BioSci 107 Lecture 2 2024 Epithelia Handout PDF

BioSci 107 Lecture 2 Tissues of the Body Epithelium 2024 1 The Tissues of the Body (i): Epithelium Objectives Describe the: general features of epithelial tissues general structure of the basement membrane and understand its functions Describe selected types of epithelial tissue and understand their...

BioSci 107 Lecture 2 Tissues of the Body Epithelium 2024 1 The Tissues of the Body (i): Epithelium Objectives Describe the: general features of epithelial tissues general structure of the basement membrane and understand its functions Describe selected types of epithelial tissue and understand their classification, location, structure and function Understand the basic morphology of exocrine and endocrine glands 2 The Tissues of the Body (i): Epithelia Epithelial tissue covers body surface lines hollow organs, cavities and ducts forms the glands of the body 3 Key Functions of Epithelial tissues Selective Barriers Secretory Protective (limit or aid transfer) (onto a free surface) (especially from abrasion) 4 The Tissues of the Body (i): Epithelia The cells of an epithelium are: 1. Arranged in continuous sheets as single or multiple layers 2. Held together by a variety of cell junctions including: Tight junctions Adherens junctions Gap junctions Desmosomes Hemidesmosomes 5 CELL JUNCTIONS 6 The different surfaces of epithelial cells (apical, lateral or basal) have specialised functions. Lateral junctions Tight junction - electrically tightNa Lateral surface Adherens junction (belt). (e.g. cadherin links to microfilament actin – cytoplasmic contractile protein) Gap junction (e.g. connexin) Desmosome (e.g. cadherin links to intermediate filament called keratin) Basal junction Hemidesmosome (e.g. integrin instead of cadherin binds7 in the BM) 8 Cytoskeleton Microfilaments (brown) – e.g. ACTIN -bundles beneath cell membrane and cytoplasm; -strength, alter cell shape; link cytoplasm to membrane; tie cells together; muscle contraction. Intermediate filaments (purple) e.g. KERATIN -Strength Martini pg 108 9 TIGHT JUNCTIONS Image from Lodish, Molecular Cell Biology text TIGHT JUNCTION Lots of these found in: stomach, intestines, bladder Individual sealing strands transmembrane More strands the tighter the junction Many proteins involved but two key ones: claudins & occludins Join the cytoskeletons of adjacent cells e.g. via ZO-1 to actin Keep cell polarity by preventing migration of proteins between apical 10 and basal surfaces 11 ADHERENS JUNCTIONS “Belt desmosome” or “adhesion belts (zonula adherens) in some epithelial cells Others cells are less continuous and are called “adhesion plaques” More basal located than tight junctions Have a plaque layer of proteins on the inside of the cell to join actin to cadherins – Cadherins (span the gap) – Catenins link the Cadherins to Actin (microfilament in cell cytoplasm) 12 Adherens junctions prevent cell separation from tension forces like in contractions Adherens junction Image from Lodish, Molecular Cell Biology text 13 14 DESMOSOME JUNCTIONS Lateral wall Have “plaque” just like adherens junctions Resist shearing forces Cadherin spans the gap and binds to Desmoplakin Links cell surface to Keratin (a cytoskeletal intermediate filament) Keratin spans from one desmosome to another on other side of the cell – structural integrity Example: they bind muscle cells; most common in skin epithelium and cardiac cells of the 15 heart to prevent pulling apart. DESMOSOME JUNCTION Figure 1. A. Typical desmosome showing intermediate line (arrow), which is bordered by the two cell membranes bearing dense plaques on their cytoplasmic aspects. Cytokeratin filaments (F) loop into the dense plaques. Epithelial mesothelioma. X149,000. Pathology Images Inc Keratin Anchoring Cadherin linker 16 17 GAP JUNCTIONS Direct connection between cells 6 connexIn protein molecules form connexOn or hemichannel 2 hemichannels make up gap junction Allows up to ~1kDa small molecules 18 through Electron microscopy of gap junctions joining adjacent hepatocytes in the mouse. The gap junction (GJ) is seen as an area of close plasma membrane apposition, clearly distinct from the tight junction (TJ) joining these cells. (Inset A) A high magnification view of the gap junction revealing the 2–3 nm “gap” (white arrows) separating the plasma membranes. (Inset B) A freeze-fracture replica of a gap junction showing the characteristic particles on the protoplasmic (P) fracture face and pits on the ectoplasmic (E) fracture face. The particles and pits show considerable disorder in their packing with an average 9-nm center-to-center spacing Cold Spring Harb Perspect Biol. 2009 Jul; 1(1): a002576. 