Epithelia

Question 1

What do epithelial cells generally do?

Answer 1

Form the boundary between a controlled internal environment + uncontrolled external environment

Question 2

What can epithelial tissues develop from?

Answer 2

All 3 germ layers:
-endoderm e.g GI
-mesoderm e.g lining of DV system
-ectoderm e.g epidermis

Question 3

Where are epithelial tissues found?

Answer 3

In every organ

Question 4

What are the functions of epithelial tissues?

Answer 4

-protection e.g skin
-barrier e/g blood brain barrier (BBB)
-diffusion
-absorption
-secretion

Question 5

Where is the basolateral membrane?

Answer 5

-at the bottom and sides
-is fixed

Question 6

Where is the apical membrane?

Answer 6

Free membrane

Question 7

What properties allow epithelial tissue to import and export substances?

Answer 7

-connected via tight junction, which decreases free diffusion
-distinct apical + basolateral domains with differing membrane properties and functions makes it polarised

Question 8

What are tight junction?

Answer 8

What connects epithelial cells and tissues

Question 9

What does it mean to say that epithelial cells are entirely cellular?

Answer 9

-avascular - no blood vessels
-lack extracellular fibres
-minimal extracellular space

Question 10

Which of the basolateral and apical membrane are specialised?

Answer 10

Both

Question 11

What is the basolateral membrane in contact with

Answer 11

Extracellular fluid compartment

Question 12

What is the basement membrane made up of?

Answer 12

-basal lamina (BL)
-reticular lamina –> reticular fibres anchor BL to underlying connective tissue

Question 13

What do tight junctions stop?

Answer 13

Paracellular movement between cells

Question 13

What are the 2 types of tightness that tight junctions can have?

Answer 13

-high barrier function –> stops most ions + water e.g renal thick ascending limb
-leaky –> allows transepithelial movement e.g renal proximal tubule

Question 14

What determines the tightness of tight junctions?

Answer 14

-protein strands (claudins)
-different combinations of claudins determine the permeability

Question 14

What do adhering junctions do and what happens if they’re disrupted?

Answer 14

-form belts around the cell under the tight junction
-if their organisation is disrupted, it can cause them to separate, leading to metastasis

Question 15

What are cadherins?

Answer 15

Adhesion molecules

Question 16

What do desmosomes do?

Answer 16

-form strong adhesion points between cells
-have extracellular domains (part of cadherin family)

Question 17

What do anchor proteins (plaques) do?

Answer 17

Link cadherin cytosolic domains to intermediate filaments

Question 18

What are the 2 main types of epithelia?

Answer 18

-simple –> single layer of cells
-stratified –> many layers of cells

Question 18

What are 2 other types of epithelia for those that don’t fit the main ones?

Answer 18

-pseudo-stratified –> 1 layer of cells but appear to be more
-transitional –> cells change as you move up through the layers

Question 18

What are the basic types of epithelia?

Answer 18

-simple squamous
-simple cuboidal
-simple columnar
-pseudostratified columnar
-stratified squamous
-stratified cuboidal
-stratified columnar
-transitional epithelia

Question 19

Describe simple squamous epithelia

Answer 19

-appear like thin ‘scales’
-facilitate rapid passage of molecules
-secretion/absorption of molecules via active transport

Question 19

Describe simple cuboidal epithelia

Answer 19

-secretion/absorption of molecules via active transport
-many have single non-motile cilium on apical membrane –> deformation ‘senses’ fluid flow

Question 20

Describe simple columnar epithelia

Answer 20

-with or without microvilli or cilia
-secretion/absorption of molecules via active transport
-majority in GI tract
-ciliated surfaces move egg in fallopian tube + remove particulates in respiratory system

Question 21

Describe pseudostratified columnar epithelia

Answer 21

-single cell layer but appear multi-layer as nuclei at different levels
-all in touch with basolateral membrane
-ciliated or nonciliated
-ciliated cells often interspersed with goblet cells

Question 22

Describe stratified squamous epithelia

Answer 22

-most common type
-apical cells appear squamous, basal cells cuboidal or columnar
-areas of high abrasion

Question 22

Describe stratified columnar epithelia

Answer 22

-rare
-allows tissue to stretch + contract

Question 22

Describe transitional epithelia

Answer 22

-cells round when relaxed
-facilitates shape change in distension without damaging epithelial lining

Question 23

Are stratified cuboidal common or not?

Answer 23

less common –> e.g glands

Question 24

What do multicellular glands have?

Answer 24

complex ducts - secrete directly onto the epithelial surface

Question 25

Where do single or different cell types secrete?

Answer 25

Directly into blood

Question 26

If secretion is via ducts, what is it called?

Answer 26

Exocrine

Question 27

If secretion is ductless, what is it called?

Answer 27

Endocrine