Kidney- Sodium, Chloride and Water Flashcards
How does the kidney handle sodium ions to change ECF volume?
To increase ECF it will increase Na+ reabsorption
To decrease ECF it will decrease reabsorption - i.e. increase excretion
What is the tonicity of the PCT ultra filtrate?
Isotonic with plasma
How do we change the volume of water in the body?
Move ions and water follows
If you move water alone you effect osmolality and we don’t want that in a sheer volume problem
How is sodium reabsorbed in the Loop of Henle?
Only in the ascending limb
What happens to sodium ions in the early distal tubule?
NaCl symport reabsoprtion
active sodium reabsoprtion
How does sodium re-uptake change along the DCT?
Early DCT sodium reabsorption is by the NaCl symporter
Late DCT still has NaCl but also has ENaC which is also seen in the collecting duct.
What would happen if we didn’t regulate the sodium reabsorption and thus the excretory rate of sodium to the ECF?
Very salty meal would cause a rise in circulating volume and if an individual became alt depleted BP would drop
How do we balance our variable sodium intake?
Kidney excretion to match sodium ingestion to maintain the balance
What is out normal g/day sodium in take?
10.5 (so thats how much we normally want to lose in urine- this will go up or down depending on the diet we have)
Where is sodium filtered?
Glomerulus
Where is sodium reabsorbed?
Proximal convoluted tubule
Thick Ascending Limb of the loop of henle
DCT and collecting duct are variable
What percentages of sodium are reabsorbed where?
67% PCT
25% Asc Limb
5-8% DCT
3% Collecting duct
Where does sodium move and water not (in the nephron)?
Ascending Loop of Henle
Where does water move but not sodium in the nephron?
Descending Loop of Henle
How much water is reabsorbed by the descending limb of the loop of hence?
10-15%
Where does sodium move and water not move (in the nephron)?
Ascending Loop of Henle
Where is water reabsorption most variable in the nephron?
Collecting duct system 5-24%
What percentage of water moves back in to the plasma in the PCT?
65%
How do we stimulate sodium reabsorption in the PCT?
RAAS
Which cells in the DCT and CD hold aldosterone receptors to give variable water re-uptake?
Principle cells
What happens to the number of Na-H antiprotons in the PCT when the BP in the renal artery increases?
Reduced number
If the blood pressure in the renal artery goes …. the Na-K ATPase activity in the proximal tubule will reduce
up
Why is it important to reduce the number of NaH antiporters and the NaK ATPase pump activity to reduce when renal artery BP increases?
Reduce the absorption of Na+ to reduce ECF
What does increased sodium excretion give?
natureisis
What would cause a diuresis interms of sodium reabsorption?
Diuresis
What is a diuresis?
More water excretion (following the naturesis)
What is transcellular absorption?
movement through the cell
What is transcellular absorption?
movement through the cell into the blood from the lumen
Where does paracellular secretion?
Movement in between the cells into the tubule
What is the glomerulus?
Capillary tuft
Which aqua porin channels are seen in the PCT?
AQP1 anf AQP7
The collecting duct has which 3 aqua porin channels?
AQP2,3,4
Which area of the kidney solely expresses AQP 1 channels?
Descending limb
In the ascending limb which aqua porins do you find?
NONE
How does chloride mainly get reabsorbed?
Transcellular (active) — some passive paracellular
Which transporters in the PCT help Na+ absorption by being present on the apical membrane ?
Na-H antiporter
Na-Glucose symporter
Na-AA co-transporter
Na-Pi
Which symporter reabsorbs sodium on the apical membrane in the Loop of Henle (ascending limb)?
NaKCC
Sodium Potassium Chloride Chloride (symporter)
Where in the tubule is the NaCl symporter on the apical membrane responsible for sodium reabsorption?
Early DCT
Which sodium transporter is important for variable Na+ absorption in the late DCT and the collecting duct?
ENaC
In the first section of the PCT which apical transporters move sodium?
S1 - fast preferntial absorption with glucose, amminoacids, and phosphate , antiported with hydrogen.
