Unit 3 Histology

    Cards (21)

    • Tissues
      collection of specialized cells and cell products that perform specific functions
    • Organs
      made up of two or more tissues
    • Histology
      study of structure of tissues
    • Four Types of Tissue
      1. Epithelial - covers exposed surfaces, lines internal passageways, produces glandular secretions
      2. Connective - fills internal spaces, provides structural support to other tissues, transports material, stores energy
      3. Muscle - contracts to produce movement, specializes for contraction
      4. Nervous - carries electrical signals from one part of the body to another
    • Epithelial Tissue Parts
      1. Epithelia (singular, epithelium) - layers of cells covering internal or external surfaces
      2. Glands - structures that produce fluid secretions
    • Functions of Epithelial Tissue
      1. Provide physical protection
      2. Control permeability
      3. Provide sensation
      4. Produce specialized secretions
    • Characteristics of Epithelia
      1. Polarity - differences between exposed (apical) surface and the attached (basal) surface
      2. Cellularity - epithelial cells are tightly bound by cell junctions
      3. Attachment - base of epithelium is bound to a noncellular basement membrane
      4. Avascularity - no blood vessels (avascular)
      5. Regeneration - continuously replaced by division of stem cells
    • Apical Surface
      1. Microvilli - increases surface area for absorption or secretion
      2. Cilia - move fluids
    • Basolateral Surface

      basal and lateral surfaces
    • Classification of Epithelia
      1. Based on Shape
      2. Squamous - thin and flat, irregularly shaped
      3. Cuboidal - boxy with central nucleus
      4. Columnar - tall and slender rectangles
      5. Transitional - transform from shape to shape
      6. Based on Number of Layers
      7. Simple Epithelium - single layer of cells
      8. Pseudostratified Epithelium - appears layered but is only one layer
      9. Stratified Epithelium - several layers of cells
    • Simple squamous epithelia
      • For absorption and diffusion
      • Found in: mesothelia lining pleura, pericardial cavities, peritoneal cavities, lining of lung alveoli
      • Mesothelium - lines body cavities
      • Endothelium - lining of heart and blood vessels
    • Stratified squamous epithelium
      • Protects against mechanical stress
      • Found in: surface of skin, lining of mouth, throat, esophagus, rectum, anus, vagina
      • Keratin adds strength and water resistance, we call this epithelium: keratinized
    • Simple cuboidal epithelium
      • For secretion and absorption
      • Forms glands and lines portions of the kidney tubules
      • Found in: glands, ducts, thyroid gland
    • Stratified cuboidal epithelium
      • Relatively rare
      • Forms ducts of sweat glands and mammary glands
      • Found in: lining of some ducts
    • Transitional epithelium
      • Cells appear cuboidal when not stretched and squamous when stretched
      • Tolerates repeated cycles of stretching without damage
      • Appearance changes as stretching occurs
      • Found in: lining of urinary bladder, renal pelvis, ureters
    • Simple columnar epithelium
      • For absorption and secretion
      • Found in: stomach, small intestine, large intestine
    • Pseudostratified columnar epithelium
      • Appears layered but is only one layer
      • Cells typically have cilia
      • Found in: lining of nasal cavity, trachea, bronchi
    • Stratified columnar epithelium
      • Relatively rare
      • Provides protection in pharynx, anus, urethra
    • Glandular epithelia
      1. Glands - collections of epithelial cells that produce secretions
      2. Endocrine glands - release hormones that enter the bloodstream, no ducts
      3. Exocrine glands - produce exocrine secretions onto epithelial surfaces, discharge secretions through ducts
    • Methods of Secretion
      1. Merocrine secretion - product released by secretory vesicles (exocytosis); ex: merocrine sweat glands
      2. Apocrine secretion - product released by shedding cytoplasm; ex: mammary glands
      3. Holocrine secretion - product released by cells bursting and dying; ex: sebaceous glands
    • Types of Secretions
      1. Serous glands - watery secretions containing enzymes
      2. Mucous glands - secrete mucins which then forms mucus
      3. Mixed exocrine glands - contain mixed population of serous and mucous gland cells
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