Histology - Epithelium Flashcards
What are the basic tissue types?
Epithelium, connective tissue, muscle, and nerve
How is epithelium involved in homeostasis?
It regulates the content of the internal milieu of organs via selective transport and by forming barriers with variable permeabilities.
What are the three domains of a polar epithelial cell?
Apical - free surface
Lateral - cell-to-cell
Basal - attached to basement membrane
In general epithelial cells rest on an underlying layer of connective tissue
When epithelial cells lack a free surface
They are considered to constitute epithelioid tissues (i.e. endocrine organs)
What germ layer(s) is(are) epithelial cells derived from?
All germ layers give rise to epithelial tissue
What is the only exception of avascular epithelium?
The stria vascularis of the inner ear
How do epithelial cells get nutrients?
Diffusion from the blood veseels in underlying connective tissue.
Mesothelium
Epithelium that lines body cavities: visceral pleura, parietal pleura, pericardium, peritoneal cavity
Endothelium
Epithelium that lines the cardiovascular system
What are the basic functions of epithelium?
- Protection of underlying tissues from abrasion or injury
- Transcellular transport of molecules across epithelial layers
- Secretion (of mucus, hormones or enzymes)
- Absorption of material from a lumen (as in the intestinal tract or kidney tubules)
- Control of movement via selective permeability (of cells or specialized junctional complexes)
- Detection of sensations (as in taste buds, cells of retina, hair cells of the inner ear)
Simple squamos
Endothelium and mesothelium
(i.e. Bowman’s capsule and the alveoli)
Simple cuboidal
Small exocrine ducts
Germinal epithelium (ovary)
Kidney tubules
Thyroid follicles
Simple columnar
GI tract
Bladder
Pseudostratified columnar
Also referred to as respiratory epithelium
Trachea
Bronchial tree
Vas deferens
Epididymis
Stratified squamos nonkeratinized
Oral cavity
Esophagus
Vagina
Stratified cuboidal
Sweat gland ducts
Large exocrine ducts
Transitional (relaxed) epithelium
Urothelium: renal calyces, ureters, bladder, urethra
Stratified keratinized
Epidermis
Stratified columnar
Largest exocrine ducts
Transitional (distended) epithelium
Fuction of simple squamos epithelium
Fluid transport
Gas exchange
Lubrication
Reduce friction so viscera move
Lining membrane
Function of simple cuboidal epithelium
Secretion
Absorption
Protection
Function of simple columnar epithelium?
Transportation
Absorption
Secretion
Protection
Function of pseudostratified epithelium?
Secretion
Absorption
Lubrication
Transportation
Protection
Function of stratified squamos (nonkeratinized)?
Secretion
Protection
Function of stratified squamos (keratizined)?
Protection
Epidermal cells are flat without nuclei
Function of stratified cuboidal?
Absorption
Secretion
Function of stratified columnar?
Secretion
Absorption
Protection
Function of transitional?
Distensible
Protection
Endothelial cells
Simples squamos cells that line blood vessels, lymphatic vessels, and chambers of the heart
Contain Weibel-Palade bodies which are storage granules that contain von Willebrand factor
Weibel-Palade bodies (contain von Willebrand factor)
What epithelium lines the pericardium?
Mesothelium
What is released when endothelium is damaged to induce clot formation?
Von Willebrand factor (contained within the Weibel-Palade bodies)
How does endothelium take part in the immune system?
By interacting with lymphocytes and expression adhesion molecules and secreting several classes of interleukins (IL-1, IL-6, and IL-8)
How do endothelial cells take part in hormone synthesis?
Growth factors: hemopoietic colony-stimulating factors, fibroblast growth factor, and platelet-derived growth actor
Growth inhibitors: heparin, transforming growth factor b
Vasoconstrictors secreted by endothelium
Endothelins
Angiotensin-converting enzyme
Vasodilators secreted by endothelium
Nitric oxide and prostacyclin
Antithrombogenic substances produced by endo/subendothelial tissue
Tissue plasminogen activator (interferes with platelet aggregation)
Thrombomodulin
Anticoagulants that are produced by endo/subendothelial tissue
Thrombomodulin
Plasminogen tissue factor
Microvilli
Contain an actin core, and are covered by a plasma membrane (appear as a brush border in some cells like intestinal epithelial cells)
Glycocalyx
glycoproteins secreted by goblet cells. The glycocalyx is adsorbed onto the surface of microvilli.
Glycocalyx serves for cell protection and cell recognition; often contains digestive enzymes.
Glycocalyx stain positively with perioidc acid Schiff (PAS)
Stereocilia
long microvilli (nonmotile)
Terminal web
Of the cytoskeleton, contains: actin, myosin, and spectrin (along with other cytoskeletal proteins)
The cortical cytoskeleton
Composed of intermediate filaments (including various cytokeratins) and the terminal web
Axoneme
the 9+2 arrangement of microtubules in cilia
9 outer doublet microtubules plus two central microtubules
Basal bodies
Found at the base of every cilium, consisting of 9 triplet microtubules and no central microtubules
Where are the dynein of cilia found?
Tight junctions
Forms zonula occlusions
Impermeable (intercellular diffusion barrier)
Do not function to hold epithelial cells together or to an underlaying basal lamina.
