Epithelia Flashcards
What are epithelia
They form a continuous sheet of cells. They are specialised for distinct functions
What is the function of epithelia
They act as barriers between the body and the external world and between fluid compartments within the body. They also transport molecules via absorptive processes
What is simple cuboidal epithelium
A single layer of cube cells. Have a central nuclei
What is the function of simple cuboidal epithelium
Secretion and absorption
What is the localisation of simple cuboidal epithelium
Kidney tubules, ducts, secretory portions of small glands and ovary surface
What is simple columnar epithelium
Basal nuclei and ciliated/non ciliated with microvilli
What is the function of simple columnar epithelium
Absorption and secretion of mucus and enzymes
What is the localisation of simple columnar epithelium
Non ciliated: digestive tract, gallbladder and excretory ducts. Ciliated: small bronchi and uterine tubes
What is simple squamous epithelium
Flat cells with disc-shaped nuclei
What is the function of simple squamous epithelium
Passage of materials by diffusion and filtration. Secretion of lubricating substances
What is the localisation of simple squamous epithelium
Kidney glomeruli, alveoli of lungs and blood vessels
What is simple pseudostratified epithelium
They look like there are multiple layers but all cells are in contact with the extracellular matrix. Several layers of nuclei. It is ciliated and non-ciliated
What is the function of simple pseudostratified epithelium
Secretion of mucus
What is the localisation of simple pseudostratified epithelium
Non ciliated: vas deferens and large glands
Ciliated: trachea and upper respiratory tract
What is stratified cuboidal epithelium
Generally 2 layers of cuboidal cells
What is the function of stratified cuboidal epithelium
Protects underlying tissue
What is the localisation of stratified cuboidal epithelium
Largest ducts of sweat glands and mammary glands
What is stratified columnar epithelium
Several cell layers. Basal cells usually cuboidal. Superficial cells are elongated and columnar
What is the function of stratified columnar epithelium
Protection and secretion
What is the localisation of stratified columnar epithelium
Urethra and conjunctiva of eyes
What is transitional epithelium
Several cell layers. Resembles stratified squamous and stratified cuboidal epithelium. Basal cells are cuboidal/columnar. Superficial cells are dome-shaped or squamous-like depending on stretch
What is the function of transitional epithelium
Stretches readily permitting distension of urinary organ
What is the localisation of transitional epithelium
Ureter, bladder, parts of urethra
What is the function of junctional proteins
They connect cells to each other and to basement membrane. Some allow intercellular communication eg. transport of ions. Also, enable polarisation
What are tight junctions
They are the most apical junction. They are a branching network of protein strands
What is the function of tight junctions
“Zipper” together neighbouring epithelial cells. Defines apical/basolateral boundary. Prevent passage of molecules and ions
What are adhering junctions
More basal than tight junctions. A “belt” that encircles epithelial cell directly beneath the tight junction
What is the function of adhering junctions
They allow cell-cell adhesion via interaction between extracellular domain
What are desmosomes
They are spot like adhesions arranged on the lateral surface of cells
What is the function of desmosomes
They allow cell-cell adhesion via interaction between extracellular domains
What are gap junctions
Lateral edges of epithelial cells
What is the function of gap junctions
Allow intercellular communication
What are hemidesmosomes
They are localised to the basal surface
What is the function of hemidesmosomes
They attach epithelial cells to the basement membrane
What are microvilli
The apical surface area can be increased by presence of a “brush border membrane”
What is the function of microvilli
They enable absorption
What can increase the basolateral surface area
Lateral interdigitations and basal foldings
What is important about the basolateral surface
It is important for transport across the epithelial layer
What are cilia
They are found on the apical surface of some epithelia. They are larger than microvilli
What is the function of cilia
They move back and forth to move particles
What is stratified squamous epithelium
Thick membrane composed of multiple cell layers. Superficial portion of cells are squamous “flattened”. Basal cells are cuboidal/columnar and metabolically active
What is the function of stratified squamous epithelium
Protects underlying tissue
