Lesson 4

Question 1

What is the carbohydrate-rich structure present on all cell surfaces and well-developed on the microvilli of epithelial cells, also containing various enzymes?

Answer 1

Glycocalyx

Question 2

What are the structures on the lateral surfaces of epithelial cells that are responsible for cell attachment and communication?

Answer 2

Junctional complexes

Question 3

What are some of the other terms used to describe structures responsible for holding epithelial cells together?

Answer 3

1. Intercellular cement,
2. intercellular bridges,
3. desmosomes,
4. terminal bars

Question 4

What are the three main classifications of junctional complexes?

Answer 4

Adhering Junctions
Impermeable Junctions
Communicating Junctions

Question 5

What are the three types of adhering junctions?

Answer 5

1. Belt desmosome (Zonula adherens or intermediate junction)
2. Spot desmosome
3. Hemidesmosome

Question 6

What is the ribbon-like adhering junction that does not encircle the cell and is found in cardiac muscle?

Answer 6

Fascia adherens

Question 7

What type of adhering junction forms a continuous or encircling band around each interacting cell near the apical surface?

Answer 7

Belt desmosome (Zonula adherens or intermediate junction).

Question 8

What filaments run along the cytoplasmic surface of the junctional plasma membrane in a belt desmosome?

Answer 8

Actin filaments

Question 9

What are the actin filaments closely associated with in a belt desmosome?

Answer 9

The terminal web

Question 10

How wide is the space separating adjacent cell membranes in a belt desmosome?

Answer 10

The space is 20 nm wide

Question 11

What molecules anchor actin filaments to the cell membrane and adjacent membranes in a belt desmosome?

anchor means secure

Answer 11

Cadherins (calcium-dependent transmembrane proteins or adhesion molecules)

Question 12

What is the function of belt desmosomes in cell adhesion?

Answer 12

They ensure that cells within tissues are bound together.

Question 13

What is a ribbon-like adhering junction found in cardiac muscles at their longitudinal terminals?

Answer 13

Fascia adherens

Question 14

What are the little structures distributed in a spotty way (macula-spot) around cells called?

Answer 14

Spot desmosomes (macula adherens)

Question 15

What are the button-like points of contact or disk-like structures around 200 to 400 nm in diameter?

Answer 15

Spot desmosomes (macula adherens)

Question 16

Shape of macula adherens?

Answer 16

button-like points of contact or disk-like structures

Question 17

What is the width of the intercellular space in spot desmosomes, and what does it contain?

Answer 17

The intercellular space is about 20 nm wide; and contains fine filamentous material connecting adjacent plasma membranes.

Question 18

What is found on the cytoplasmic surface of each interacting plasma membrane in spot desmosomes?

Answer 18

An attachment plaque

Question 19

They are composed of a series of attachment proteins like desmoplakins and plakoglobins.

Answer 19

Attachment plaque

Found in spot desmosomes cytoplasmic surface

Question 20

What network of filaments either terminates in or passes along the surface of the attachment plaques?

Answer 20

Keratin filaments

Question 21

What is the function of spot desmosomes in epithelial sheaths?

Answer 21

1. They serve as anchoring sites for keratin filaments.
2. For forming a network of fibers across the epithelial sheath to resist mechanical stress and maintain structural integrity.

Question 22

Where are spot desmosomes prominent, and how do they appear under the light microscope in processed tissues?

Answer 22

1. They are prominent in the stratum spinosum of Epidermis
2. They appear as dark-stained spiny processes (also called intercellular bridges).

Question 23

Where are desmosomes abundant in, and what is their function in tissues?

Answer 23

Desmosomes are abundant in tissues subject to severe mechanical stress (Neck of Uterus, Cardiac Muscle, Skin)

Question 24

What is the first and most superficial of the junctional complexes located near the apex of cells?

Answer 24

Zonula occludens (tight junction)

Question 25

How are adjacent plasma membranes held together in tight junctions?

Answer 25

By **continuous strands of junctional proteins**. They meet across the intercellular space where they fuse or form ridges.

Question 26

What transmembrane junctional proteins bind to each other at the fusion sites to seal the intercellular space?

