L10: Intercellular junctions & basement membrane (alyaa) Flashcards
Epithelial cells have 3 surface domains:
(Dont forget to list what we find in each of those domains)
- Apical: microvilli, cilia, Stereocilia and flagellum
- Lateral (another name is intracellular): cell junctions
- Basal: basal lamina/basement membrane (names used interchangeably)
Define apical domain?
- Free surface always directed toward exterior or lumen of the enclosed body cavity.
- May have surface modifications depending upon specific function
What are microvilli?
Closely packed, finger-like projections of cytoplasm that increase surface area of the cell
Shsalfat il finger-like projections of the cytoplasm in microvilli?
Mohim 7ag absorption + increases surface area of cell
number and shape of Microvilli depends on?
The absorptive capacity of the epithelium
(intestine, glomerulus of the kidney)
Microvilli Can be seen under ? + describe its appearance under that magnification
Light Microscopy (LM)
Appearance: brush border, striated border
Describe the cell junction of microvilli
What is usually present on the surface of microvilli; what is surrounding it?
amorphous cell coat of glycoprotein “glycocalyx”.
True or false
Usually present on surface of microvilli is an amorphous cell coat of Villin.
False, villin is a protein found in the tip of the microvillin structure, what surrounds the whole surface is glycoprotein “glycocalyx”.
What allows the microvillus to contract?
myosin I & myosin II filaments
Where would you find microvilli?
Kidney and intestine
(Makes sense bc fee wayed absorption going on there)
What’s spectrin?
- Spectrin anchors terminal web to apical membrane of cell.
- It also stabilizes actin filaments
What is the terminal web in the microvillus structure made of?
- Horizontal network of Actin filaments lying just below base of microvillus.
- These Actin filaments are stabilized by Spectrin.
- Spectrin anchors terminal web to apical membrane of cell.
By LM, cilia appear as?
hair-like structures from apical surface.
Cilia are anchored into apical cytoplasm by a?
Basal body
Describe the structure of the basal body
a. Modified centriole that contains nine microtubule triplets in its core forming a ring structure.
b. Under LM, basal bodies appear as a thin, dark-staining band at cilia base.
Which section of the cilia contains 9 doublets/pairs of microtubules?
Basal body wala inner core?
Inner core.
Dsecribe the structure of the inner core of the cilia.
-In the inner core of the cilium, there are nine pairs or doublets of microtubules that are circularly arranged around 2 central microtubules.
-The microtubules composing each doublet are designated as the “A microtubule” and the “B microtubule”
Describe the Microstructure of a Cilium (il microtubule thingy)
1.Each doublet contains a “pair of arms” (contains dynein) that extends off the “A” microtubule to form cross-bridges with the “B” microtubule in the adjacent doublet.
2.The protein “nexin” links the doublets together.
3.Spokes extend from the nine outer doublets to the central doublet.
How did you know that this is the upper part of the cilium?
Because in the lower part (basal body), there’s no central microtubules and it’s arranged in triplets not doublets
Laish stereocilia is viewed as microvilli more than cilia?
Bc even though mn bara its long like cilia, il insides (junctions) are completes different than cilia, it resembles mal microvilli akthar
Out of these 3, which structure has cytoplasmic bridges?
- Cilia
- Stereocilia
- Microvilli
Stereocilia
Define stereocilia
-Long microvilli.
-Apical cytoplasmic protrusions, with intermingling thin and thick regions.
-Cytoplasmic bridges interconnect thick regions
In stereocilia, where do cytoplasmic bridges interconnect?
In the thick regions (makes sense ya3ni fee mokan akthar)
Describe the microstructure/junction of the stereocilia
-Actin filament bundles that are cross-linked by fibrin (to support them)
-Actin bundles in stem portion are anchored to network of α-actinin present in cross-bridges and apical cytoplasm of cell
-Erzin, a plasma membrane molecule, anchors the actin bundles to plasma membrane.
-Villin is not found in tip of stereocilium.
