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Chapter 5

Chapter 5. Epithelial Tissue. Introduction. A tissue is composed of similar cells that are specialized to perform a common function(s) Four adult primary types of tissues form the "fabric" of the human organism: epithelial tissues (ET)= covering/lining connective tissues (CT)= support

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Chapter 5

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  1. Chapter 5 Epithelial Tissue

  2. Introduction • A tissue is composed of similar cells that are specialized to perform a common function(s) • Four adult primary types of tissues form the "fabric" of the human organism: • epithelial tissues (ET)= covering/lining • connective tissues (CT)= support • muscle tissues (MT)= movement • nervous tissues (NT)= control

  3. Extracellular Fluid (ECF) • Surrounding all body cells is Extracellular Fluid (ECF) • Functions are many: • medium to dissolve solutes • transport • site of chemical reactions • Four types of ECF: • interstitial fluid which fills the spaces between cells in tissues • plasma which is the liquid portion of blood • Lymph which is in lymphatic vessels • Transcellular fluid which includes cerebrospinal fluid, synovial fluid, humors of the eye, serous fluid and exocrine secretions

  4. Epithelial Tissues

  5. General Structural Characteristics • Cellularity: ETs are composed of tightly packed sheet(s) of cells with little intercellular material between them • Polarity: • ETs exhibit polarity and always have a free surface ("apical surface") which opens to the outside or to an internal space (lumen) • This free surface may possess modifications • microvilli (increases membrane surface) • cilia (aid in movement of a substance across the layer)

  6. General Structural Characteristics • Basement Membrane: • The "basal surface" of ETs are anchored to underlying CT by a distinct basement membrane • Specialized contacts that ETs may possess include: • tight junctions (zipper-like junctions that prevent intercellular leakage) • desmosomes (hold adjacent cells, and therefore the layer of cells, together)

  7. General Structural Characteristics • Avascularity: • ETs contain no blood vessels. • ET is nourished by nutrients which diffuse upward from underlying connective tissue through the basement membrane • Regeneration: high regeneration capacity, due to rapid cell division

  8. Polarity of Epithelial Cells

  9. Stratified Cuboidal epithelium • 2-3 layers of cuboidal cells • Functions=protection • Locations: • mammary glands • sweat glands • salivary glands • pancreas

  10. Stratified columnar epithelium • Top layer of elongated cells • deeper layers of cube shaped cells • Functions: • protection • secretion • Locations • part of male urethra • part pf pharynx

  11. Glandular epithelium • usually simple cuboidal or columnar ET • Function = secretion • two major types: • Exocrine glands secrete products into a duct, which opens onto: • an external surface (i.e. sweat gland) or • an internal space/lumen (i.e.. gastric gland) • Endocrine glands secrete hormones into the blood. These glands are ductless and will not be discussed until chapter 13.

  12. Exocrine glands • Exocrine glands structure varies tremendously • Single cells (unicellular) – goblet cells • Many cells (multicellular) • Simple – unbranched • Compound – branched • Tubular – tube-like • Alveolar – sac-like • Exocrine glandular secretions are classified according to whether they consist of cellular products or portions of glandular cells:

  13. Types of Exocrine Secretions • Merocrine: secrete fluid through cell membranes into a duct with no loss of glandular cells • Fluid product • Example = salivary glands, salivary glands, pancreas • Apocrine: lose small portion of cells with secretion • Cellular product • Example = mammary glands, ceruminous glands

  14. Types of Exocrine Secretions cont. • Holocaine: release entire cells into secretion • Secretory products • Example = sebaceous glands in skin (oil) Extra: • Carcinoma = a tumor (cancer) originating from epithelial tissue

  15. Connective Tissue

  16. General Characteristics • Wide Range of Vascularity: from cartilage, which is avascular, to bone, which has a rich blood supply • Structural Elements: cells plus extracellular matrix (ground substance plus fibers) • Ground Substance: • amorphous material that fills the space between cells and fibers • functions as a molecular "sieve" through which nutrients and gases can diffuse between cells and blood capillaries

  17. Major Cell Types • fixed cell in each CT type: maintains constant numbers • blast cells = undifferentiated cells that secrete matrix • fibroblast in CT proper • makes fibers • chondroblast in cartilage • osteoblast in bone • Once the matrix has been formed, these "blast" cells assume their less active role as "-cytes" (but they can be reactivated if needed) • i.e osteocyte, chondrocyte

  18. Major Cell Types • wandering cells= are not always there • 2 types: • macrophages or phagocytes • Eat foreign material • mast cells: Secrete heparin to prevent excessive blood clotting • Secrete histamine to promote inflammation

  19. Connective Tissue Fibers • 3 types: • Collagen fibers are composed of the protein collagen • provide high tensile strength to matrix • stain pink • Elastic fibers are composed of the protein elastin • provide rubbery resiliency to matrix • stain purple • found in skin, lungs, and blood vessels • Reticular fibers are fine collagenous fibers • form delicate networks • found in basement membranes • stain purple

  20. Epithelial Membranes

  21. Introduction • An epithelial membrane is a continuous multicellular sheet composed of at least two primary types of tissue: • an epithelium bound to a discrete underlying CT tissue

  22. Cutaneous and Mucous Membranes • Three Common Types: • Cutaneous Membrane: • skin • consists of keratinized stratified squamous ET firmly attached to a thick layer of dense irregular CT • Mucous Membranes (mucosae): • line body cavities that open to the outside • include lining of digestive, respiratory and urinary tract • are "wet" or moist membranes (through secretions of mucus) • consist of a layer of epithelium (varies depending upon location) firmly attached to a layer of loose areolar CT

  23. Serous Membranes • Serous Membranes (serosae): • are found in closed ventral body cavities • consist of two layers with a potential space (cavity) between them • visceral membrane surrounds an organ • parietal membrane lines a body cavity • secrete a thin watery fluid called serous fluid into the cavity between the membranes • function = lubrication

  24. Serous Membranes cont. • each membrane consists of a thin layer of simple squamous ET resting on a thin layer of areolar (loose) CT • are named for the organs that occupy each cavity: • pleural = lungs • pericardial = heart • peritoneal = abdominal organs

  25. Synovial Membrane • composed entirely of connective tissue • lines joints

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