Epithelium and Glands Flashcards
what are the four basic tissue types?
Epithelium, nerves, connective tissue, muscle
What is the definition of epithelium?
Single or multilayered sheet of cells that cover the free or open surface of the body to the internal or external environment
What is the epithelium that lines the peritoneal, pleural, and pericardial cavities called?
mesothelium
what is the epithelium that lines blood and lymphatic vessels called?
endothelium
what are some of the functions of epithelium?
protection, secretion (glands), absorption (intestines), gas exchange (lung alveoli), and transport between blood and tissues (vascular endothelium)
What are the two types of layering of epithelium? and 3 shapes?
simple and stratified; cuboidal, columnar, squamous
what dictates that classification of the epithelium?
the cell on the apical surface
what are some examples of simple squamous epithelium?
It is very hard to see the cytoplasm here. examples are mesothelium and endothelium
examples of simple cuboidal?
small ducts of exocrine glands, collecting ducts of kidney
characteristics and examples of simple columnar epithelium?
taller than they are wide, nuclei are often but not always at the same level, and can be elongated like the entire cell. Found on surfaces of the digestive tract and is found in the excretory ducts of many glands
what are the characteristics of stratified squamous?
cells next to basal lamina are cuboidal, and are often referred to as “basal cells”, squamous cells nearer the surface are flattened. Many layers. It can be nonkeratinized or keratinized for protection
what are keratinized cells?
cells containing a thickened plasma membrane and bundles of tonofilaments. they have no nucleus.
where can stratified cuboidal cells be found?
the ducts of sweat glands
what types of cells are found beneath the most apical cells for stratified columnar and stratified cuboidal?
polyhedral cells
Where can stratified columnar cells be found?
largest ducts of exocrine glands
What characterizes pseudostratified columnar?
All cells will contact the basal lamina, but not all will reach the free surface. most nuclei are not aligned! The cells that reach the surface will be columnar. i.e. goblet cells in the respiratory epithelium which secrete mucus
What is transitional epithelium?
The shape of the apical cells can change. In a relaxed state, the apical cells are generally dome-shaped. In a stretched state, the apical cells are flattened to look like squamous cells. (i.e. urinary bladder)
why might the lateral domain contain interdigitations?
to increase the surface area for cell-cell interactions. this is especially important with the epithelial cells risk facing shear forces
what is the primary function of the basal domain?
to attach the epithelium to the underlying connective tissue
what is the cytoskeletal component of cilia?
The axoneme, microtubules arrange in a 9+2 fashion
what anchors cilia to the rest of the cell?
The basal body. There are 9 triplet microtubules
what is the function of cilia?
Oscillation, to move things along the epithelial surface
what is the cytoskeletal component of microvilli?
core of actin filaments
what protein crosslinks actin to the terminal web in microvilli?
spectrin
what protein crosslinks actin to the terminal web in stereocilia?
alpha-actinin
what proteins link microvilli to the plasma membrane as it extends out?
myosin 1, and calmodulin, which is calcium-dependent. keep in mind that microvilli are found in the intestine
What protein links stereocilia to the plasma membrane?
ezrin
What protein controls the beating of the cilia?
dynein. holds on to neighboring doublet of microtubules
since multiple adjacent actin make up a microvilli, what protein crosslinks them?
villin and fimbrin
since multiple adjacent actin make up a stereocilia, what protein crosslinks them?
fimbrin
only microvilli use VILLIN
what is the primary function of microvilli?
increase surface area for absorption or secretion
what is the primary function of stereocilia?
sensation or other function. often found in ears. Also found in male reproductive system in epididymis and ductus deferens
What is a good sign of immotile cilia syndrome?
they are hereditary and generally characterized by chronic respiratory problems, since the cilia of simple columnar cells are compromised
What is Kartagener’s syndrome
caused by absence of dynein arms in cilia, males are sterile due to immotile flagella in sperm
What is Young’s syndrome
characterized by malformation of radial spokes and dynein arms in cilia
what are the striated border and brush border?
striated border - microvilli associated with intestinal absorptive cells
brush border - microvilli associated with kidney tubule cells
what is the purpose of the glyocalyx on microvilli?
glycoproteins interact with external environment and also help trap molecules. It often contains digestive enzymes since microvilli are found in the intestines
How can microvilli be differentiated from stereocilia
stereocilia are long, slender, immotile structures, whereas microvilli arent nearly as long
what sometimes links thinner stereocilia?
cytoplasmic bridges
What is one key feature that endocrine glands do not have?
they have no ducts. they release the products into surrounding connective tissue, which ultimately takes them into the bloodstream or lymphatic system
what is a unicellular vs multicellular endocrine gland?
in unicellular, the cells are isolated and distributed single in a tissue. i.e. one enteroendocrine cell sending signal to rest of body. multicellular is grouped together
What is the junctional complex and what is it called when it can be visualized via light microscope?
