Post on 31-Mar-2022
Causes of dyspnoea
Epithelia
Assoc. Prof. Angela Barbour Department of Pathology
angela.barbour@unimelb.edu.au
Unless otherwise specified, images are the author’s own
Foundations of Biomedical Science 2015
Kerr, Atlas of Histology Mosby. Fig 14.10b 0
Introduction
• Epithelia are an important part of most organs in the body
• Some epithelia line surfaces, others are the major cell type of organs e.g. liver, thyroid, pancreas
• Many diseases involve epithelia • The most common cancers arise in epithelia
e.g. in breast, prostate, colon, lung, skin
Lecture outline
• Types and characteristics of epithelia • Surface epithelia
– Classification – Functions – Types – Polarity and cell adhesion – Basement membrane – Mucosa and serosa
• Glandular epithelia – Endocrine, exocrine – Morphological types – Types of exocrine secretion
• Skin
Objectives Following this lecture and after further reading and study students should be able to:
• Name the different types of surface epithelia and their locations
• Relate the structure of the different types of surface epithelia to their function
• Recognise the different types of surface epithelia
• Name and explain different surface specialisations of epithelia including cell junctions and cell adhesion molecules
• Explain the structure and function of basement membranes
• Explain the terms mucosa and serosa
• Name and explain the main types of glandular epithelia
• Appreciate that exocrine glandular epithelia have varying morphologies and secrete a variety of different substances
• Explain the basic nature and role of myoepithelial cells
• Understand and explain relevant terminology
Epithelial tissue
• Surface epithelium: lines surfaces and lumina. Everything that enters or leaves the body must pass across an epithelium
• Skin • Gastrointestinal tract • Respiratory system • Kidney • Reproductive tract
• Glandular epithelium: predominantly involved in secretion. Include – Single cells – Invaginations of multiple cells forming glands – Solid organs e.g. pancreas, thyroid
• Surface epithelia may also be components of glands e.g. ducts
Functions
• Protection • Barrier, selective diffusion • Absorption • Secretion • Receptors e.g. smell, taste
Characteristics of epithelial cells
• Exhibit polarity: apical, lateral and basal domains
• Connected by cell junctions
• Supported by a basement membrane
• Avascular
Classification of surface epithelium
• Based on – Number of cell layers
• Simple • Stratified
– Shape of cells (of top-most layer for stratified epithelium) • Squamous • Cuboidal • Columnar
– Surface specialisations e.g. • Cilia • Keratinisation
Functions of surface epithelium
• Protection • Absorption • Secretion • Barrier, selective diffusion
Simple squamous
e.g. mesothelium, endothelium, lining of alveoli, glomeruli
Simple cuboidal
e.g. thyroid follicles, renal tubules
Simple columnar
• Non-ciliated e.g. stomach, small and large intestines, gallbladder and bile ducts, endocervix
• Ciliated: Fallopian tubes, bronchioles
Pseudostratified ciliated columnar
e.g. respiratory tract (Non-ciliated: epididymis and vas deferens)
Stratified squamous
• Keratinising: skin • Non-keratinising: oral cavity, oesophagus, anus, vagina, ectocervix
Stratified cuboidal
e.g. some ducts
Other stratified
• Surface columnar layer overlying myoepithelial layer – Breast – Sweat glands – Salivary glands
• Surface columnar layer overlying basal layer – Prostate
Transitional/urothelium
Renal pelvis, ureters, bladder
Polarisation
• Outer (apical) surface – Microvilli, stereocilia, cilia – Biochemical modifications
• Inner (basal) surface attaches to basement membrane
• Lateral surfaces attach to adjacent epithelial cells • Each surface functionally specialised
Apical surface: microvilli
• 0.5 - 1μm in length • Most epithelia have only a
few, some have numerous: striated or brush border, just seen on LM
• Increase surface area by a factor of 20 e.g. in small intestine and proximal renal tubules
• Contain cytoskeletal elements
Kerr, Atlas of Histology Mosby. Fig 13.18
Kerr, Atlas of Histology Mosby. Fig 13.3c
Apical surface: cilia
• Longer finger-like projections
• 2 - 10 μm long • Organised core of
microtubules allowing movement in co-ordinated waves
• E.g. in respiratory tract, fallopian tubes
Kerr, JB, Atlas of Functional Histology, Mosby, 0723430721, Fig. II.2b
Cilia
Junqueira et al, Basic Histology 9th ed Lange. Fig 17-2 Junqueira et al, Basic Histology 9th ed Lange. Fig 17-3
Intercellular junctions
http://www.columbia.edu/itc/hs/medical/sbpm_histology_old/lab/lab02_micrograph.html
Tight junction http://163.178.103.176/Fisiologia/general/celulas/FG03_14a.jpg
Seal intercellular spaces to block passage of substances between cells, form a continuous circumferential band around the apex of cells