But they maintain apical and basolateral membrane domains, thus limiting the movement of proteins with the plane of the lipid bilayer and therefore contributing to the functional polarity of epithelial cells
(Tight junctions are Ca2+ dependent but for as needed with no protein synthesis)
Found at the apical surface of epithelial cells (from proteins occludins and claudins)
Adherin junctions
Zona adherens and Macula adherens
Provide mechanical stability by linking the cytoskeleton of one cell to another (or to basal lamina)
Also, importgant for cell-to-cell recognition and singal transduction
Communicating junctions (gap junctions)
Allow for chemical and electrical coupling between cells; coordinating cellular activity related to homeostaasis
Transmembrane proteins call connexons (hexameric protein) that open and close in response to changing pH and Ca2+.
Connexons of neighboring cells line up to form patent channels
What cell types contain actin? What cell types contain keratin?
Actin - virtually all cell types
Keratin - unique to epithelial cells
Zonula
belt-like structure that encircles apical portion of the cell
Maculae
Spot-like or button-like structures
Zonula adherens (ZA)
Belt desmosomes
A belt-like junction around apical portions of an epithelial the cell, but immediately below the level of tight junctions. ZA interacts with actin in the cortical cytoskeleton.
The membranes of adjacent cells approximate, do not contact ZA
Macula Adherens
MA is known as a desmosome
(or spot desmosome to contrast with “belt desmosome” – an older term for ZA). Desmosomes are located below the level of the zonula adherens and they interact with intermediate
filaments (keratins in epithelia cells) of the cytoskeleton.
Calcium dependent “spot welds” that bind adjacent cells together
Resist shear forces
The intercalated disc is a highly specialized type of MA
Actin molecules of adjacent cells are attached to? By?
(Desmosomes)
Attached to E-cadherin-catenin complexes by alpha-actinin and vinculin
E-cadherin and catenin are membrane proteins
alpha-actinin and vinculin are cytoskeletal proteins
Pemphigus vulgaris
Individuals produce autoantibodies to desmosomal proteins. Those affected can suffer fluid loss through the skin and mucous membranes (this can be fatal)
Disruption of desmosomal proteins causes epithelial cells in the basal layers of the skin to lift off their underlying basal lamina and for cells (keratinocytes) in the middles and upper layers to lose continuity with each other.
Where in epithelium can desmosomes be found?
Throughout the lateral domains, but below the level of the zonula occludens and zonula adherens
Hemidesmosomes: create static or very stable links between the cytoskeleton and extracellular matrix on the basal membrane domain of epithelial cells. Hemidesmosomes are abundant in mature organs.
Focal adhesions
Create dynamic links between the cytoskeleton and extracellular matric on the basal membrane domain of epithelial cells. They are abundant during embryonic development when cells are migrating.
Hemidesmosomes
Robustly anchor epithelial cells to their underlying basal lamina by forming attachements to keratin (very stable protein)
Focal adhesions
Dynamically anchor epithelial cells to their underlying basal lamina by forming attachments to actin.
Basement membrane
Composed of basal and reticular lamina
Basal lamina - synthesized by epithelial cells and consists primarly of collagen type IV, laminins, entactin, proteoglycans, and fibronectin. Nidogens function as glue and perlecan (heparan sulfate bound to nidogen)
Reticular lamina - synthesized by connective tissue cells and consists primarily of collagen type III
Collagen IV
unique to basal lamina (lamina densa) and provides the structural framework for the basal lamina. Collagen IV is heavily glycosylated and is comprised of small fibrils that do not form large fibers typical of many collagens. Collagen IV is highly flexible; its C-terminal
ends (indicated by the dark balls on the drawing)
dimerize while its N-terminal ends form extensive
networks.
Laminin
A protein found in the basal lamina of the basement membrane. Laminin is a large, cross-shaped glycoprotein that binds components of basal lamina to each other and to epithelial cells. There are three components (alpha, beta, and gamma)
A - Simple squamos
B - Simple cuboidal
C - Simple columnar
D - transitional
E - endothelium
F - stratified squamos
G - ciliated pseudostratified columnar (respiratory)
I - endothelium
Cadherin
Calcium dependent adhesion protein
Found in desmosomes
E-cadherin lost in breast cancer cells - metastasis
A principal cytoskeletal component associated with the zonual adherens in epithelial cells is
Actin
What mesothelium is the only example of non-simple structure?
The germ mesothelium of the ovary is simple cuboidal
Ducts within organs are lined with what type of tissue interiorly?
Typically squamous lines interior duct
Ducts that exit an organ
Tissue type - Histo
Typically stratified cuboidal epithelium lines duct
Where can ciliated pseudostratified columnar epithelium be found other than the respiratory tract?
Parts of the male reproductive system
What is the predominant protein found in cilia?
Tubulin
What is the predominant protein found in microvilli and stereocilia?
Actin
Epithelium of the urinary bladder
Transitional epithelium (only found in the bladder and the most proximal parts of the ureter)
Transitional epithelium is often binucleated (also can either polyploid or monoploid)
What forms the internal glandular tissue?
Hair follicle
Stratified squamos epithelium of the hair follicle
What cell junction is disrupted in endothelial cells to cause edema (leaking of cellular fluid into extracellular space)?
Tight junctions (Zonula occludens)
PAS Stain on goblet cell
Stains the glycocalyx
What cells are within the blue oval?
Resident lymphocytes in the intestines
Metaplasia
A reversible transformation of a mature cell type into another cell type that is not native to that specific region in response to chronic irritation or cell injury (e.g., transformation of squamous epithelium into columnar epithelium in the case of Barrett esophagus).
Abmoss
