Epithelial Tissues: VetPrep Summary PDF

EPITHELIUM Dr Matthew Valentine BVMS MRCVS PhD Dipl ACVP Lecture overview 1. Definitions, functions, relevance 2. Characteristics of epithelium (sg.) 3. Types and classification of epithelia (pl.) 1. Definitions Cells > Tissues > Organs > Systems Tissues = an aggregation of cells and extracellular s...

EPITHELIUM Dr Matthew Valentine BVMS MRCVS PhD Dipl ACVP Lecture overview 1. Definitions, functions, relevance 2. Characteristics of epithelium (sg.) 3. Types and classification of epithelia (pl.) 1. Definitions Cells > Tissues > Organs > Systems Tissues = an aggregation of cells and extracellular substances with a common purpose The organs of the body are made up of only four basic types of tissue: o Epithelial tissue o Connective tissue o Muscular tissue o Nervous tissue Three Types of Epithelium 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). 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 and all glands have an epithelial component. – Tumors / neoplasia : terminology. Characteristics of Epithelium Supported by connective tissue (CT) Avascular Basement membrane (BM) present Epithelial cells are cohesive Epithelial cells are polarised Lining epithelium Basement membrane Capillary blood vessel Capillary blood vessel Connective Tissue Glandular epithelium Epithelial Cells are Polarized Apical surface Lateral surface Basal surface Epithelial cells have Apical (free) surface Lateral surfaces Basal surface Basement membrane 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 Lining epithelia Simple Columnar Epithelium Tall, narrow cells with ovoid nucleus located near the base of the cell. Example of simple columnar epithelium: – Lining the luminal surface of stomach, small and large intestine, gall bladder From: Wheater’s Functional Histology, 2008 Example: Simple Columnar Epithelium Lining the Gall Bladder From: Wheater’s Functional Histology, 2008 NOTE: H&E = Hematoxylin & Eosin stain – the most common type of histological staining 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. Can be ciliated (motile) Examples of pseudostratified epithelium include: – Nasal cavity, upper respiratory tract From: Wheater’s Functional Histology, 2008 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 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 Stratified Squamous Epithelium, Keratinized 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 are modified epithelia TUBULAR: straight or coiled (sweat gland, stomach glands, intestinal glands) ACINAR: pie-shaped, small lumen (pancreas, salivary glands) ALVEOLAR: larger luminal space (mammary gland, prostate, sebaceous glands) 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 Acini with small central lumen (arrows) Lung alveoli 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 Classification According to Product Serous: watery product, contains enzymes. E.g.: sweat 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 Cerumen is the secretion of modified sweat glands in the skin of the external auditory canal