Adherens junction http://163.178.103.176/Fisiologia/general/celulas/FG03_14b.jpg
Adhering junctions and desmosomes: mechanically strong attachments between cells, link cytoskeletons
Gap junction http://163.178.103.176/Fisiologia/general/celulas/FG03_14c.jpg
Gap, nexus or communicating junctions: allow passage of small molecules, communication
Junctional complex
http://www.columbia.edu/itc/hs/medical/sbpm_histology_old/lab/lab02_micrograph.html
Hemidesmosome http://celljunctions.med.nyu.edu/hemidesmosomes/hemiframe.html
Modified desmosomes that link epithelial cells to underlying basement membrane
Cell adhesion molecules (CAMS)
• Transmembrane proteins • Link with CAMS on neighbouring cells or matrix • Involved in cell adhesion, intracellular and extracellular
communication, cell movement and differentiation • Different types on different cells • 4 main groups
– Cadherins: component of adherens junctions – Integrins: interact between actin and extracellular matrix
molecules – Selectins: mediate white blood cell-endothelial cell interactions – Immunoglobulin superfamily: mediate homotypic cell-cell
adhesions e.g. ICAM, CCAM, PECAM
Basement membrane
• Interface between support tissues and parenchymal cells e.g. epithelia
• Mainly produced by the cells being supported i.e. epithelia • 3 layers on EM • Components
– Extracellular matrix: predominantly collagen IV, heparan sulphate and structural glycoproteins: laminins, fibronectin. Laminins and fibronectin are involved in linking integrins of epithelial cells to extracellular matrix
• Underlying collagen VII and reticulin • Collagen VII involved in attachment of BM to underlying
connective tissue
Basement membrane
PAS/haematoxylin
Methanamine silver
http://www.dako.com/au/ar41/p235751/prod_products.htm
Basement membrane
• Muscle cells, adipocytes and Schwann cells surrounded by similar layer (basal lamina)
• Usually too thin to see on LM • Functions
– Structural support – Control of epithelial growth – Links epithelium to underlying tissue – Selective barrier to nutrients
• Underlying connective tissue
Epithelium and underlying connective tissue
http://163.178.103.176/Fisiologia/general/celulas/Membrane%20Structure%20and%20Function.htm
Related terms • Epithelium and its underlying connective tissue are given names in certain
situations • Mucosa or mucous membrane
– Lines body passages that communicate with the exterior e.g. respiratory and alimentary tracts
– Comprises surface epithelium and underlying supportive connective tissue (lamina propria), sometimes also with an underlying layer of smooth muscle (muscularis mucosae)
– Associated glands that secrete mucus or other secretions onto the epithelium
• Serosa, serous membrane – Lines pericardial, pleural, peritoneal cavities and tunica vaginalis – Comprises surface mesothelium and underlying supportive connective
tissue
Glandular epithelium
• Predominantly involved in secretion – Exocrine: secrete contents onto epithelial
surface or duct • Single cell: goblet cell • Invaginations forming secretory structures • Solid organ
– Endocrine: secrete into blood • Single cell: neuroendocrine • Solid organ
Types of exocrine gland structures
Junqueira et al., 1998, Basic Histology, 9ed, 0-8385-0590-2, Lange, Fig 4.16
Simple tubular
e.g. colon
Simple coiled
e.g. sweat glands
Simple branched tubular
e.g. stomach
What do exocrine glands secrete?
• Proteins, lipids or glycoproteins • Serous secretion: protein in aqueous medium
– E.g. pancreatic acini, salivary glands, lacrimal glands
• Mucous secretion: glycoprotein in aqueous medium – E.g. respiratory, GIT, cervix
Goblet cells
• Mucus secreting cells packed with membrane bound mucous droplets
• Nucleus, organelles displaced basally
• Mucus non-staining in H&E • Unicellular glands
Gartner and Hiatt, Colour Textbook of Histology 2nd ed WB Saunders. Fig 5-21
Kerr, Atlas of Histology Mosby. Fig 13.3c
Serous acini
• Serous cells often form a secretory unit called an acinus
• Secrete into common, narrow lumen
• Secretion carried away by a duct
• Basophilic at base, acidophilic at apex
Kerr, Atlas of Histology Mosby. Fig 3.18
Gartner and Hiatt, Colour Textbook of Histology 2nd ed WB Saunders. Fig 18-1
Acinus
Secretory parts connect to duct system
Gartner and Hiatt, Colour Textbook of Histology 2nd ed WB Saunders. Fig 18-5 Ross and Pawlina, 2011 Histology, a Text and Atlas, 6 ed Walters Kluwer. Fig 51
DUCT
ED = excretory duct, SD = Striated duct
Myoepithelial cells
Breast, salivary and sweat glands
Renewal of epithelial cells
• Epithelial cells have finite life span • Are labile or stable • Replaced from stem cells, in basal layer of
stratified epithelia • Cells move upwards – shed at surface • Frequently become malignant: carcinoma • Contain cytokeratin intermediate filaments:
can be used to identify epithelial phenotype