Epithelia & Glands Case-Based Learning PDF

12/9/20 Epithelia and Glands Peer Group Learning: our clinical case… A 59-year-old female with no past medical history presented with a lesion on the pin...

12/9/20 Epithelia and Glands Peer Group Learning: our clinical case… A 59-year-old female with no past medical history presented with a lesion on the pinky finger of her right hand. She first noticed the sore about 2–3 months prior. It was not painful, but it had started to distort her fingernail. Questions for you: the key points… Reich D., Psomadakis C.E., Buka B. (2017). In: Top 50 Dermatology Case Studies for Primary Care. Springer, Cham. https://doi.org/10.1007/978-3- 319-18627-6_39 1  12/9/20 Peer Group Learning: our clinical case… Questions for you: describe the lesion in relation to the normal skin… What’s next… Reich D., Psomadakis C.E., Buka B. (2017). In: Top 50 Dermatology Case Studies for Primary Care. Springer, Cham. https://doi.org/10.1007/978-3- 319-18627-6_39 Peer Group Learning: our clinical case… e-Histology Questions for you: normal vs abnormal Types of tissue and the way cells are organized… https://www.virtualpathology.leeds.ac.uk/slides/library/view.php?path=%2FR esearch_4%2FTeaching%2FEQA%2FSkin%2FCirculation_M%2F211693.svs 2  12/9/20 Epithelia: Overview - Specialized layers of tissue arising from all three embryonic germ layers: ectoderm, mesoderm, and endoderm - Line the internal and cover the external surfaces of the body except in certain areas such as tooth surfaces and articular cartilages - Forms endocrine and exocrine secretory glands Epithelia: Overview Skin Intestine 3  12/9/20 Epithelia: Overview - Consists of a sheet of cells lying close together with little extracellular space - These cells have distinct biochemical, functional, and structural domains that confer polarity (sidedness): apical, lateral, and basal epithelial domains (or basolateral domain) Epithelia: Overview Nat Rev Mol Cell Biol. 2008 Nov;9(11):887-901 4  12/9/20 Epithelia: Classification - Various types based on: a) the number of cell Layers and b) the shape of the superficial cells Back to our clinical case… https://www.virtualpathology.leeds.ac.uk/slides/library/view.php?path=%2FR esearch_4%2FTeaching%2FEQA%2FSkin%2FCirculation_M%2F211693.svs 5  12/9/20 Epithelia: Overview 1. A basement membrane, composed of a basal lamina and a lamina reticularis, separates the epithelium from underlying connective tissue and blood vessels 2. Epithelia are avascular and receive nourishment by diffusion of molecules through the basal lamina to which they are attached 3. Capable of renewal and regeneration Epithelia: Classification 6  12/9/20 Epithelia: Classification Epithelia: Classification 7  12/9/20 Epithelia: Classification 1. All cells composing a simple epithelium contact the basal lamina 1. In stratified epithelia only the deepest cell layer contacts the basal lamina Epithelia: Classification 3. Pseudostratified epithelia give the appearance of having multiple cell layers, but they are composed of a single cell layer only: all cells that compose this type of epithelium are in contact with the basal lamina 8  12/9/20 Epithelia: Classification Pseudostratified ciliated columnar epithelium with goblet cells lining the trachea Epithelia: Function 1. Transcellular transport of molecules from one epithelial surface to another occurs by various Processes: a. Diffusion of oxygen and carbon dioxide across the epithelial cells of lung alveoli and capillaries b. Carrier protein-mediated transport of amino acids and glucose across intestinal epithelia 9  12/9/20 Epithelia: Function c. Vesicle-mediated transport of immunoglobulin A (IgA) and other molecules 2. Absorption - via endocytosis or pinocytosis in various organs (e.g., the proximal convoluted tubule of the kidney) 3. Secretion of various molecules (e.g., hormones, mucinogen, proteins) - by exocytosis Epithelia: Function 4. Selective permeability: tight junctions between epithelial cells and permits fluids with different compositions and concentrations to exist on separate sides of an