Building tissues from cells (epithelium)

Question 1

Tissue

Answer 1

Collections of similar cells and the material surrounding them

Question 2

How are tissues classified?

Answer 2

Structure of cells
Composition of extracellular
Functions of the cells

Question 3

What are the major types of cell tissues?

Answer 3

Muscle
Epithelial
Nervous
Connective 
(MENC)

Question 4

Where do epithelia exist?

Answer 4

The cover body surface and line all of the body’s cavities

Question 5

How do epithelial tissues get their nutrients

Answer 5

Blood vessels never pass through epithelial tissues, so they depend upon diffusion.

Question 6

Basement membrane definition

Answer 6

Extracellular matrix of proteins outside the cell.

Question 7

What is used to classify epithelial cells?

Answer 7

Cell shape
Layer structure
Surface specialisation
Location + function

Question 8

What are the cell shape classifications of epithelial cells?

Answer 8

Squamous, cuboidal and columnar

Question 9

What are the layer structure classifications of epithelial cells?

Answer 9

Simple (clear, single layer)
Pseudostratified (single layer pretending not to be single)
Stratified (multilayer, in which only basal cells attach to basal membrane)

Question 10

Surface specialisation classification of epithelial cells

Answer 10

Ciliated (resp. tract; cilia have microtubules)
Brush border (rigid as made of actin - increases SA)
Keratinsed

Question 11

Location and function classification of epithelial cells

Answer 11

Respiratory (contains goblet cells)

Transitional (shape of cell varies, found only in urinary tract)

Question 12

How does the epithelial layer in the urinary tract show transitional behaviour?

Answer 12

When the bladder is empty, the epithelial layer in cuboidal; as it fills they flatten out and become squamous - but don’t separate.

Question 13

What is the difference between endocrine and exocrine glands?

Answer 13

Exocrine secrete to free surface; endocrine secrete to blood stream.

Question 14

What are the forms of exocrine secretion?

Answer 14

Holocrine - entire secretory cell broken down and discharged; found in sebaceous cells of skin only
Apocrine - top half of cell broken down and discharged, apical cytoplasm lost; found in mammary and prostate glands
Merocrine - normal exocytosis
(HAM)

Question 15

Basal lamina

Answer 15

Basement membrane

Question 16

What are the linker proteins in a desmosome?

Answer 16

Desmoplakin + plakoglobin

Question 17

What are the adhesion proteins in a desmosome?

Answer 17

Desmoglein + desmocollin

Question 18

What type of proteins are adhesion proteins in a desmosome?

Answer 18

Cadherin family

Question 19

How do desmosomes work?

Answer 19

A keratin intermediate filament is connected to a linker protein (desmoplakin, plakoglobin) which is connected in turn to an adhesion protein (desmocollin, desmoglein). The adhesion molecule binds homophillically to another copy of the same adhesion molecule from the other cell; which is connected via a linker protein to the intermediate filament in the next cell.

Question 20

How is the strength of a junction achieved?

Answer 20

Clustering of linker proteins (plakoglobin, desmoplakin)

Question 21

What’s the difference between desmosomes and hemidesmosomes?

Answer 21

Desmosomes connect adjacent cells; hemidesmosomes connect a cell to the basal membrane/lamina.

Question 22

How do adherens junctions work?

Answer 22

Same as desmosomes; intermediate filament is actin in this case. Also adhesion proteins are adherin dimers.

Question 23

Where are adherens junctions found?

Answer 23

In the walls of columnar epithelial cells, actin filaments are rigid so helps pull sides together keeping width narrower - maintaining columnar shape.

Question 24

What are the anchoring junctions?

Answer 24

Desmosomes; hemidesmosomes; adherins

Question 25

What are the non-anchoring junctions?

Answer 25

Tight and gap

Question 26

How does a tight junction work?

Answer 26

Brings membranes of adjacent cells so close together at spots that nothing can pass between them.

Question 27

Give an example of a place in which a tight junction is important

Answer 27

In the lumen of the gut, prevents water from within the gut lining from moving out between cells by osmosis into the lumen of the gut where the solute potential is lower. Also in the lumen of the gut a tight junction prevents the diffusion of nutrients out of the cells back into the lumen of the gut.

Question 28

What proteins are involved in the tight junction?

Answer 28

Claudin and occludin.

Question 29

What are gap junctions

Answer 29

Cytoplasmic bridges between cells which allow the movement of small substances between cells.

Question 30

What proteins are involved in a gap junction

Answer 30

6 connexin proteins come together in a hexagonal arrangement with a central hydrophilic pore - a connexon.

Question 31

Why are gap junctions important in epithelial cells?

Answer 31

Epithelial cells need diffusion for nutrition; gap junctions allow substrates to diffuse from cell to cell so every cell gets nutrients from the blood vessels regardless of how far away it is.

Question 32

What is the intermediate filament made of in desmosomes?

Answer 32

Keratin

Question 33

Size of microvillus

Answer 33

0.5-1um

Question 34

Describe a goblet cell

Answer 34

Modified columnar epithelial cell; synthesises and secretes mucus.

Question 35

Size of cilia

Answer 35

7-10um

Question 36

Describe cilia

Answer 36

Core of 20 microtubules arranged as 9 doublets around a central pair.

Question 37

Why is keratinization beneficial?

Answer 37

Protection (UV, thermal, mechanical)

Prevention of dessication