BMS1025 Cell Biology: Epithelial Tissue PDF

BMS1025 Cell Biology Epithelial Tissue Dr Patrizia Camelliti Senior Lecturer in Cardiovascular Biology University of Surrey [email protected] Office: 31 AY 04 Outline ➢ What is Epithelial Tissue? ➢ Where is it? ➢ What does it do and how? • Functions and characteristics ➢ How is it classifi...

BMS1025 Cell Biology Epithelial Tissue Dr Patrizia Camelliti Senior Lecturer in Cardiovascular Biology University of Surrey [email protected] Office: 31 AY 04 Outline ➢ What is Epithelial Tissue? ➢ Where is it? ➢ What does it do and how? • Functions and characteristics ➢ How is it classified? • Structure / location / function of different classes ➢ Glands (Secretory Epithelium) Levels of Structural Organisation Cellular level Cells are made up of molecules More than 200 different cell types in the human body! Chemical level Atoms combine to form molecules Tissue level Tissues consist of similar types of cells Remaining weeks Organ level Organs are made up of different types of tissues Organism level The human organism is made up of many organ systems Organ system level Organ systems consist of different organs that work together closely What is Tissue? Groups of cells similar in structure and function Nervous tissue control Muscle tissue movement Epithelial tissue covering Connective tissue support Four types of tissues in the body: • Epithelial • Connective • Muscle • Nerve What is Epithelial Tissue? ⚫ ⚫ ⚫ Epi = “on” or “around” Thelial = “surface/sheet” A continuous layer of closely packed cells that covers the external body surface and lines body cavities, and generally marks off our insides from our outsides Where is Epithelial Tissue? ⚫ Covers all internal and external body surfaces Skin a real human cadaver Section through Mouth Blood vessels Stomach Lungs Liver ….. Functions of Epithelial Tissues 1. Provide physical protection (from abrasion, dehydration, destruction) 2. Control permeability (selectively filter biochemical substances; eg. capillaries and lung alveoli) 3. Provide sensation (sensory epithelium which contains sensory cells – nose, ear, eyes) 4. Absorb nutrients (eg. in digestive tract) 5. Secretion (glandular epithelium – hormones, mucus, etc.) 6. Transport (ciliated epithelia sweep mucus, cells and other particles along the surface of the epithelium) Characteristics of Epithelial Tissue 1. Polarity: apical and basal surfaces 2. Specialised contacts: cell junctions, closely packed cells 3. Attachment: via basement membrane to underlying connective tissue 4. Avascularity: no blood vessels (but richly innervated) 5. Regeneration: can replace lost cells by cell division Characteristics of Epithelial Tissue 1. Polarity Apical surface Smooth x surface area, increase absorptive capacity Microvilli 20 (lining intestine & kidney tubules) Cilia help to move materials (mucus, etc…, lining trachea) Uneven distribution of organelles & membrane proteins Basal surface Basement membrane Human anatomy & Physiology, Pearson, 9th ed, page 146 Characteristics of Epithelial Tissue 2. Specialised contacts Cell Junctions Tight Junctions Desmosomes Final lecture Gap junctions Strength & impermeability Human anatomy & Physiology, Pearson, 9th ed, page 146 Characteristics of Epithelial Tissue 3. Attachment Basement membrane Basal lamina: glycoproteins secreted by epithelial cells; selective filter for molecules between connective tissue and epithelium. Reticular lamina: layer of extracellular 4. Avascularity material (collagen) produced by connective tissue, gives the basement membrane its strength. No Blood vessels: nutrients arrive by diffusion from blood vessels in connective tissue. Human anatomy & Physiology, Pearson, 9th ed, page 146 Characteristics of Epithelial Tissue 5. Regeneration ⚫ Epithelial tissue has high regenerative capacity: can reproduce rapidly. ⚫ Epithelial cells have a hard life: exposed to mechanical friction, disruptive enzymes, toxic chemicals & bacteria ⚫ Regeneration is essential to maintain tissue