L9 Epithelia

Question 1

What are junctional complexes?

Answer 1

Structures involved in cell adhesion and communication

Junctional complexes include tight junctions, adhering junctions, and gap junctions.

Question 2

What do tight junctions (TJ) do?

Answer 2

Impedes paracellular movement

Tight junctions restrict the passage of substances between cells.

Question 3

What determines the ‘tightness’ of tight junctions?

Answer 3

Protein strands called claudins

The ‘tightness’ can vary significantly, influencing permeability.

Question 4

What is the permeability variation range of tight junctions?

Answer 4

10,000 fold

Permeability varies between different tissues, such as small intestine and bladder.

Question 5

What are adhering junctions?

Answer 5

Form a belt around the cell, linked by actin filaments and cadherins

These junctions help maintain tissue organization.

Question 6

What is epithelial-mesenchymal transition (EMT)?

Answer 6

Reversible process of epithelial assembly

EMT allows epithelial cells to disassemble and migrate.

Question 7

What role do gap junctions play?

Answer 7

Allows laterial communication between epithelial cells
Permit small molecule diffusion between neighboring cells

They allow electrical coupling of cells.

Question 8

What separates epithelial cells from underlying connective tissue?

Answer 8

Basement membrane

The basement membrane is composed of ECM proteins like collagen IV.

Question 9

What are the main functions of epithelial cells?

Answer 9

Secretion - gland, diffusion - lung, protection - skin, absorption - small intestine

These functions are essential in various organs.

Question 10

What do desmosomes do?

Answer 10

Form strong adhesion points between cells

They connect intermediate filaments to cadherin proteins.

Question 11

What are the two main types of epithelial classification?

Answer 11

Simple and stratified

Simple epithelium has a single cell layer (lung), while stratified has multiple layers (skin)

Question 12

What is the appearance of simple squamous epithelium?

Answer 12

Thin ‘scales’

This structure facilitates rapid passage of molecules.

Question 13

What is a characteristic of stratified squamous epithelium?

Answer 13

Apical cells appear squamous, basal cells are cuboidal or columnar

Common in areas of high abrasion, such as the skin.

Question 14

What are goblet cells?

Answer 14

Unicellular glands that secrete mucus

Often found interspersed in columnar epithelium.

Question 15

What types of glands are classified as exocrine?

Answer 15

Glands with ducts that secrete substances onto epithelial surfaces

Examples include salivary glands and sebaceous glands.

Question 16

What type of epithelium allows for shape change without damage?

Answer 16

Transitional epithelium

Found in the bladder, it accommodates distension.

Question 17

What is the role of stem cells in epithelial tissues?

Answer 17

Continual cell replacement for tissue homeostasis

This is crucial due to the hostile external environment.

Question 18

What are the two uncommon epithelial types that do not fit into simple or stratified categories?

Answer 18

Pseudostratified and transitional epithelia

Pseudostratified epithelium is found in the upper respiratory tract.

Question 19

What type of epithelial cells line the GI tract?

Answer 19

Simple columnar epithelium

This type may have cilia or microvilli for absorption and secretion.

Question 20

What is a characteristic feature of stratified cuboidal epithelium?

Answer 20

Less common, found in glands

It typically consists of two or more layers of cuboidal cells.

Question 21

True or False: All epithelial tissues are avascular.

Answer 21

True

Epithelial tissues lack blood vessels and rely on diffusion for nutrients.

Question 22

What are the common properties of epithelial cells?

Answer 22

Polarity
Cellularity
Junctional complexes
Avascular (lacking blood vessels)
Minimal extracellular space
Lack extracellular fibres

Question 23

What does ECM proteins mean? And examples?

Answer 23

ECM - Extracellular matrix.
Collagens, Laminin, Proteoglycans

ECM is s a diverse group of molecules that form a complex network surrounding cells

Question 24

What are the membranes of an epithelial cell?

Answer 24

Apical membrane
Basolateral membrane

Apical - Faces the lumen or external environment
Basolateral - Faces underlying connective tissue

Question 25

What properties facilitate the import or expel of substances in epithelial cells?

Answer 25

1. Polarity
2. Tight junctions

1. Distinct apical and basolateral domains with differing membrane properties and functio
2. Connects the epithelial cells together

Question 26

What are the types of junctions you need to know about?

Answer 26

Adhering junctions
Gap junctions
Tight junctions

Question 27

How do epithelial cells regenerate?

Answer 27

Through stem cells

Question 28

What four characteristics do all epithelia share despite their differences?

Answer 28

Cellularity
Polarity
Avascularity
Rgeneration

Epithelial tissues composed of closely pacjed cells with minimal extracellular matrix

Question 29

What is the function of a simple squamous epithelia?

Answer 29

Primary function is to facilitate rapid diffusion and absorption of molecules

Question 30

What are the types of epithelia?

Answer 30

Based on number of cell layers:
Simple epithelium
Stratified epithelium
Pseudostratified epithelium

Based on the shape of the cells:
Squamous epithelium
Cuboidal epithelium
Columnar epithelium

Pseudostratified - Appears to have multiple layers but all cell touch the basement membrane

Question 31

What type of epithelia is found in the small intestine?

Answer 31

The simple columnar epithelia

Apical surface covered with microvilli

Question 32

What is psuedostratified columnar epithelia?

Answer 32

Despite having multiple layers of cells, it consists of asingle layer of cells of varying heights so single cell layer attached to the basement membrane.

Cilitated cells often interspersed with goblet cells

Question 33

What is the most common type of stratified epithelium in human body?

Answer 33

Stratified squamous epithelia

Question 34

What shape do the transitional epithelia cells look when relaxed?

Answer 34

Rounded

Question 35

What are the two types of glands?

Answer 35

Exocrine (ducts)
Endocrine (ductless)

Secretes directly onto the epithelial surface
Secretes directly into blood