lesson 5 gritti Flashcards
name of the epithelium that surrounds blood vessles. and what is the type of epithelium?
endothelium, simple squamous
name of the epithelium that surrounds inner cavities and inner organs and what is the type of epithelium?
mesothelium, simple squamous
SEM
scanning electron microscopy, 3D images, black and white, you see the surface of the object
TEM
transition electron microscopy, colorless images, you see the inside of the objects, you go through the cells
what is the criteria of classification of an epithelium type?
you classify the epithelium based on the outer cell layer
pseudostratified epithelium, what’s the usual type of pseudostratified epithelium?
only one layer, all the cells are attached to the same basal membrane but the positions of the nuclei make it look like the epithelium is stratified. Pseudostratified is usually columnar
transitional epithelium
its a stratified epithelium. the outermost layer of the epithelium changes its shape based on the distension of the organ. EX: if the organ is full of liquid, the outer layer is flattened and the cells appear flattened. if its empty, the cells of the outermost layer appear to have a cuboidal shape (dome shaped cells)
can be found in the uretra or in the bladder
which types of epithelium can be ciliated or non ciliated?
cuboidal, columnar and pseudostratified
which type of epithelium can be keratinized or non keratinized? meaning of keratinized epithelium?
the squamous epithelium.
keratinized: cells in the outermost cell layer are dead, no nuclei are present
non keratinized: cells in the outermost layer are no dead, nuclei are present
what is the main goal of flattened cells of squamous epithelium?
rapid diffusion of gasses.
simple squamous epithelium is present in the alveoli where the rapid diffusion of gasses is really important
characteristics of the epithelial tissue
high cellularity
cells are polarized
no blood vessles, the nourishment comes from the underlying connective tissue
protective function
gives impermealization
main function of the epithelium that sorrounds the internal organs is absorbtion
the epithelium can also performs secretion (ex: parenchymal cells of glands)
a tissue is defined by?
cells and their products
simple cuboidal epithelium
cells with a cuboidal shape
lines small ducts, tubules (typically lines the ducts of exocrine glands)
can have a secretory, excretory or absorptive function
cells can be characterized by apical modifications (like cilia)
what is the epithelium that lines the interlobular duct of the pancreas?
simple cuboidal epithelium
what is the epithelium that lines the surface of the ovary?
simple cuboidal epithelium
simple columnar epithelium
more elongated in the apical part
can be specialized–>in the intestine is specialized for absorption (often characterized with apical modifications)
can have secretory and/or absorptive function
lines the duct of many exocrine glands
goblet cells
cells not easily identifiable with H and E
secrete mucus in the intestinal tract
usually scattered between the columnar cells
simple columnar epithelium lining the small intestine
characterized by a brush boarder: a structure formed by densely packed microvilli on the apical surfaces of the simple columnar cells
what is the prototype organ that has a pseudostratified columnar epithelium?
trachea
what is related to the ability of protection in a stratified epithelium?
the number of layers: higher the n of layers, higher the protection
where do you have the turnover in the stratified epithelium?
in the basal layer: where the cells differentiate into the cell types we can find in all the other layers
in the skin what can you find?
a keratinized stratified squamous epithelium
the outer layer is squamous and the cells are dead. dead cells are filled with keratin that gives protection to mechanical stimuli, impermealization and protection from microbes…
what do you need in a stratified epithelium for extreme protection other than an high number of layers?
you need keratin
where is the thickness of the keratinized layer higher?
in thick skin
type of epithelium of the tongue
stratified squamous non keratinized
stratified cuboidal epithelium
lines small or big ducts
most often has only 2 layers of cuboidal cells
stratified columnar, where can we find it?
very rare
almost found only in the male urinary tract
epithelial metaplasia, what is it?
when a type of epithelium converts into another type postnatally due to a specific stressful condition. (ex: a less protective type of epithelium is changed into a more protective one due to a stress it has to face). If the danger is not eliminated, the metaplasia can become cancerous–>the epithelium is modified and so it doesn’t perform the function is supposed to perform. if the danger becomes chronic the metaplastic region can become cancerous
apical modifications
cilia
stereocilia
microvilli
lateral modifications
junctions–>connect one cell laterally to the other
tight junctions, adherens, desmosomes, gap junctions
basal modifications
anchors the cell to the basal lamina that connects the epithelium with the underlying connective tissue
-hemidesmosomes and focal adhesions
microvilli
made of a core of actin filaments (kept together by cross linking proteins) that are connected with the cytoskeleton below the plasma membrane. the actin filaments+ the cytoskeleton form the terminal web. The microvilli make up the brush border common of the simple columnar epithelium of the small intestine. The microvilli have contractile properties thanks to the myosin present in the cytoskeleton. The thick glycocalix covering the microvilli is made of membrane bound proteins and enzymes that favor digestion of macromolecules
stereocilia
-characterized by passive movements
-similar structure of microvilli but with different proteins
-longer than microvilli
-can facilitate absorption or act as sensory mechanoreceptors
cilia
-longer than microvilli
-contain microtubules organized in an axoneme
1. primary cilia
-non motile
-9 pairs of peripheral microtubules+0 in the middle
2. secondary cilia
-sensory function
-motile
-9 pairs of peripheral microtubules+ 2 microtubules in the middle–>doublets of microtubules are associated with dyneins (that allow movements) and nexins (that allows elasticity)
3. nodal cilia
9+0
push morphogens on a specific side thanks to their specific rotational movement
where are you if you see a pseudostratified columnar epithelium with cilia?
in the trachea
tight junctions
-seal two cells together like a zip
-associated to occluding and Claudin proteins
-apical part of the cells
-molecules can’t pass inside the junction (molecules can go inside the cell–>transcellular pathway, not through the junction–>paracellular pathway)
adherens
-like a belt between two cells
-in the cytoplasmic side cadherins(which mediate the cell adhesion) bind to actin filaments.
cadherins to work needs calcium ions
-NB: adherens connect actin filaments of adjacent cells
desmosomes
-similar to adherens junctions
-act through cadherins that bind to intermediate filaments
-Provide mechanical strength by connecting the intermediate filaments of adjacent cells.
gap junctions
-channel between cells
-6 connexins form one channel
-each channel can be made by different types of connexins
-each channel can be in an open or closed conformation
-allows the passage of small molecules only
hemidesmosomes
connect the basal surface of epithelial cells to the basal lamina via intermediate filaments.
the transmembrane proteins associated are integrins
focal adhesion
connects the basal surface of epithelial cells to the basal lamina via actin filaments
what makes up the basal membrane?
basal lamina and lamina reticularis
the basal lamina is composed of?
lamina lucida and lamina dense
the lamina reticularis is composed of?
reticular fibers of the connective tissue
