Epithelium and Glands_2023.pdf

Epithelium and Glands Faizan Alawi DDS Professor of Pathology Professor of Dermatology Conflict of Interest • None to report Terminology • Anatomy – study of bodily structure • Histology – microscopic study of tissue structure • Physiology – study of normal organismal function • Pathology...

Epithelium and Glands Faizan Alawi DDS Professor of Pathology Professor of Dermatology Conflict of Interest • None to report Terminology • Anatomy – study of bodily structure • Histology – microscopic study of tissue structure • Physiology – study of normal organismal function • Pathology – study causes and effects of disease with laboratory examination of samples for diagnostic or forensic purposes Terminology • Anatomy – study of bodily structure • Histology – microscopic study of tissue structure • Physiology – study of normal organismal function • Pathology – study causes and effects of disease with laboratory examination of samples for diagnostic or forensic purposes Terminology • Anatomy – study of bodily structure • Histology – microscopic study of tissue structure • Physiology – study of normal organismal function • Pathology – study causes and effects of disease with laboratory examination of samples for diagnostic or forensic purposes Terminology • Anatomy – study of bodily structure • Histology – microscopic study of tissue structure • Physiology – study of normal organismal function • Pathology – study causes and effects of disease with laboratory examination of samples for diagnostic or forensic purposes Levels of resolution Light vs Electron microscopy How we see actual structure • Hematoxylin – • Eosin – • Collagen stains blue Epithelium and muscle stain red/orange Verhoeff-Van Gieson elastic stain – H&E Cytoplasmic elements stain pink-red Trichrome – – • Nucleic acids stain blue Stains elastic fibers black How we see actual structure • Hematoxylin – • Eosin – • H&E Trichrome Cytoplasmic elements stain pink-red Trichrome – – • Nucleic acids stain blue Collagen stains blue Epithelium and muscle stain red/orange Verhoeff-Van Gieson elastic stain – Stains elastic fibers black How we see actual structure • Hematoxylin – • Eosin – • Collagen stains blue Epithelium and muscle stain red/orange Verhoeff-Van Gieson elastic stain – Elastic stain Cytoplasmic elements stain pink-red Trichrome – – • Nucleic acids stain blue Stains elastic fibers black Periodic acid Schiff (PAS) Grocott methenamine silver (GMS) Stains mucopolysaccharides magenta Stains Type III collagen, fungus and other microbes black Ziehl-Neelsen acid-fast bacilli stain (AFB) Neutrophils observed in tissue stained with H&E Neutrophils observed in blood smear stained with Giemsa Giemsa stains red blood cells pink and leukocyte nuclei purple Immunocytochemistry Used to visualize proteins within cells using biomolecules capable of binding target of interest Immunohistochemistry H&E Immunofluorescence What are tissues? • Organized aggregates of cells that function in collective and coordinated manner • Four major tissue types – – – – Epithelium Connective tissue Muscle Nervous Embryonic origins of epithelium • Branchial arches – Covered by ectoderm externally – Endoderm lines internal surfaces – Mesoderm forms core of each arch Missinglink.ucsf.edu Embryonic derivation – Ectodermal origin • • • • • Epithelium of the mouth, nose, paranasal sinuses, part of pharynx Epidermis Hair Nails Prepuce of genital organs Embryonic derivation – Ectodermal origin • • • • • • Sebaceous glands, eccrine glands, salivary glands, mammary glands Lens of the eye Cornea Tooth enamel Pituitary gland, pineal gland, adrenal medullae Anal canal Embryonic derivation – Endodermal origin • • • • • • Alimentary tract Gastrointestinal tract Respiratory tract Liver Pancreas Endocrine glands Embryonic derivation – Mesodermal origin • • • Kidneys and ureters Adrenal cortex Gonads and genital ducts • Endothelium of blood vessels and lymphatic vessels • Mesothelium of various body cavities – – – – Thoracic (pleura) Abdominal (peritoneum) Pericardium (heart sac) Surrounds male internal organs Epithelial function • Dependent upon location and organ – Skin  barrier protection, thermoregulation, sweat, synthesis of Vitamin D – Intestines and kidneys  nutrient absorption – Glands  secretion – Teeth  produce enamel matrix Classification of epithelium is based on cell morphology and organization • 3 cell types – – – Squamous Cuboidal Columnar • Simple – one cell layer thick • Complex or stratified – two or more cell layers • Basement membrane (basal lamina) connects all epithelium to connective tissue – Non-cellular structure – protein and polysaccharide-rich Wikipedia Simple squamous • Endothelium and mesothelium • Flattened cells with central nucleus • Function – Oxygen exchange – CO2 exchange – Protective barrier Simple cuboidal • Glandular ducts, kidney tubules, thyroid follicles • Cube-shaped with central nucleus • Functions – Absorption – Secretion – Active ion transport Simple columnar • Intestinal lining cells, ameloblasts • Rectangular-ish • Nucleus positioned to one side • Functions – Absorption – Secretion Stratified squamous epithelium • Squamous cells arranged in layers over basement membrane • Avascular and variable thickness Pseudostratified columnar • Line respiratory tract • Appears multi-layered • Columnar shape – Some elongated, some shorter • Variable nuclear position • Ciliated • May be intermixed with mucous-secreting goblet cells Transitional epithelium • Stratified epithelium – Ability to contract and expand • Surface cells are rounded • Urothelial structures – Urinary bladder http://www.histologyguide.org/ Chapter 2 - Epithelium Cytokeratins • Produced by all epithelial cells • Intermediate filament proteins Epithelial cell polarity • Apical “free” surface – • Lateral surfaces – • Cell surface specializations Cell – cell adhesion and communication Basal surface – Cell – extracellular matrix adhesion (basement membrane) Apical specializations Microvilli Cross-linked actin filaments Stereocilia Similar to microvilli but longer Cilia Microtubule core arranged in “9+2” orientation Epithelial cell junctions • Occluding (tight) junctions • Gap (communicating) junctions • Anchoring junctions – Desmosomes and hemidesmosomes Occluding (tight) junctions • Found on lateral wall near apical surface • Protein complex structures where cell membranes join together • Determine and maintain epithelial polarity – – Impermeable to water and solutes (no paracellular transport) Forces cells to actively pump its nutrients (transcellular pathway) Gap (communicating) junctions • Not restricted to epithelial cells • Directly connect cytoplasm of two cells • Allow direct passage of small molecules between adjacent cells Exocrine gland • Produce secretions that exit onto epithelial surfaces via ducts – Salivary glands – Sweat glands • Eccrine glands • Apocrine glands – – – – Sebaceous glands Mammary glands Ceruminous glands Lacrimal glands vs Endocrine gland • Produce secretions (hormones) that enter into blood stream – – – – – – – Pituitary gland Pancreas Ovaries Testes Thyroid gland Parathyroid gland Adrenal gland Exocrine gland secretions • Merocrine – – • Apocrine – – • Membrane-bound vesicles fuse to plasma membrane in apical surface with exocytosis of contents eg pancreas, salivary glands Secretions surrounded by plasma membrane eg lipid droplets incorporated into breast milk Holocrine – – Secretory product and dying cell debris discharged together eg sebaceous glands of skin Exocrine glands – unicellular vs multicellular Unicellular glands Multicellular glands Single secretory cells distributed among nonsecretory cells Simple Compound The End