What is found in the tip of microvilli but not stereocilia?
Villin
What anchors the actin bundles to plasma membrane?
Erzin
What is erzin?
a plasma membrane molecule, that anchors the actin bundles to plasma membrane.
Where is stereocilia found?
limited to the:
- Male reproductive tract 👨🏻 (epididymis and ductus deferens)
- Receptor hair cells in the ear 👂
Define Flagellum?
An extremely long, isolated cilium is called a flagellum
The only flagellated cells in the human body are….
Male sperm
Function of the flagella
Sperm use their flagella to swim through the female reproductive tract
Classification of cell junctions (lateral surface)
Features of tight junctions ?
(location, how they’re fused)
*Tight junctions are typically located in the apical region of most epithelial cells
*At tight junctions the adjacent cells are so close that some proteins in their plasma membranes are fused
*Fusion forms a seal that closes off the extracellular space
*This prevents molecules from passing between apical and lateral surfaces of epithelial cells
What mediates cell-cell adhesion?
CAMs (Cell adhesion molecules) mediate cell-cell adhesion
What is the most common cell junction type?
Desmosomes
____________ are the main junctions for binding cells together and are scattered along cell margins.
Desmosomes
Lateral Surface Features (DESMOSOMES):
*The surface of each plasma membrane has an area called the circular plaque
*The plaques of adjacent cells are joined by linker proteins called cadherins
*Cadherins project from the cell membranes of both cells and interdigitate like the teeth of a zipper in the extracellular space
*Intermediate filaments which are cytoskeletal elements that resist tension insert into each plaque from the inner cytoplasmic side
*This distributes tension forces evenly across the entire epithelial sheet (providing mechanical strength to cells and tissues).
Why are intermediate filaments in the desmosome so important?
imagine many cells and there is a force in only one of them, if there is no proper distribution of the force; the cell will be damaged.
Therefore, Intermediate filaments properly distribute the tension
What are
1. Desmocollin
2. Desmoglein
Cadherins
What is the basement membrane made up of?
1.Basal Lamina:
- Lamina Lucida (laminin)
- Lamina Densa (Type IV collagen)
**2.Attaching proteins ***(between Basal and Reticular Laminae):
*
* Type VII collagen (anchoring fibrils)
* Fibrillin (microfibrils)
3.Lamina Reticularis:
- Type III collagen
Type IV collagen in the lamina densa is coated with __________, rich in _________ __________
Type IV collagen in the lamina densa is coated with perlecan, rich in heparan sulfate
Type _____ collagen is found in the Lamina Reticularis
Type III collagen
Type IV collagen forms a meshwork of _________for __________ and ____________ in the basal lamina.
Type IV collagen forms a meshwork of procollagen for support and filtration in the basal lamina.
Type VII collagen __________ the basal lamina to the underlying type ____ and ____ collagens of lamina reticularis of the basement membrane.
Type VII collagen anchors the basal lamina to the underlying type I and III collagens of lamina reticularis of the basement membrane.
Function and importance of the basement membrane? (3)
- Primary function: anchoring down the epithelium to its loose CT underneath by cell-matrix adhesions through substrate adhesion molecules (SAMs).
- Mechanical barrier: preventing malignant cells from invading the deeper tissues.
- Angiogenesis (development of new blood vessels): Basement membrane proteins have been found to accelerate differentiation of endothelial cells
Early stages of malignancy that are thus limited to the epithelial layer by the basement membrane are called ?
Carcinoma in situ (doesn’t cross basement membrane)
The many folds of the BM provide ______________(3) for _______ of absorbed fluids and ions into the ____________.
The many folds of the BM also provide increased cell surface for passage of absorbed fluid and ions into the peritubular capillary below.
EM of base of epithelium of proximal convoluted tubule. Note basement (basal) lamina and the great infolding of the cell membrane.
These folds, plus the many mitochondria lying in them, tend to give the cytoplasm a ___________ look in light microscopy.
(Idk if this slide is important but i added it just in case)
A striated look
