Histology Lecture 2 - Epithelial Tissues and Glands PDF

University of Alkafeel, College of Medicine, Year 2, Course 1 Histology - Lecture 2 Epithelial Tissues and glands By: Assistant Professor Dr. Rasha Dosh 1...

University of Alkafeel, College of Medicine, Year 2, Course 1 Histology - Lecture 2 Epithelial Tissues and glands By: Assistant Professor Dr. Rasha Dosh 1  Learning objectives Define epithelium and describe the structural and functional characteristics that Describe the classification of epithelial tissue. Identify & describe the structure, function, and localization of each type of epithelia. Identify & describe the structure, function, and localization of cilia, microvilli, and stereocilia. Identify & describe the structure, function, and localization of different cellular junctions (zonula occludens, zonula adherens, gap junctions, desmosomes, and hemidesmosomes). Compare and contrast exocrine vs. endocrine glands. List and describe the three modes of secretion in exocrine glands. Describe the classification of multicellular exocrine glands. Identify & describe serous glands, mucous glands, and mixed glands 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 2  Basic Human Tissues Four basic tissue types: ▻ Epithelium ▻ Connective tissue ▻ Muscle ▻ Nerve 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 3  Overview of Epithelium  Epithelial are derived from all 3 embryonic germ layers, have little amount of intracellular matrix.  Cells are closely apposed & adhere to each other Specialized cell to cell junctions  Exhibit functional & morphological polarity 3 surface domains ✓ Free surface/apical domain ✓ Lateral domain ✓ Basal domain  Basal surface attached to underlying basement membrane Cell to matrix junctions  Lining of hollow organs (Stomach) and covering of outside surfaces (Skin).  Most epithelia rest on connective tissue.  Epithelial cells are modified to form glands 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 4  Basement membrane Basal surface of all epithelia rests on a thin extracellular, felt-like sheet of macromolecules referred to as the basement membrane Semi-permeable. Structure: Basal Lamina Rich in type IV collagen, proteoglycans and glycoproteins. Reticular Lamina Type III & Type VII collagen Functions: provides structural support to the overlying ep. serves as an impermeable barrier that allows only water & small molecules to pass through 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 5 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 6  Cell Shapes  Squamous (flat) cells with height much less than width. They show a central thickening at the site of nucleus (flat), function for diffusion.  Cuboidal (cube-like) cells have about the same height and width with spherical nucleus. Function of secretions or absorption.  Columnar (rectangular) cells are taller than they are wide with elongated/ ovoid nucleus. Protect underlying tissue, may have cilia, function of secretion or absorption. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 7  Simple squamous epithelium  Formed by flattened cells.  Present in: the loop of Henle in the kidney, lining all the blood vessels, forming Bowman’s capsule in the renal cortex.  Function: Gases exchange, lubrication, reducing friction, lining membrane Blood vessel 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 8  Simple cuboidal epithelium Cell appear as squares with round central nuclei. Present in :  Duct of exocrine glands  Surface of ovary Thyroid follicles  Kidney tubules  Thyroid follicles Function: Secretion, absorption and surface barrier Kidney Tubules 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 9  Simple columnar epithelium Comes in two forms: 1- Non-ciliated columnar epithelia do not have cilia, and are found in the stomach, small and large intestine, and the gallbladder where they perform secretion and absorption. Specialized cells containing microvilli perform absorption. Goblet cells secrete mucus. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 10 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 11  2- Ciliated simple columnar epithelium Consists of a single layer of ciliated rectangular cells. Aids in movement. Move mucus and other substances via cilia, found in the Fallopian tubes, the uterus, and the central part of the spinal cord. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 12  Pseudostratified Epithelium The epithelium has nuclei at different levels giving the appearance of several layers. In fact, all of the cells attach to a common basal lamina but not all reach the surface. The epithelium is therefore a simple epithelium. Trachea As the cells are columnar in form this is a pseudostratified columnar epithelium. It is found in the trachea and some of the airways where (nasal cavity, bronchi ) thus it is sometimes know as respiratory epithelium and Epididymis in parts of the male reproductive tract. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 13  Stratified Epithelial Tissue - It has more than one layer. - Found in areas of high abrasion such as the skin or lining the mouth. - Only the basal layer being in contact with COMPOUND EPITHELIA the basement membrane, suffering from division and pushing older cells toward the surface. SQUAMOUS CUBOIDAL COLUMNAR TRANSITIONAL - It is classified according to the cell shape of the superficial layer into :- 1- Stratified Squamous Epithelial Tissue 2- Stratified cuboidal Epithelial Tissue 3- Stratified columnar Epithelial Tissue 4- Transitional Epithelial Tissue 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 14  Stratified squamous epithelium is divided into two types: 1- Stratified squamous non keratinized epithelium Has a mechanically protective function, being resistant to abrasion.  