19 Lateral Junctions in profile Anchoring protein Linking protein Many e.g. Occludin protein 20 Image Source : wikipedia 21 Hemidesmosome Connect epithelia to basement membrane Links cellular basal intermediate filament (Keratin) to basement membrane Hemidesmosome – INTEGRIN linker protein (instead of cadherin) – binds to LAMININ in the BM and, – to Keratin intermediate filament in cytoplasm Pathology Images Inc Ultrastructure of tracheal hemidesmosomes (darkened areas with arrows) Nguyen et al. Respiratory Research 2006 7:28 doi:10.1186/14659921-7-28 22 The different surfaces of epithelial cells (apical, lateral or basal) have specialised functions. Lateral junctions Tight junction - electrically tight- Na+ etc (e.g. of content: Occludin) Lateral surface Adherens junction. (e.g. transmembrane Cadherin links to microfilament Actin – cytoplasmic contractile protein) Gap junction (e.g. Connexin) Desmosome (e.g. transmembrane glycoprotein cadherin links to intermediate filament called Keratin) Basal junction Hemidesmosome (e.g. Integrin instead of cadherin binds to Laminin in the BM and Keratin intermediate filament in cytoplasm) The combination of: tight junction, adherens junction and desmosome is called a “junctional complex” 23 The Basement Membrane All epithelia overlay a basement membrane composed of two parts: i. BASAL LAMINA (secreted by the epithelial cells) containing collagen, laminin, other proteoglycans, glycoproteins, etc ii. RETICULAR LAMINA (produced by cells of the underlying connective tissue known as fibroblasts) containing fibrous proteins such as fibronectin, collagen etc Hemidesmosomes reside here; integrin binding to laminin The basement membrane is thus found between the epithelium 24 and connective tissue. Epithelia contain nerves but do not contain blood vessels (avascular). The exchange of nutrients and wastes takes place by diffusion from vessels in the connective tissue. 25 Functions of the Basement Membrane: i. Supports the overlying epithelium ii. Provides a surface along which epithelial cells migrate during growth and wound healing Platelet and fibrin clot iii. Acts as a physical barrier iv. Participates in the filtration of substances in the kidney. 26 The basement membrane can act as a barrier to invasion by malignant melanoma. Once the barrier has been penetrated, the chances of metastasis (spread) occurring increase. BM www.tustison.com Tumor Depth Approximate 5 year survival 4 mm 50% The ABCD of melanoma warning signs: A for asymmetry: one half of a mole doesn’t match the other; B for border irregularity: edges are ragged, notched or blurred; C for colour: mix of brown, black, red, white, or blue; D for diameter greater than 6 mm. 27 There are TWO types of Epithelial tissue I. Covering and Lining Epithelia – Outer Covering e.g. skin and some internal organs. – Inner Lining e.g. example blood vessels II. Glandular Epithelia – Constitute the secretory portion of glands. 28 Outer covering of the skin and of some internal organs Covering Epithelia Cover exposed surfaces and internal cavities Often have scattered secretory cells in them Epithelial Tissues Inner lining of blood vessels, ducts and body cavities, and the interior of the respiratory, digestive, urinary and reproductive systems Exocrine Secrete onto external surfaces and into passages (ducts) Glandular Epithelia Secretory cells predominate Endocrine Hormones or precursors into interstitial fluid 29 Two major types Covering Epithelia Cover exposed surfaces and internal cavities Often have scattered secretory cells in them Epithelial Tissues Outer covering of the skin and some internal organs Inner lining of blood vessels, ducts and body cavities, and the interior of the respiratory, digestive, urinary and reproductive systems Exocrine Secrete onto external sur\faces and in to passages (ducts) Glandular Epithelia Secretory cells predominate Endocrine Hormones or precursors into interstitial fluid 30 Two major types Covering Epithelia Cover exposed surfaces and internal cavities Often have scattered secretory cells in them Epithelial Tissues Outer covering of the skin and some internal organs Inner lining of blood vessels, ducts and body cavities, and the interior of the respiratory, digestive, urinary and reproductive systems Exocrine Secrete onto external sur\faces and in to passages (ducts) Glandular Epithelia Secretory cells predominate Endocrine Hormones or precursors into interstitial fluid 31 Image: Animals 2022, 12, 2447. https://doi.org/10.3390/ani12182447 Two major types Covering Epithelia Cover exposed surfaces and internal cavities Often have scattered secretory cells in them Epithelial Tissues Outer covering of the skin and some internal organs Inner lining of blood vessels, ducts and body cavities, and the interior of the respiratory, digestive, urinary and reproductive systems Exocrine Secrete onto external surfaces and in to passages (ducts) Glandular Epithelia Secretory cells predominate Endocrine Hormones or precursors into interstitial fluid then often to 32 blood COVERING AND LINING EPITHELIA 33 I. Covering and Lining Epithelia Classified according to: a. the ARRANGEMENT of cells b. the SHAPES of the cells. 