IAS20 Epithelial and Glandular Tissues 2024.pdf

Epithelial and Glandular Tissues Part I: Embryonic origins, Functions and Properties Dr Jada C.D. Lee Lecturer Learning outcomes At the end of this video, you will be able to: - Indicate the developmental origins of the epithelial tissues - Outline the general functions of epithelia and their...

Epithelial and Glandular Tissues Part I: Embryonic origins, Functions and Properties Dr Jada C.D. Lee Lecturer Learning outcomes At the end of this video, you will be able to: - Indicate the developmental origins of the epithelial tissues - Outline the general functions of epithelia and their structural characteristics - Associate the close and interactive relationship between the epithelial and connective tissues Developmental Origins of Epithelial Tissue From all three embryonic germ layers Ectoderm e.g. Epithelium of the skins Mesoderm e.g. Kidney tubules, endothelium, mesothelium Endoderm e.g. Respiratory and gastrointestinal tracts Respiratory epithelium General Functions of Epithelial Tissue ⎼ Protection e.g. epidermis of the skin, epithelial linings of the oesophagus, vagina and urinary bladder ⎼ Absorption and Excretion e.g. intestinal epithelium, endothelium of blood and lymphatic vessels, pulmonary alveolar epithelium ⎼ Secretion e.g. glandular epithelium ⎼ Sensation e.g. retina and olfactory epithelia Association with Connective Tissue Connective tissue Alberts et al., Molecular biology of the cell Basement Membrane ⎼ Acellular ⎼ Formed by secretions of both epithelium and connective tissue ⎼ Possible functions: - Attachment to connective tissue - Guide cell migration during tissue repair - Tissue-specific functions e.g. acts as a filter in the nephrons of the kidney Basement membrane Under light microscopic level BM: Basement membrane Kidney Basement Membrane Basement membrane can be divided into: Under electron microscope level Basal lamina - Contains type IV collagen - Secreted from epithelial cells Reticular lamina - Contains type III collagen Kierszenbaum, et al. Histology and cell biology: An introduction - Secreted from fibroblasts in the to pathology. connective tissues Characteristics of Epithelium 1. Rest on the basement membrane 2. Junctional complex 3. Avascular - dependent on the underlying connective tissue for exchange of materials 4. Exhibit functional and morphological polarity 5. Contains cytokeratin 6. Little or no intercellular matrix All of the above properties are absent in connective tissue Epithelial and Glandular Tissues Part II: Classification and Types of Epithelia Dr Jada C.D. Lee Lecturer Learning outcomes At the end of this video, you will be able to: - Classify the epithelia in terms of the cell shape and number of cell layers Classification of Epithelia Classification of epithelia Cell shape Number of cell layers Simple Stratified (one layer) (multiple layers) Squamous Cuboidal Columnar Pseudostratified Transitional (one layer) (multiple layers) Classification of Epithelia 1. Simple Squamous Epithelium - Aims to facilitate the exchange of materials, absorption and secretions - Example: Lining the heart, blood vessels and lymphatics Lowrie, D. J. Histology: An essential textbook. Kühnel Wolfgang. Color atlas of cytology, histology, and microscopic anatomy. Endothelium Simple squamous epithelium from the Electron microscopy; magnification: × 3000 inner lining of the heart Classification of Epithelia 1. Simple Squamous Epithelium - Example: Lining the peritoneal and pleural cavity Young et al. Wheater's Functional Histology: A Text and Colour Atlas. Epithelial lining Mesothelium (peritoneum) covering the surface of the appendix (ohiostate.pressbooks.pub) Pleura of the lung Classification of Epithelia 2. Simple Cuboidal Epithelium - Major functions are secretion, excretion and absorption - Example: Ducts of glands, kidney tubules A pancreatic duct lined by a single layer of Cuboidal epithelium of the proximal convoluted tubules cuboidal epithelial cells Ross, M. H., & Pawlina, W. Histology: A text and Atlas. Kühnel Wolfgang. Color atlas of cytology, histology, and microscopic anatomy. Classification of Epithelia 3. Simple Columnar Epithelium - Major