L7

Question 1

what are epithelia

Answer 1

they are barriers

they separate body compartments (organs)

Question 2

what do epithelia act as

Answer 2

to act as gatekeepers

they facilitate movement of ions and molecules between external and internal environments

Question 3

what are some areas where epithelia separate internal and external environments

Answer 3

Skin

Intestinal tract

Nephrons of the kidneys/urinary tract

Respiratory tract, reproductive tract

Regions of the eye and auditory system

Question 4

what are the properties of epithelia

Answer 4

Separate internal and external environments

Control exchange of material between body and the
environment

Define the composition of the luminal fluid of hollow
organs

Question 5

what is an example of where epithelia control exchange of material between body and the
environment

Answer 5

Intestinal tract and nephron/urinary tract

Question 6

what are some examples of where epithelia define the composition of the luminal fluid of hollow
organs

Answer 6

Reproductive tract, respiratory tract, intestinal tract, kidney nephron, oviduct, and vas deferens, etc.

Question 7

what is the basic structure of epithelial tissue

Answer 7

it has 1 or more layers of epithelial cells, a basement membrane and supporting tissues (extracellular matrix, cells)

Question 8

the structure of epithelial tissue depends on what

Answer 8

where it is located in the body and its function

Question 9

what is an example of serosal/interstitial fluid

Answer 9

blood

Question 10

what is another name for the intERcellular space

Answer 10

the basolateral space

Question 11

what membrane of the epithelium faces the mucosal solution

Answer 11

apical membrane

Question 12

what does the basement membrane face

Answer 12

serosal solution (blood)

Question 13

what are the 2 ways that substances can cross the epithelium

Answer 13

Paracellular = substances can travel between the epithelial cells

Transcellular = through the cells

Question 14

what is the difference between gap and tight junctions

Answer 14

Gap = communication they are a passage and tight junctions are barrier proteins

Question 15

describe the apical membrane

Answer 15

Faces the lumen (outside)
of the organ

it can be called the apical, mucosal, luminal
membrane or brush border

often has microvilli (MV)

Question 16

describe the basolateral membrane

Answer 16

Faces the interstitial fluid
(inside) ‘internal body’

it can be called the basolateral membrane,
serosal membrane

Question 17

what are the 2 parts of the basolateral membrane

Answer 17

Basal membrane (BM)

Membrane lining the lateral
intercellular space (LIS)

Question 18

where does the basolateral membrane spann from

Answer 18

tight junction to tight junction

Question 19

what is vectorial transport

Answer 19

transport in a specific diffection

It involves active and passive transport of ions & solutes and depends on active transport (e.g. Na/K-ATPase) and osmosis

Question 20

how do we sweat

Answer 20

Sweat glands are specialised parts of the skin epithelium. What these glands do is they secrete salt. water follows salt which is how we sweat

Question 21

what is the natural environment made up of

Answer 21

electrical and chemical

Question 22

why are epithelial cells capable of fluid and electrolyte transport

Answer 22

because they are polarised/asymmetrical
cells

they have structural and functional asymmetry

Question 23

what is meant by structural asymmetry

Answer 23

the apical and basolateral membranes are different which makes it polar (because it is different on either side)

Question 24

why do epithelial cells have functional asymmetry

Answer 24

because apical and basolateral membranes are
functionally different

They contain different set of channels and transporters which have properties distinct from each other

Question 25

what are some common characteristics of the basolateral membrane

Answer 25

High K+ permeability relative to Na+, Cl High water permeability it also contains housekeeping transporters Attached to the basement membrane

Question 26

what is the reason that the basolateral membrane his a high K+ permeability relative to Na+, Cl

Answer 26

because it contains lots of K+ channels

Question 27

why is the basolateral membrane so permeable to water

Answer 27

because it contains lots of aquaporins

Question 28

what are some examples of housekeeping transporters located in the basolateral membrane

Answer 28

Na+/K+ ATPase Ca2+ ATPase and Na+/Ca2+ exchanger Na+/H+ exchanger (NHE-1)

Question 29

what are some common characteristics of the apical membrane

Answer 29

Selectively permeable to various ions no housekeeping transporters variable water permeability

Question 30

the apical membranes permeability to ions depends on what.... with examples

Answer 30

Permeability depends on the type of epithelium and what channels and transporters that membrane has Na+ absorbing epithelia, high Na + permeability – Range of transporters and channels Secretory epithelia, high Cl- permeability – Cl- channels Determines the transport properties of the epithelium

Question 31

Typical functional features of the basolateral membrane of an epithelial cell are: A. faces the external environment, does not have K+ channels, does not contain aquaporins. B. has microvilli, faces the interstitial fluid, touches neighbouring cells. C. contains Na+ channels, has K+ channels, is permeable to water. D. faces the interstitial fluid, has Na+-K+-ATPase, is permeable to K+.

