epithelial tissue

Question 1

functions of epithelium

Answer 1

Covers body surface
Lines body cavities
Constitutes glands.
- Glands: secretes essential molecules such as hormones.

Question 2

what is the traditional classification of epithelium is based on 2 factors

Answer 2

1. no. of cells
2. shape of surface cells

special categories:
- Pseudostratified
- Transitional

Question 3

why does the pseudostratified looks like stratified epithelium

Answer 3

due to cells that does not reach the basal surface

Question 4

what is the specific characteristics that transitional epithelium has

Answer 4

Distensible (stretchable)
- shape changes depending on the amt. of fluid it holds.

Question 5

location and function of each epithelium tissue

Answer 5

transes

Question 6

briefly explain the cell polarity

Answer 6

different sides that perform specific functions

1. apical domain (top/ free surface)
   - Faces the external environment or lumen
   - Absorption, secretion or interaction with the external environment/ coordinate with free extracellular fluid.
2. lateral domain (sides)
   - Located between neighbouring cells
   - Facilitates cell-to-cell communication and adhesion
   [cell stick tgt and communicate]
3. basal domain (bottom)
   - Connects the cell to the underlying CT
   - Anchoring the cell and facilitating molecular exchange with the CT
   [keeping the cell stable and allowing nutrient exchange]

Question 7

what are the structural surface modifications of the apical domain

Answer 7

microvilli
stereocilia
cilia

[these helps w absorption, movement or sensing environment]

Question 8

Finger-like cytoplasmic projections on the apical surface of most epithelial cells.

Answer 8

microvilli
- tiny-finger-like projections
- 20 to 30 actin filaments
- found on cells that absorbs nutrients

Question 9

key parts of microvilli

Answer 9

[actin filaments - the “bones” inside the microvillus
vilin: holds tgt at base
terminal web: network at the base, keep then stable]

1. actin-building proteins
   - fascin, epsin, fimbrin (tightly packed tgt)
2. myosin l
   - binds actin filaments to the plasma membrane
3. terminal web
   - horizontal network of actin filaments.
   - spectrin stabilize actin filaments
4. myosin ll and tropomyosin
   - slight movement by tightening or loosening the network

Question 10

how does microvilli move

Answer 10

moves passively

do not actively move like cilia.
way slightly when the terminal web contracts
[like blades of grass swaying in the wind.]

Question 11

where can stereocilia be found and its function

Answer 11

male reproductive system (epididymis & ductus defers) - absorption and fluid balance

inner ear (sensory E) -detect sound vibrations

Question 12

what are the key parts of stereocilia

Answer 12

core: actin filaments (give structure and strength)
fibrin holds actin filaments tgt

📍 Stereocilia in the Genital Ducts (Epididymis & Ductus Deferens)
- contain ezrin and a-actin (help anchor)

📍 Stereocilia in the Sensory Epithelium (Inner Ear)
- contain epsin (connect to surrounding = can detect vibrations)

Question 13

Hair-like extensions present on nearly every cell in the body.

Answer 13

cilia
- contains axoneme, made of microtubules arranged in organized pattern
- basal body anchors axoneme to the cell

Question 14

briefly explain the different types of cilia

Answer 14

index card

Question 15

A rare genetic condition in which the position of the heart and abdominal organs is reversed.

Answer 15

Situs inversus
- caused by absence or immotile nodal cilia
- aka primary ciliary dyskinesia.

[Nodal cilia are responsible for generating fluid flow that helps direct the placement of organs in the correct locations.
If the cilia don’t function properly, the organs can be positioned incorrectly.]

Question 16

it is the specific structural components that make up the barrier and the attachment sites, and are responsible for joining individual cells together.

Answer 16

Junctional complex

3 types:

Question 17

what are the 3 types of junctional complexes

Answer 17

Occluding junctions (aka tight junctions)
Anchoring junctions
Communicating junctions (aka gap junctions)

Question 18

It forms tight seals between adjacent cells, effectively inhibiting the movement of large molecules and ions.

Answer 18

Occluding Junctions (Zonula Occludens)

• create a narrow region where the plasma membranes of two cells meet tightly, closing off the space between them.
• apical domains (top parts of cells) are often shaped like polygons, and their points create junctions where three cells meet.

Question 19

Main Components of Occluding Junction

Answer 19

claudins:
These proteins are the backbone of tight junctions and help form small water channels between cells.
Example: In the kidneys, claudins help create channels that allow water to pass through cells, which is important for filtration and reabsorption.

occludin:
This protein helps maintain the barrier between cells.
It also restricts the movement of lipids and proteins between the top and side parts of the cells, helping keep the cell’s structure intact and properly functioning.

junctional adhesion molecule:
Part of the immune system’s protein family (IgSF).
JAM increases electrical resistance across the cell membrane, which helps control ion flow and keeps the balance of ions intact.

tricellulin:
This protein seals the weak points where three cells meet (called tricellular contacts), ensuring that the tight junction barrier stays strong and prevents leakage.

Question 20

these are regulatory and signaling proteins that attach to the four proteins

Answer 20

PDZ domain proteins
- the 4 proteins are claudins, occludin, junctional adhesion molecule, tricellulin

(index card)

Question 21

what are the junctionalcomplexes infections

Answer 21

bacteria:
Clostridium perfringens
Helicobacter pylori

virus:
Oncogenic adenovirus
Papillomavirus

miscellaneous parasites:
Dermatophagoides pteronyssisnus
- Aka dust mites.
- Release protein that can damage junctional complexes in the respiratory tract, leading to allergic reactions and respiratory issues.

Question 22

it provides lateral adhesions between epithelial cells.

