Kidney Function 2 Flashcards
What is the equation for renal clearance?
concentration of urine * volume of urine / concentration in plasma
Why does the clearance of insulin measure GFR?
It is:
- freely filtered
- not reabsorbed
- not secreted
- not metabolised
- easily measured
What is used in the clinic to test for glomerular filtration rate?
Is this an over or under estimate and why?
Creatinine
Over because some creatinine is slightly secreted.
What is the value for insulin clearance?
What does it mean if the value for a molecule below or above this?
120ml/min
<120ml means clearance
= 120ml means no reabsorption or secretion
>120m means secretion
What is the value for the renal plasma flow approximation?
How much of this do blood cells occupy in %? How about plasma?
600ml/min
Blood cells - 45%
Plasma - 55%
What is the formula for blood flow?
(plasma flow)/ (1-haematocrit)
If haematocrit is a % then you do 100 - haematocrit instead.
What is osmolarity and explain this?
It is a measure of water concentration. The higher the solution osmolarity, the lower the water concentration.
Which one of these has a wider range? Plasma osmolarity or urine?
Urine
If urine has an osmolarity over 300mosm/l, what does this mean?
It is concentrated
Why do we use osmolality instead of osmolarity?
It is not affected by temperature.
What is the most osmotically active solute in plasma?
What is plasma sodium concentration?
Where is sodium freely filtered?
Sodium
135-145mmol/l
At the renal corpuscle
What is sodium balance linked to in the body?
Blood pressure
Where does reabsorption mainly occur?
In the PCT
What are 4 places in the nephron for sodium reabsorption have lots of mitochondria?
1) Proximal tubule
2) Thick ascending limb
3) Distal tubule
4) Collecting duct
Why does the descending limb of the loop of Henle have few mitochondria?
No sodium reabsorption.
Sodium moves between cells in thick ascending limb passively. Energy is not required for this process.
Explain the 4 steps of sodium reabsorption
1) Proximal tubule - sodium moved into the cell for exchange of H+. Positive charged inside ell and negative charges repel chloride on outside. (65% of NaCl absorbed here)
2) Thick ascending limb - potassium moves against its concentration gradient into the cell. High concentration inside the cell so it can leave and return to filtrate here. Positive charge inside loop supports movement of sodium between cells. (25% of NaCl absorbed here
3) Distal tubule - Has a NaCl co-transporter. (2-5% of NaCl reabsorbed here)
4) Collecting duct - sodium channel on luminal membrane, cells in collecting duct include intercalated cells. (5% of NaCl reabsorbed)
What is the role of intercalated cells in the kidney?
Intercalated cells are epithelial cells traditionally associated with the regulation of acid-base homeostasis in distal segments of the kidney tubule
What 3 things does water reabsorption depend on?
- Osmosis
- Sodium reabsorption
- Tubule permeability
Give details on the coupling of water reabsorption to sodium reabsorption?
Isotonic reabsorption - tight junctions have a high water permeability.
Also membrane expression of aquaporin water channels.
Filtrate volume reduced but not osmolarity.
Sodium moves into epithelial cells and this decreases osmolarity so water moves out he tubule lumen and then is reabsorbed into the capillary.
What two things produce concentrated urine?
Explain them
- Separating Na+ and water reabsorption
- Generate a renal medulla interstitial fluid with high osmolarity to drive water reabsorption
1=Two limbs are separated by the interstitial fluid. Flow is said to be countercurrent. Ascending limb is where sodium is reabsorbed and water will not follow as ascending is impermeable to water. Water leaves the descending loop as this is permeable to water.
2 = Setting up a medullary interstitial gradient. Osmolarity of 300 inside the loop. The ascending loop is activated and water will leave the descending loop.
Where is the highest osmolarity in the loop?
Around the turn
What are vasa recta and explain some of their properties?
Blood vessels running alongside the loop of Henle.
They have the same shape running along so blood can fully supply. They supply blood without washing the gradient away.
Does plasma leaving the vasa recta have a higher or lower osmolarity?
Higher
What are the 3 places that urea goes to when being recycled by the kidney?
- Proximal tubule (passive reabsorption of urea by moving across plasma membrane).
- Loop of Henle (apical secretion via urea transporters - secreting urea into filtrate)
- Inner medullary collecting duct (apical reabsorption via UT-A1)
40% of that filtered is excreted