34 a. ARRANGEMENT i. Simple: single layer (secretion; absorption; filtration) ii. Stratified: two or more layers (protective) iii. Pseudostratified: appears to have multiple layers as judged by positions of nuclei. Pseudostratified: Not all cells reach the apical surface. All cells are in contact with the basement membrane i.e. actually a simple epithelium (secretion). 35 Pseudostratified ciliated nasal epithelium b. SHAPE i. Squamous: flat and thin (helps allow passage by diffusion) ii. Cuboidal: about as tall as they are wide (secretion; absorption) iii. Columnar: more tall than wide (secretion; absorption) iv. Transitional: a stratified epithelium in which the cells can change shape from cuboidal to flat shape depending on organ shape (allow stretch e.g. urinary bladder) Rounded (relaxed) cells on epithelial surface Connective tissue 36 The arrangement of cells and their shapes can be combined to provide an overall description of the different types of covering and lining epithelia. We will consider in more detail only five* of the eight different types of covering and lining epithelia (but you need to look up and know about others) : i. Simple (single layer) Simple squamous* Simple cuboidal* Simple columnar* (ciliated and non-ciliated) ii. Stratified Stratified squamous* (keratinized and non-keratinized) Stratified cuboidal Stratified columnar Transitional iii Pseudostratified (actually a single layer) Pseudostratified columnar* (ciliated and non-ciliated) 37 Simple Squamous Epithelium Features Most delicate epithelium Where there is filtration (kidney); diffusion (lung); secretion where slippery surface needed (e.g. outer layer of serous membranes); Appearance Thin flat and somewhat irregular like jigsaw Cells are “like fried eggs” or paving stones Specialised Subtypes Mesothelium lines pericardial, pleural, peritoneal cavities Endothelium lines inside of heart and the blood and lymphatic vessels 38 Simple Squamous Epithelium (filtration, diffusion, secretion) A serous membrane (serosa) lining the body cavity and viscera (mesothelium + connective tissue) Peritoneum Mesothelium: a layer of squamous epithelial cells covering the serous membranes (peritoneum, pericardium, pleura) of the adult. Other Location examples: In Bowman’s capsule of kidney, lines cardiovascular and lymphatic systems, inside eye, alveoli of lungs, visceral cavity linings, inside 39 blood vessels and inside heart Simple Cuboidal Epithelium Features Where there is SECRETION and ABSORPTION Appearance Cuboidal or hexagonal boxes. The distance between adjacent nuclei is approx. the height of epithelium Specialised Subtypes Nil Location examples: Pancreas ducts; parts of kidney tubules, smaller ducts of many glands; secretory chambers of thyroid; anterior surface of lens; pigmented epithelium at posterior of retina; secretory part of some glands like thyroid40 Function : see features above Membrane Modifications columnar epithelium 41 Microvilli wikipedia “Brush Boarder” name for appearance 42 SEM micrograph of the cilia projecting from respiratory epithelium in the lungs wikipedia The “mucociliary escalator or elevator” “Fallopian tube mover” 43 Simple Columnar Epithelium Appearance Rectangular Often hexagonal but taller and more slender than cuboidal Nuclei often elongated and near the base of the cell Height of cell is several times the distance between adjacent nuclei Features More cytoplasm so more organelles Often more metabolically active than squamous cells Come in two major subtypes i. Non-ciliated simple columnar epithelium ii. Ciliated simple columnar epithelium Specialised Subtypes Simple columnar epithelium can have: cilia or microvilli 44 i) Non-Ciliated Simple Columnar Epithelium Features Single layer Microvilli on apical surface Have goblet cells interspersed Can have Microvilli (e.g. small intestine) Non-motile cytoplasmic projections. Increase surface area for absorption. “Brush boarder” Goblet cell is a modified columnar cell Location examples of non-ciliated columnar epithelium: Examples: lines gut mucosa from stomach to anus; ducts of many glands; gall bladder. 45 Function: secretion and lubrication (mucus goblet cells) ; absorption; ii) Ciliated Simple Columnar Epithelium (move materials) Features Single layer Have goblet cells as well Location Examples: Examples: some bronchioles, uterine fallopian tubes, sinuses; central canal of spinal cord, ventricles of brain Function: synchronous movement assists motility of mucus and foreign objects 46 or oocytes Stratified Squamous Epithelium Appearance Cells form layers like plywood or pancakes in upper layers Lower layers maybe cuboidal or columnar Cells furthest from nutrition are thinner, and less active. Features Located where mechanical or chemical stresses are severe All forms protect against microbes Apical cells are packed with keratin in places where mechanical stress and dehydration are a major issue– makes the surface tough and waterproof. Specialised Subtypes