Outline the basolatteral sodium transporters in S1 of the PCT.
Sodium Potassium pump
NaHCO3- cotransporter
How does water move in the PCT?
Follows water by aquaporin 1 and 7
What happens to chloride and urea in s1 of the PCT?
Flow into the tubule to compensate for the loss of glucose
important Cl- gradient establishes to flow back in S2 and S3
Outline the tubular cells of S2 and S3 in the PCT.
The apical membrane reabsorbs sodium by NaH antiporter.
The H+ in the tubule binds HCOO-, this HCOOH can flow back into the cell. This will dissociate in the cell. Net effect we’ve moved HCOO- into the cell.
The H+ in the cell will flow out by the NaH antiporter. The HCOO- will be antiported with Cl-
Cl- and K+ are symported on the basolateral membrane into the blood.
Na+ is antiproton into the blood and potassium moves back into the cell.
Cl- will move paracellularly as well
In S2, S3 whats the osmotic gradient for water movement?
Favours water uptake from the lumen by 4mOsmol
In the late PCT which cells can be reabsorbed paracellularly and why?
Cl- and Na+
Cl- becomes major anion in the lumen as HCO3- is reabsorbed
Which capillaries surround the PCT?
peritubular
What drives reabsorption in the PCT?
Osmotic gradient established as solute reabsorption happens. (interstitial becomes hypertonic and get a raised hydrostatic pressure)
The Oncotic pressure of the capillary is increased because 20% of volume lost at glomerulus.
How does water move out of the descending limb?
Passively- thin flat epithelium and no tight junctions + AQP1
Which part of the loop of Henle is active?
Ascending limb- tight junctions and totally impermeable to water
What happens in the thin ascending limb to sodium?
Passive reabsoprtion. (water doesn’t move here but its because of the water reabsorption in the descending limb that sodium can now move passively here)
What tonocity is the filtrate from the descending limb?
Water left but no sodium so hyperosmotic
The NKCC2 transporter moves all these ions into the cell in the TAL from the lumen, how do they move at the basolatteral membrane and which ion is secreted back into the lumen?
K+ secreted by ROMK and Maxi-K (keeps NKCC2 working)
Cl-/K+ simper into blood
Sodium potassium pump
Chloride channel in basolateral membrane
Which segment is the diluting segment?
ascending - no water is being reabsorbed but NaCl is leaving
After filtrate leaves the Loop of Henle what is its tonicity compared to plasma?
Hypo-osmotic- its just moved though the diluting segment
How does the early DCT dilute urine?
Active Na+ absorption
Which hormone effects how much water and sodium we take up in the DCT and CD?
ADH
Which diuretic effects the early DCT and late DCT?
Thaiazides inhibit the NaCl cotranspoter in the apical membrane
Which diuretic inhibits ENaC?
Amiloride
Where is the major site of calcium reabsoption?
DCT
NCX exchanger is responsible and this is tightly regulated by 1,25-dihydroxyvitamin D and PTH
Outline the transporters seen in the collecting duct.
Aquaporin, Na, K and Cl uniporters on the apical (K moves into lumen everything else into cell)
BAsolateral memebrane has the sodium pump and then Cl- and K+ uriporters into the blood
What percentage of collecting duct cells are principles and what sodium transporter do they hold?
70%
ENaC like late DCT (DCT2) - driven by basolateral NaKATPase
This active Na+ movement sets up paracellular Cl- gradient and lets K+ secretion occur
What are intercalated cells and where do you find them?
Collecting duct cells that actively reabsorb Cl-, secrete H+ or HCO3- dependent on pH
two types
AIC- acid secreting
BIC- bicabonate secreting
Which transporter on the AIC allows for secretion of H+?
H+ ATPase
How does bicarbonate move in the CD?
Type B intercalated cells can take HCO3- in from the lumen with Na+ and extrude Cl- by the NDCBE.
Pendrin lets Cl- extrusion and HCO3- absorptrion by the exchanger.
In the basolateral membrane is we need to become more basic we reabsorb bicarbonate and sodium together by AE4