functions are for transportation of fluids, secretion and absorption - Examples: Epithelial linings of the intestine and gall bladder Simple columnar epithelium of gall bladder Simple columnar epithelium of the intestine Kühnel Wolfgang. Color atlas of cytology, histology, and microscopic anatomy. with microvilli Classification of Epithelia 4. Simple Ciliated Columnar Epithelium Young et al. Wheater's Functional Histology: A Text and Colour Atlas. Fallopian tube (oviduct) Classification of Epithelia 5. Stratified Squamous Epithelium (non-keratinized) - For protection - Superficial layers of squamous cells contain nuclei (living cells) Young et al. Wheater's Functional Histology: A Text and Colour Atlas. Stratified squamous epithelium from uterine cervix Classification of Epithelia 6. Stratified Squamous Epithelium (keratinized) - For surface protection and preventing desiccation - Superficial layers contain rich in amount of keratin fibres but without any nuclei (dead cells) Lowrie. Histology: An essential textbook. The keratinized layer Stratified squamous keratinized epithelium from the sole of the foot Classification of Epithelia Stratified Squamous Epithelium Non-keratinized or Keratinized? Non-keratinized Keratinized Classification of Epithelia 7. Stratified Cuboidal Epithelium - Uncommon - Protection, secretion and limited absorption - Example: Excretory duct of exocrine gland (e.g. sweat gland ducts, salivary gland ducts) Young et al. Wheater's Functional Histology: A Text and Colour Atlas. Salivary gland Classification of Epithelia 8. Stratified Columnar Epithelium - Uncommon - Protection and secretion - Example: Larynx, larger ducts of exocrine glands (e.g. mammary gland duct) Young et al. Wheater's Functional Histology: A Text and Colour Atlas. Lining of larynx Classification of Epithelia 9. Transitional Epithelium - For protection and to accommodate high degree of stretching - Found only in mammal’s urinary tract (ureter and urinary bladder) ohiostate.pressbooks.pub Young et al. Wheater's Functional Histology: A Text and Colour Atlas. Transitional epithelium from the lining urinary bladder (urothelium) Lowrie. Histology: An essential textbook. Classification of Epithelia 10. Pseudostratified Ciliated Columnar Epithelium - Confined to the airways of the respiratory system in mammals - Also termed as Respiratory Epithelium ohiostate.pressbooks.pub Young et al. Wheater's Functional Histology: A Text and Colour Atlas. Respiratory epithelium of trachea Functional Characteristics of Epithelium Summary Diffusion, filtration, secretion and Cell layers Simple absorption Protection, against abrasion Stratified Diffusion, filtration Squamous Cell shapes Secretion and Absorption Cuboidal Highly active secretion and Columnar absorption Epithelial and Glandular Tissues Part III: Surface Specializations of Epithelium Dr Jada C.D. Lee Lecturer Learning Outcomes At the end of this video, you will be able to: - Understand the structural arrangements and functions of different surface specializations of epithelium: - Microvilli and cilia (apical surface) - Junctional complex (lateral surface) - Membranous folding (basal surface) Morphological Polarity of Epithelial Cells Lateral (Coradini et al., 2011) Distinct specializations are found on different surfaces of the epithelial cells Specializations at the Apical Surface - Microvilli (non-motile; for absorption) e.g. GI tract - Cilia (motile; for movement of fluid) e.g. Respiratory epithelia, oviduct Lowrie. Histology: An essential textbook. Specializations at the Apical Surface Microvilli (non-motile) Microvilli - Finger-like or hair-like projections - Also termed as brush border or striated border - Actins are present in microvilli Actin filaments Terminal web Kühnel Wolfgang. Color atlas of cytology, histology, and microscopic anatomy. Ross, M. H., & Pawlina, W. Histology: A text and Atlas.  