Keratinised Non-keratinised Location examples: Keratinised: skin Non-keratinised: mouth, throat, tongue, esophagus, anus, and vagina 47 Stratified Squamous Epithelium (non-keratinized) This gives the name Examples: mouth, throat, tongue, esophagus, anus, and vagina Function: protection from abrasion, defence from microbes, require secretions from glands 48 Stratified Squamous Epithelium (keratinized) SKIN Microscopy of keratin filaments inside cells (Wikipedia) 49 Psuedo-stratified Columnar Epithelium Appearance Nuclei at all different levels Appears to have several layers but it is not actually the case Features All cells contact BM but not all reach the apical surface of the tissue Actually a simple epithelium Specialised Subtypes i) Pseudostratified ciliated columnar epithelium i) Cilia on some cells ii) Secrete mucus (from goblet cells) ii) Pseudostratified non-ciliated columnar epithelium i) No cilia ii) Lack goblet cells 50 Pseudostratified Columnar Epithelium (con’t) Ciliated has goblet cells (Non-ciliated have no goblet cells) Examples: Ciliated: most of upper airways Non-ciliated: larger ducts of glands, epididymis, part of male urethra. Function: Ciliated: – secrete mucus, and move it Non-ciliated: absorption and protection 51 Classification of Some Covering and Lining Epithelia Arrangement Classification Some key Examples Simple Simple squamous Endothelium lining blood vessels; Mesothelium visceral cavity lining. In Bowman’s capsule, inside eye, alveoli, Simple cuboidal Pancreas ducts; parts of kidney ducts; secretory chambers of thyroid; lens surface; pigmented epithelium at posterior of retina Simple columnar Non-ciliated: gastrointestinal tract from stomach to anus ; ducts of many glands; gall bladder Ciliated: parts of upper respiratory tract. some bronchioles, fallopian tubes, sinuses; central canal of spinal cord, Ventricles of brain Stratified Stratified squamous Keratinized: Skin epithelium Non-keratinized: lining of mouth, tongue and oesophagus, anus and vagina Pseudostratified Pseudostratified columnar Ciliated: Parts of upper respiratory tract Non-ciliated: larger ducts 52 Classification of Some Covering and Lining Epithelia (note these below in your course book if you wish) Arrangement Classification Example Stratified Stratified cuboidal Ducts of adult sweat glands; esophageal glands, male urethra Stratified columnar Rare: Part of urethra; some large gland ducts such as oesophageal glands; anal mucosal membrane, part of conjunctiva of the eye Stratified Transitional BLADDER (some parts of ureter and urethra) Note: in stratified epithelium the outer layer determines the subtype 53 GLANDULAR EPITHELIA 54 Glandular Epithelia Glands consist of a single cell or a group of cells that secrete substances into ducts, onto a surface or into blood. They are classified according to where they secrete their substances. The function of all glandular epithelia is secretion. 55 Classification of the Glands Classification Secretion pathway Example Endocrine gland Exocrine gland Secrete directly into blood via traversing interstitial fluid Pituitary, pineal, thyroid, parathyroid Generally distant strong effects Secrete into ducts that Sweat and salivary empty onto the surface glands; oil glands; wax of a covering or lining glands; pancreas; epithelium. Generally local effects Note: Some glandular organs such as the pancreas are mixed secreting into ducts and into the blood. 56 Endocrine Gland 57 Exocrine Gland Note the duct is lined with stratified cuboidal cells Sweat gland 58 Organ with Exocrine and Endocrine glandular tissues Image: Martini and Ober pg 803 59 EXOCRINE GLANDULAR EPITHELIA SINGLE OR MULTICELLULAR 60 Single Cell Gland (e.g, goblet cells) Goblet cells are type of mucous single cell exocrine gland (Not all mucous cells are goblet shaped) Images: Martini and Ober 61 Multicellular Exocrine glands Images: Tortora 62 3 characteristics used to describe structure of multicellular glands i. Structure of duct ii. Structure of secretory area iii. Relationship between the two Images: Martini and Ober Sometimes all called “flask-like” 63 “Branched” terminology not used in “compound” glands Images: Martini and Ober 64 The Tissues of the Body (i): Epithelium Objectives Describe the general features of epithelial tissues Describe the general structure of the basement membrane and understand its functions Describe selected types of epithelial tissue and have an understanding of their classification, location, structure and function Understand the basic morphology of exocrine and endocrine glands 65 Text Book Resources Tortora and Derrickson 1. 2. 3rd Asia and Pacific Edition 144-161 2nd Asia and Pacific Edition 168-188 1. 2. (14th Edition: pages 106-121) (13th Edition: pages 113-128) Image Acknowledgements: Various editions of the course text books or Wikipedia (free creative commons) were the sources for the images used in BioSci 107 Lectures 1-5; unless otherwise stated. 66