Epithelial Tissues

Epithelial Tissues

1. DEFINITION: Tightly packed cells that form a continuous layer, covering all body surfaces, line body cavities and hollow organs. They are considered as the major tissue in glands.

2. Simple Epithelium

   • -Single layer of cells.
     • Cuboidal Epithelium
       • -Cube shaped cells. -They are found in areas where absorption or secretion occur.
         • Their main fuction are secretion and absorption.
           • They can be found on the ovaries, renal tubules, eyes and thyroid.
     • Columnar Epithelium
       • -Elongated cells. -They are designated for protection, secretion, or absorption.
         • -It secretes digestive enzymes and it also absorbs the digested food. -They aid mucus and reproductive cells movement.
           • Found in the small intestine, stomach, large intestine, rectum, etc.
     • Squamous Epithelium
       • -Flattened cells. -They are found in the areas where filtration or diffusion take place.
         • Facilitate the diffusion of gases and small mlecules.
           • They are found in the skin, nephrons of kidneys, capillary walls, glomeruli, etc.
       • CHARACTERISTICS
         • FUNCTIONS
           • EXAMPLES
     • Pseudostratified Columnar Epithelium
       • -Columnar cells. -Multiple layered nuclei.
         • -Collect materials to be able to cough or sneeze them out. -Protect the lungs from irritants.
           • Found in the trachea linings and the upper repiratory tract.

3. Glandular Epithelium

   • -Epithelium that secretes a product. -Glands consist of a single cell or a group of cells that work to to secret substances into either ducts, surface or blood. They can be endocrine or exocrine.
     • Endocrine
       • -Ductless glands.
         • They release hormones without ducts into the bloodstream.
           • -Pineal glands. -Thyroid glands. -Adrenal glands. -Pituitary glands.
     • Exocrine
       • They are glands that secretes by way of a duct
         • Their function is to excrete their products into ducts
           • -Salivary glands. -Sweat glands. -Mammary glands
     • CHARACTERISTICS
       • FUNCTION
         • EXAMPLES

4. Stratified Epithelium

   • -Multiple layers of cells
     • Stratified Squamous Epithelium
       • -Squamous epithelial cells. -They rest on a basal membrane. -Its layers adhere to eachother to maintain the structure integrity. -Only one layer is in contact with the basement membrane.
         • -Its main functions is to protect the underlying structures from harm. -Protect the body from water loss and desiccation.
           • They are found in many organs that come into close contact with the outside environment, such as the skin, respiratory, digestive, reproductive and excretory systems.
       • CHARACTERISTICS
         • FUNCTIONS
           • EXAMPLES
     • Stratified Cuboidal Epithelium
       • -It's made up of cube-shaped cells. -From two to three layes of cells.
         • Secretion and protection, as it builds up barriers between two distict surfaces of the body.
           • Located in sweat glands, mammary glands, and salivary glands.
     • Stratified Columnar Epithelium
       • -It's considered as a rare type of epithelial tissue. -Its top layer is made up pf columnar elongated epithelial cells. -Cube shaped cells.
         • Its main function is to provide protection and secretion.
           • This type of tissue is found in the conjuctiva of the eye, uterus, salivary glands, pharynx, etc.
     • Transitional Epithelium
       • -Cube-shaped elongated cells. -Its cells are able to contract and expand depending on the distension that it requires.
         • They provide protection. -Allow vessels to expand and accomodate fluid.
           • It's located in the prostatic urethra, urinary bladder and ureters.