It is the adhesion junction that runs around epithelial cells like a belt. It is called the terminal bar when visible by LM
What is the zonula occludens?
Tight junction located immediately below apical surface. Membranes of adjoining cells are very close.
What are the transmembrane proteins that form tight junctions? What are the peripheral proteins involved?
Claudin and occluden (zonula occludens). ZO-1, ZO-2, and ZO-3 link these to the actin cytoskeleton
What is the function of zonula occludens?
Holds membranes tight enough that ionic gradients can be made and kept across cells. Important in transport epithelium
What is the zonula adherens?
Located just below Z. occludens in junctional complex, it is an adhesion junction between cells. Utilizes calcium-dependent adherins (Cadherins) to link neighboring cells
What protein links cadherins to the microfilaments?
catenins. This is Z. adherens. Actin linkage / terminal web
What is the macula adherens?
Also called desmosome, they are spot welds that are generally located just below the Z. adherens, but really they can be anywhere and are not always there
What are the transmembrane linker proteins for desmosomes?
Desmoglein and desmocollin
What links the transmembrane linkers and the cytoskeleton of desmosomes? Why is this easy to remember?
There is a visible plaque that forms on the inside of the plasma membrane. The proteins are called desmoplakin, and plakoglobin.
What causes pemphigus folliaceous?
Auto-antibodies against desmoglein I cause loss of skin-skin adhesion and thus blistering
What are gap junctions?
They are channels on the lateral domain between celsl which carry small regulatory molecules and ions
What proteins make up gap junctions?
6 connexins make up a pore-like structure called a connexon
What is the basal lamina?
A specialized extracellular matrix structure secreted by epithelial cells that is between the epithelial cells and underlying connective tissue
What are the two regions of the basal lamina
Lamina lucida (electron lucent) - mostly the extracellular portions of adhesion molecules, which are fibronectin and laminin receptors Lamina densa (electron dense) - lower down, contains heparan sulfate, fibronectin, laminin, type IV collagen, and entactin, which links laminin and type IV collagen.
What are the functions of the basal lamina?
Structural attachment, transport barrier between epithelium and connective tissue, filtration (as in kidney epithelium), creating functional polarity, and a site of regeneration following wounding
What is the basement membrane?
Basal lamina + lamina reticularis. Sometimes used interchangeably with basal lamina
What is the lamina reticularis?
Layer of basement membrane closest to connective tissue. It’s produced by fibroblasts, a connective tissue cell. Made up of reticular fibers (Type 3 collagen). Most easily visualized with PAS stain for carbohydrates, but can be seen as an eosinophilic line if thick enough.
Where are hemidesmosomes usually found?
In epithelia that require strong adhesion to underlying connective tissue. Found on cells attached to basal lamina, basal surface adherence.
What type of cytoskeletal filaments link desmosomes and hemidesmosomes to the cell?
intermediate filaments: keratin in epithelial cells
What proteins form the plaques on the intracellular surface of hemidesmosomes?
BP230 and plectin. They link to integrins, the transmembrane linker of hemidesmosomes
What is the transmembrane linker of hemidesmosomes? What does it connect to on the connective tissue?
integrin, links to laminin-5 and collagen type IV in lamina lucida
What causes bullous pemphigoid?
autoantibodies against BP230 in the hemidesmosome results in epithelial disconnect from underlying connective tissue and subsequent edema / blistering
What are focal adhesions?
Just another transient link between actin and the proteins of the basal lamina, via integrins
What is a simple gland? Compound?
When the duct is a straight and unbranched tube, it is simple. When it branches repeatedly, it is compound
What are acini?
secretory clusters, also called alveoli
What is a tubular gland?
When the secretory cells are arranged in a tube, the gland is tubular
What is an acinar gland?
If the secretory cells are arranged in rounded structures (roughly spherical), they are alveolar or acinar
what is a tubuloacinar gland?
mixture of tubular and rounded secretory elements
How do mucous glands differ from serous glands in staining?
Mucous glands stain much paler with H&E, because serous glands secrete protein and enzyme-rich watery fluid
What is merocrine secretion?
the release of products at apical surface by exocytosis. Most common
What is apocrine secretion?
part of the apical cytoplasm is lost, along with the membrane surface as product is released in membrane-bound vesicles. i.e. lactating mammary gland
What is holocrine secretion?
Entire cell dies and becomes part of the secretory product. i.e. sebaceous glands of skin.
