intro to epithelial solute and water transport Flashcards
1
Q
what makes up the ECF?
A
plasma + ISF + trans cellular fluid
2
Q
gives examples of trans cellular fluid
A
CSF, synovial fluid, intraocular fluid
3
Q
give examples of external space fluid
A
GI tract, kidney tubules and salivary ducts
4
Q
what is epithelium a barrier between?
A
ECF + external space
5
Q
what do tight junctions separate?
A
- neighbouring cells
- also apical and basolateral membranes — allows for asymmetric expression of transport proteins
6
Q
what does the basolateral membrane face?
A
interstitium
7
Q
what are adhering junctions and desmosomes for?
A
support
8
Q
what does the apical membrane face?
A
external space
9
Q
what do cells communicate via?
A
gap junctions
10
Q
what do tight junctions restrict?
A
para cellular movement
11
Q
what is para cellular movement?
A
movement between cells
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
13
Q
what is the phospholipid bilayer impermeable to?
A
ions and polar molecules
14
Q
membrane transporters are required for the movement of ____ molecules between the ICF and ECF that cant pass by ________?
A
- polar
- simple diffusion
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
16
Q
phospholipid bilayer head vs tails?
A
heads = hydrophilic
tails = hydrophobic
17
Q
what kind of transporter is the NaKATPase?
A
ion pump
18
Q
ion pump uses energy from what?
A
ATP hydrolysis
19
Q
describe NaK ATPase
A
- uses energy from ATP hydrolysis
- transports 3Na+ out for every 2K+ in
- creates and maintains electrochemical gradients
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
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
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
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
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
25
ICF vs ECF in terms of Na+ and K+ conc
ICF = high K+ and low Na+
ECF = low K+ and high Na+
26
water flow through aquaporins is driven by what?
osmosis
27
what is osmosis?
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
what establishes electrochemical gradient?
NaK ATPase
29
glucose crosses the basolateral membrane via what?
facilitated diffusion
30
Cl- enters via what? then it exits the apical membrane in the gut lumen through what?
- Cl- in via Na+ gradient
- exits apical membrane through chloride channels
31
transport may occur via what 2 pathways?
trans cellular or paracellular
32
respiratory gases such as oxygen cross membranes via what?
simple diffusion
33
transport proteins are required to transport IONS AND POLAR MOLECULES across cell membranes — eg. ____ and ____
K+ and glucose
34
what does transepithelial transport require?
asymmetric expression of transport proteins on the apical and basolateral membranes
35
describe serous mucous
ion-rich, watery
36
where does saliva secretion begin?
acinus = sac-like cavities within the salivary glands surrounded by acinar cells that feed into the salivary ducts
37
what are the 2 acinus types?
serous vs mucous
38
what type of acinar cells are mainly found in each of the salivary glands?
1. parotid = mainly serous acinar
2. submandibular = serous and mucous acinar
3. sublingual = mainly mucous acinar
39
human parotid salvia secretions and rich in what?
Na+, HCO3- and Cl-
40
what maintains the more alkaline pH of saliva?
HCO3-
41
what is the 2 stage process of saliva secretion?
1. primary secretion by acinar cells
2. modification of primary saliva by salivary duct cells
42
primary secretion by acinar cells:
NaK ATPase role
- 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
primary secretion by acinar cells:
Na+ K + 2Cl- cotransporter (NKCC1, SLC12A2) role
- 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
primary secretion by acinar cells:
K+ channels (BK and IK1) role
recycles K+ and maintains membrane potential
no net movement of K+
45
primary secretion by acinar cells:
Ca2+ activated Cl- channel (TMEM16A) role
- allows Cl- efflux down its electrochemical gradient
Cl leaves via chloride channels across apical membrane
46
primary secretion by acinar cells:
what drives Na+ secretion via the para cellular pathway?
small -ve potential in lumen (Cl- in lumen)
47
primary secretion by acinar cells:
what allows H2O reflux driven by a small osmotic gradient?
aquaporin 5 water channel (AQP5)
48
what separates acinar cells?
tight junctions
49
modification of primary saliva by salivary duct cells:
Na+ enters the cell passively via what?
ENaC channels
50
modification of primary saliva by salivary duct cells:
Na+ leaves across the basolateral membrane via what?
NaK ATPase
51
modification of primary saliva by salivary duct cells:
small +ve potential on the blood side draws Cl- through the cell via what?
Cl- channels
52
modification of primary saliva by salivary duct cells:
Cl- also taken up from saliva in exchange for HCO3- via what?
apical Cl-/HCO3- exchangers
53
modification of primary saliva by salivary duct cells:
intracellular HCO3- is generated from CO2 and water by what enzyme?
carbonic anhydrase
54
modification of primary saliva by salivary duct cells:
what do basolateral Na+/H+ exchangers extrude?
H+
55
what are duct cells impermeable to, unlike acinar cells? result?
H2O — therefore little water reabsorption — therefore hypotonic saliva
56
primary vs final saliva?
primary saliva = isotonic
final saliva = hypotonic
57
ACh raises what?
intracellular Ca++
58
NA raises what?
intracellular cAMP
59
describe the role of ACh in PS stimulation
- 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
what acts as a signalling molecule to activate other ion channels?
Ca++
61
parasympathetic vs sympathetic nerves on saliva
62
parasympathetic neuronal activation promotes ____ secretion
sympathetic neuronal activation promotes _____ secretion
1. PS = salt and water secretion
2. S = protein secretion
63
salivary duct cells reabsorb ___ and ____ but are impermeable to ____ resulting in a _____ final saliva
- Na+ and Cl-
- H2O
- hypotonic