The lower cells are roughly polygonal in shape.  As cells migrate towards the surface they become flattened.  The flattened cells of the epithelium surface layer are living cells, retaining their nuclei.  Found in areas requiring protection such as mouth, lower pharynx, epiglottis, oesophagus, anal canal and vagina. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 15  2- Stratified squamous keratinized epithelium Thin skin The cells form many layers, and the cells closer to the underlying connective tissue are usually cuboidal or low columnar. The cells become irregular in shape and flatten as they accumulate keratin in the process of keratinization and are moved progressively closer to the surface where they become thin, metabolically inactive Thick skin squamous of keratin lacking nuclei. This surface layer of cells helps protect against water loss across this epithelium, resistant to friction, helps repel bacteria. This type is found mainly in the epidermis of skin. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 16  Stratified cuboidal epithelium Consists of several layers of cells in which the top layer is cube- shaped. Function is mainly absorption and secretion. Located in testis tubules, ducts of sweat glands, sebaceous glands, some ducts of salivary gland, and part of the lactiferous sinus of mammary gland. Duct of sweat gland 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 17  Stratified columnar epithelium Consists of several layers of cells in which the top layer is rectangular. Usually basal layers are shortened, irregular polyhedral cells. It protects and mucus secreting. Its found in the conjunctiva lining the eyelids. Portion of male urethra, some parts of salivary gland and mammary gland. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 18  Transitional epithelium (urothelium ) It is capable of stretching Consists of several layers of cells whose appearance is variable, whether stretched or relaxed. It represents the transition stage between stratified squamous and stratified cuboidal epithelium. A superficial layer is very large, polyhedral or umbrella cells which is occasionally bi-or multinucleated. It lines the (kidney calyces, ureter, bladder and parts of urethra) 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 19  In relaxed state (contracted) state, transitional epithelium appear to be about 4-5 layers thick. basal cells are roughly cuboidal , the intermediate cells are polygonal, and the surface cells are large and rounded and may contain 2 nuclei. Stretched state, it appears 2-3 cells thick (although the actual number of layers remains constant) and the intermediate and surface layers are extremely flattened 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 20  Cell Surface Specialization of Epithelium SURFACE SPECIALISATIONS OF EPITHELIUM CELLS Cilia FOR TRANSPORT FOR ABSORPTION FOR PROTECTION ex. Trachea CILIA MICROVILLI KERATINISATION Microvilli STEREOCILIA ex. Cortex of kidney Stereocilia ex. Epididymis 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 21  Cilia Are specialized projections of the plasma membrane, which contain a core of microtubules arranged as a central pair surrounded by nine other pairs arranged in a circle (the “9+2 structure”). Cilia are a motile projections. So, have the transport function, permit movement of materials across the cell surfaces. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 22  Cilia Trachea Oviduct (Fallopian Tube) 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 23  Microvilli Microvilli (MV) are finger-like projections from the apical surface of (usually columnar) epithelial cells. They increase the surface area of the cell surface and are found in areas involved with absorption such as the small intestine and proximal convoluted tubule of the kidney. In these two areas they are often referred to as a “brush border” Their shape is maintained by microfilaments of actin. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 24  Microvilli Epith. of small intestine Cortex of kidney 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 25  Stereocilia: Are elongated microvilli, which are non-motile, and have an absorptive function. Stereocilia are found lining the tubules of epididymis. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 26  Keratinisation Characteristically found in the skin, this adaptation is for protection. Mitotic figure Keratin layer The thickness of the keratin layer varies. It is thickest in the sole of the foot and thinnest on the outer surface of the Papillae lip. Keratinized stratified epithelium from the skin. The basal layers are folded forming papillae. These serve to attach the epithelium to the underlying tissues. Cells lost at the surface of stratified squamous epithelium are replaced by division of cells in the basal layers. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 27  Cell Adhesion & Cell Adhesion Molecules Cell adhesion is the process whereby cells are anchored to each other and to the extracellular matrix (ECM) This process is achieved via the use of cell adhesion molecules (CAMs) CAMs are transmembrane proteins that are embedded in the plasma membrane of cells Interact with components in the cytoplasm of the cells intracellularly, and other CAMs, specific receptors of other cells or components in the ECM extracellularly to help to anchor the cells. Collections of CAMs are called Cell Junctions. