Human Anatomy Histology I - Epithelial Tissue PDF

HUMAN ANATOMY HISTOLOGY I – TISSUE (EPITHELIAL) I. CHARACTERISTICS & CLASSIFICATION OF EPITHELIAL TISSUE II. FREE SURFACE MODIFCATIONS III. SECRETORY ADAPTATIONS I. CHARACTERISTICS & CLASSIFICATION OF EPITHELIAL TISSUE * Cells = cannot function independently Tissues = aggregati...

HUMAN ANATOMY HISTOLOGY I – TISSUE (EPITHELIAL) I. CHARACTERISTICS & CLASSIFICATION OF EPITHELIAL TISSUE II. FREE SURFACE MODIFCATIONS III. SECRETORY ADAPTATIONS I. CHARACTERISTICS & CLASSIFICATION OF EPITHELIAL TISSUE * Cells = cannot function independently Tissues = aggregation of cells with similar functions/structures Organs = form from different arrangements of tissues * Tissue (to weave) = a functional aggregation of cells and their inter-cellular material that performs related functions Tissues perform most vital body functions * Important features of tissues Communication Cells within tissue communicate with each other Thru intercellular junctions - cells pass electrical signals & small molecules Result = many cells are coordinated together Structural integrity Extracellular matrix = complex network of cells & fibers that hold tissue cells together Great variation in extracellular matrix & junctions among tissue types Ex. Epithelial tissue = many rows of cells & little extracell matrix Cells bear most of stress- via strong intra-cellular filaments * There are types of tissue Epithelium = covering Connective = supporting Muscle = movement Nervous = control * Epithelial tissue (epithelium) Specialized component of many organs Derived from all germ layers Primary characteristics Continuous sheets of cells… that…  Cover a body surface (or) Lines a body cavity (or) Forms a gland Endothelium = term given to flattened cells lining cardiovascular & lymph passageways Mesothelium = term given to the tall columnar cells lining peritoneal & pleural & pericardial cavities Parynchyma = secretory cells of glands Other characteristics Cellularity = composition is mostly cells Polarity = all epithelial cells have specialized regions Upper free apical surface Lower attached basal surface Basal lamina = thin acellular layer below basal surface Part of basement membrane Connective tissue support = all epithelial sheets are supported by CT Avascular = lacks blood vessels Nutrients diffuse from capillaries in underlying CT into epithelia Innervated = nerve endings present * Functions of epithelial cells Absorption = food across digestive tract walls Transport = ions Digestion = enzymes secreted by glandular epithelium Secretion = excretion Barrier = protection from external mechanical trauma, loss of moisture & noxious substances Sensory reception = smell, taste, vision & hearing Filtration = fluids Reproduction = epithelial cells form gametes (sex cells) * Potential problems within Epithelial Tissue Acne Dermatitis Obesity Psoriasis Scabies Shingles (Herpes zoster) Melanoma (skin cancer)  Skin cancers * Nutrients important to maintain healthy epithelia Vitamins = bind up free radical molecules that damage cell organelles/membranes Vitamin C Vitamin E Vitamin A Minerals Zinc = antibacterial action Water Fiber = absorbs toxins in gut that eventually are eliminated through epithelial tissue * General classification Based upon early LM studies, epithelia cells were classified using… Shape only- NO function involved Arrangement of cells into 1 or more layers Main groups 1. Simple Squamous Single sheet of flat cells joined together Nuclei are disk shaped Specialized names in certain areas Endothelium = lines heart, blood & lymph vessels Mesothelium = lines peritoneal, pleural & pericardial cavities 2. Simple cuboidal Single sheet of polygonal cells- cell height, width & depth are the same (cube) Nuclei = spherical & centrally placed Location Duct walls in exocrine glands Parynchyma of most glands Lining most kidney tubules Function = produce hormones & enzymes 3. Simple columnar Single sheet of rectangular cells- height at least 2x width Nuclei are oval & basal Location Lines = GI tract, gallbladder, uterus, oviducts, large ducts of glands & small bronchioles  Function Secretion = enzymes & mucus Absorption = nutrients & fluids 4. Stratified squamous Multiple layers of cells of different shape Upper layer cells = flat (MOST cells are flat) Lower level cells = polygonal THICKEST epithelia = best for protection Forms epidermis Layers Stratum corneum (surface) Stratum lucidum Stratum granulosum Stratum spinosum Stratum basale (deepest) Covers abraded body surfaces = skin, mouth, esophagus & vagina 5. Stratified cuboidal / columnar Rare = forms large ducts in some glands 6. Pseudostratified columnar Single layer of rectangular cells that appears to be several layers- since nuclei lie at various levels Tightly packed- all cells sit on a common basal lamina Short cells are undifferentiated- and give rise to taller cells Location Lines certain areas within intestines Lines respiratory tract (these have cilia) = pseudostratified ciliated columnar epithelium (PSSCE) Goblet cells (secrete mucus) = often associated with PSC 7. Transitional Multiple layers of cells having different shape Distinctive feature = dome-shaped & bi-nucleate cells Cells change shape As organs stretch = 5-6 layers thin to 2-3 cell layers  round cells flatten –or- "transition" in shape Location Lining = ureters & bladder Function = provides an impermeable barrier II. FREE SURFACE MODIFCATIONS * MOST modifications are on plasma membrane Modifications are on