Epithelium Flashcards
What are the functions of epithelial tissue (5)?
protection (close together) , secretion, absorption (has polarity), filtration, and sensory; however this tissue is avascular and has specialized junctions
What are the developmental origins of epithelium?
All germ layers: ectoderm, mesoderm, endoderm
What are 2 types of glands found in epithelium?
- Exocrine - maintain connection to free surface via ducts or tubes; salivary, sebaceous, goblet
- Endocrine - do not have ducts, so secretes in surrounding tissue; adrenal, parathyroid, pituitary, islets of langerhans (insulin)
What are three types of exocrine glands?
Merocrine - deliver via a vesicle that fuses with membrane, apocrine - pinches off into the lumen of gland after secreted from apical side, and holocrine - which does apoptosis in order to secrete into the lumen of the duct.
What are the 2 ways we classify epithelium?
By # of layers (stratified or simple) and cell shape (squamous, cuboidal, columnar).
Where can you find simple squamous vs stratified squamous?
An example of simple squamous (flat nuclei) are those that make up vessel endothelium, lining the cavities such as peritoneum, pleura, and pericardium. Examples of stratified squamous are the vagina, mouth, and skin.
Where can you find cuboidal and columnar epithelium?
Simple cuboidal makes up most glands and ducts, for example the thyroid gland. These cuboidal cells have round nuclei. Simple Columnar are found in digestive tract, gallbladder, and upper respiratory tract (trachea). Their nuclei are basally located and oval.
What is transitional epithelium?
Found in the urogenital tract, kidney, and bladder; that consists of a stratified layer of cuboidal cells that can be single or multinucleate. This epithelium consists of three layers: basal, intermediate, and superficial. The superficial layer is dome shaped, and upon distention from fluid these cuboidal cells flatten and appear squamous.
What are some apical specializations?
Microvilli - short actin bundles that increase surface area to increase absorption. This is found at the striated border (intestine) and brush border (kidney tubule cells). Cilia are arranged microtubules that are either motile (9+2), primary, or nodal, and coordinated by dynein arms. They can be located in airways that move mucous. Stereocilia - these bundles of actin are anchored to the terminal web, and longer than microvilli. They are found in the cochlear hair cells and the male reproductive system.
What are types of lateral specializations (domains)?
Zonula Occludins (tight junctions) - it's closest to apical side, built from claudin and occludin complexes that restricts paracellular leakiness. Cholera and C. perfinges attack these tight junctions causing diarrhea and dehydration. Zonula Adherens: below occludins, formed by e-caderin/ catenin Ca2+ dependent complex. This complex anchors actin to the cytoskeleton to resist mechanical stress. Macula Adherens: plaques of desmocolins + desmogleins are anchored to intermediate filaments. This resist skin abrasion. Gap Junctions: formed by connexins which is form communication.
What happens with a mutation of gene GJB2 (connexin protein)?
mutation of GJB2 causes sensorineural autosomal deafness. The mutation prevents movement of K+ between cochlear hair cells without gap junctions, and the cells die.
What is function of basal domain?
consists of focal adhesion and hemidesmosomes that anchors into the basement membrane (reticular layer (CT) + basal lamina (epith)).
What are specific apical specializations (domains) of columnar cells?
In stratified border of intestine there is a coat of glycocalyx (microvilli sugar coat) + microvilli that appear like a blurred ribbon under a microscope. In upper respiratory, there are pseudostratified columnar with cilia which are more defined and long than microvilli. In the cochlear hair cells or sperm, there are stereocilia which appears thinner and branchier than cilia (more blurred).
Microvilli
simple squamous
Simple squamous in small intestine
simple cuboidal thyroid gland
Simple columnar with microvilli
The microvilli are more ribbon (blurred) like than cilia
Pseudostratified columnar with cilia and goblet
Stratified non keratinized squamous of the esophagus
stratified keratinized squamous of epidermis
transitional epithelium of ureter
Stratified columnar and cuboidal epithelium of salivary glands
good comparison of cilia in trachea and microvilli in striated border
