Epithelial Tissues PDF Lecture Notes

Epithelial Tissues Dr Ashik Srinivasan School of Medical Sciences Last edit: 22-Apr-2024 Lecture date: 23-Apr-2024 Thank You: Dr Belal Chami (author of previous version of this lecture) Learning Objectives Define types...

Epithelial Tissues Dr Ashik Srinivasan School of Medical Sciences Last edit: 22-Apr-2024 Lecture date: 23-Apr-2024 Thank You: Dr Belal Chami (author of previous version of this lecture) Learning Objectives Define types of epithelia and their characteristics How different epithelia relate to function and location Describe cell adhesion mechanisms, and relate to function and location Differentiate histologically the features of skin and buccal epithelia Identify that epithelial cells can be specialised cells serving structural and endocrine functions  A Basic Body Plan Epithelium Covers Outside Epithelium covers Invaginations of : Gastrointestinal, Respiratory, Renal, Reproductive Epithelium Keeps: Epithelium lines body You In cavities (pericardium, Infections Out peritoneum, pleura) Most tissues are either Epithelium or Connective Tissues These are the main types of tissues found in the mouth: Keratin Intermediate Filaments Image – Alberts et al., Molecular Biology of the Cell, 5th Ed, 2008 Epithelial Tissues Epithelia line and cover all body surfaces (except the tooth enamel and the anterior surface of the iris) Epithelia may be embryologically derived from ectoderm, Histology and Cell Biology: An Introduction to Pathology. mesoderm, or endoderm 4th Edn, 2012. Cells are tightly bound together Rest on a Basement membrane Distinct polarity Most epithelial – structural and functional No Vascular Supply cells renew – Nutrients are delivered by continuously by diffusion. mitosis.  Roles of Epithelia Protection (skin) Absorption (small and large intestine), transport of material at the surface (mediated by cilia) Secretion (glands) Excretion (tubules of the kidneys) Gas exchange (lung alveolus), Image - ‘Histology’, Ross, Romrell & Kaye, Williams & Wilkins, 1995 Example of epithelial transition – Vagina to Cervix Vagina The transformation zone is vulnerable to Transformation HPV invasion zone and subsequent immortalisation (cancer) of cervical epithelial cells. Cervix  Squamous (squame = scale) Cuboidal Columnar Simple Stratified Pseudo-stratified (looks stratified but all cells actually in contact with basement membrane) Basement Membrane Specialized ECM Sheet Structure Intertwining collagen fibres Image – Alberts et al., Molecular Biology of the Cell, 5th Edn, 2008 Cell Junctions  Desmosomes & Hemi-Desmosomes Keratin Binding ‘Prickle Cells’ of Stratified Squamous Epithelium Permeable to H2O2 and ions Able to resist mechanical stress Image –Alberts et al., Molecular Biology of the Cell, 5th Edn, 2008  Desmosomes Keratin Intermediate Filaments Hemidesmosomes Basal lamina Anchoring fibrils Collagen fibrils Examples: Skin, Intestines, Respiratory tract Image – Berkovitz, Holland & Moxham. A Colour Atlas & Textbook of Oral Anatomy Absent in fibroblasts and Histology & Embryology. Wolfe, 1992 endothelial cells Desmosomes Dense plaque of anchor proteins Pemphigus Vulgaris Intermediate filaments IgG-mediated autoimmune disease of stratified squamous epithelia. Categorised by blistering of skin and mucous membranes Autoantibodies directed against Cadherin-family cadherin-family adhesion proteins adhesion proteins https://doi.org/10.1016/B978-0-12-394311-8.00005-4in  Tight Junctions ‘Glue’ connecting cells – water tight Forces most material to enter the cells (via diffusion or active transport) Examples: Bladder, Kidney, Intestines, Skin  Gap Junction ‘Tunnels’ Permeable to water and ions Often found in cells that spread action potentials i.e nerves and cardiac muscles Examples: Cardiac cells, Neurons, Uterus Summary Image –Alberts et al., Molecular Biology of the Cell, 5th Edn, 2008 Stratified Squamous Epithelium Latinized Name Anglicized