Epithelial Tissue Lecture Slides - Gulf Medical University PDF

Epithelial Tissue Dr.Sapna Shevade Assistant Professor of Anatomy February 13, 2025 www.gmu.ac.ae COLLEGE OF ALLIED HEALTH Learning objectives Describe the general characteristics of epithelial tissue...

Epithelial Tissue Dr.Sapna Shevade Assistant Professor of Anatomy February 13, 2025 www.gmu.ac.ae COLLEGE OF ALLIED HEALTH Learning objectives Describe the general characteristics of epithelial tissues; Differentiate between various types of epithelial tissues in terms of structure, location, and functions. Define the term gland; Describe the unicellular and multicellular glands; Differentiate between the exocrine and endocrine glands and Classify the glands on the basis of structure, mode of secretion and their secretions. Tissues – Introduction A group of similar cells specialized to carry on a particular function. Tissue = cells + extracellular matrix 4 types Epithelial = protection, secretion, absorption Connective = support soft body parts and bind structures together Muscle = movement Nervous = conducts impulses used to help control and coordinate body activities Epithelial Tissues – two types Epithelia: Layers of cells covering internal or external surfaces Glands: Structures that produce secretions I. DEFINITION: - A sheet of cells which covers external surface or lines interior of the organs/ body cavities. Characteristics of epithelial cells: 1. Apical surface is free &exposed to air, fluid. 2. Basal surface of the cells rest on an basement membrane which separate the cells from vascular connective tissue. 3. The lateral surface of the cell membrane which is touch with neighbor cells Epithelial Classifications Classified based on shape and cell layers Shape squamous = thin, flat cells cuboidal = cube-shaped cells columnar = tall, elongated cells Number Simple = single layer Stratified = 2 or more layers Specializations Microvilli increase absorption or secretion Cilia (ciliated epithelium) move fluids Classes of Epithelia Based on shape and layers Simple epithelium 1. Simple squamous epithelium 2. Simple cuboidal epithelium 3. Simple columnar epithelium Simple squamous Capillary endothelium epithelium Squama = scale like Cells are flat and thin Flattened nuclei Helps in diffusion of gases and nutrients E.g., endothelium, mesothelium, epithelium of the alveoli Alveoli Simple cuboidal epithelium Height and breadth of the cell is equal Nucleus is rounded Thyroid follicles E.g., covering of ovary, lining of ducts, lining of thyroid follicle Ovary Renal ducts Simple columnar epithelium Height of the cell more than its width Elongated oval nuclei Types Secretory simple Secretory goblet Absorptive with microvilli Ciliated Pseudostratified ciliated columnar epithelium Single layer of cells appears to be 2 layered. Cells are at different layers, only few reach the lumen. Nuclei are also at different levels and hence looks stratified. E.g., respiratory tract B. Stratified Epithelium 1. Stratified squamous epithelium keratinized & non keratinized. 2. Transitional epithelium 1. Stratified squamous epithelium – Multiple layers. – Basal cells are active & columnar in shape – The intermediate layers have polygonal cells. – Surface cells are flattened squamous.  – Found in places where there is wear and tear. Function: – Protection & prevents water loss.  Non keratinized e.g. oral cavity, upper esophagus, conjunctiva, vagina. If keratinized, surface cells lose their nuclei ,cytoplasm replaced by keratin e.g. Skin 2. Transitional epithelium: – Consists of many cell layers. – Basal cells are low columnar – Several intermediate layers of polygonal cells – Surface layer of large rounded cells like umbrella. Site: Urinary tract (urothelium). Function: – Protection, capability of distention. – No secretion and No absorption. Empty bladder Distended(full) bladder 3. Stratified Cuboidal Epithelium Sweat gland ducts 4. Stratified Columnar Epithelium Rare Salivary gland duct Figure 4–4b CLASSIFICATION OF THE GLANDS BASED ON THE type a. Unicellular glands: Single secretory cell E.g. goblet cells (flask shaped) that are scattered all over the mucous membranes b. Multicellular glands. Sheet of epithelial cells The secretion is discharged either directly or through duct system. CLASSIFICATION OF MULTICELLULAR GLANDS: With ducts: exocrine glands Without ducts: endocrine glands Exocrine: pour their secretions onto an epithelial surface, directly or through ducts. Endocrine (ductless): pour their secretions directly into the blood. Classification of exocrine glands Based on shape of secretory unit & branching pattern of duct Based on mechanism of release of their product Based on the nature of their secretion  Classification of the exocrine glands based on the duct system a. Simple exocrine glands = unbranched duct. b. Compound exocrine glands = repeatedly branching duct. N.B: In the simple branched tubular gland, branched here means multiple secretory units not branched duct. Classification of the exocrine glands based on shape of the secretory unit Secretory cells may the the shape of: a. Tubular: which may be straight, coiled or branched. b. Acinar (rounded structure with narrow lumen) c. Alveolar (rounded structure with wider lumen) d. Tubulo – acinar/ tubulo- alveolar Structural classification of multicellular exocrine glands  Mechanisms of gland secretion Apocrine Holocrine Merocrine The apical parts of the Release their Secrete their epithelial cells are lost products & the products by during the process of secretion. whole cell rupture. exocytosis livary. glands, sweat glands Mammary glands Sebaceous Glands  Classification based on the nature of secretion A. Serous glands B. Mucous glands C. Mixed glands A. Serous glands Secretion: thin, watery, rich in enzymes, protein in nature. Cells stain darkly with H/E stain Nuclei: rounded & more to the basal side. Cells are Pyramidal in shape. B. Mucous glands Secretion: contains muco- polysaccharides which collects in the apical part of cell. Stain very lightly with H/E stain & therefore gives empty look. Nuclei: basally placed & flattened Cells are short columnar , pyramidal in shape C. Mixed glands Contain both serous & mucous secretory units. Sometimes serous cells form crescentic caps on mucous acini called as serous demilunes.