Histology Week 1 Epithelium PDF

EPITHELIUM Dr Diana Bochynska DVM dipECVP (previous instructors Matthew Valentine Dr. I. Irimescu, C. Fuentealba, M. Smith, M Zibrin, L Bogdanovic) Lecture overview 1. Definitions, origin, functions, relevance 2. Characteristics of epithelium (sg.) 3. Classification of epithelia (pl.) A. Surface/ Li...

EPITHELIUM Dr Diana Bochynska DVM dipECVP (previous instructors Matthew Valentine Dr. I. Irimescu, C. Fuentealba, M. Smith, M Zibrin, L Bogdanovic) Lecture overview 1. Definitions, origin, functions, relevance 2. Characteristics of epithelium (sg.) 3. Classification of epithelia (pl.) A. Surface/ Lining epithelia B. Glandular epithelia 1. Definitions Tissue = an aggregation of cells and extracellular substances The organs and systems of the body are made up of different proportions of only four basic types of tissue: o Epithelial tissue o Connective tissue o Muscular tissue o Nervous tissue Epithelium Is a tissue composed of closely aggregated cells with very little extracellular substance. 3 main types: Lining (surface) epithelia form sheets that cover body surfaces or line luminal organs, tubular structures, and body cavities. Glandular epithelia have specialized cells that synthesize, store and release various products. Special epithelia contain sensory nerve endings; found in the skin, ears, and on the tongue; (in nose and eyes there are modified NEURONS). Origin/ Histogenesis of Epithelia Three main germ layers ECTODERM  epidermis of skin MESODERM  mesothelium (lining of body cavities), endothelium (lining vessels and heart chambers) ENDODERM  epithelial lining and glands of most of the gastrointestinal (GI) tract, including liver and pancreas, of the respiratory system; of the urinary bladder Functions of Epithelial Tissues Protection (the epidermis protects from mechanical abrasion/injury, harmful chemicals, invading microbes, and from excessive loss of water.) Friction reduction (smooth endothelial cells line the entire circulatory system to reduce friction between blood and walls of the blood vessels and of heart chambers) Cleaning (ciliated respiratory epithelium assists in removing dust particles/foreign bodies from air passages) Diffusion (endothelium of capillaries promotes the diffusion of gases, liquids and nutrients) Absorption (certain epithelial cells lining the small intestine absorb nutrients from digested food) Secretion (specialized epithelial tissue secretes chemical substances such as enzymes, hormones and lubricating fluids) Sensation: specialized epithelial tissue containing sensory nerve endings convey sensations from the skin, ears, and the tongue Relevance Basic understanding of tissue organization, development and functioning. Essential to understand: – Systemic histology: many organs have an epithelial component. – Glandular diseases – Skin diseases – Tumors/ neoplasia, particularly: terminology and tumor progression. 2. Characteristics of Epithelium Is a tissue with high cellular density and very little intercellular substance Is closely associated to supporting connective tissue (CT) Lining epithelium is avascular, with few nerve endings Basement membrane (BM) present Epithelial cells are polarized Epithelial cells are cohesive Low vs High Cellular Density Connective tissue Lots of intercelllular matrix Few cells 1000x H&E stain 1000x Hepatic tissue (glandular epithelium) Little intercellular matrix High cellular density Interface with Connective Tissue (CT) Lining epithelium-> Glandular epithelium-> Epithelial and connective tissue are interfaced by an extracellular basement membrane (a selective barrier). Small blood capillaries never enter an epithelium across it. Usually not visible under light microscopy; Stains prominently with PAS (Periodic acid Schiff) for carbohydrates Note: In some textbooks when only a part of this membrane is present between two epithelial layers; this dense sublayer is referred to as a basal lamina. Epithelial Cells are Polarized Apical surface Lateral surface Basal surface Epithelial cells have Apical (free) surface Lateral surfaces Basal surface Basement membrane Epithelial Cells are Cohesive Epithelial tissues subject to pressure and traction have marked intercellular adhesion. (e.g.: in epidermis, urinary bladder, etc.) Cohesiveness is due to cell junctions transmembrane glycoproteins (E-cadherins) Basal and lateral There are 3 Types of Intercellular Junctions: Tight junctions Desmosomes Gap Junctions Infolding plasma membrane Gap Junctions Also called communicating junctions Provide cytoplasmic channels or tunnels from one cell to an adjacent cell. Consist of special membrane proteins that surround a pore, through which ions, sugars, amino acids, and other small molecules may pass. Are necessary for communication (chemical and electrical signals) between cells in many types of tissues. Example: heart muscle and nervous tissue. http://www.phschool.com/science/biology_place/bioco ach/biomembrane2/gap.html 