Kidney 2 Flashcards
What is the difference between osmolarity and osmolality?
Osmolarity = mmol/L
Osmolality = mmol/kg
How would you work out the amount of sodium filtered per minute?
Use the calculation:
Plasma Na concentration (mmol/L) x GFR (L/min) NB: both have to be in L
135mmol/L x 0.125L/min
= 17mosm/min
Is sodium reabsorption passive or active?
Active, requires ATP from the NA/K ATPase pumps to create the Na gradient used for various other methods of Na reabsorption
Which locations (including percentages) in the nephron are involved in Na reabsorption?
PCT = 65%
Thick ascending limb = 25%
DCT = 5%
Collecting duct = 3%
Each of the X4 sites of sodium reabsorption uses different mechanisms for the Na reabsorption process.
What are the mechanisms used at the PCT?
1) Na/K ATPase on basolateral surface creates a Na gradient
2) Na can them enter the cell via Na/H antiporters on the cells luminal surface (NHE3)
3) there also exists Na-nutrient co-transporters on the luminal cell surface which exploit the Na gradient
How does Cl ion reabsorption occur in the PCT?
Passively between cells
Each of the X4 sites of sodium reabsorption uses different mechanisms for the Na reabsorption process.
What are the mechanisms used at the thick ascending limb?
1) the Na/K ATPase pump creates the gradient (as always)
2) there is a Na/K/Cl co-transporter in the luminal surface which transports the ions at a 1:1:2 ratio respectively.
In the thick ascending limb, other than the Na reabsorption channels, what other channels exist?
What do they do?
What is their impact on Na reabsorption and the charge of the the filtrate in the lumen?
There are K ion channels allowing K back into the lumen down its concentration gradient.
This makes the filtrate positive and helps repel other positive ions between the cells and into the capillaries (such as Na!)
Each of the X4 sites of sodium reabsorption uses different mechanisms for the Na reabsorption process.
What are the mechanisms used at the DCT?
1) Na/K ATPase creates the gradient (as always)
2) in the luminal membrane there is a Na/Cl co-transported which is exploiting the Na gradient through secondary active transport
Each of the X4 sites of sodium reabsorption uses different mechanisms for the Na reabsorption process.
What are the mechanisms used at the collecting duct?
What cell types exist in the collecting duct and which of the types is involved in Na reabsorption?
Here there are X2 cell types:
1) intercalated cells = H ion transport
2) principal cells = Na reabsorption
In the principal cells:
1) Na/K ATPase creates a gradient (as always)
2) there is a simple Na channel for facilitated diffusion on the luminal surface.
What is the main mechanism of water reabsorption?
What does it depend on?
Osmosis
Therefore it depends on the movement of Na and the permeability of each section of the tubule to water.
What are the channels through which water moves?
Which surfaces have varying expression of these channels which therefore affect water reabsorption?
Aquapourins
The luminal surface, as the basolateral surfaces have aqua pouring through the length of the nephron
Which aquapourin channels are found in the PCT?
What other method does water use to be reabsorbed in the OCT?
AQP1
Between the cells
What is the change in osmolarity of the filtrate in the PCT due to reabsorption?
No change! It is the same as that I’m the bowmans capsule from which it came which is the same as the plasma (285 - 295mosm/L).
This is because the water is following the Na therefore the ratio is changing as one.
What X2 things need to happen in order for concentrated urine to be produced?
1) Na reabsorption needs to be separated from water reabsorption
2) the renal medullary interstituim needs to generate a high osmolarity to drive water reabsorption