integrity and is achieved via cell division from stem cells. ⚫ Skin Renewed once every 35 days (200 times by your age) Stem cells in the basal layer divide & migrate to outer layers Human anatomy & Physiology, Pearson, 9th ed, page 147 Stem Cells 1. Undifferentiated cells (not committed to a specific cell type/function) 2. Self-renewable (able to go through numerous cycles of cell division while still maintaining their undifferentiated state) 3. After division, each daughter cell has a choice: it can either remain a stem cell, or it can embark on a course that commits it to terminal differentiation 4. Different tissues have different regenerative capacity: high in epithelial tissue; very low in cardiac and nervous tissue Classification of Epithelial Tissue ⚫ *Number of cell layers ⚫ Simple: one layer ⚫ Stratified: more than one layer Simple Basement membrane Stratified Basement membrane ⚫ *Cell shape ⚫ Squamous: flat ⚫ Cuboidal: cube ⚫ Columnar: tall/column * These are linked to the specific function of different epithelial tissue (protection / absorption / filtration) Squamous Cuboidal Columnar Human anatomy & Physiology, Pearson, 9th ed, page 147 Classes of Epithelial Tissue Based on shape and layers Human anatomy & Physiology, Pearson, 9th ed, page 146 Simple Epithelial Tissue Based on shape and layers Simple Squamous Epithelium Description: Single layer of flat cells with disc-shaped central nuclei; the simplest of the epithelia. Function: Allows material to pass by diffusion and filtration in sites where protection is not important. Lung tissue Air sacs (alveoli) of lung tissue Nuclei of squamous epithelial cells Location: Lining many body cavities: lung alveoli (air sacs - gas exchange) and capillaries (permeability). Photomicrograph: Simple squamous epithelium forming alveoli (air sacs) wall (125x). Function: exchange of gases (O2 and CO2) by diffusion. Human anatomy & Physiology, Pearson, 9th ed, page 148 Simple Squamous Epithelium Description: Single layer of flat cells with disc-shaped central nuclei; the simplest of the epithelia. Lung tissue, Top view Nuclei of squamous epithelial cells Function: Allows material to pass by diffusion and filtration in sites where protection is not important. Location: Lining many body cavities: lung alveoli (air sacs - gas exchange) and capillaries (permeability). Blood vessel Endothelium: Epithelium lining the entire vascular system. Function: exchange of nutrients and wastes between blood and tissue. Human anatomy & Physiology, Pearson, 9th ed, page 148 Simple Cuboidal Epithelium Description: Single layer of cube-like cells with large, spherical central nuclei. Kidney Tubules Simple cuboidal epithelial cells Function: Secretion and absorption. Location: Lining kidney tubules; ducts and secretory portions of small glands. Basement membrane Connective tissue Photomicrograph: Simple cuboidal epithelium in kidney tubules (430x). Function: absorption of water and small molecules from kidney filtrate into the blood & secretion of wastes from blood into urine. Human anatomy & Physiology, Pearson, 9th ed, page 149 Simple Cuboidal Epithelium Description: Single layer of Cube-like cells with large, spherical central nuclei. Kidney tubule Simple cuboidal epithelial cells Function: Secretion and absorption. Basement membrane Location: Lining kidney tubules; ducts and secretory portions of small glands. Photomicrograph: Simple cuboidal epithelium in kidney tubules (430x). Human anatomy & Physiology, Pearson, 9th ed, page 149 Simple Columnar Epithelium Description: Single layer of tall cells with oval nuclei located near the basement membrane; some cells have cilia or microvilli; may contain mucus-secreting unicellular glands (goblet cells). Digestive tract Microvilli Function: Absorption of nutrients; secretion of mucus, enzymes & digestive fluids; ciliated type moves materials (mucus or eggs) by ciliary action. Location: Nonciliated lines most of the digestive tract (stomach to rectum) & ducts of some glands; ciliated