Answer 26

Claudins and occludins

Question 27

What structure is **formed by the chain of junctional proteins in *tight junctions***, and what is its function?

Answer 27

A belt-like structure that completely encircles each cell in the sheet. ## Footnote it **acts as a seal** **between adjacent cells**, preventing the passage of substances from the lumen to the cell interior or between cells.

Question 28

Why are the tight junction and belt desmosome termed "zonula"?

Answer 28

zonula = a little encircling band ## Footnote they encircle cells like a little band

Question 29

What structures form gap junctions, and what are they made of?

Answer 29

formed by **connecting channels made up of 6 integral membrane proteins** *(connexins),* that **assemble to form structures called *connexons***.

Question 30

What is the pore size of the connecting channels in gap junctions, and what size molecules can pass through them?

Answer 30

The **pore size is 1.5 nm**, allowing the passage of molecules smaller than 1000 to 1500.

Question 31

What is the **common type of cell junction** seen in many tissues, and what is its primary function?

Answer 31

**Gap junctions;** they **allow small water-soluble molecules to pass directly from the cytoplasm** of one cell **to another**.

Question 32

What are the **two layers of the basement membrane under the electron microscope (EM**)?

Answer 32

1. The basal lamina 1. lamina reticularis

Question 32

What are the **three essential functions** of gap junctions?

Answer 32

1. **Conduction of electrical impulses** (spread of action potentials in nerve cells). 1. **Functional synchronization** (e.g., cardiac and smooth muscle synchronization). 1. **Metabolic cooperation of cells** (passage of small water-soluble molecules).

Question 33

is a **dense, homogeneous** structure described as a “**structureless**” membrane upon which **all epithelia rest.**

Answer 33

Basement Membrane

Question 33

These are cytoplasmic folds on the lateral surfaces of adjacent cells that interdigitate with each other.

Answer 33

Cellular Interdigitations

Question 34

What are the two layers of the basal lamina?

Answer 34

Lamina lucida Lamina densa

Question 35

**Situated just beneath the epithelium** and composed **mainly of extracellular glycoproteins** (laminin, entactin) and **transmembrane glycoproteins** (integrins and dystroglycans)

Answer 35

Lamina lucida

Question 36

A meshwork of type IV collagen, proteoglycan (perlacan), heparin sulfate, and fibronectin.

Answer 36

Lamina densa

Question 37

# 1. They are transmembrane proteins similar to cell membrane receptors that form bonds with ligands.

Answer 37

Integrins

Question 38

They are important for adhesion and can activate signaling pathways leading to cell cycle activation, differentiation, cytoskeletal reorganization, apoptosis, and gene expression.

Answer 38

Integrins

Question 39

They are glycoproteins composed of β-dystroglycan and extracellular δ-dystroglycan that bind laminin of the basal lamina.

Answer 39

Dystroglycans

Question 40

Dystroglycans are glycoproteins composed of what materials?

Answer 40

β-dystroglycan and extracellular δ-dystroglycan | δ is delta, β is beta

Question 41

It consists of type I and type III collagen, manufactured by fibroblasts.

Answer 41

Lamina Reticularis

Question 42

What is the function of the lamina reticularis?

Answer 42

It functions to **attach the lamina densa to the underlying connective tissue.**

Question 43

What are the **four functions of the basement membrane?**

Answer 43

1. **Separates cells from the underlying or surrounding connective tissue** (e.g., epithelial cells, Schwann cells, and fat cells). 1. **Functions as a highly selective membrane** (e.g., kidney glomerulus and lung alveolus). 1. I**nduces cell differentiation** and influences cell metabolism. 1. **Provides scaffolding support for tissue regeneration after injury** (e.g., for muscles and epithelia).

Question 44

They are **vesicular structures** associated with the **transport of fluids and solutes across the cell membrane**, particularly in endothelial and epithelial cells.

Answer 44

Caveolae or Pinocytotic Vesicles

Question 45

They resemble spot desmosomes but consist of only one-half of the spot desmosome.