3. Classification of Epithelia Simple (one layer of cells) A. Lining squamous cuboidal columnar Pseudostratified columnar ciliated non-keratinized keratinized squamous Stratified cuboidal - rare columnar - rare transitional - special type B. Glandular Exocrine Both can be unicellular and Endocrine multicellular C. Specific: pigment, seminiferous, sensory e.g. olfactory A. Lining Epithelia Simple Squamous Epithelium Composed of flat, elongated cells, with a round to oval nucleus, often centrally located. Common locations: – lining of body cavities, generally called mesothelium (pleural, pericardial and peritoneal); – alveolar walls in lungs; – Inner lining of blood vessels and lymphatic vessels; called endothelium. From: Wheater’s Functional Histology, 2008 Note location and shape of nucleus Example: Vascular Endothelium E = endothelial cell nuclei From: Wheater’s Functional Histology, 2008 NOTE: H&E = Hematoxylin & Eosin stain – the most common type of histological staining Simple Cuboidal Epithelium Cuboidal shape, all sides are approximately the same size, cell limits are often well‐defined. Examples of cuboidal epithelium: – Lining ducts of many glands – Choroid plexus in brain – Lining follicles of thyroid gland. – Lens of the eye From: Wheater’s Functional Histology, 2008 Example: Collecting Tubule in Kidney Notice euchromatic, round nuclei, and distinct cell limits Collecting tubule in kidney (transverse cut, LM) From: Wheater’s Functional Histology, 2008 Simple Columnar Epithelium Tall, narrow cells with ovoid nucleus located near the base of the cell. Examples of simple columnar epithelium: – Lining the luminal surface of stomach, small and large intestine, gall bladder – Lining the uterus and uterine tube From: Wheater’s Functional Histology, 2008 Example: Simple Columnar Epithelium Lining the Gall Bladder From: Wheater’s Functional Histology, 2008 Simple Columnar Ciliated (C) Epithelium: (a) diagram and (b) lining of oviduct stained with Azan stain From: Wheater’s Functional Histology, 2008 Pseudostratified Epithelium Composed of a single layer of irregularly shaped and sized cells. All cells touch the basement membrane, but not all of them reach the apical surface. Ciliated (usually motile) or stereociliated (non-motile) versions exist Examples of pseudostratified epithelium include: From: Wheater’s Functional Histology, 2008 – Nasal cavity, upper respiratory tract – Male reproductive: Epididymis and ductus deferens Example: Pseudostratified Ciliated Columnar Epithelium lining the Trachea Trachea, 400x HE Cilia Lumen Goblet cell BM When things go wrong with cilia: Chronical respiratory infection due to the absence of cleansing activity of cilia in upper air ways Male sterility resulting from non‐motile sperm cells Normal activity of cilia https://makeagif.com/i/iFbgDh Stratified Squamous Epithelium Epithelium composed of several layers of cells Superficial cells determine the name = the superfical cells have a squamous shape There are 2 types of squamous epithelium: – Keratinized (cornified) – Non‐keratinized From: Wheater’s Functional Histology, 2008 Esophageal Epithelium (Non-keratinized) Squamous cell 1000x Stratified Squamous Epithelium, Keratinized Cells on the surface lost their nuclei and are composed mainly of keratin (K), a protective, water‐resistant protein. From: Wheater’s Functional Histology, 2008 Stratified Squamous Epithelium, Keratinized Papilla (teat) of mammary gland, dead keratinized cells slough off (arrows). Dental pad in ruminants, red layer consists of many dead keratinized cells. Transitional Epithelium (Urothelium) Lines urinary passages. Example: urinary bladder The superficial cells have a specialized plasma membrane providing an osmotic barrier between urine and tissue fluids. From: Wheater’s Functional Histology, 2008 From: Ross Histology, 2008 Source: www2.highlands.edu Epithelial Repair Epithelial cells are constantly lost and replaced Stem cells are present which have high mitotic potential Location of stem cell varies depending on epithelial type and function E P I D E R M Cells are pushed by the new layers away from the BM and are shed off Stem cells are located in a basal cell layer (stratum basale) Stratified squamous keratinized epithelium Exfoliative cytology Harvesting cells shed from surface tissues, from mucous membranes, or found in body liquids and examining them under a microscope. Examples: Skin surface cytology (differential diagnosis of dermatitis) Urine sediment analysis (screening of lesions or neoplasia - e.g. transitional cell carcinoma) Vaginal smear analysis (bitches) – the type of epithelial cells observed indicates phase of the estrus cycle Fine needle biopsy of masses B. Glandular Epithelia Criteria of classifications: Number of cells in the gland (unicellular or multicellular) Shape of duct and shape of secretory units (adenomeres) Type of product Mode of secretion Unicellular Glands Found in epithelial lining and glands of intestine