Name Stratum corneum Keratinized layer Stratum granularis Granular cell layer Stratum spinosum Prickle cell layer Stratum basals Basal cell layer Lamina propria Lamina propria  Epidermis ‘Thick’ skin contains a 5th layer called the stratum lucidum. All skin except that of the palms and soles are ‘thin’ skin. The epidermis contains no blood vessels All cells, except in the stratum basale are called keratinocytes – manufactures and stores the protein keratin Keratin – intracellular fibrous protein found in hair, nails and skin which gives it the https://courses.lumenlearning.com/wm-biology2/chapter/epidermis/ hardiness and water resistant properties. Image - Junqueira, Carneiro & Contopoulos, ‘Basic Histology’, Lange, 1977 Cells mature from basal layer through to surface layer and then shed Stratum Basale Single layer of cells – cuboidal shaped stem cell that is a precursor of the keratinocytes of the epidermis Two other cell types Merkel cell – functional cells which are responsible for stimulating sensory nerves which the brain receives as touch Melanocytes – produces pigment melanin. Discussed later. Image – Bhaskar et al. ‘Orban’s Oral Histology & Embryology’, Mosby, 1976 Mitotic figures in Basal Layer  Stratum Spinosum – Prickle cell layer Spiny or ‘prickly’ appearance post-fixation due to high presence of desmosomes Typically composed of 8-10 layers of keratinocytes Interspersed among the keratinocytes are Langerhan cells (macrophage – like cells that engulf bacteria, foreign particles and damaged cells in this layer) Stratum Granulosum – Granular layer Keratinocytes look flatter and obtain a grainy appearance Grainy appearance is due to large amounts of granules within the cells containing keratin and keratohyalin. Produces lipid rich secretions The nuclei and other cell organelles begin to disintegrate as the cell dies  Stratum Corneum – Keratinized layer Most superficial layer composed of 15 to 30 layers of cells The dry and dead layabout helps prevent penetration of microbes and the dehydration of underlying tissue Also provides mechanical protection against separation Cells in this layer shed periodically and replace by cells pushed upward from the stratum granulosum Entire layer is replaced approximately every 4 weeks. Microdermabrasion is a cosmetic technique to remove some of the dry upper layer with the aim to keeping the skin looking ‘fresh’ and healthy. Review Image – Bhaskar et al. ‘Orban’s Oral Histology & Embryology’, Mosby, 1976  Oral epithelium 3 types of epithelium are found in the oral cavity Non-keratinized epithelium is associated with the lining mucosa Permeable to water Orthokeratinized and parakeratinized epithelium are both associated with masticatory mucosa. https://pocketdentistry.com/9-oral-mucosa/ Stratum Corneum Stratum Granulosum Stratum Spinosum + Straum Basale + + Lamina Propria Orthokeratinised Parakeratinised Non-keratinised seen in Human gingiva: Human gingiva: buccal epithelium, No nuclei in keratinised Keratin squames retain pharynx and esophagus Surface layer pyknotic nuclei Light Skin/Mucosa Dark Skin/Mucosa Skin Colour Melanosome Production & Degradation Image - ‘Histology’, Ross, Romrell & Kaye, Williams & Wilkins, 1995 Adnexal Structures Hair – Nails – Sweat Glands Image - ‘Histology’, Ross, Romrell & Specialized Epithelial Structures Kaye, Williams & Wilkins, 1995 Glands – From Epithelial Invasion of C.T. Similarly for Epithelial Organs (eg Lungs, Kidney, Liver) Image - ‘Histology’, Ross, Romrell & Kaye, Williams & Wilkins, 1995 Image – Berkovitz, Holland & Moxham. A Colour Atlas & Textbook of Oral Anatomy Histology & Embryology. Wolfe, 1992  Goblet cell microvilli Small Intestinal Mucosa Simple Columnar Epithelium Gastric Mucosa P - Pits Image - ‘Histology’, Ross, Romrell & Kaye, Williams & Wilkins, 1995  Image - ‘Histology’, Ross, Romrell & Kaye, Williams & Wilkins, 1995 Mucociliary Apparatus: Cilia + mucus + airway surface liquid layer