Epithelia Flashcards
What are the functions of the epithelium (5)?
Protection, absorption, secretion, contractility, sensory
Describe Microvilli
to increase surface area for secretion/absorption. made with actin filaments and anchored by villin. TW can move to expose them to new environment but they cannot move themselves.
Describe mobile cilia
made with microtubule cores in 9+2 doublets, use dynein to bend to one side and then passively snap back into place. Useful for moving things along apical surface. much larger than microvilli. stem from basal body MTOC.
What are some places you might find motile cilia?
respiratory tract, uterine tract, ventricles, middle ear cavity
Describe primary cilia.
these are sensory cilia, still composed of MTs, but with a 9+0 conformation, so they cannot move. usually they are only 1/cell.
What are some functions for primary cilia?
Sensory. Also important for establish a left/right plane in early gestation.
Describe flagella. Where might one be found?
Flagella is an extremely long cilia used for transportation. Found on sperm. there is only 1/cell. They have the classic 9+2 setup with extensive mitochondria.
What are stereocillia? Where are they found?
Misnomer- they are actually long microvilli and form the sensory hairs of the inner ear.
What are the 4 junctions found on the lateral side?
Tight junction (zonula occludens), adherent junction (zonula adherens), desmosome (macula adherens) and gap junctions
Describe tight junctions.
Go all the way around the cell, most apical junction. Formed by connections between claudin and occluden proteins. Regulate paracellular pathway (between cells) and provides diffusion barrier for cellular proteins.
Describe adherent junctions
Formed by cadherin proteins and attached to actin filaments, they connect the terminal webs of adjacent cells
What does cadherin do?
Found in adherent junction and desmosome, forms linkage between adjacent cells
What does claudin do?
one of the linking proteins in tight junctions
What does occludin do?
one of the linking proteins in tight junctions
Describe desmosomes.
Spotweld junctions. cadherins bind to IFs and provide significant structural connection between adjacent cells. These are the strongest connections
Describe gap junctions
Proteins called connexins group together in sets of 6 to form connexons which forms the pore in gap junctions. One gap junction has 100s of pores and allows the passage of small ions
Describe the basal membrane.
All epithelia grow on a basement membrane. it contains no cells, but instead is made of type 4 collage, fibronectin, laminin, proteoglycans, and enactin
What are the functions of the basal membrane (4)?
- limits growth
- allows diffusion
- provides structure for growth
- provides signaling
What does fibronectin do?
It is a protein found in the basement membrane
What does laminin do?
it is a protein found in the basement membrane.
What does enactin do?
it is a protein found in the basement membrane.
List the specializations of the basal membrane
hemidesmosome and focal adherens
Describe the hemidesmosome.
Integrin froms a connection between the laminin and fibronectin and the IFs of the cell to secure them to the basement membrane
Describe the focal adherens.
Intergin forms a connection between actin and laminin and fibronectin.
Where might you find simple squamous cells?
blood vessels or mesentaries of organs
Where might you find simple cuboidal cells?
kidney tubules or ducts
Where might you find simple columnar with microvilli?
Intestines
Where might you find simple columnar with cilia?
respiratory tract
where might you find pseudostratified cells?
upper respiratory tract- always have cilia
where might you find non-keratinized stratified squamous cells?
esophogus or vagina
where might you find stratified squamous keratinized cells?
skin
What is the benefit of keratinizing cells?
It prevents water loss
Where might you find stratified cuboidal?
sweat glands
What are urothelium cells and where might you find them?
They appear rounded on top because they are made to stretch. They can be found in the urinary tract.
What is metaplasia?
When cells are exposed to stressors, they can change their type (ie squamous to columnar) to adapt. However, this flexibility makes them more susceptible to cancers (carcinomas)
What is an exocrine gland?
secretes to the surface of the epithelia
What is an example of a unicellular gland?
Goblet cell- secretes mucus. Found in respiratory and intestinal tracts.
What is the difference between a compound and simple gland.
simple glands have a 1 duct / 1 gland ratio. Compound glands have many more glands/ 1 duct.
Difference between tubular and acinar glands?
tubular are like tubes, acinar is like a circle (also called alveoli)
What are the 3 secretion mechanisms and how do they differ?
holocrine- entire contents of cell
apocrine- secreted in vesicles- more lipids b/c of membrane
merocrine- secreted without the vesicle- most common
How can you tell the difference between mucous and serous secretions?
Mucous are clear on stains because they have no proteins, serous are dark because the proteins within them stains.
What are the three sides of epithelia?
apical (towards environment), lateral, basal (away from environment)
