Epithelia Flashcards
What are the four categories of tissues?
Epithelia, CT, muscle, neural tissue
What is hematoxylin and eosin (H&E)?
Light Microscopy staining technique. Hematoxylin (basic dye) staining basophilic molecules - DNA + RNA in blue. Eosin (acidic dye) staining acidophilic molecules - proteins in pink.
Where does epithelia cover?
It covers all internal and external surfaces of the body.
What is a cutaneous membrane (skin)?
Epidermis (epithelium covering the external body surface) + underlying CT= cutaneous membrane
What is a mucous membrane?
Epithelia/epithelium (internal body surfaces: internal passage ways that opens to the exterior) + underlying CT = mucous membrane
What is endothelium?
simple squamous epithelium lining vessels, including arteries, veins, heart chambers, lymphatic vessels
How are covering epithelium classified?
- Simple epithelia: 1 layer of cells (@ sites of molecular transfer)
- Stratified epithelia: > 1 layer of cells (@ sites of protection)
What is mesothelium?
simple squamous epithelium lining internal body cavities not opened to the exterior cavities
What is a serous membrane?
Mesothelium + underlying CT = serous membrane @ following cavities
- pleural (lung)
- pericardial (heart)
- peritoneal (abdomen)
Epithelial Characteristics
- Cellularity: densely packed cell and little material in between
- Polarity: apical, later, and basal surface
- Specialized intercellular junctions (jxn): connects physically & functionally
- attached to basement membrane + CT
- Regeneration (mitosis)
- Avascular (no blood supply; dependent only on diffusion of CT) and innervated (nerve supply)
What a basement membrane?
Acellular layer between epithelium + CT; contains no cells itself
Function:
- physically supporting the epithelium structure
- along with CT, keeps epithelia attached
- semipermeable molecular filter
- epithelial repair + regeneration
Epithelia Function
structurally and functionally specialized based on location:
1. physical protection
2. controls permeability - transcellular (through) / paracellular (between cells) molecular transport
3. sense (touch, temperature, pain, vision, hearing, balance, smell)
4. specialized secretion production @ glandular epithelia
Epithelia Development
@ embryo in the form of simple sheets covering the surface and becomes:
a) remain as simple epithelium (respiratory - alveoli)
b) stratified epithelium (skin)
c) gland: specialized in secreting and producing cell products; either multi/uni cellular
How do glandular epithelia develop?
Exocrine Glands: outward secretion to surface often via duct
Endocrine Glands: inward secretion to tissue fluid to deliver hormones to target tissue via cardiovascular system
What do multicellular exocrine glands consist of?
- Acinus - secretory portion with vesicles
- Duct - conducts & modifies secretory products
What is the functional classification of exocrine glands?
- Secretion Type
- mucous glands: mucinogens secretion
- serous glands: protein-rich watery solution secretion
- mix seromucous glands - Secretion Mode
- merocrine: exocytosis
- apocrine: shred a part of cytoplasm + products in vesicles via “pinching”
- holocrine: entire cell releasing cytoplasmic content
List all of the multicellular exocrine glands.
Simple tubular - @ intestinal glands
Simple coiled tubular - @merocine& sweat glands
Simple branched tubular - @ gastric glands
Simple alveolar (acinar; spherical) - not in adults
Simple branched alveolar - @sebaceous glands
Compound tubular - @mucous glands
Compound alveolar - @mammary glands
Compound tubuloacinar - @salivary glands
What are goblet cells?
unicellular form in exocrine glands interspersed amongst epithelial cells; apically secretes mucus to protect the covering epithelia
@respiratory epithelium & digest tract
What are multicellular endocrine glands?
ductless foldable epithelial tissue surrounded by BM & CT
secretes cell products into the interstitial fluid to taken yo by BVs (systemic distribution)
What are unicellular endocrine glands?
@ covering epithelia
diffuse neuroendocrine cells (ex. enteroendocrine /EE cells from GI)
secretes cell products across BM and CT
- influence adjacent cells via paracrine signalling (EE cells -> secrete gastrin -> influence adjacent cells to secrete acid -> aid digestion)
- systemic distribution via endocrine signalling (EE cells -> CCK -> digestive hormones release from pancreas + bile to gall bladder)
EE cells from small intestine
What is specialized at the apical surface of covering epithelia?
