Tissues

Tissues

1. Epithelial

   • Basic cell type
   • Tight cohesive sheet - moves as 1 - close together
   • Characteristics
     • Highly cellular
     • Cells bind to each other and to basement membrane via adhesions/junctions
     • Avascular - no blood vessels
     • Capable of regeneration
       • important in tissues experiencing 'wear and tear'
     • Derived from all 3 germinal layers
       • Ectoderm
       • Endoderm
       • Mesoderm
     • Have structurally and functionally distinct cell surfaces
       • Free apical surface
         • In contact with environment - not attached to other cells
         • Often lines lumen of ducts and cavities
         • Specialisations
           • Microvilli - cytoplasmic protrusions, 'brush border'
             • Often found on epithelium, lining internal passages
             • Increases SA
             • Found with lots of transport
           • Stereocilia - like microcvilli but longer
             • Non-motile (unlike cilia)
             • Limited distribution - epididymis/vas def & sensory hair cells, inner ear
             • Not as common as microvilli
           • Cilia - motile hair like protrusions
             • several hundred per cell
             • Beat in coordination to move substances over them
             • Found in respiratory epithelium and fallopian tubes
             • Smoking reduces cilia movement - impaired movement of mucous - reduced protection against bacteria
       • Lateral surface
         • Attached to other epithelial cells
         • In the middle
         • Basolateral specialisations
           • Epithelial cells extremely cohesive and closely apposed
           • Specialisations at basolateral surface between cells or with underlying basement membrane
             • Junctions - maintain polarised state and join cells together - exchange information and metabolites
               • Occluding/tight junctions
                 • Seals cells together - prevents leaking
                 • Zona occludens - apicial part of lateral domain - almost fusing 2 cells
                 • Found a lot in brain - forms blood-brain barrier
               • Anchoring junctions
                 • Mechanically attaches cells to neighbours
                 • Abundant in tissue subject to severe stress - e.g. skin, cardiac muscle
                 • Zona adherens or Desmosomes - strong junctions joining cells at lateral domain
                 • Hemidesmosome - strong in basal domian
               • Communicating/gap juctions
                 • Passage of chemical/electrical signals between cells
       • Basal surface
         • Attached to basement membrane which attaches epithelia to underlying tissues
       • Each surface has own specialisations
   • Combines with nervous tissue to make special senses
   • Cell functions
     • Protecting underlying structures
       • Covers and protects surfaces of body, - both internal and external
         • Line internal cavities and vessels
         • Form glandular structures
         • Form barriers
     • Permitting passage of some substances through it
       • Any substances entering or leaving must cross epithelium
       • Some more permeable than others
     • Secreting substances
       • Discharged onto epithelial surface or released into body/blood
     • Provide sensations
       • Large sensory supply to provide info about environment
   • Classifications
     • Number of layers
       • Simple - single layer, good for absorption/secretion, fragile
       • Stratified - 2 or more layers of cells, good for protection
       • Pseudostratified - one layer of a mixture of cell shapes
     • Shapes of cells - at surface layer
       • Squamous - flat shpaed
       • Cuboidal - cube shaped
       • Columnar - tall cylindrical shaped, nucleus generally at base
       • Transitional - readily change shape, acccomodates stretching
     • Surface specialisations
       • cilia, keratin etc.

2. Connective

   • Abundant and widely distributed
   • Makes up every part of the body
   • Cells separated from each other by extracellular matrix (ECM)
   • Three main classes - there are more subclasses
     • Connective tissue propper
     • Supporting connective tissue
     • Fluid connective tissue
   • Functions
     • Enclosing/Protection - capsules/bones
     • Separation - sheaths (2 muscles)
     • Cushioning/Insulation - adipose tissue
     • Storage - adipose tissue
     • Support - bones/cartilage
     • Connection - tendons/ligaments
     • Transportation - blood
   • Components
     • Cells
       • Each major class of connective tissue has resident cells
         • Do have extra cell types too
       • Blasts - create the ECM
       • Cytes - maintain the ECM
       • Clasts - break down the ECM
     • Extra cellular matrix (ECM)
       • Matrix properties allow CT to bear weight and withstand tension/trauma
       • Ground Substance
         • Fluid that fills space between cells
         • Gel like - contains water and 2 main groups of soluble protiens
           • Cell adhesion proteins - connective tissue glue
           • Proteoglycans - macromolecule with a protein core to which GAGs are attached
         • Arrangement confers high viscosity and low compressibility
           • Good for joints
           • Higher GAGs content gives more viscous fluid
             • Important GAGs - hyaluronic acid, chondroitin sulfate, heparan sulfate, dermatan sulfate, keratan sulfate
       • Fibres
         • Provide support
         • Tissue type generally governed by fibre type
         • Collagen
         • Elastic
         • Reticular
           • Short fine fibres - 0.5 - 2 um diameter
           • Type III collage fibres
           • Branch extensively forming networks - fill spaces between tissues and organs
           • Allow more 'give' than collagen fibres
           • Abundant in liver, spleen, and lymph nodes
   • Differences to other tissues
     • Common germ layer origin - only comes from mesoderm
     • Contains ECM
   • Connective tissue disorders

3. Nervous

4. Muscle

5. General

   • Each specialised tissue/cell has special functions
     • structure and function are closely related - can predict one from the other