Case 1 - epithelial solute and water transport Flashcards
how much of our body weight does fluid account for
60%
what makes up the extracellular fluid
the transcellular fluid, interstitial fluid, and the plasma
what separates the extracellular fluid form the outside world
the epithelial cells
what is considered outside of the body
anything on the apical side of the epithelium e.g GI tract, kidney tubules and salivary ducts
diagram showing the organisation of the body compartments
where does the apical membrane face
the outside
where does the basolateral membrane face
the inside
what do tight junctions do
separates the basolateral and apical membranes and also found between neighbouring cells
this allows for asymmetric expression of transport protiens
what provide support in epithelia structure
desmosomes and adhering junctions provide structure
what is tight junction permeability determined by
claudin family proteins
what are phospholipid bilayers
have hydrophilic head groups facing aqueous environments and hydrophobic lipid tails in the lipid bilayer
is the phospholipid bilayer permeable?
no, it is impermeable to ions and polar molecules
what is permeability provided by instead
membrane proteins (transporters)
what is sterol
provides structural integrity and provides precursors for fat soluble vitamins and steroid hormones
what does the integral protein spanning proteins include
all of the cell surface receptors, G proteins, and our membrane transporters
what are the three types of membrane transporters
ion pumps
ion channels
transporter
what do ion pumps do
they move ions against their concentration gradients
what do ion pumps use energy from
ATP hydrolysis
do ion pumps use active transport
yes
features of the sodium pump
2 K+ in, 3 Na+ out
what do ion pumps do
creates and maintains electrochemical gradients
what gradient generates the membrane potential and what is the membrane potential value
the K+ gradient and membrane potential is approx -60mV
what gradient drives other passive transporters
Na+ gradient = secondary active transport
what are ion channels
highly selective protein pores in the membrane (specifically dependent on protein structure)
what is ion flow driven by in ion channels
driven by concentration gradient and membrane potential: electrochemical gradient - passive transport
what may ion channels be gated by
intracellular or extracellular messengers, or by membrane potential changes
what are transporter (carrier) proteins
highly selective carrier protein in the membrane
is transport active or passive in carrier proteins
passive
what is transporter (carrier proteins) driven by and what is another name for it
driven by concentration gradient alone
facilitated diffusion!!!
what is secondary active transport
cotransporters and exchangers
what are the most common cotransporters
Na+, K+, Cl-
what does inwards movements of Na+ drive
uptake of Cl- against its gradient
what is the Na+/H+ exchanger
an anti porter
inwards movement of Na+ drives extrusion of H+ against its gradient
what is the composition values of intracellular fluid
low in Na+ and high in K+
what is the composition values of extracellular fluid
high in Na+ and low in K+
what is passive transport
simple or facilitated diffusion
molecules move along the concentration gradient
high to low concentration
what is active transport
moves molecules against the concentration gradient
hydrolysis of ATP - ion pumps
secondary active transport
what is different about secondary active transport
the gradient has usually been established by another ion
what are aquaporins
pore is highly selective to water
water flow is driven by osmosis
what is osmosis
osmosis is the diffusion of water through a semi-permeable membrane
from a region of lower total solute concentration to one of higher total solute concentration
diagram showing transcellular transport
mostly glucose and Cl-
what is the only thing to mediate active transport
pumps
how may transport occur
via transcellular or paracellular pathways
what are the main salivary glands
parotid - the largest
submandibular
sunlingual
what are the cells found in the parotid gland
mainly serous acinar cells
what are the cells found in the submandibular gland
serous and mucous acinar cells
what are the cells found in the sublingual gland
mainly mucous acinar cells
how much saliva do humans secrete in a day
1L
what technically determines the pH value of saliva
the higher the incidence of bicarbonate
secretion as a two stage process diagram
secretion as a two stage process diagram
features of the acinus part of secretion
secretion of Na, Cl, and HCO3 by active transport
high water permeability
isotonic, plasma like primary secretion
features of the duct part of secretion
reabsorption of NaCl
some secretions of K and HCO3
low water permeability
hypotonic final saliva
where does the saliva become hypotonic
the duct
what is primary secretion performed by and what pump is responsible for setting the ion gradient
primary secretion by acinar cells and the sodium pump sets the ion gradient
what happens when chlorine moves into the lumen (negatively charged ion)
leads to a small negative charge building up within the lumen and that then draws positive ions like Na+, paracellularly, passively down its electrochemical gradient
what do acinar cells express in the apical and basolateral membranes and what does this do
express aquaporin 5
this lets water move via osmosis
primary secretion by acinar cells diagram
summary of the Na+, K+, ATPase pump
maintains concentration gradients for Na+ and K+
small direct contribution to membrane potential
summary of the Na+, K+, 2CL cotransporter
electrically neutral
uses inward gradient for Na+ to drive coupled uptake of Cl-
secondary active transport
what are examples of the Na+, K+, 2Cl- cotransporter
NKCC1, SLC12A2
summary of K+ channels
recycles K+ and maintains membrane potential
examples of K+ channels
BK ans IK1
summary of Ca2+ activated Cl- channels
allows Cl- efflux down its electrochemical gradient
example of Ca2+ activated Cl- channel
TMEM16A
what drives Na+ secretion via the paracellular pathway
small negative potential in the lumen
summary of the aquaporin 5 water channel
allows H20 efflux driven by a small osmotic gradient
example of an aquaporin channel
AQP5
modification of primary saliva by salivary duct cells diagram
what is the difference between acinar and salivary duct cells
salivary duct cells are impermeable to water
what is the final saliva
more hypotonic
how does Na+ enter the salivary duct cell
passively via ENaC channels
how does Na+ leave the salivary duct channels
cross the basolateral membrane via Na+,K+ ATPase
what draws Cl- through the cell via Cl- channels
small positive potential on the blood sie
what is Cl- also taken up from the saliva in exchange for
HCO3- via apical Cl-/HC03- exchangers
what is intracellular HC03- generated from
from CO2 and water by an enzyme called carbonic anhydrase
what extrudes H+
basolateral Na+/H+ exchangers
what ensures little water reabsoprtion
low water permeability
what raises the amount of saliva produced
stimulation of parasympathetic nervous system
parasympathetic nervous system stimulation
acetylcholine raises intracellular Ca2+
acetylcholine will bind to M1 and M3 muscarinic G protein coupled receptors
this activates a signalling cascade
we get activation of phosphoplipase C
leads to increase in inositol triphosphate
the binding of this to calcium channels then leads to:
triggers Ca2+ release from the endoplasmic reticulum
calcium then acts as a signalling molecule to activate other ion channels
parasympathetic nerve stimulation diagram
what effect does the sympathetic nervous system have
noradrenaline raises intracellular cAMP
diagram showing this effect
what does raised intracellular cAMP lead to
protein secretion
diagram summing up parasympathetic and sympathetic nerve activation
