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PBL SEM 4 > intro to epithelial solute and water transport > Flashcards

intro to epithelial solute and water transport Flashcards

1
Q

what makes up the ECF?

A

plasma + ISF + trans cellular fluid

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2
Q

gives examples of trans cellular fluid

A

CSF, synovial fluid, intraocular fluid

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3
Q

give examples of external space fluid

A

GI tract, kidney tubules and salivary ducts

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4
Q

what is epithelium a barrier between?

A

ECF + external space

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5
Q

what do tight junctions separate?

A
  • neighbouring cells
  • also apical and basolateral membranes — allows for asymmetric expression of transport proteins
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6
Q

what does the basolateral membrane face?

A

interstitium

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7
Q

what are adhering junctions and desmosomes for?

A

support

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8
Q

what does the apical membrane face?

A

external space

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9
Q

what do cells communicate via?

A

gap junctions

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10
Q

what do tight junctions restrict?

A

para cellular movement

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11
Q

what is para cellular movement?

A

movement between cells

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12
Q

what is tight junction permeability determined by?

A

claudin family proteins

  • TJs in some epithelial are ‘leaky’ to small ions and water eg. transport epithelia
  • in others they are ‘tight’ and impermeable eg. in skin
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13
Q

what is the phospholipid bilayer impermeable to?

A

ions and polar molecules

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14
Q

membrane transporters are required for the movement of ____ molecules between the ICF and ECF that cant pass by ________?

A
  • polar
  • simple diffusion
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15
Q

what is the function of sterol in the phospholipid bilayer?

A

give structure and integrity and provide precursors for fat-soluble vitamins and steroid hormones

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16
Q

phospholipid bilayer head vs tails?

A

heads = hydrophilic
tails = hydrophobic

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17
Q

what kind of transporter is the NaKATPase?

A

ion pump

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18
Q

ion pump uses energy from what?

A

ATP hydrolysis

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19
Q

describe NaK ATPase

A
  • uses energy from ATP hydrolysis
  • transports 3Na+ out for every 2K+ in
  • creates and maintains electrochemical gradients
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20
Q

roles of the K+ and Na+ gradient in NaK ATPase

A
  • K+ gradient generates the membrane potential (approx - 60mV)
  • Na+ gradient drives other passive transporters — secondary active transport
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21
Q

describe ion channels

A
  • highly selective protein pores in the membrane (specificity dependent on protein structure)
  • ion flow is driven by conc gradient and membrane potential : electrochemical gradient - Passive transport
  • may be gated by intracellular or extracellular messengers, or by membrane potential changes

high —> low conc

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22
Q

describe transporter (carrier proteins)

A
  • highly selective carrier protein in the membrane
  • transport is passive
  • driven by the conc gradient alone
  • FACILITATED DIFFUSION
  • rate can become saturated
  • conformational change upon ligand binding
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23
Q

describe the Na+K+2Cl- cotransporter

A
  • symporter (all same direction)
  • inward movement of Na+ drives uptake of Cl- against its gradient
  • secondary active transport
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24
Q

describe the Na+/H+ exchanger

A
  • antiporter (opposite directions)
  • inward movement of Na+ drives extrusion of H+ against its gradient
  • secondary active transport
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25
Q

ICF vs ECF in terms of Na+ and K+ conc

A

ICF = high K+ and low Na+

ECF = low K+ and high Na+

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26
Q

water flow through aquaporins is driven by what?

A

osmosis

27
Q

what is osmosis?

A

the diffusion of water through a semi-permeable membrane from a region of lower total solute conc to one of higher total solute conc

28
Q

what establishes electrochemical gradient?

A

NaK ATPase

29
Q

glucose crosses the basolateral membrane via what?

A

facilitated diffusion

30
Q

Cl- enters via what? then it exits the apical membrane in the gut lumen through what?

A
  • Cl- in via Na+ gradient
  • exits apical membrane through chloride channels
31
Q

transport may occur via what 2 pathways?

A

trans cellular or paracellular

32
Q

respiratory gases such as oxygen cross membranes via what?

A

simple diffusion

33
Q

transport proteins are required to transport IONS AND POLAR MOLECULES across cell membranes — eg. ____ and ____

A

K+ and glucose

34
Q

what does transepithelial transport require?

A

asymmetric expression of transport proteins on the apical and basolateral membranes

35
Q

describe serous mucous

A

ion-rich, watery

36
Q

where does saliva secretion begin?