epithelial layer (e.g., intestinal epithelium) 5. Protection from abrasion and injury, provided by the epidermis (the epithelial layer of the skin) 10  12/9/20 Cell Polarity Apical, lateral and basal domains Nature Reviews Immunology 10, 131-144 11  12/9/20 Microvilli (Striated Border) 12  12/9/20 Microvilli - Fingerlike projections of epithelia - extending into a lumen - Increasing the cell's surface area - A glycocalyx (sugar coat) on their surfaces - A bundle of approximately 25 to 30 actin filaments runs longitudinally through the core of each microvillus: from the tip of the microvillus into the terminal web, a zone of intersecting filaments in the apical cytoplasm Microvilli (Core of Actin Filaments) 13  12/9/20 Microvilli - Myosin II and tropomyosin molecules located at the terminal web can interact to contract the apical region of the cell: to diverge from each other - increasing the intermicrovillar spaces – the increased transport of materials into the cell - Constitute the brush border of kidney proximal tubule cells and the striated border of intestinal absorptive cells Cilia (on the Respiratory Epithelial Cells) 14  12/9/20 Actively Motile Cilia - 7 to 10 μm long extending from certain epithelia (e.g., tracheobronchial and oviduct epithelium) that propel substances along their surfaces - A core of longitudinally arranged microtubules (the axoneme), which arises from a basal body during ciliogenesis Actively Motile Cilia - The axoneme: 9 doublet microtubules uniformly spaced around 2 central microtubules (9 + 2 configuration) - The basal body: a cylindrical structure at the base - nine triplet microtubules arranged radially in the shape of a pinwheel (9 + 0 configuration). It resembles a centriole, but has a less complex central organization 15  12/9/20 Actively Motile Cilia - Ciliary movement: the dynein arms of a doublet grasp and "climb" along the "back" of the adjacent doublet, thereby bending the cilia in a preferred direction - Energy-requiring process fueled by the ATPase activity of the dynein arms 16  12/9/20 Actively Motile Cilia - Transport of material occurs within the motile cilia, primary cilia, and flagella: axonemal transport - The transport of tubulin dimers and other molecules - via carrier proteins: raft proteins that pick up cargo Actively Motile Cilia - The raft proteins then become attached to kinesin or to dynein, motor proteins that ferry cargo along microtubules in an anterograde or retrograde direction, respectively 17  12/9/20 What structures hold the cells together and attaches the epithelium to the connective tissue? 18  12/9/20 (Mv, microvilli; TJ, tight junction; AJ, adherens junction; DS, desmosome.) Nature Reviews Molecular Cell Biology 2, 285-293 (April 2001) Desmosomes (maculae adherentes) 19  12/9/20 Desmosomes (maculae adherentes) Hemidesmosomes 20  12/9/20 Back to our clinical case… https://www.virtualpathology.leeds.ac.uk/slides/library/view.php?path=%2FR esearch_4%2FTeaching%2FEQA%2FSkin%2FCirculation_M%2F211693.svs Questions for you: describe the lesion in relation to the normal tissue… Possible origin of the lesion… 21  12/9/20 Formation of Glands from Covering Epithelia Glands - They originate from an epithelium that penetrates the connective tissue and forms secretory units - Structure: a functional portion (parenchyma) of secretory + ductal epithelial cells - separated by a basal lamina from supporting connective tissue elements (stroma) 22  12/9/20 Glands - Groupings of cells specialized for secretion - Secretion - process by which small molecules are taken up and transformed, by intracellular biosynthesis, into a more complex product that is then actively released from the cell Glands: Classification Three types based on the site of secretion: - Exocrine glands: secrete into a duct or onto a surface - Endocrine glands: secrete into the bloodstream - Paracrine glands: secrete into the local extracellular space Exocrine (ducts) and endocrine (ductless) glands 23  12/9/20 Exocrine Glands B order Goblet Cells Striated Simple Columnar Epithelium Exocrine Glands - Unicellular