Tissue types and structure

• define a tissue: a group of similar cells that usually have common embryonic origin and function together to perform specialised functions
• 4 tissue types:

  epithelial

  connective

  muscle

  nervous
• Mesoderm derived tissues

  epithelial

  connective

  muscular
• ectoderm derived tissues

  epithelial

  nervous
• Endoderm dervived tissues

  epithelial
• Cell junction types

  tight

  adherens

  desmosomes

  hemidesmosomes

  gap
• Tight junctions: A type of junction between cells that prevents the passage of substances from one cell to another

  • adjacent plasma membrane
  • intercellular space
  • strands of transmembrane proteins
• Adherens junctions: Connects adjacent cells and are found in epithelial tissue

  • microfilament (actin)
  • plaque (dense layer of proteins that attache membrane proteins)
  • transmembrane glycoprotein (cadherin)
  • intercellular space
  • holds themself together to reduce stresses and strain on the cell
• Desmosome:

  • commonly makes up the epidermis and cardiac muscle
  • Prevents separation under tension and contraction (mechanical strength)
  • Contains plaque and transmembrane glycoproteins (cadherins)
  • Cadherins extend into intercellular space and attach cell membranes together
  • plaque attaches to intermediate filament (keratin)
  • intermediate filament extend from desmosome one to the other side of the cell across the cytosol
• Hemidesmosomes:

  • secures cells to the basement membrane
  • intermediate filament (keratin) is attached to transmembrane glycoprotein (integrin)
  • Integrin attaches to laminins (basement membrane)
• Gap junction:

  • membrane proteins (Connexin) form tiny fluid-filled tunnels (connexons) that connect neighboring cells
  • Separated by a very narrow intercellular gao through connexons, ions and small molecules can diffuse through from the cytosol
  • transfer of waste and nutrients in avascular tissue
  • tissue are coupled allowing the order to be carried out (right order)
  • allow cell communication e.g developing embryo
• Nervous tissue:

  Detects internal and external changes in conditions and ats to maintain homeostasis

  1. neurons
  2. neuroglia
• Neurons

  generate and conduct nerve impulses

  • cell body contains a nucleus and other organelles
  • Dendrites receive signals
  • axons allow conduction over a long distance
• Neuroglia

  non-conducting.

  roles:

  • insulate
  • support
  • protect neurons
• Types of neuronal cell:

  • unipolar (1 linking the cell body to dendrites)
  • bipolar ( 2 process linking the cell body to dendrites)
  • multipolar
• CNS divisions:

  motor ouptut (somatic and autonomic)

  sensory system
• Frontal lobe:

  Executive functions, thinking, planning, organising and problem solving, emotions and behavioural control, personality
• Motor cortex:

  movement
• Sensory cortex:

  sensations
• parietal lobe:

  perception, making sense of the world, arithmetic, spelling
• Occipital lobe

  vision
• Temporal lobe

  memory, understanding, language
• Types of muscle tissue

  • skeletal
  • cardiac
  • smooth
• Skeletal muscle

  Long, cylindrical cells contain many peripheral nuclei

  • myofilament arrnagement gives tissues a striated appearance
  • Attached to bones of skeleton
  • parallel fibres
  • Voluntary under conscious control
• Smooth muscle

  • no striations
  • cells thick in the middle and taper at each end
  • central nucleus
  • found in walls of hollow structure (blood vessels, lung airways, intestines...)
  • connected via gap junctions in intestines
• Epithelial tissue

  forms continuous sheets

  • Function: covers body surfaces, lines hollow organs, forms gland
  • Avascular
  • innervated
  • High proliferative potential
• Cutaneous membrane

  • covers the entire surface of the body
  • contains epidermis and deeper portion called the dermis
  • The epidermis consists of keratinised stratified squamous epithelium which protects connective tissue and areolar connective tissue
• Synovial membrane

  • lines cavities of free movable membranes line structures that do not open to the exterior, lack an epithelium,
  • composed of a discontinuous layer of cells called synoviocytes.
  • synoviocytes secret some synovial fluid lubricates and nourishes the cartilage at movable joints and contain macrophages that remove microbes and debris from the join cavity
• Cardiac muscle

  Found in heart walls

  • central nuclei
  • cells joined end to end via intercalated discs
  • striated and involuntary
• Epithelia tissue:

  • forms continuous sheets in single or multiple layers with very little intercellular space
  • function: cover body surfaces, lines hollow organs, forms glands, selective barrier that limits or aids in transfer of substances
  • avascular (associated with a lack of blood vessels)
  • innervated (supply of blood vessels)
  • generally high proliferative potential
• Structure of epithelium

  Apical (free surface)

  Lateral surface

  basal surface
• Apical surface:

  • face body surface, a body cavity (lumen) or tubular duct
  • contain cilia or microvilli
• Lateral surface:

  • Face adjacent cells
  • contain tight, adherens, desmosomes and gap junction
• Basal surfaces

  • opposite to apical surface
  • hemidesmosomes
  • multiple layers
  • deepest layer of cells
• Basement membrane:

  • extracellular layer that commonly consist of 2 layers basal lamina and reticular lamina
• Basal lamina

  • contains laminin and collagen (proteins)
  • contains proteoglycans (glycoproteins)
  • Laminin adhere to integrins in hemidesmosomes
• Reticular lamina

  contains collagen produced by fibroblasts
• Function of basement membrane:

  • support epithelial tissue
  • surfaces which epithelial cells migrate during growth/healing
  • restrict passage of larger molecules between epithelium and connective tissue
  • participate in filtration of blood in kidneys
• Classification of epithelium:

  • Layers
  • shape
• Describe arrangement of cells in layers

  • simple = 1 layer
  • stratified = more than 1 layer
  • pseudostratifed = 1 layer but nuclei are in different layers