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 28  Lateral Specializations of Cells Lateral surface / domain Junctional complexes: 1. Occluding junctions ▻Tight junction (zonula occludens) Functions as a tight seal on apical surface to prevent leakage of larger solute molecules from cell to cell. Clinical Correlation: - Inflammatory bowel disease, Blood Brain Barrier (BBB). 2. Anchoring junctions ▻ Adhering junctions (zonula adherens) ▻ Desmosomes (macula adherens) Functions: - Maintain physical integrity of cells by assisting with cell attachment to adjacent cells. Help anchor cells (e.g., muscle cells) to the extracellular matrix (ECM) through interaction with actin cytoskeleton 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 29  Clinical Correlation: - Skin blistering diseases such as pemphigus vulgaris 3. Communicating junctions ▻ Gap junctions Present in a variety of tissues - Epithelium - Muscle (Smooth & Cardiac) - Nerve Help coordinate activity between adjacent Cells. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 30  Basal Specializations of Cells Hemidesmosome: Anchoring junctional complex - Cell-to-Extracellular matrix Junctions. - Helps to anchor epithelial cells to basement membrane. - Half the component of a desmosome. - Transmembrane proteins = Integrins. - Clinical Correlation: - Bullous pemphigoid Disease characterized by blister formation at epithelium attachment to basement membrane. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 31  Glandular epithelium 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 32 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 33 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 34 Based on Number of ducts: Simple: - Secretion poured to surface by un-branched duct Compound: - Duct divides into branches to form elaborated/complex duct system - Each smaller terminal duct receive secretion from it’s own secretory end piece - These ducts unite to form larger ducts which finally drain on to the surface 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 35  Based on Shape of Secretory End Piece: Tubular: (Simple / Compound) - Secretory end piece is like tubule - Straight, branched or coiled 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 36  Based on Shape of Secretory End Piece: Based on Shape of Secretory End Piece: Alveolar: (Simple/ Compound) Acinar: (Mostly Compound) - Secretory end piece Flask shaped - Secretory end piece Round shaped with large lumen with small lumen - Un-branched or branched - Mostly branched Simple Simple branched Compound Un-branched Sebaceous gland Mammary gland Urethral gland 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 37  Based on Shape of Secretory End Piece: Tubulo-Aleveolar / Acinar: - Combination of both Tubular and alveolar / Acinar - Mostly branched Compound Tubulo- Alveolar / Acinar Sublingual gland Submandibular gland 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 38 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 39 Based on Mode of Secretion: Based on Mode of Secretion: Merocrine Apocrine - Secretion discharged through intact - Apical portion (luminal) of cell cell membrane disintegrate to discharge its secretion - By exocytosis - Nucleus and basal portion remain intact - No loss of cytoplasm from which cell can regenerate - Partial loss of cytoplasm Example: Protein content of mammary Example: gland Lipid content of mammary Parotid gland Pancreas Atypical sweat gland (Axilla Typical sweat gland and Groin) 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 40  Based on Mode of Secretion: Holocrine - Entire cell disintegrate to discharge its secretion - Result in death of cell - Complete loss of cytoplasm Example: Sebaceous gland 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 41 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 42  Mucous Acinus / Gland Secretion: Thick Viscous – Which collects in the apical part Cells: Low Columnar & Large with distinct boundaries Cytoplasm: Mucinogen droplets – Stain very lightly with H/E stain & – Looks empty Nuclei: Flattened & basal (mucoid pushes nuclei towards base) Size of lumen: Large Function: Protection & Lubrication Example: Sublingual glands 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 43 Serous Acinus / Gland Secretion: Thin, watery – Rich in enzymes, protein in nature Cells: Pyramidal & Small with Indistinct boundaries Cytoplasm: Granular (Zymogen) – Rich in rER – Stain darkly with H/E stain Nuclei: rounded & basal / central Size of lumen: Small Function: Enzymatic Example: Parotid & Lacrimal glands 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 44 Mixed Acinus / Gland Contain both serous & mucous secretory units Sometimes serous cells form crescentic caps on mucous acini called as Serous Demilunes Example: Submandibular gland 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 45  References 1- Junqueira’s Basic Histology: Text and Atlas, 16th Edition, by Anthony L. Mescher. 2- A Text and Atlas: With Correlated Cell and Molecular Biology, 8th edition, by Wojciech Pawlina, Michael H. Ross. 25/9/2024 Email :[email protected] Website :http://Alkafeel.edu.iq 46