A

acinus = sac-like cavities within the salivary glands surrounded by acinar cells that feed into the salivary ducts

37
Q

what are the 2 acinus types?

A

serous vs mucous

38
Q

what type of acinar cells are mainly found in each of the salivary glands?

A
  1. parotid = mainly serous acinar
  2. submandibular = serous and mucous acinar
  3. sublingual = mainly mucous acinar
39
Q

human parotid salvia secretions and rich in what?

A

Na+, HCO3- and Cl-

40
Q

what maintains the more alkaline pH of saliva?

A

HCO3-

41
Q

what is the 2 stage process of saliva secretion?

A
  1. primary secretion by acinar cells
  2. modification of primary saliva by salivary duct cells
42
Q

primary secretion by acinar cells:

NaK ATPase role

A
  • maintains conc gradients for Na+ and K+
  • small direct contribution to membrane potential
  • 2K+ in for every 3Na+ out
  • Na out against conc gradient via active transport
43
Q

primary secretion by acinar cells:

Na+ K + 2Cl- cotransporter (NKCC1, SLC12A2) role

A
  • electrically neutral
  • uses inward gradient for Na+ to drive coupled uptake of Cl-
  • secondary active transport
  • Na moves back in down conc grad, bringing Cl- with it
  • Cl- moves in against conc grad and accumulates in cell
44
Q

primary secretion by acinar cells:

K+ channels (BK and IK1) role

A

recycles K+ and maintains membrane potential

no net movement of K+

45
Q

primary secretion by acinar cells:

Ca2+ activated Cl- channel (TMEM16A) role

A
  • allows Cl- efflux down its electrochemical gradient

Cl leaves via chloride channels across apical membrane

46
Q

primary secretion by acinar cells:

what drives Na+ secretion via the para cellular pathway?

A

small -ve potential in lumen (Cl- in lumen)

47
Q

primary secretion by acinar cells:

what allows H2O reflux driven by a small osmotic gradient?

A

aquaporin 5 water channel (AQP5)

48
Q

what separates acinar cells?

A

tight junctions

49
Q

modification of primary saliva by salivary duct cells:

Na+ enters the cell passively via what?

A

ENaC channels

50
Q

modification of primary saliva by salivary duct cells:

Na+ leaves across the basolateral membrane via what?

A

NaK ATPase

51
Q

modification of primary saliva by salivary duct cells:

small +ve potential on the blood side draws Cl- through the cell via what?

A

Cl- channels

52
Q

modification of primary saliva by salivary duct cells:

Cl- also taken up from saliva in exchange for HCO3- via what?

A

apical Cl-/HCO3- exchangers

53
Q

modification of primary saliva by salivary duct cells:

intracellular HCO3- is generated from CO2 and water by what enzyme?

A

carbonic anhydrase

54
Q

modification of primary saliva by salivary duct cells:

what do basolateral Na+/H+ exchangers extrude?

A

H+

55
Q

what are duct cells impermeable to, unlike acinar cells? result?

A

H2O — therefore little water reabsorption — therefore hypotonic saliva

56
Q

primary vs final saliva?

A

primary saliva = isotonic

final saliva = hypotonic

57
Q

ACh raises what?

A

intracellular Ca++

58
Q

NA raises what?

A

intracellular cAMP

59
Q

describe the role of ACh in PS stimulation

A
  • ACH activates M1 and M3 muscarinic receptors
  • activated G protein
  • activates phospholipase C
  • increases inositol 1,4,5-trisphosphate (IP3)
  • increases Ca++ release from endoplasmic reticulum
  • Ca++ has a positive effect on Cl- and K+ channels
  • increases the flow rate of ions throguh these channels
  • more ion movement
  • more chloride movement
  • more Na+ movement
  • more osmotic movement of H2O
60
Q

what acts as a signalling molecule to activate other ion channels?

A

Ca++

61
Q

parasympathetic vs sympathetic nerves on saliva

A
62
Q

parasympathetic neuronal activation promotes ____ secretion

sympathetic neuronal activation promotes _____ secretion

A
  1. PS = salt and water secretion
  2. S = protein secretion
63
Q

salivary duct cells reabsorb ___ and ____ but are impermeable to ____ resulting in a _____ final saliva

A
  • Na+ and Cl-
  • H2O
  • hypotonic

PBL SEM 4 (50 decks)

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