and in the epithelial lining of the respiratory tract. Example: Goblet cells have a “cup” – goblet shape due to presence of abundant mucinogen granules in the apical part of the cell Trachea, 400x HE Goblet cells Mucinogen granules stain blue with Alcian blue. LUMEN Simple columnar epithelium of the colon with goblet cells Multicellular Glands Secretion released Structure Examples EXOCRINE On body surface or internal cavity/tract Duct and adenomere Gastric glands Uterine glands Salivary glands Exocrine Pancreas ENDOCRINE Into blood stream Ductless Adrenal gland Parathyroid gland Pituitary gland Thyroid Endocrine Pancreas Secretory Units vs. Ducts of Exocrine Glands Cells of the exocrine secretory end‐piece are also known as an adenomere. This secretory unit manufactures the product, then specialized cells (myoepithelial cells) express it into a duct system. Ducts convey products to needed location (e.g. salivary gland to oral cavity). Ducts may be: – Simple ‐ one opening – Compound ‐ many branches of a duct system Ducts may be lined with a simple cuboidal, simple columnar, or stratified cuboidal/columnar epithelium. Types of Adenomeres TUBULAR: straight or coiled (sweat gland, stomach glands, colon glands) ACINAR: pie-shaped, small lumen (pancreas, salivary glands) ALVEOLAR: larger luminal space (mammary gland, prostate, sebaceous glands) General Classification According to the Shape of Duct & Adenomere Simple Tubular Gland(s) (a. Diagram and b. Small Intestine ‐ HE) From: Wheater’s Functional Histology, 2008 Tubular Adenomeres: pay attention to the way the tissue was cut Intestinal glands in large intestine Longitudinal cut Transverse cut Goblet cells Goblet cells HE staining Alcian blue (stains mucus) Simple Coiled Tubular Gland (a. Diagram and b. Sweat Gland ‐ HE) From: Wheater’s Functional Histology, 2008 Acinar shape Acinar shape corresponds to a rounded secretory unit vs Alveolar shape Alveolar shape corresponds to a bigger luminal space From: Wheater’s Functional Histology, 2008 From: Gartner’s Histology 2nd Ed Lung alveoli Other Cells of Epithelia Myoepithelial cells – contractile, associated with salivary, mammary, and sweat glands. Oval dense nucleus Round euchromatic nucleus Gartner’s Histology 2nd Ed Compound glands & Parenchyma The collective of secretory units and ducts of a compound gland is termed parenchyma; the connective tissue elements comprise the stroma. Large glands are divided into lobes. These are further subdivided by connective tissue into lobules. Lobules Stroma Salivary gland, 40X HE Ducts, lobules and lobes Adenomere (A) A * Intralobular duct (*) Lobule with multiple adenomeres drains into an intralobular duct (intercalated and striated) Interlobular duct (D) M Lobar duct (L) Main (excretory) L Lobe D D D duct (M) Lobe Interlobular ducts arise from between lobules and lead to a lobar duct Classification According to Product Serous: watery product, contains enzymes. E.g.: sweat Cerumen is the secretion of modified sweat glands in the skin of the external auditory canal Mucous: slick, viscous secretion. E.g.: tracheal mucus Mixed: a gland producing both mucus and serous secretion. E.g.: saliva Sebaceous: oily secretion, often known as sebum Serous Gland: Cells with round nuclei, the cytoplasm is basophilic in the basal portion and acidophilic in the apical part (zymogen granules) BM Serous cells (purple near the basal side, red towards the apical surface) Mucous Gland: Cells with flat heterochromatic nuclei at the base of each cell Cytoplasm is vacuolated (frothy) and pale Mucinogen granules are not detectable with routine stains Lumen Cytoplasm Basal nucleus Mixed Gland: Mucous and serous cells sharing a common duct system, mucous acinar units with associated crescent of serous cells, a “serous demilune”. Mucous cells with basal nucleus Lumen Serous cells with crescent (“demilune”) shape Mixed acinus Mixed Salivary Gland. 1000x Sebaceous gland Centrally located nuclei (arrow) Cytoplasm is pale and ‘foamy’ as lipid droplets are washed out during processing 1000x Classification according to the mode of secretion Merocrine: smooth lumen, no cytoplasm lost producing secretion Apocrine: apex bulges, some cytoplasm is lost producing secretion Holocrine: entire cell is the product Endocrine: secreted product is directed toward the blood vessels MEROCRINE method: Cell remains intact; contents of small secretory granules are released as the secretory product E.g.: merocrine sweat gland, salivary glands exocrine pancreas, Merocrine sweat gland httwww.gettyimages.com/detail/photo/light-micrograph-ofmerocrine-sweat-glands-high-res-stockphotography/128631740ps:// APOCRINE method: Cell bulges, a portion of cell is lost with the product. E.g.: predominant sweat gland of domestic mammals, prostate gland, mammary gland Apocrine sweat gland 400x CT HOLOCRINE method: Disintegrated cells with contents become the secretion. E.g.: sebaceous glands Sebaceous gland of hair follicle, 200x HE