Epithelial+Tissues+Lab


 * 29 August 2006**
 * Microanatomy Lab – Epithelial Tissues Lab**
 * Dr. Robert Crissman, Ph.D.**

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=**Epithelium**=


 * Avascular
 * Nutrients supplied by connective tissue below the epithelium
 * Basement membrane
 * Thick band under the basal region of the epithelium
 * Basement membrane is a light microscope term
 * Basal lamina is an electron microscope term (on EM level, basement membrane has 3 layers)
 * Part of connective tissue
 * Polar
 * Apical surface contains cilia; basolateral does not, etc.
 * Cellular junctions
 * Dark band below cilia is the terminal bar where junctional complex resides
 * Zonula occludens, zonula adherins, and macula adherins
 * Zonula occludens form a tight junction, blocking passage of materials and forcing them to cross through epithelial cells rather than around them
 * Terminal web is nearly the same place, where cilia microtubule axoneme attaches
 * Free surface
 * Highly cellular, forming a sheet

**Jejunum**

 * Surface modifications:
 * Brush-border composed of microvilli
 * Microvilli on apical surface forming a continuous band called the brush-border
 * Microvilli too small to see individually on light level
 * Function of microvilli
 * Increased surface area for absorption
 * Goblet cell
 * Located in G.I. tracts, found in epithelial tissue
 * Unicellular mucus gland
 * Terminal Web
 * Located underneath the apical membrane
 * Core actin filaments of microvilli are attach to terminal web
 * Epithelium
 * Elongated simple columnar cells

**Epididymis**

 * Surface modification:
 * Stereocilia
 * Diagnositic characteristics: longer than microvilli and can be seen in clumps
 * Length of stereocilia up to 20-25% length of cell
 * Not motile
 * Structure
 * Actin filament core
 * Epithelium
 * Pseudostratified columnar

**Trachea & Esophagus**

 * Surface modification:
 * Cilia
 * Diagnostic characteristic: Taller and denser than brush border microvilli but shorter than stereocilia
 * Individual striations visible
 * Function
 * Motile – moving mucus along surface
 * Beat in synchronization – coordinate beating between cells by gap junctions
 * Gap junctions composed of connexons made of connexins
 * Not visible on light microscope level
 * Gap junctions are all over the basalateral component of epithelium in addition to being in the terminal bar
 * Epithelium
 * Pseudostratified ciliated columnar
 * Diagnostic characteristics: layered nuclei but columnar cell
 * Cells not seen one on top of another
 * All cells sit on basement membrane
 * Cells in connective tissue
 * Could be fibroblasts, macrophages, lymphocytes
 * Asthmatic patient
 * May have influx of immune system cells

**Spermatozoa**

 * Flagella
 * Composed of microtubules in an axoneme
 * Longer than cilia and only one per cell
 * Moves the whole cell
 * Has a mitochondria wrapped around it

**Artery, Vein, and Nerves**

 * Nerves
 * Packed full of neurons, no lumen
 * Artery
 * Has a lumen with thick layer of muscle cells
 * Inside layer of smooth muscle cells is the internal elastic lamina
 * Epithelium
 * Simple squamous
 * Very thin to allow passage of nutrients and waste through the epithelium
 * Nucleus is typically a squished disk
 * On the lumen of the vessel
 * All blood and lymph vessels in body are simple squamous
 * Vein
 * Larger more irregular lumen

**Thyroid**

 * Made up of follicles – hollow spheres
 * Have a wall of simple, cuboidal epithelium
 * Round nuclei, cell is long as it is tall, single cells
 * Free space is the hollow sphere so basement membrane is on the other side of the epithelium
 * Kind of like swiss cheese the hollow areas where the apical surface is

**G.I. Tract**

 * Epithelium
 * Simple columnar – Tall narrow cells in one layer
 * Brush-border on apical surface
 * Be aware of planar artifacts
 * In some portions, it appears to be pseudostratified because the section is cutting through different layers of cells
 * However, further downstream, most cells look more simple columnar, indicating the correct epithelial type, and suggesting that the pseudstratified look in upstream cells is in reality a planar artifact

**Skin**

 * Epithelium
 * Keratinized stratified squamous
 * Cell on surface lack nuclei because they are so full of keratin that the cells have died
 * Five layers – that you don’t have to know
 * Stratum Basale
 * Germinal layer that produces new skin cells, pushing cells towards the surface
 * Cells differentiate on the way to the surface
 * Stratum Spinosum
 * Straum Granulosum
 * Stratum Lucidum
 * Stratum Corneum

**Esophagus**

 * Epithelium
 * Non-keratinized stratified squamous
 * Nuclei of cells reaches the apical surface, so they are non-keratinized

**Urinary Bladder**

 * Non-Distended Epithelium
 * Translational epithelium or uroepithelium
 * Diagnostic characteristics: Look at surface cells for shape, and determine if they extend over several layers of cells.
 * Translational epithelium looks like stratified with lots of nuclear layers with cuboidal surface cells but cells aren’t the same size the whole way down and extend over several layers of underlying cells
 * Stratified epithelium has cells all the same size and don’t overlap
 * Distended Epithelium
 * Epithelium is stretched out with maybe 3-5 layers on surface
 * Appear to be squamous cells now, but still overlap several cells under it

=**Glands**=


 * Classified structurally, mode of secretion, secretion type, presence/absence of ducts

**Axillary Skin**

 * Sebaceous gland
 * Associated with hair follicle
 * Multicellular simple alveolar holocrine sebum gland
 * Cells in gland start out looking alive with nuclei but gradually disappear as they approach the duct – indicates cells are dying as they are secreted
 * Sebum – oiling secretion
 * Clincal – acne is when bacteria reach into gland and cause inflammation
 * Eccrine Sweat gland
 * Simple coiled tubular merocrine serous gland
 * Secretory portion is simple cuboidal epithelium
 * Duct portion is stratified cuboidal epithelium (2 layers of nuclei)
 * Apocrine sweat gland
 * Simple coiled tubular merocrine serous gland
 * **Apocrine sweat gland is a misnomer**
 * Larger with bigger lumen in secretory portion
 * Secretory portion is simple cuboidal epithelium
 * Duct portion is stratified cuboidal

**Salivary Gland**

 * Submandibular Gland
 * Multicellular compound tubular alveolar merocrine mixed gland
 * Serous vs. Mucus
 * On high magnification, mucus cells are lighter staining because the mucus gets sucked out of cells during preparation, leaving a light lacy apparent of cytoplasm in mucus cells
 * Serous cells secrete serous secretions very quickly and don’t get left in the cell, leaving only the machinery (ribosomes, etc.) behind
 * If both cells are present, then it’s a mixed gland
 * Epithelium of duct is simple high cuboidal or low columnar