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Cells to Tissues

  • As human body develops from single to multicellular, cells specialize.
  • Body is interdependent system, malfunction of one group of cells is catastrophic.
  • Cells specialize into types of tissues, then interspersed into organs.

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Tissues = groups of cells that are similar in structure and function.

  • Epithelium
    • Coverings
    • Linings of surfaces

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  • Connective
    • Support
    • Bone, ligaments, fat
  • Muscle
    • Movement

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  • Nervous
    • Control
    • Brain, nerves, spinal cord

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EPITHILIAL TISSUE

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Function of Epithelial Tissue

  • Protection
    • Skin protects from sunlight & bacteria & physical damage.
  • Absorption
    • Lining of small intestine, absorbing nutrients into blood
  • Filtration
    • Lining of Kidney tubules filtering wastes from blood plasma
  • Secretion
    • Different glands produce perspiration, oil, digestive enzymes and mucus

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Characteristics of Epithelial Tissue

  • Form continuous sheets (fit like tiles)
  • Apical Surface
    • All epithelial cells have a top surface that borders an open space – known as a lumen
  • Basement Membrane
    • Underside of all epithelial cells which anchors them to connective tissue
  • Avascularity (a = without)
    • Lacks blood vessels
    • Nourished by connective tissue
  • Regenerate & repair quickly

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Classification of Epithelial Tissue

  • Cell Shape
    • Squamous – flattened like fish scales
    • Cuboidal - cubes
    • Columnar - columns
  • Cell Layers
    • Simple (one layer)
    • Stratified (many layers)
      • Named for the type of cell at the apical surface.

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Simple Squamous Epithelium

  • Structure
    • Single Layer of flattened cells
  • Function
    • Absorption, and filtration
    • Not effective protection – single layer of cells.
  • Location
    • Walls of capillaries, air sacs in lungs
    • Form serous membranes in body cavity

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Simple Cuboidal Epithelium

  • Structure
    • Single layer of cube shaped cells
  • Function
    • Secretion and transportation in glands, filtration in kidneys
  • Location
    • Glands and ducts (pancreas & salivary), kidney tubules, covers ovaries

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Simple Columnar Epithelium

  • Structure
    • Elongated layer of cells with nuclei at same level
  • Function
    • Absorption, Protection & Secretion
    • When open to body cavities – called mucous membranes
  • Special Features
    • Microvilli, bumpy extension of apical surface, increase surface area and absorption rate.
    • Goblet cells, single cell glands, produce protective mucus.
  • Location
    • Linings of entire digestive tract

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Pseudostratified Epithelium

  • Structure
    • Irregularly shaped cells with nuclei at different levels – appear stratified, but aren’t.
    • All cells reach basement membrane
  • Function
    • Absorption and Secretion
    • Goblet cells produce mucus
    • Cilia (larger than microvilli) sweep mucus
  • Location
    • Respiratory Linings & Reproductive tract

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Cilia

Basement Membrane

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Stratified Squamous Epithelium

  • Structure
    • Many layers (usually cubodial/columnar at bottom and squamous at top)
  • Function
    • Protection
    • Keratin (protein) is accumulated in older cells near the surface – waterproofs and toughens skin.
  • Location
    • Skin (keratinized), mouth & throat

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Keratin

Stratified Cubodial (layers of cubodial only)

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Transitional Epithelium

  • Structure
    • Many layers
    • Very specialized – cells at base are cuboidal or columnar, at surface will vary.
    • Change between stratified & simple as tissue is stretched out.
  • Function
    • Allows stretching (change size)
  • Location
    • Urinary bladder, ureters & urethra

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Glands

  • One or more cells that make and secrete a product.
  • Secretion = protein in aqueous solution: hormones, acids, oils.
  • Endocrine glands
    • No duct, release secretion into blood vessels
    • Often hormones
    • Thyroid, adrenal and pituitary glands
  • Exocrine glands
    • Contain ducts, empty onto epithelial surface
    • Sweat, Oil glands, Salivary glands, Mammary glands.

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Shapes of Exocrine glands

  • Branching
    • Simple – single, unbranched duct
    • Compound – branched.
  • Shape: tubular or alveolar
    • Tubular – shaped like a tube
    • Alveolar – shaped like flasks or sacs
    • Tubuloalveolar – has both tubes and sacs in gland

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Modes of Secretion

  • (How the gland’s product is released)
  • Merocrine
    • Just released by exocytosis without altering the gland at all.
    • Ex: Sweat glands and salivary glands
  • Holocrine
    • The gland ruptures and releases secretion and dead cells as well.
    • Sebaceous (oil glands on the face) only example