- Microvilli: finger-like extensions with minimally motile which increase SA for more absorption and secretion; not viewable in LM
and size = rate of molecules moving through apical CM
focused on the small intestine (increased the rate of nutrient absorption) + kidney
- finger-like extension with highly motile and synchronized which moves fluid along the luminal surface (>microvilli); viewable in light microscopy
core consists with microtubules and associated proteins (dynein)
focused on respiratory epithelia + uterine tubes
What is simple squamous epithelia?
a thin epithelia with rapid and passive (usually) transport
@ alveoli (as “pneumocytes”), blood vessel (as endothelium), and mesothelia
What is simple cuboidal epithelia?
height = width of the cell
active secretion and absorption
may have microvilli to increase SA of the apical membrane and rate of molecular transport
@kidney
What is simple columnar epithelia?
height > width of the cell performing high rates of secretion and absorption
@small intestine
@gall bladder with microvilli
- paracellular mvt prevention via tight junction
- transports water out
- stores and concentrate bile
What is pseudo-stratified epithelium?
fakes stratified, all cells contact BM - simple epithelium
often ciliated
@respiratory tract (ciliated pseudostratified epithelium + goblet cells = cleans air)
What is stratified squamous non-keratinized epithelium?
internal surface protection that is kept moist in all time by glandular secretion
@mouth, throat, esophagus, rectum, anus, vagina, cervix epidermal cells joined by desmosomes
What is stratified squamous keratinized epithelium?
external surface and dehydration (epidermal layer) protection
@palm of the hand
keratinization: a dead sheet of surface cells strongly connected by desmosomes to develop water-resistant properties
What is transitional epithelium?
stratified epithelium allowing stretches and recoiling
no tension (empty organ) = domed surface cells
tension (filled organ) = flat cell
round apical nuclei
@urinary bladder and ureter
What are the functional classes of intercellular junctions?
internally attached into a functional unit:
- Anchoring junctions - mechanical strength by connecting each other by cytoskeleton and to BM
- Occluding junctions - blocks the intercellular space; control paracellular (btw cells) molecular mvm
- Communicating/gap junctions - ionic and molecular mvt control btw adjacent
How do cells anchor each other?
- Zonula adherens
- belt: surround cells with an actin microfilament network to bind in all directions (@ small intestine, epithelial sheet) and distribute shear (parallel) forces
-the intercellular space linked by cadherins; cadherins + proteinaceous plaque –> actin microfilaments - desmosomes
- bolt: joining the laterally linking cytoskeletal intermediate filament network of adjacent (@skin, epithelial sheet) and distributing shear forces
- the intercellular space linked by cadherins
- more desmosomes = more cell-cell adhesion
What are hemidesmosomes?
half desmosome linking cytoskeletal intermediate filament network on basal anchoring epithelium to BM (@ skin, epithelial sheet)
integrins (transmembrane protein) link BM across extracellular space
What is the function of tight junctions and its implications?
prevents / controls paracellular movement and back diffusion of actively transported molecules
creates [gradient] and maintains
barrier can be:
tight - small bowel + blood-brain barrier
leaky - kidney
@ blood-brain barrier, blood-testis barrier, blood thymus barrier
claudins (integral transmembrane glycoproteins) branches and determines TJ permeability
zonula occludens arranged in a belt form interacting with signalling molecules
What is a junctional complex?
Combination of tight junction, zonula adherens and desmosomes occurring together
@ small intestine
What is the function and parts of gap junction?
intercellular communication (metabolically and electrically) via intercellular connection with adjacent cells to coordinate cellular function
- permits the passage of ion + small molecules from cell to cell
- open/close conformation change
-synchronous movement
connexin (the pore of the gap junction): complex of 6 transmembrane proteins in the lateral CM
@bone cells, cardiac myocytes, and SM cells to coordinate cellular function
