2. cardiac: striated
                     Cardiocyte – cardiac muscle cell


                      Specializations: intercalated discs

              3. smooth (visceral): nonstriated

IV. Nervous (neural) Tissue
         – Specialized for conducting electrical impulses

          –   Rapidly senses internal or external environment

          –   Processes information and controls responses

          –   Forms the brain, spinal cord, nerves

      •Two types of cells: neurons & supporting cells (neuroglia)
      Neurons: conduct nerve impulses
            - 3 parts: dendrite, cell body & axon

              -need continuous supply of?

      Neuroglia cells:

Tissue Response to Injury: (pg. 142)
      Tissues respond to injuries to maintain homeostasis

      Cells restore homeostasis via:

      1. Inflammatory Response (inflammation)
      immediately after injury area is isolated while damaged cells and microorganisms are
      cleaned up

      • infection: presence of pathogens

      •Inflammation: short term (acute) inflammation has 4 symptoms:
             1.                  2.                   3.                      4.

      •what causes this?
      1. initial injuryt causes release of chemicals (histamine, heparin, prostaglandins)from
                      neutrophils, macrophages, mast cells

              -these chemicals cause vasodilation of blood vessels which increases blood flow
              to injured area = heat, redness

              -histamine increases permeability – makes blood vessels “leaky” = swelling

              -swelling puts pressure on nerve endings = pain

              -why is this good?
                     1. helps dilute toxins & remove wastes

                     2. brings oxygen & nutrients

                     3. brings phagocytes

                     4. increases temperature

                     5. brings antibodies

                     6. removes toxins & wastes

             -necrosis: tissue/cell death

             lysosomes: release enzymes to destroy injured cells and surrounding area –
             produces debris, fluid, dead/dying cells known as pus

             abcess: accumulation of pus in enclosed tissue space

      2. stasis: "standing"
             -slowdown of blood flow

      Repair: 2 major ways:
      1. regeneration:

      2. fibrosis: scar tissue

Read the text pages 143-144 on aging, tissue structure & cancer. Also read Applications
Manual - Tissue Structure and Disease pgs. 38-39.