Answer 45

Hemidesmosomes or Half-desmosomes

Question 46

They attach the basal surface of epithelial cells to the underlying basal lamina.

Answer 46

Hemidesmosomes

Question 47

They are seen in the stratum basale of the epidermis, where they anchor epithelial cells to the underlying basement membrane.

Answer 47

Hemidesmosomes

Question 48

Where are hemidesmosomes seen?

Answer 48

Hemidesmosomes are seen in the stratum basale of the epidermis

Question 49

What **specific examples show how membrane proteins in the luminal surface of epithelial cells differ** from those **in the lateral or basal membrane**?

Answer 49

* Kidney tubular epithelial membranes contain alkaline phosphatase. * Intestinal epithelial cell membranes contain enzymes to hydrolyze sugars.

Question 50

# 1. They are responsible for increasing the surface area for absorption.

Answer 50

Microvilli

Question 51

How will you describe the appearance of Microvilli?

Answer 51

They are **slender, cylindrical (finger-like) cellular processes projecting from the apical** or luminal surfaces of the cells, giving the surface a striated or brush border appearance.

Question 52

What is the structure of each microvillus? (Individual microvilli)

Answer 52

* Each **microvillus is covered by the cell membrane**. * The **core is composed of 40 actin filaments** that **run in parallel bundles** across its length. * The **actin filaments are embedded in amorphous material at the tip.** * **At the base, the microvillus extends into the terminal web**, a perpendicular network of filaments consisting of myosin and actin.

Question 53

What is the role of actin filaments in microvilli?

Answer 53

Actin filaments are **responsible for the extension, retraction, and mechanical stiffening** of microvilli.

Question 54

Where are microvilli highly developed?

Answer 54

Microvilli are highly developed in the **cells of the small intestine** and the **proximal tubules of the kidney.**

Question 55

They are found in the **epithelium of the epididymis**, where t**hey serve an absorptive function**.

Answer 55

Stereocilia

Question 56

These are extremely long, branched microvilli that are non-motile and have an absorptive function.

Answer 56

Stereocilia

Question 57

What is the structure of stereocilia?

Answer 57

Stereocilia contain **a core of actin filaments** responsible for their rigidity and ability to detect minute movements of their fluid medium.

Question 58

Why is the name “stereocilia” considered a misnomer? | misnomer means a wrong or inaccurate name or designation.

Answer 58

Because stereocilia do not have the same structure as cilia

Question 59

These are motile processes found in the epithelial lining of the respiratory system and male and female reproductive tracts.

Answer 59

Kinocilia

Question 60

Where are kinocilia found?

Answer 60

1. In the respiratory tract, they entrap and transport foreign particles. 1. In the reproductive tract, they aid in the movement of ova or spermatozoa.

Question 61

# 1. Long, cylindrical, tapered (hair-like) processes containing an axoneme and covered by a cell membrane. Tubules extend from the apex to the basal body at the base of the cilium.

Answer 61

Kinocilia

Question 62

How are kinocilia's microtubules structurally described?

Answer 62

Microtubules are arranged with a central pair surrounded by nine doublets connected by fine filaments.

Question 63

What is the primary function of kinocilia?

Answer 63

To propel fluid or mucus films over the surface epithelium through vibratory movement.

Question 64

What is a flagellum, and where is it found?

Answer 64

A flagellum is a single long cilium found in mammalian spermatozoa, where it may measure several hundred micrometers long.

Question 65

It propels the cell through undulatory movements.

Answer 65

Flagellum

Question 66

They are invaginations of the cell membrane during pinocytosis.

Answer 66

Caveolae or Pinocytic Vesicles

Question 67

How do **simple epithelia** that are **not differentiated** for absorption and secretion regenerate?

Answer 67

They regenerate by **mitosis of the epithelial cells themselves.**

Question 68

How do **highly differentiated** simple epithelia regenerate?

Answer 68

They regenerate **by mitosis of undifferentiated stem cells**, such as those at the bases of intestinal glands.

Question 69

How do **stratified epithelia** regenerate?

Answer 69

By **mitosis of stem cells located at the basal layer** of the epithelium, such as in the stratum basale of the epidermis.