L10: Intercellular junctions & basement membrane (alyaa)

Question 1

Epithelial cells have 3 surface domains:
(Dont forget to list what we find in each of those domains)

Answer 1

1. Apical: microvilli, cilia, Stereocilia and flagellum
2. Lateral (another name is intracellular): cell junctions
3. Basal: basal lamina/basement membrane (names used interchangeably)

Question 2

Define apical domain?

Answer 2

• Free surface always directed toward exterior or lumen of the enclosed body cavity.
• May have surface modifications depending upon specific function

Question 3

What are microvilli?

Answer 3

Closely packed, finger-like projections of cytoplasm that increase surface area of the cell

Question 4

Shsalfat il finger-like projections of the cytoplasm in microvilli?

Answer 4

Mohim 7ag absorption + increases surface area of cell

Question 5

number and shape of Microvilli depends on?

Answer 5

The absorptive capacity of the epithelium
(intestine, glomerulus of the kidney)

Question 6

Microvilli Can be seen under ? + describe its appearance under that magnification

Answer 6

Light Microscopy (LM)

Appearance: brush border, striated border

Question 7

Describe the cell junction of microvilli

Answer 7

Question 8

What is usually present on the surface of microvilli; what is surrounding it?

Answer 8

amorphous cell coat of glycoprotein “glycocalyx”.

Question 9

True or false

Usually present on surface of microvilli is an amorphous cell coat of Villin.

Answer 9

False, villin is a protein found in the tip of the microvillin structure, what surrounds the whole surface is glycoprotein “glycocalyx”.

Question 10

What allows the microvillus to contract?

Answer 10

myosin I & myosin II filaments

Question 11

Where would you find microvilli?

Answer 11

Kidney and intestine

(Makes sense bc fee wayed absorption going on there)

Question 12

What’s spectrin?

Answer 12

• Spectrin anchors terminal web to apical membrane of cell.
• It also stabilizes actin filaments

Question 13

What is the terminal web in the microvillus structure made of?

Answer 13

• 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.

Question 14

By LM, cilia appear as?

Answer 14

hair-like structures from apical surface.

Question 15

Cilia are anchored into apical cytoplasm by a?

Answer 15

Basal body

Question 16

Describe the structure of the basal body

Answer 16

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.

Question 17

Which section of the cilia contains 9 doublets/pairs of microtubules?

Basal body wala inner core?

Answer 17

Inner core.

Question 18

Dsecribe the structure of the inner core of the cilia.

Answer 18

-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”

Question 19

Describe the Microstructure of a Cilium (il microtubule thingy)

Answer 19

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.

Question 20

How did you know that this is the upper part of the cilium?

Answer 20

Because in the lower part (basal body), there’s no central microtubules and it’s arranged in triplets not doublets

Question 21

Laish stereocilia is viewed as microvilli more than cilia?

Answer 21

Bc even though mn bara its long like cilia, il insides (junctions) are completes different than cilia, it resembles mal microvilli akthar

Question 22

Out of these 3, which structure has cytoplasmic bridges?

1. Cilia
2. Stereocilia
3. Microvilli

Answer 22

Stereocilia

Question 23

Define stereocilia

Answer 23

-Long microvilli.

-Apical cytoplasmic protrusions, with intermingling thin and thick regions.

-Cytoplasmic bridges interconnect thick regions

Question 24

In stereocilia, where do cytoplasmic bridges interconnect?

Answer 24

In the thick regions (makes sense ya3ni fee mokan akthar)

Question 25

Describe the microstructure/junction of the stereocilia

Answer 25

-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.

Question 26

What is found in the tip of microvilli but not stereocilia?

Answer 26

Villin

Question 27

What anchors the actin bundles to plasma membrane?

Answer 27

Erzin

Question 28

What is erzin?

Answer 28

a plasma membrane molecule, that anchors the actin bundles to plasma membrane.

Question 29

Where is stereocilia found?

Answer 29

limited to the: - Male reproductive tract 👨🏻 *(epididymis and ductus deferens)* - Receptor hair cells in the ear 👂

Question 30

Define Flagellum?

Answer 30

An extremely long, **isolated cilium** is called a flagellum

Question 31

The only flagellated cells in the human body are….

Answer 31

Male sperm

Question 32

Function of the flagella

Answer 32

Sperm use their flagella to *swim* through the female reproductive tract

Question 33

Classification of cell junctions (lateral surface)

Answer 33

Question 34

Features of tight junctions ? (location, how they’re fused)

Answer 34

*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

Question 35

What mediates cell-cell adhesion?

Answer 35

**CAMs** (Cell adhesion molecules) mediate cell-cell adhesion

Question 36

What is the most common cell junction type?

Answer 36

Desmosomes

Question 37

____________ are the main junctions for binding cells together and are scattered along cell margins.

Answer 37

Desmosomes

Question 38

Lateral Surface Features (DESMOSOMES):

Answer 38

*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).

Question 39

Why are intermediate filaments in the desmosome so important?

Answer 39

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**

Question 40

What are 1. Desmocollin 2. Desmoglein

Answer 40

Cadherins

Question 41

What is the basement membrane made up of?

Answer 41

**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

Question 42

Type IV collagen in the lamina densa is coated with __________, rich in _________ __________

Answer 42

Type IV collagen in the lamina densa is coated with **perlecan**, rich in **heparan sulfate**

Question 43

Type _____ collagen is found in the Lamina Reticularis

Answer 43

Type **III** collagen

Question 44

Type IV collagen forms a meshwork of _________for __________ and ____________ in the basal lamina.

Answer 44

Type IV collagen forms a meshwork of **procollagen** for **support** and **filtration** in the basal lamina.

Question 45

Type VII collagen __________ the basal lamina to the underlying type ____ and ____ collagens of lamina reticularis of the basement membrane.

Answer 45

Type VII collagen **anchors** the basal lamina to the underlying type **I** and **III** collagens of lamina reticularis of the basement membrane.

Question 46

Function and importance of the basement membrane? (3)

Answer 46

1. Primary function: **anchoring** down the epithelium to its loose CT underneath by cell-matrix adhesions through substrate adhesion molecules (**SAMs**). 2. **Mechanical barrier:** preventing malignant cells from invading the deeper tissues. 3. **Angiogenesis** *(development of new blood vessels):* Basement membrane proteins have been found to accelerate differentiation of endothelial cells

Question 47

Early stages of malignancy that are thus limited to the epithelial layer by the basement membrane are called ?

Answer 47

**Carcinoma in situ** *(doesn't cross basement membrane)*

Question 48

The many folds of the BM provide ______________(3) for _______ of absorbed fluids and ions into the ____________.

Answer 48

The many folds of the BM also provide **increased cell surface** for passage of absorbed fluid and ions into the **peritubular** capillary below.

Question 49

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)

Answer 49

A striated look