Tissues: Epithelium

Tissues: Epithelium

1. Simple Epithelium

   • Filtration, Diffusion, secretion, and absorption
     • Cuboidal
       • glands
       • tubules of the kidney
       • terminal bronchioles of the lungs
       • ducts of reproductive tracts
     • Columnar
       • line the gastroins\testinal tract
         • secretion
         • absorption
           • Absorption: Certain epithelial cells lining the small intestine absorb nutrients from the digestion of food.
       • may have micriovilli
         • enhance the surface are of the cell and increase the rate of diffusion of materials into the cell
       • Uterus (womb)
     • pseudostratified columnar
       • often have cilia
         • Cilia are used to move the cell or to move objects over the surface of the cell with power strokes
           • Cleaning: Ciliated epithelium assists in removing dust particles and foreign bodies which have entered the air passages.
       • ducts of reproductive tracts
       • air condition pathways of the respiratory tract
     • Diffusion: Simple epithelium promotes the diffusion of gases, liquids and nutrients. Because they form such a thin lining, they are ideal for the diffusion of gases (eg. walls of capillaries and lungs).
   • fast absorption
     • Squamous
       • Heart cavaties
       • Internal surfaces of all blood and lymph vessels
         • Reduces Friction: The smooth, tightly-interlocking, epithelial cells that line the entire circulatory system reduce friction between the blood and the walls of the blood vessels.
       • air cells of lung
       • filtration capsules and thin tubules in the kidney
         • Excretion: Epithelial tissues in the kidney excrete waste products from the body and reabsorb needed materials from the urine.
           • Sweat is also excreted from the body by epithelial cells in the sweat glands.
       • major body cavaties
   • Sensation: Specialised epithelial tissue containing sensory nerve endings is found in the skin, eyes, ears, nose and on the tongue.

2. Stratified Epithelium

   • resistant to wear and tear because of ready replacement of cells
     • Squamous
       • skin
         • keratin
           • scleroprotein
           • protects epithelial cells from damage or stress that has potential to kill the cell
           • Keratin is a type of filament protein, called an intermediate filament. The filaments anchor the cells to each other, which prevents the cells from pulling apart
         • protection: protect underlying tissue from mechanical injury, harmful chemicals, invading bacteria and from excessive loss of water
         • Epidermis
       • oral cavity
       • vocal folds
       • esophagus
         • pherein "to carry" (see infer) + -phagos, from phagein "to eat" (see -phagous).
       • vagina
       • anus
       • basal layers can be squamous, cuboidal or columna
     • Transitional
       • contracted, bumpy surface allows urinary organs to bend and stretch
         • bladder
         • ureters
         • prostate
     • Cuboidal
       • Protects glands

3. Glandular Epithelium

   • Secretion: In glands, epithelial tissue is specialised to secrete specific chemical substances such as enzymes, hormones and lubricating fluids.
     • Exocrine (out)
       • retain a duct to the free surface fo the cavity or skin
     • Endocrine (in)
       • dense capillary networks

4. Basal side: Holds to connective tissue

5. Apical side

6. Functions

   • Protection: skin
   • Sensation: sensory
   • Secretion: glands
   • Absorption: digestive system
   • Excretion: kidneys, sweat glands
   • Diffusion: gases, liquids, nutrients.
   • Cleaning: celia
   • Reduce friction: circulatory system

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