Epithelial Tissue 2023-1.ppsx

Epithelial Tissue Chapter 5 OBJECTIVES:        List & describe the functions of epithelial tissues Describe the structure & function of the basement membrane Describe the general characteristics of epithelia List & describe features used to classify epithelia List & describe the types o...

Epithelial Tissue Chapter 5 OBJECTIVES:        List & describe the functions of epithelial tissues Describe the structure & function of the basement membrane Describe the general characteristics of epithelia List & describe features used to classify epithelia List & describe the types of epithelia, the functions of each type & give examples of where each is found in the body List & describe the features used to classify glands Understand the difference between endocrine & exocrine glands Functions of Epithelia       Covers, lines & protects other tissues Filters biochemical substances Absorbs nutrients Provides sensory output Secretion Excretion General Characteristics  Polar – have apical & basal surfaces  Lateral surfaces are connected to adjacent cells by junctional complexes  Avascular – lack blood vessels  Most are innervated & provide sensory input Classification  Number of layers of cells    Shape of cells    Simple Stratified Squamous, cuboidal, columnar Classed based on shape on exposed surface Presence of surface specializations    Microvilli Cilia Keratin Types of Epithelia Simple Squamous  Lines surfaces involving passage of gas or liquid (pulmonary alveoli, renal glomeruli)  Lines surface of body cavities   mesothelium Lines vessels (reduce friction)  Endothelium Allows diffusion, filtration, secretion & absorption Types of Epithelia Simple Cuboidal  Lines exocrine gland & biliary ducts  Lines bronchioles (ciliated)  Line renal tubular cells (some w/ microvilli)  Lines follicles in thyroid gland Functions in absorption & secretion and in transporting secretions/particles Types of Epithelia Simple Columnar  Lines stomach, gallbladder (secretion) & intestines (secretion (goblet cells) & absorption)  Lines excretory ducts of some glands  Lines (ciliated) uterine tubes & small bronchi = simple ciliated columnar epithelia Functions in absorption & secretion and in transporting Types of Epithelia Stratified Squamous  Skin (keratinized)  Lines mucous membranes (nonkeratinized) – oral cavity, esophagus, vagina, prepuce Cuboidal cells make up basal cells -> divide and push towards the surface -> flatten and lose cytoplasm, nucleus & organelles -> slough off Protective function; in areas prone Types of Epithelia Stratified Cuboidal  Usually only 2 cell layers, both cuboidal  Lines large excretory ducts (salivary, sweat & mammary glands) Functions in secretion, absorption & protection of Types of Epithelia Stratified Columnar  Rare – lines large ducts of mammary gland, select parts of respiratory & digestive tracts & small portion of urethra of some male animals  Basal layer is cuboidal Functions in secretion & protection Types of Epithelia Pseudostratified Columnar  Not truly stratified but appears so because nuclei are at different levels & not all cells reach the luminal surface  Forms a single layer so is a simple epithelium  Usually ciliated; lines nasal cavity, larynx, pharynx, trachea & bronchi & parts of male repro. tract Has surface layer of mucus that functions to trap particles that cilia Types of Epithelia Transitional Epithelium  Stratified w/ cuboidal or columnar basal layer; superficial layer is cuboidal or squamous depending on degree of distension/contraction  Lines portions of urinary tract where changes in volume occur (renal calyxes, ureters, bladder, urethra)  Prevents diffusion of urine into abdominal cavity Basement Membrane  = basal lamina  Meshwork of fibers connecting the epithelial cells to the underlying connective tissue  Oxygen & nutrients supplied to and waste excreted from epithelium by diffusion through basal lamina from/to capillaries in underlying connective tissue Glands Classification  Exocrine or endocrine (ducts)  Unicellular or multicellular  Simple or compound ducts  Structure -> tubular, acinar or tubuloacinar  Type of secretion -> mucous, serous, mixed  Method of secretion storage & release > merocrine, apocrine, holocrine Glands Endocrine  No ducts or tubules  Secrete regulatory chemicals (hormones) into circulation -> distributed throughout the body Exocrine  Have ducts (except for unicellular goblet cell)  Secrete via ducts locally, not into Exocrine Glands Unicellullar  Goblet cell  = modified columnar epithelial cell  Among columnar cells of resp. & GI tracts & in conjunctiva of eye  Secretes mucin (glycoproteins & proteoglycans) that becomes mucus when mixed w/ water  Protects cell surfaces; traps microbes & particles Exocrine Glands Multicellular  Secretory unit & duct  +/- myoepithelial cells (aid in discharge of secretion into duct)  Most exocrine glands Simple  Main duct unbranched Compound  Main duct branched Exocrine Glands Structure of Secretory Unit  Tubular – long channel of even width  Alveolar (acinar) – rounded sac  Tubuloalveolar/tubuloacinar – combo (See Table 5.1, pg 121) Type of Secretion  Serous – watery w/ high conc. of enzymes  Mucous – thick & viscous and composed of glycoproteins  Mixed – both serous & mucous Exocrine Glands Method of Storage & Release  Merocrine    Apocrine   Secretion packaged in granular units & released via exocytosis Cells remain intact Granules stored until apex of cell is full -> cell pinches in two & releases apex into the duct Holocrine  Granules stored until needed & entire cell degenerates to release them