Answer 31

D

Question 32

there are 2 types of absorptive epithelia

Answer 32

lecky and tight

Question 33

what are the characteristics of absorptive epithelium

Answer 33

Net transport is from mucosal to serosal solution | Absorption driven by the active transport of Na+ Na/K-ATPase

Question 34

what are some examples of where you can find absorptive epithelium

Answer 34

Intestine and nephron

Question 35

what are the characteristics of secretory epithelium

Answer 35

Net transport from serosal to mucosal solution | Secretion is driven by the active transport of Cl- NKCC

Question 36

what are some examples of secretory epithelium

Answer 36

Salivary glands, pancreas, sweat glands

Question 37

what are some examples of epithelia that is both secretory and absorptive

Answer 37

Small and large intestine, kidney nephron, | airways

Question 38

what is the difference between tight and leaky absorptive epithelia (5 points)

Answer 38

They are separated on basis of.... Transport properties derived from electrical characteristics Apical membrane transport pathways Hydraulic conductivity (relative water flow) Responsiveness to hormones Location within organs

Question 39

what is transepithelial voltage

Answer 39

Voltage that develops across an epithelium due to active transport of ions This is talking about going across the whole cell not just across the membrane (thats a mp)

Question 40

what is the transepithelial voltage range for leaky absorptive epithelium

Answer 40

0 - 5 mV

Question 41

what is the transepithelial voltage range for tight absorptive epithelium

Answer 41

20 - 100 mV

Question 42

what are the electrical characteristics of absorptive epithelium

Answer 42

transepithelial voltage and transepithelial resistance

Question 43

what is transepithelial resistance

Answer 43

Electrical resistance to flow of ions across an epithelium Unit: ohms/cm^-2

Question 44

what is the transepithelial resistance range for tight absorptive epithelium

Answer 44

Leaky absorptive epithelia 20 - 100 ohms/cm^-2 therefore it is ‘Easy’ for ions to move across epithelium Tight absorptive epithelia 300 - 10,000 ohms/cm^-2 therefore it is difficult for ions to move across epithelium

Question 45

how many x larger is the resistance for tight absorptive epithelia compeered to lecky

Answer 45

15 – 100 x higher

Question 46

what is the reason for the difference in transepithelial resistance between tight and leaky absorptive epithelia

Answer 46

Leaky epithelia have lots of paracellular transport because they have less tight junctions The number and the type of tight junctions in the epithelia determines the electrical resistance

Question 47

electrical resistance is a measure of what

Answer 47

Electrical resistance is a measure of how much substances and solutes can pass the epithelium through the paracellular pathway vs the transcellular pathway

Question 48

Why do we have leaky and tight epithelia within the same tissue within the same organ? with example

Answer 48

The distal part of the kidney we have tight epithelium 200L of fluid goes through the kidneys per day and the majority of that is reabsorbed. To reabsorb this we have leaky and tight absorptive epithelium leaky does bulk (to reduce time and make it more efficient) tight is for specific things for fine tuning of homeostasis

Question 49

if you have a high resistance what does that mean for the flow of ions

Answer 49

that there is a slow rate of transport (flow)

Question 50

how does Na cross the apical membrane in leaky absorptive epithelia

Answer 50

Leaky epithelia - Na+ dependent cotransporters | and/or exchangers (counter transporters)

Question 51

how does Na cross the apical membrane in tight absorptive epithelia

Answer 51

Tight epithelia - Na+ selective channels (e.g. | ENaC: epithelial Na+ channel)

Question 52

describe hydraulic conductivity in leaky absorptive epithelia what kind of fluid will it absorb

Answer 52

high hydraulic conductivity as it has a range of aquaporins and tight junctions (number and types) it absorb large amounts of isosmotic fluid therefore it is efficient and effective

Question 53

describe hydraulic conductivity in tight absorptive epithelia

Answer 53

low hydraulic conductivity under basal conditions increases under hormonal control absorb variable amounts of hyperosmotic fluid because tight can produce large osmotic gradients as it stops the water from moving back

Question 54

describe the effect of hormones on leaky epithelium

Answer 54

has very little effect as leaky have a constant rate of transport

Question 55

describe the effect of hormones on tight absorptive epithelium

Answer 55

very responsive to hormones ion and water transport is closely regulated by hormone

Question 56

what are the 2 hormones which have an effect on tight absorptive epithelia

Answer 56

aldosterone and vasopressin

Question 57

what is the effect of aldosterone on tight absorptive epithelia

Answer 57

aldosterone, regulates Na+ transport through ENaC

Question 58

what is the effect of vasopressin on tight absorptive epithelia

Answer 58

vasopressin also called antidiuretic hormone (ADH) | regulates water transport Aquaporin 2 (AQP2)

Question 59

why do tight and leaky epithelia respond to hormones

Answer 59

to regulate blood pressure

Question 60

where is leaky epithelia usually located within organs? why?

Answer 60

proximal regions of organs in these regions because this is where ‘bulk’ transport occurs

Question 61

where is leaky epithelia usually located within the nephron

Answer 61

proximal tubule of the nephron

Question 62

where is leaky epithelia usually located within the small intestine

Answer 62

duodenum, jejunum and ileum of small intestine

Question 63

where is tight absorptive epithelia usually located within organs? why?

Answer 63

distal regions of organs as this is where ‘fine tuning’ (highly controlled absorption) takes place

Question 64

where is tight absorptive epithelia usually located within the nephron

Answer 64

late distal tubule and collecting duct of nephron

Question 65

where is tight absorptive epithelia usually located within the large intestine

Answer 65

distal colon of the large intestine

Question 66

Leaky absorptive epithelia A. have a high transepithelial resistance. B. can mainly be found in distal parts of organs. C. do not have tight junctions. D. have a low hydraulic conductivity. E. possess mainly Na+ dependent co-transporters/exchangers in their apical membrane.

Answer 66

E