lines respiratory tract and uterus. Simple columnar epithelial cell Mucus of goblet cells Basement membrane Photomicrograph: Simple columnar epithelium of the digestive tract (660X). Function: absorbing and transporting nutrients. Human anatomy & Physiology, Pearson, 9th ed, page 149 Stratified Epithelial Tissue Stratified Squamous Epithelium Description: Thick: several layers of flat cells. Basal cells are cuboidal or columnar, metabolically active, divide and produce the cells of the more superficial layers. In the keratinized type, the surface cells are full of keratin and dead. Esophagus Stratified squamous epithelium Function: Protects underlying tissues against abrasion, pathogens, & chemical attack. Location: Lining esophagus, mouth & vagina; keratinized type in the epidermis of the skin & outer surface of the cervix. Nuclei Basement membrane Connective tissue Photomicrograph: Stratified squamous epithelium lining the esophagus (285x). Function: protection from hot food and bacteria. Human anatomy & Physiology, Pearson, 9th ed, page 151 Stratified Cuboidal Epithelium • Description: Generally, two layers of cuboidal cells. • Location (rare): Lines lumen of mammary glands and sweat glands. • Function: Secretion Sweat gland duct Human anatomy & Physiology, Pearson, 9th ed, page 150 Stratified Columnar Epithelium • Description: Several layers of cells in which basal cells are cuboidal and superficial cells are columnar. • Locations (rare): Large ducts of mammary glands, salivary gland ducts and urethra. • Functions: Secretion and protection. Salivary gland duct Human anatomy & Physiology, Pearson, 9th ed, page 150 Classes of Epithelial Tissue Surface cells dome shaped/flat (depending on stretch of bladder) Appears stratified but it’s not! Basal cells cuboidal/columnar Pseudostratified columnar epithelium Transitional epithelium Pseudostratified Columnar Epithelium Description: Single layer of cells (some tall, some short); all in contact with basement membrane; some not reaching the free surface; nuclei seen at different levels; may be ciliated. Function: Secrete substances, particularly mucus; movement of mucus by ciliary action (dusttrapping mucus in trachea). Cilia Pseudostratified epithelial layer Location: Lines part of the male reproductive tract & the respiratory system (eg. Trachea). Basement membrane Trachea Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (800x). Human anatomy & Physiology, Pearson, 9th ed, page 150 Transitional Epithelium Description: Several cell layers. Basal cells cuboidal or columnar; surface cells dome shaped or flat (depending on degree of organ stretch). Transitional epithelium Function: Stretches to permit distension of urinary bladder. Location: Lines urinary bladder. Basement membrane Connective tissue Photomicrograph: Transitional epithelium lining the urinary bladder, relaxed state (360X); note the rounded appearance of the cells at the surface; these cells flatten and become elongated when the bladder is filled with urine. Human anatomy & Physiology, Pearson, 9th ed, page 150 Transitional Epithelium ⚫ ⚫ ⚫ Transitional epithelium is designed to distend and return to its normal size. In empty bladder: epithelium is thick and multilayered, with rounded, domelike cells on the luminal surface. In full bladder: epithelium stretches and thin out (squamous cells). Urinary bladder Epithelial Tissues by Virtual Microscope Virtual Microscope https://learn5.open.ac.uk/mod/htmlactivity/vie w.php?id=19 By Prof David Male & Andy Sutton, Open University Relevant samples are in Basic: 8: Cervix (stratified squamous non-keratinised) 10: Lung (simple squamous epithelium) 18: Kidney (simple cuboidal epithelium) 14 & 17: Skin (stratified squamous epithelium keratinised) Glands: Glandular epithelium What are Glands? ⚫ Specialised epithelial tissue structures that secrete substances. ⚫ Secretion: Goblet cell mucin Thyroid gland hormones Adrenal gland enzymes electrolytes & waste products What are Glands? ⚫ Secretion is an active