Answer 22

anchoring junction

2 types:
Zonula adherens
Macula adherens (desmosome)

Question 23

5 major families of CAMs (Cell Adhesion Molecules) in anchoring junctions

Answer 23

index card

Question 24

it is a transmembrane proteins that are part of anchoring junctions, and interact with CAMs of neighboring cells.

Answer 24

Cell adhesion molecules (CAMs)
[found on the surface of cells. They help cells stick to each other and to the structures around them. CAMs are involved in creating anchoring junctions that keep cells connected.]

Heterotypic binding: When CAMs from different types of cells stick together.

Homotypic binding: When CAMs from the same type of cell stick together.

Question 25

provide lateral adhesion between epithelial cells, and is composed mainly of cadherins and nectins.

Answer 25

Zonula adherens - E-cadherin-catenin complex: binds to vinculin and a-actinin. - Weak nectin-based adhering: junctions are formed specialized areas where junctions are exposed to dynamic regulation.

Question 26

provides localized spot-like junction between epithelial cells, and represent major anchoring cell-to-cell junction by providing anchoring sites for immediate filaments.

Answer 26

Macula adherens (desmosome) - On the inside of the cell, there's a desmosomal attachment plaque, which helps to connect the cell membrane to the skeleton. - In the space between the cells, there are special proteins called desmogleins and desmocollins. These proteins belong to the cadherin family and help the cells stick together by forming a "cadherin zipper". - These proteins interact with plakoglobin and desmoplakin, which help connect the cell membrane to the cytoskeleton, making the junction strong and stable. Desmosomes = Strong spot-like junctions. Desmogleins and Desmocollins = Proteins that help cells stick together. Plakoglobin and Desmoplakin = Help anchor the junction to the cell's inner structure.

Question 27

are the only known cellular structures that permit the direct passage of signaling molecules from one cell to another.

Answer 27

Communicating junctions (gap junctions, nexuses) - formed by 12 subunits of connexin protein family = connexons - signaling molecules (like ions or small chemicals) pass directly from one cell to another. - channels can open and close in response to signals such as voltage changes, calcium levels, pH, or other chemical signals.

Question 28

Why are plicae (folds) important in epithelial cells?

Answer 28

increase surface area, which helps in more efficient absorption, secretion, or communication in organs.

Question 29

Where are morphologic modifications, like plicae, commonly found?

Answer 29

In organs where absorption, secretion, or communication are crucial, like the intestines or glands.

Question 30

what are the several features that basal domain of epithelial cells is characterized by

Answer 30

Basement membrane Cell-to-extracellular matrix junctions Basal cell membrane infoldings

Question 31

what are the special stains needed for the basement membrane to be seen under a microscope

Answer 31

PAS (+) Periodic Acid-Schiff: A stain that makes the basement membrane stand out. Silver-reactive: Another stain that highlights the basement membrane. Mallory stain: A stain that can also be used to see the basement membrane.

Question 32

the 2 parts that basement membrane are made up of

Answer 32

basal lamina: The part that is made by the epithelial cells. [is the structural attachment site for overlying epithelial cells and underlying connective tissue.] reticular lamina: The part made by the connective tissue (CT).

Question 33

what are the components oof the basal lamina

Answer 33

collagens (Types IV, VII, XV, and XVIII) laminins entactin/ nidogen proteoglycans

Question 34

what are the several anchoring structures used to connect the basal lamina to the underlying CT

Answer 34

Anchoring fibrils (Type VII collagen): These fibers hold the basal lamina in place and attach it to type III collagen in the connective tissue (the most common type). Fibrillin microfibrils: These help attach the basal lamina to elastic fibers, giving more support. Projections of the lamina densa: These are small extensions that connect the basal lamina to the connective tissue, helping to form additional bonds with type III collagen.

Question 35

It maintains morphologic integrity of the epithelium-connective tissue interface.

Answer 35

Cell-to-Extracellular Matrix Junctions (index card ) Focal Adhesions – Connect actin filaments inside the cell to the basal lamina (part of the basement membrane). Hemidesmosomes – Anchor intermediate filaments inside the cell to the basement membrane, providing strong attachment. [Focal adhesions connect cells to the extracellular matrix (outside the cell). Desmosomes connect cells to each other, strengthening the tissue.]

Question 36

What is the purpose of morphologic modifications in epithelial cells?

Answer 36

increase surface area (SA) to improve absorption, secretion, and adhesion.

Question 37

Structural folds in the basal surface of epithelial cells that increase SA for better transport & absorption.

Answer 37

basal infoldings - strengthen cell connections by involving structures like tight junctions, adherens junctions, & desmosomes.

Question 38

Why do glands have morphologic modifications?

Answer 38

: To increase efficiency in secreting substances.

Question 39

type of glands and their mechanism of secretion

Answer 39

exocrine glands - holocrine - apocrine - merocrine endocrine glands paracrine glands autocrine signaling

Question 40

glands that release their secretions (like mucus, sweat, or digestive enzymes) onto a surface (e.g., skin, digestive tract).

Answer 40

Exocrine glands - unicelular glands: Made of just one cell that produces and releases substances. Example: Goblet cells in the intestine secrete mucus. - multicellular glands: Made of many cells working together. They have different structures that help classify them further. Example: Salivary glands produce saliva.

Question 41

mucous secretions vs serous secretions

Answer 41

Mucous secretions → Thick, sticky, and slimy (e.g., mucus from goblet cells in the respiratory tract). Serous secretions → Thin, watery, and fluid-like (e.g., saliva from salivary glands).

Question 42

Epithelial Cell Renewal

Answer 42

continuously renewing cell populations: Surface epithelia (like skin and gut lining) have fast turnover (new cells form quickly). For example, the small intestine renews every 4-6 days, and skin renews in about 47 days. stable cell populations: liver, cells don't renew as quickly stable cell population, meaning cell division happens rarely, and the cells live longer.