Ch. 4 Tissues

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  1. 1. Epithelium ("covering")
    2. Epithelial tissue occurs in two different forms:
    • 1. is a sheet of cells that cover a body surface or lines a body cavity
    • 2.
    • Covering and lining epithelium covers the outer and inner surfaces of most body organs (Ex. Skin)
    • Glandular epithelium forms most of the body glands
  2. Special Characteristics of Epithelia
    • Cellularity
    • Specialized contacts
    • Polarity
    • Support by connective tissue
    • Avascular but innervated
    • Regeneration
  3. 1. Glands
    2. Secretion
    • epithelial cells that make and secrete a product
    • the products of glands are aqueous fluids that usually contain protein
    • 2. is the process whereby gland cells obtain needed substances from the blood and transform them chemically into a product that is then discharged from the cell 
    • RER creates protein→Golgi Apparatus→exocytosis
  4. Glands are classified as:
    • endocrine (internal secretion)
    • exocrine (external secretion)
    • and
    • unicellular ("one-celled") 
    • multicellular ("many-celled")
    • most multicellular glands develop by invagination of an epithelial sheet into the underlying connective tissue
  5. Endocrine Glands
    • Ductless Glands
    • produce messenger molecules called hormones
    • ↓ released into the extracellular space
    • ↓ enter nearby capillaries and travel through bloodstream to specific target organs
    • target organ and endocrine gland are usually far apart
  6. Exocrine Glands
    • secrete their products onto body surfaces (skin) or into body cavities (digestive tube)
    • multicellular have ducts that carry products to the epithelial surfaces
    • secretion is local; the secretion acts near the area where it is released 
    • Ex. sweat and oil glands
  7. Goblet Cell=Unicellular Exocrine Glands
    • are scattered within the epithelial lining of the intestines and respiratory tubes, between columnar cells with other functions
    • produce mucin, a glycoprotein that dissolves in water when secreted
    • mucin+water=mucus
  8. Three factors act to bind epithelial cells to one another:
    • (1) Adhesion proteins in the PM of the adjacent cells link together in the narrow extracellular space
    • (2) the wavy contours of the membranes of adjacent cells join in a tongue-and-groove fashion
    • (3) there are special cell junctions
  9. Tight Junction or zonula occludens ("small zone that shuts off")
    • in the apical region of most epithelial tissue, a beltlike junction extends around the periphery of each cell
    • the adjacent cells are so close that some proteins in their PM are fused
    • this fusion forms a seal that closes off the extracellular space; thus preventing molecules from passing between the cells of epithelial tissue
  10. Adhesive Belt Junction (zonula adherens)
    • located just below the tight junctions in epithelial tissues
    • a type of anchoring junction 
    • this junction reinforces the tight junctions, particularly when the tissues are stretched
  11. Gap Junction or nexus
    • is a tunnel-like junction that can occur anywhere along the lateral membranes of adjacent cells
    • connected by hollow cylinders of protein=connexons
    • function in intercellular communication by allowing small molecules to move directly between neighboring cells
  12. Basal Lamina
    • at the border between the epithelium and the connective tissue 
    • functionally, acts as a selective filter; it determines which molecules from capillaries in the underlying connective tissue are allowed to enter the epithelium
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Ch. 4 Tissues
2014-09-23 18:45:56
Human Anatomy
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