Specializations at the Apical Surface Cilia (motile) Lowrie. Histology: An essential textbook. - Capable of moving fluid along the cell surface - Contains an organized core of microtubules - in a 9+2 doublets arrangement pattern - Joins with the basal bodies - in a 9+0 triplets arrangement pattern 9+0 Motile cilia Basal body (Djenoune et al., 2022) (Axoneme) Morphological Polarity of Epithelial Cells Lateral Junctional complex Gap Junction (Coradini et al., 2011) Distinct specializations are found on different surfaces of the epithelial cells Specializations at the Lateral Surface Junctional Complex 1. Tight junctions/ Zonula occludens (ZO) - There are 3 components 2. Adhering junctions/ Zonula adherens (ZA) 3. Desmosomes Lowrie. Histology: An essential textbook. Specializations at the Lateral Surface Junctional Complex: Tight Junctions/ ZO - Nearest to the apical aspect of the cell - Tight seal between the adjacent cells - Restricting movement of substances Specializations at the Lateral Surface Junctional Complex: Adhering Junctions/ ZA - Consists of a layer of proteins on the inside of the plasma membrane that attaches both membrane proteins and microfilaments of the cytoskeleton - Composes of transmembrane glycoproteins, Cadherins, to join the cells - Provides physical strength for cell-cell interactions Specializations at the Lateral Surface Junctional Complex: Desmosomes - Provide mechanical strength for cell-cell interaction - Interact with the keratin intermediate filament network Specializations at the Lateral Surface Junctional Complex Tight junction Adhering junction Cell A Cell B Desmosome Ross, M. H., & Pawlina, W. Histology: A text and Atlas. Specializations at the Lateral Surface Gap Junctions. - For communication between Young et al. Wheater's Functional Histology: A Text and Colour Atlas adjacent cells - Allow ions and small molecules to pass to the neighboring cell Gap junctions in intestinal epithelium Specializations at the Basal Surface Example Kidney tubules and striated ducts in the salivary gland  active absorption and secretion. Young et al. Wheater's Functional Histology: A Text and Colour Atlas Epithelia of kidney tubules Epithelial and Glandular Tissues Part IV: Specialization for Secretion of Glandular Epithelium Dr Jada C.D. Lee Lecturer Learning Outcomes At the end of this video, you will be able to: - Understand the differences between exocrine and endocrine glands - Classify the exocrine glands by their structures - Outline the secretory component and function of each structure listed Glandular Epithelium Exocrine and Endocrine Glands Endocrine gland Exocrine gland Ducted Secretory Ductless portion Lowrie. Histology: An essential textbook. Classification of Exocrine Glands Exocrine gland Number of secretory cells Ducted Structure of the gland Secretory Nature of secretory products portion Method of secretions Classification of Exocrine Glands Goblet cells (single cell gland) Ross, M. H., & Pawlina, W. Histology: A text and Atlas. - Present in tracheal and intestinal epithelia Goblet cells Karp et al. Karp's Cell and Molecular Biology: Concepts and Experiments. Respiratory Epithelium (X1,800) Classification of Exocrine Glands Structure of the glands Exocrine gland Ducted Secretory portion Rehfeld, A et al. Compendium of histology a theoretical and practical guide.  Classification of Exocrine Glands Nature of Secretory Products * Nuclei * Mucous gland Serous gland Mixed gland - Flattened nuclei - Round nuclei - Serous + mucous glands - Secrets glycoprotein (mucin) - Secrets proteins/enzymes e.g. Salivary gland - Pale cytoplasm (watery) - e.g. Salivary gland - Basophilic staining *serous demilune e.g. Pancreas serous cells arranged as a cap on the mucous cells Kühnel Wolfgang. Color atlas of cytology, histology, and microscopic anatomy. Classification of Exocrine Glands Mode of secretions Merocrine secretion Apocrine secretion Holocrine secretion The cell ruptures and secrete No loss of cytoplasm Production of membrane- the secretory products Secretions leaves by bound vesicles e.g. sebaceous gland exocytosis e.g. mammary gland e.g. sweat gland Classification of Exocrine Glands Summary Single cell Number of secretory cells Exocrine gland Multicellular Simple Branching Ducted of the duct Compound Structure of the gland Tubular Shape of the Secretory secretory parts Acinar portion Mucin Alveoli Nature of secretory products Protein Mixed Merocrine Method of secretions Apocrine Holocrine