Changes In Plasma Volume Flashcards
How do kidneys (generally) regulate extracellular volume?
Regulating excretion of NaCl
What separates intracellular and extracellular fluid?
Cell membrane
Concentration of Na inside and outside a cell?
Extra - 145mM
Intra - 12mM
Concentration of Cl- inside and outside a cell?
Extra - 123mM
Intra - 4.2mM
Concentration of potassium inside and outside of the cell?
Extra - 4mM
Intra - 155mM
Concentration of calcium inside and outside the cell?
Extra - 1.5mM
Intra - 10^-7 M
Is sodium a passive or active process (mainly)?
Active
What percentage of sodium is reabsorbed in the PCT?
67%
What is the glomerular tubular balance?
A proportion of Na+ that is always reabsorbed, no matter what the actual amount is that is filtered
What is glomerular tubular balance good for?
It blunts sodium excretion response if GFR changes too much
Autoregulation usually prevents it from changing too much
What percentage of glucose is absorbed in the first section of the PCT?
100%
What sodium channels are there in section 1 of the PCT?
Sodium and glucose co-transporter Na-H exchange Co-transport with amino acids/carboxylic acids Co-transport with phosphate Aquaporin
What compensates for loss of ions in section 1 of the PCT?
Urea and Cl- concentration increases down S1
What does the increase in chloride concentration in section 1 allow for?
A concentration gradient for chloride reabsorption in S2 and 3
What transporters does the apical membrane of sections 2 and 3 of the PCT have?
NaH exchange
Para cellular Cl- reabsorption
Transcellular Cl- reabsorption
Aquaporin
What is reabsorbed in sections 1, 2 + 3 of the PCT?
Section 1 - sodium and glucose
Sections 2+3 - sodium and water
In relation to the blood, is filtrate hypertonic, isotonic or hypotonic at the start and the end of the PCT?
Isotonic the whole way
What is the driving force of PCT reabsorption?
Osmotic gradient established by solute absorption
- osmolality in interstitial space increases
- hydrostatic force in interstitium increases
- oncotic force in peritubular capillary due to loss of 20% of filtrate at glomerulus
What happens to cardiac output and arterial blood pressure and GFR if ECF volume increases?
They increase
What allows for water reabsorption in the descending limb?
The increase of intracellular concentration of sodium set up by the PCT
What happens to the filtrate as it goes through the descending limb?
Water is transported out, concentrating sodium and chloride. Increase in osmolarity
Which part of the loop of Henle is impermeable to water?
The ascending limb
What happens in the descending limb?
The increase of intracellular concentration of sodium from action of the PCT allows water to be reabsorbed
What happens to the osmolarity of the filtrate in the descending limb
Increases - becomes more hypertonic
What happens in the thin ascending limb?
Passive sodium reabsorption Paracellular route (between epithelial cells)
What happens in the thick ascending limb?
NaCl transport from the lumen into cells by NaKCC2 transporter
K+ ions diffuse via ROMK into the lumen
Cl- into ECF as does Na+ via NaKATPase
What does the NaKCC2 transporter move?
2 chloride
1 sodium
1 potassium
All in the same direction
Which part of the nephron is the most sensitive to hypoxia?
Thick ascending limb
Uses more energy than any other part of the nephron
What is transported in the early DCT?
Active reabsorption of Na+
Major site for calcium reabsorption
What percentage of Na+ is absorbed in the early DCT?
5.8%
What transporter for sodium is found in the early DCT?
NaCC
What does the NaCC transport?
Na and Cl in the same direction
What maintains the calcium gradient for calcium reabsorption in the early DCT?
NCX on the basolateral membrane
Exchanges a calcium into ECF for a sodium into the cell
What happens to the fluid in the early DCT?
Goes from being hypo-osmotic (hypotonic) to even more hypo-osmotic
What happens to the osmolarity of the filtrate in the thick ascending limb?
It goes from high to low
Loses ions
What does the late DCT and the collecting duct do?
What cells are present?
Fine tunes the filtrate
Has principal cells (70%) and intercalated cells
What do principal cells do?
Reabsorption of Na via ENa channel on apical membrane
Produces a negative luminal charge - driving force for Cl-ion reuptake via Paracellular rout
K+ secretion
Variable water uptake through aquaporin - depends on ADH
