Chapter 4 - Epithelial Tissue Flashcards
Epithelial tissue
- aggregated polyhedral cells
- lining of surface of body cavities; glandular secretion (exocrine, sweat glands, etc.)
- barrier tissue, plays a role in signaling, proliferation, and cell migration
How are epithelial cells arranged?
maximum cell to cell contact; packed very tightly w/ minimal extracellular material btwn them
Where is epithelial tissue located?
- rests on basal lamina/basement membrane
What are epithelial cells held together by?
intercellular junctions
Is epithelial tissue vascularized?
No
Does epithelial tissue/cells have any surface modifications?
Yes, depending on where in the body, it may have cilia or microvilli, etc.
Are epithelial cells polarized?
Yes, the top/outer surface has different proteins than the basal surface
Intercellular junctions
- barrier movement of molecules btwn adjacent cells
- holds cells together tightly
- allow intercellular communication
Zonulae occludens/tight junctions/occluding junctions
- occlude cells, molecules cannot pass btwn cells w/o being transported into the cell first
- encircle apical region of cell (like a belt), always at the top of the cell
- adjacent cell membranes are fused
Zonulae adherens
- adhesion of adjacent cells
- web/belt of microfilaments (actin), encircle the cell
- thicker than tight junctions
- cells are held tightly together, but not fused; not as occlusive as tight junctions
- always beneath the tight junctions
Maculae (spot) adherens/desmosome
- “spot welds btwn adjacent cells, do not encircle the cell
Intermediate filaments
- filament of the cytoskeleton, inserts into the maculae adherens
- can be used in the diagnosis of the origin of a tumor
Gap junctions/communicating junctions
- ions and small molecules can pass through (like calcium)
- formed by connexons
- important in intercellular communication (especially in cardiac cells)
Connexons
- form gap junctions
- a pore than can open and close; made of a protein called connexin
Cilia
- Move in unison to propel material past the cell surface
- covered by the cell/plasma membrane
- mainly found moving mucus in respiratory and reproductive systems in animals
- ATP-dependent movement
Structure of cilia
- longer than microvilli
- similar to flagella, but longer
- supported by microtubules arranged in a 9+2 assembly (circle of 9 pairs of microtubules, w/ one pair in the middle)
- insert into the basal body for stability
- contains the protein dymein, which forms arms on the microtubules to grab adjacent microtubules, causing the cilia to bend, thus allowing it to move
- dymein cannot function without ATP
Microvilli
- fingerlike extensions of the cell that increase cell surface area for absorption
- covered by cell/plasma membrane
- supported by actin filaments
- about 1 micrometer in length
- found on cells whose functions is absorption (intestinal epithelium, renal tubular epithelium)
Surface epithelia
- cover and line things
- classified by number of layers (simple and stratified) and shape of cells (squamous, cuboidal, columnar)
Simple squamous
- surface epithelia
- single layer of squamous epithelia
- mesothelium (embryonic tissue, forms peritoneum), endothelium of blood vessels, alveoli
Simple cuboidal
- surface epithelia
- single layer of cuboidal epithelia
- roughly the same in height and width, nuclei are round and in the middle
- renal tubules
Simple columnar
- surface epithelia
- single layer of columnar epithelia
- tall and skinny, nuclei are oval and sometimes towards the bottom
- intestinal epithelium, gall bladder
Stratified squamous
- surface epithelia
- multiple layers of squamous epithelia
- underlayers appear cuboidal or columnar, outer layers become thin and squished
- provides protection from abrasion (oral cavity, esophagus, vagina, cervix, skin)
What are the two types of stratified squamous epithelia?
- nonkeratinized - covers wet surfaces/surfaces where mucus is present
- keratinized - waterproof, covers dry surfaces, cells become packed with keratin and the outer cells die/slough off when come in contact with abrasion
Transitional epithelium
- multilayered epithelia, outermost layer is dome-like when relaxed and become flattened when stretched
- lines things that need to expand
- urinary bladder, ureters, urethra
Pseudostratified ciliated columnar epithelium (PSCCE)
- appears to be stratified, but all cells are attached to basal lamina
- respiratory tract ONLY (nasal cavity/sinuses, trachea, bronchi)
- contains many different types of cells - cilia, goblet cells, stem cells, mitotic figures, etc.
How are glands derived from epithelial tissue?
- during fetal development, epithelial cells proliferate and penetrate the underlying connective tissue
- cells may or may not maintain a connection with the surface epithelium
- exocrine maintain contact w/ surface epithelia, endocrine do not
Glandular epithelium
- function: synthesis, storage, secretion of proteins, or lipids
- derived from epithelial tissue during embryonic development
What are the different types of glandular epithelium?
- unicellular - goblet cells in intestinal and respiratory tracts
- multicellular - clusters of cells
- exocrine - secretions released into ducts, which empty into epithelium (goblet cells)
- endocrine - secretions enter circulatory system
What cells turn into epithelial cells during mitosis?
stem cells; found in basal layer of stratified epithelia
What is the rate of division for epithelial cells?
- have high turnover rate, tend to divide quicker than other types of tissue in the body (intestine = 7 days, skin =10-14 days)
- chemo inhibits the rapid replenishment of epithelial cells, which is why pts. w/ cancer often have intestinal issues
Metaplasia
- abnormal conversion of one cell type to another
- in smokers, bronchial PSCCE can convert to stratified squamous
Carcinoma
a malignant tumor of epithelial origin
Adenocarcinoma
- malignant tumor from glandular epithelium
- Immunocythochemistry used to determine origin of tumors