ALL cell surfaces: free & basal & lateral Intra-cellular specializations of cytoskeleton are present in some * Microvilli Extensions of free (apical) surface Most / longest in absorptive cells (kidney & small intestine) Radically increase surface area (~30x) Stereocilia = NOT cilia - but unusually long microvilli NON-mobile Ex. Epididymis & cochlear hair cells * Cilia Specialized extension of cell microtubule network (cytoskeleton) Internal structure resembles a centriole Core = axoneme = 9 + 2 complex microtubule doublets in circle surrounding doublet in center Origin = basal bodies Structures identical to centrioles in apical cytoplasm = 9 + 0 complex Found in respiratory tract & fallopian tube Move in COORDINATED waves- to ensure fluid moves in direction only Sliding microtubule hypothesis Microtubules have small arms made of dynein (a protein) ATP used to activate dynein to ratchet up/down adjacent tubule Flagellum = long isolated cilia (on sperm cells only) Functions Moving fluid over surface Cell motility * Membrane plaques RIGID apical areas ONLY in cells lining urinary tract When bladder is empty- they fold down into cell to increase luminal surface area Bladder full- they unfold & increase surface area * Surface molecules Glycocalyx = proteins (eg., enzymes) & glycoprotein (or) sugar residues on surface (appear fuzzy in EM) Function = cell recognition, adherence, immune system activity & enzyme activity * Keratinization Stratified squamous epithelial cells fill with protein (keratin) as they migrate toward surface Result = tough & waterproof layer Process Cells differentiate & move upward Cytokeratin proteins within cells change to higher molecular weight forms Lamellar bodies form Made of extracellular membrane bound granules - that form sheets between cells in upper epithelium As cells move apically & genes begin to code for specialized proteins that interact with keratin filaments in cytoplasm  forms keratin Cells near apical surface fill with keratin & die Top layers are shed III. SECRETORY ADAPTATIONS * Epithelial cells are VERY active Many are specialized to form glands Result = many have structural specializations related to production/secretion of enzymes & mucins & steroids Result = many specializations for the secretion/transport of ions * Protein secreting epithelial cells MANY rER at base of cells MANY granules at apical pole * Mucin secreting epithelial cells Mucins = glycoproteins + proteoglycans MANY basal rER Function Lubricant = in mouth Barrier = in stomach * Steroid hormone secreting epithelial cells Many sER Location Mainly in adrenal glands & gonads (ovary & testes) * Ion pumping epithelial cells Plasma membrane folded to increase surface area (more ion pumps) Many mitochondria Tight junctions between cells- prevent back diffusion  Location Kidney tubules & ducts of other glands & epithelium of stomach (H&) * Epithelial glands have 4 mechanisms of secretion Aggregates of secretory cells- are called GLANDS Products are aqueous (watery) & contain protein Types of gland 1. Endocrine glands = endocytosis from cell base into blood NO ducts Product = hormones ("exciters") 2. Exocrine glands Excretions pass from cells thru ducts to body surfaces (or) into cavities Vesicle holding a product pinches off apical cytoplasm Functions Thermoregulation Waste secretion Lubricate epidermis Types 1. Sebaceous glands Associated with hair follicles Product = oily lipid (sebum) Functions = antibacterial action & lubrication (hair) Type of secretion Holocrine = whole cell is discharged into duct  breaks apart 2. Sweat glands Product = watery (aqueous) solution Function = flush epidermal surface Type of secretion Merocrine = vesicle pinches off from apical cell surface Widespread over body Controlled by nervous system Function Thermoregulation & excretion Apocrine = vesicle + part of cell is pinched off apical surface Location = axillae & groin & nipples Odorous thick secretion Influenced by hormones Becomes active at puberty Special types  Ceruminous glands = form ear wax Mammary glands = produce milk Goblet cell = the ONLY unicellular exocrine gland Product = mucin = a glycoprotein dissolving int water that forms mucus Location = scattered thru lining of intestine & respiratory tract Function = lubricates & protects surface lining Clinical considerations * Hyperkeratosis = keratin layer thick (otherwise normal) * Parakeratosis = thick keratin & nuclear remnants (no granular layer) * Acanthosis = abnormal epidermal thickening (stratum spinosum) * Naevi = moles = most common skin lesion = aggregates of pigmented cells Malignant melanoma (highly malignant tumor of epidermal melanocytes) * Dermatitis = common term used to describe a variety of inflammatory conditions with many causes Many cases = histologic changes  clue or precise diagnosis of cause Ex. Lichen planus = hyperkeratosis & thickening of granular layer & destruction of basal cells. Dermis shows chronic inflammatory inflitrate Affects mouth & vulva  blistering & erosion Ex. Psoriasis = erythematous scaly lesions. Histo  acanthosis with elongated rete pegs. Dilated cappilaries & alternating thick/thin epidermis * Basal cell carcinoma = most frequent From basal cells of epidermis  invades dermis  ~ never metastasises On light exposed areas of skin (face)  ulceration * Squamous carcinoma = malignant neoplasm from squamous epithelium Highly keratinizing & numerous keratin pearls. May invade dermis & lymphatics * Adenocarcinoma = carcinoma from glandular epithelium