Epithelia PDF

Biological tissues I: Epithelia Dr Rebecca Shepherd By the end of this session: Intended Learning Outcomes Classify tissues into four basic types Identify the types of epithelium Identify the surfaces of epithelial cells Describe cell attachments What is a tissue? “an assemblage of similarly special...

Biological tissues I: Epithelia Dr Rebecca Shepherd By the end of this session: Intended Learning Outcomes Classify tissues into four basic types Identify the types of epithelium Identify the surfaces of epithelial cells Describe cell attachments What is a tissue? “an assemblage of similarly specialized cells united in performing a specific function” Cell Tissue Organ Organ system Organism How many types of tissue are there in the human body? Epithelia Epithelial cells form sheets of cells, called ‘epithelia’, which function mainly as: o A covering or lining for body surfaces, for example, skin, gut, respiratory and genitourinary tracts, blood vessels, body cavities and ducts o The functional units of secretory glands and solid organs, for example, salivary tissue and liver. Cell polarity All epithelia are supported by a basement membrane which separates the epithelium from underlying supporting tissues. Cell-Cell Connections Many types: Desmosomes: connect the intermediate filament networks of adjacent cells Hemidesmosomes: attach epithelial cells to the underlying basement membrane Tight junctions: form a seal between cells that is so strong that not even ions can pass across it. Epithelium Classification The classification of epithelia is based on: Cell shape How they are stacked together Special features Structure and functions of keratin proteins in simple, stratified, keratinized and cornified epithelia Hermann H. Bragulla, Dominique G. Homberger First question Is it surface epithelium (lining the outside or inside of the body) or glandular epithelium (forming a gland) What shape are the cells Flat Squamous Square Cuboidal Rectangular Columnar Squamous (Protective) Squamous epithelia cells (a) have a slightly irregular shape, and a small, centrally located nucleus. These cells can be stratified into layers, as in (b) this human cervix specimen. Cuboidal (Secretory) Columnar (Absorptive) Pseudostratified One Simple Keratinised? How many layers of cells? More than one Stratified Transitional Only one layer of cells, but looks like more? Pseudostratified Nothing Simple Stratified Cilia Finger like projections Microvilli Stereocilia Special function? Mucous producing? Secretory Enzyme producing? Hormone producing? Finger like projections Microvilli – absorption Cilia – Motile (movement) Stereocilia – Non-motile (sensory) Glands Tubular –intestine, uterine glands Coiled – sweat glands Compound - pylorus Glands Secretory cells Exocrine glands - release their contents onto an epithelial surface either directly or via a duct Endocrine glands - have no duct system but release their secretions into the bloodstream to act on distant tissues Summary There are 4 types of tissue: epithelium, connective, muscle & nervous There are apical, lateral and basal sides to each epithelial cells There are squamous, cuboidal and columnar cell types. They are attached to each other by desmosomes and hemi-desmosomes. Recommended Resources Stevens and Lowe’s Human Histology (eBook via Bristol Library) Wheaters Functional Histology (eBook via Student Clinical Key) https://histologyguide.com/ https://www.histology.leeds.ac.uk/ https://www.anatomyatlases.org/MicroscopicAnatomy/Microsco picAnatomy.shtml The Remarkable Life of Skin, Monty Lyman Any questions? [email protected]