Epithelial Tissues Flashcards
Role of epithelial tissues?
Selective diffusion Absorption Secretion Physical protection Containment
Epithelial cells are closely bound to one another by?
Cell junctions
Role of epithelial cell junctions?
Provide physical strength
Mediate exchange of “information” and metabolites
Epithelial are supported by…?
Basement membrane
Role of basement membrane
Separate epithelia from underlying support tissues
How is epithelia classified?
- Number of cell layers (simple vs stratified)
- Cell shape (squamous, cuboidal, columnar)
- Presence of surface specializations (cilia, villi, microvilli)
Where is simple squamous epithelium found?
Lung (pleural), heart (pericardial), or abdominal (peritoneal) cavities
Where is simple squamous epithelium found?
Lung (pleural), heart (pericardial), or abdominal (peritoneal) cavities
What is the function of simple squamous epithelium?
Passive transport of either gases or fluids
Where is simple cuboidal epithelium found?
On small ducts and tubules
Function of simple cuboidal epithelium?
Has excretory, secretory, or absorptive functions
Where is simple columnar epithelium found?
highly absorptive surfaces like the small intestine
What is the function of simple columnar epithelium?
Absorption and secretion
What is the function of simple columnar ciliated epithelium?
Cilia move in a wave-like manner to propel fluid or minute particles
Where is pseudostratified columnar ciliated epithelium found?
Large airways in the respiratory tract (which is why its also known as respiratory epithelium)
Why is respiratory epithelium called “pseudostratified”
All cells lie on one basement membrane but the nuclei are on different levels
What is the main function of stratified epithelia?
Protection
Where is stratified squamous epithelium located?
Oral cavity, pharynx, esophagus, anal canal, uterine cervix, and vagina
Where is keratinized stratified squamous epithelium found? How does the keratin help?
Found on epithelial surface of skin (epidermis). Helps withstand constant abrasion and desiccation
Where is stratified cuboidal epithelium located?
Lines larger excretory ducts (eg. salivary glands)
Where is transitional epithelium located? What is its other name?
Urinary tract, urothelium
Where is transitional epithelium located? What is its other name?
Urinary tract, urothelium
What makes transitional epithelium unique?
Has both features from stratified cuboidal and stratified squamous epithelium
What are the three types of cell junctions?
Occluding (tight) junctions, Adhering junctions, communicating (gap or nexus) junctions
What is the role of tight junctions?
Seal intercellular spaces and prevent migration of “floating” membrane proteins
What is the role of adhering junctions?
Tightly bind constituent cells of epithelium together and act as anchorage sites for cytoskeleton of each cell
What are the types of adhering junctions and their respective roles?
Zonula adherens - forms a continuous band and provides structural reinforcement
Desmosomes - provide stability and strength
What is the role of the communicating junctions?
Permits passage of small molecules between adjacent cells
What is the role of the communicating junctions?
Permits passage of small molecules between adjacent cells
What are the luminal surface specializations?
Cilia, microvilli, stereocilia
What is the structure and role of cilia?
Structure: long, motile structures, has a central core axoneme made of 20 microtubules arranged as a central pair surrounded by nine peripheral doublets. Each complete tubule has arms made of dynein that extend towards incomplete tubule of adjacent doublet and towards the central microtubule pair.
Role: moves in a wave-like motion to propel surface films of mucus or fluid in a consistent direction
What is the structure and role of microvilli?
Structure: minute finger-like projections, cytoplasmic core of each microvillus has fine actin filaments that insert into terminal web. Terminal web anchored to zonula adherens
Role: increase surface area available for absorption
What is the structure and role of stereocilia?
Structure: extremely long microvilli, internal structure is a filamentous skeleton, found in small numbers in parts of the male reproductive tract
Role: facilitate absorption
What are the basal surface specializations?
hemidesmosomes
Role of hemidesmosomes
Means of anchorage of cell via its cytoskeleton to basement membrane + underlying support tissues
What are exocrine glands?
glands that discharge secretory product via duct onto epithelial surface
What are endocrine glands?
ductless glands with secretory products that diffuse directly into the bloodstream
What’s the difference between a simple and compound gland?
Simple glands don’t have a branched duct. Compound branches do have a branched duct
What are the types of secretion from exocrine glands?
Eccrine - mainly proteins secreted via exocytosis
Apocrine - discharge of membrane-bound vesicles containing secretory product, mainly lipids
Holocrine - disintegration of secretory cell to release secretory product
Secretory products of some exocrine glands are embraced by contractile cells called ______
Myoepithelial cells
The secretory products of endocrine glands are called hormones. True or False?
True
Endocrine gland products only affect activity locally. True or False?
False, controls activity of cells and tissues far removed from site of secretion
How do endocrine glands release spread hormones?
Via the network of small blood vessels that surround them