process: glandular cells obtain substances from blood and transform them chemically into secretion product. ⚫ Glandular epithelial cells have prominent ER, Golgi apparatus and secretory granules. Glands – Classification ⚫ Classified by: ⚫ Site of product release – endocrine (internally secreting) or exocrine (externally secreting) Endocrine Exocrine Blood vessel ⚫ Relative number of cells forming the gland – unicellular or multicellular Duct Unicellular (goblet cell) Multicellular Human anatomy & Physiology, Pearson, 9th ed, page 154 Glands: Endocrine / Exocrine ⚫ Endocrine: ⚫ Secrete their products hormones directly into extracellular space (by exocytosis) ⚫ Hormones enter blood or lymphatic fluid and travel to target organs ⚫ Target organs respond in some characteristic way ⚫ Ductless glands: secretions not released into a duct ⚫ Example: thyroid gland Human anatomy & Physiology, Pearson, 9th ed, page 152 Glands: Endocrine / Exocrine ⚫ Exocrine: ⚫ Secrete their products onto body surfaces (skin) or into body cavities ⚫ More numerous than endocrine glands ⚫ Secrete products into ducts (except for goblet cells – unicellular glands) ⚫ Unicellular or multicellular ⚫ Examples: sweat and salivary glands, liver (secretes bile), pancreas (secretes digestive enzymes) Human anatomy & Physiology, Pearson, 9th ed, page 154 Unicellular Exocrine Gland: Goblet cell ⚫ Found in epithelial linings of digestive and respiratory tracts ⚫ Produce mucin: complex glycoprotein that dissolves in water to form mucus ⚫ Mucus: slimy coating that protects and lubricates surfaces ⚫ In digestive tract: mucus blocks microorganism, toxins, bacteria, digestive enzymes Columnar cells Mucin of goblet cell Digestive tract: small intestine Human anatomy & Physiology, Pearson, 9th ed, page 153 Unicellular Exocrine Gland: Goblet cell ⚫ In respiratory tract: mucus traps dust particles, bacteria and other inhaled debris; cilia move the mucus towards the pharynx to be swallowed – protects lungs from infections Respiratory tract: trachea Human anatomy & Physiology, Pearson, 9th ed, page 153 Unicellular Exocrine Gland: Goblet cell Microvilli Secretory vesicles containing mucin Golgi apparatus Rough ER Nucleus Human anatomy & Physiology, Pearson, 9th ed, page 153 Histology Diagram Multicellular Exocrine Glands ⚫ Multicellular exocrine glands are composed of a duct and a secretory unit (secretory cells) Epithelium ⚫ Formed by invagination of epithelium into underlying connective tissue ⚫ Connective tissue provides support and nutrients to glands (blood vessels) ⚫ Classified by mode of secretion Connective tissue Human anatomy & Physiology, Pearson, 9th ed, page 154 Exocrine Glands: Mode of secretion ⚫ Merocrine glands – most – secrete products by exocytosis (sweat glands, salivary glands & pancreas) ⚫ Apocrine glands glands: a portion of plasma membrane buds off the cell, containing the secretion (mammary glands) ⚫ glands the entire cell disintegrates to Holocrine glands: secrete its product (sebaceous glands) Intact cell Secretion Pinched-off portion of cell (secretion) Disintegrating cell and its contents (secretion) Cell dividing Merocrine gland Apocrine gland Holocrine gland Human anatomy & Physiology, Pearson, 9th ed, page 153 Exocrine Glands: Mode of secretion Merocrine Apocrine Holocrine Learning Outcomes By the end of these lectures, you should be able to: ⚫ Explain the functions of epithelial tissue ⚫ Name the 5 characteristics of epithelial tissue ⚫ Name the classes of epithelial tissues and briefly describe structures and functions of each ⚫ Describe classification of glands on the basis of site of product release ⚫ Explain the function of glands ⚫ Describe the mode of secretion of merocrine, apocrine and holocrine glands ⚫ Have acquired epithelial tissue structure and function knowledge that will help you for practical 3 & practical 4 Further Reading Alberts Molecular Biology of the Cell Ch. 22 Stem Cells and Tissue Renewal Marieb & Hoehn (9th Edition) Human Anatomy & Physiology Ch. 4 Tissue