glands: composed of a single cell (e.g., goblet cells in tracheal epithelium) - Multicellular glands: - according to duct branching: simple glands (duct does not branch) or compound glands (duct branches) - according to the shape of the secretory unit: acinar or alveolar (saclike or flasklike) or tubular (straight, coiled, or branched) 24  12/9/20 Exocrine Glands - A connective tissue capsule may surround the gland, or septa of connective tissue may divide the gland into lobes and smaller lobules Exocrine Glands Ducts: - Between lobes (interlobar) - Within lobes (intralobar) - Between lobules (interlobular) - Within lobules (intralobular), such as striated and intercalated ducts 25  12/9/20 Exocrine Glands Multicellular glands secrete various substances - Mucous - a viscous material that usually protects or lubricates cell surfaces - Serous secretions - watery and often rich in enzymes - Mixed secretions - both mucous and serous components Mucous Cells 26  12/9/20 Mucous Cells - Flattened basal nuclei - The apical region: filled with secretory granules - mucin (like that of goblet cells) - The basal region: RER, nucleus, and a well- developed Golgi apparatus - Mucus contains many glycoproteins with important water-binding properties Mucous Cells Electron micrograph of a longitudinal section through a Goblet Cell from the ilium of the small intestine. G, Golgi Apparatus; L, lumen of intestine, MD, Mucus droplets; MV, Microvilli cut in longitudinal section; N, Nucleus of Goblet Cell; RER, rough Endoplasmic Reticulum. 15,000 X 27  12/9/20 Serous Cells Serous Cells - The apical ends - eosinophilic due to the abundant immature and mature secretory granules - The basal ends - large rounded nuclei, and an abundance of rough ER, making the cells highly basophilic basally 28  12/9/20 Serous Cells Electron micrograph of a thin section taken through an exocrine cell of the monkey pancreas. L, lumen of Acinus; M, mitochondrion; N, Nucleus, Nu, Nucleolus; RER, rough Endoplasmic Reticulum; S, secretory granule; S', secretory granule pouring its contents into lumen of Acinus. 129,000 X Seromucous (compound tubuloacinar gland) 29  12/9/20 Mechanisms of Secretion - In merocrine glands (e.g., parotid gland) - by exocytosis - In apocrine glands (e.g., lactating mammary gland) - part of the apical cytoplasm of the secretory cell is released along with the contents - In holocrine glands (e.g., sebaceous gland) - the entire secretory cell along with its contents is released Mechanisms of Secretion 30  12/9/20 Holocrine Glands Source: https://cnx.org/contents/FPtK1zmh@ 6.5:oWqVExrJ@3/Epithelial-Tissue Exocrine Glands - Several exocrine glands (e.g., sweat, lachrymal, salivary, and mammary glands) contain stellate or spindle-shaped myoepithelial cells located between the basal lamina and the basal pole of secretory or duct cells - Myoepithelial cells - connected to each other and to the epithelial cells by both gap junctions and desmosomes - Specialized for contraction 31  12/9/20 Title (36 points) - Myoepithelial cells Endocrine Glands - Unicellular (e.g., individual endocrine cells in gastrointestinal and respiratory epithelia) - Multicellular (e.g., adrenal gland): secretory material is released into fenestrate capillaries, which are abundant just outside the basal lamina of the glandular epithelium Lack a duct system 32  12/9/20 Endocrine Glands: Hormones - Generally polypeptide or lipid-derived factors that are released into the interstitial fluid - Diffuse into the blood for circulation and bind specific receptors on target cells Two Secretory Pathways - Regulated Secretion: Secretory granules accumulate in cells and the granule content is released by exocytosis upon stimulation - Constitutive Secretion: The secretory product is not concentrated into granules but is released continuously in small vesicles 33  12/9/20 Back to our clinical case… https://www.virtualpathology.leeds.ac.uk/slides/library/view.php?path=%2FR esearch_4%2FTeaching%2FEQA%2FSkin%2FCirculation_M%2F211693.svs Questions for you: Differential diagnoses… Workup… Conclusions… 34