Renal lectures 2013 2-2[1]

1. Reabsorption of salt and water &
Renal plasma clearance

2. Reabsorption of salt, water and glucose
The kidneys filter about 180 l per day,
but the urine excreted is about 1 – 2 l (1%)
Per day.
This means that 99% of the ultrafiltrate is
reabsorbed and 1% excreted.
The minimum volume of urine required
per day to eliminate the metabolic wastes
is 400 ml (obligatory water loss).
Water reabsorption in the proximal
tubules is by osmosis.

3. Salt and water reabsorption

4. Reabsorption of glucose
Glucose is easily filtered by the glumeruli
into the renal tubules.
375 mg/min is reabsorbed and the rest is
excreted (Glycosuria).
This occur in the proximal tubule by
secondary active transport which
transport glucose with sodium.

5. Reabsorption of salt and water
• ~ 65 % of salt and water which were
filtered at the glomerulus are
reabsorbed back into blood in the
proximal tubule.
• Another 20% of water is reabsorbed in
the descending loop of the Henle.
65% water
reabsorbed
• The total 85% salt and water which are
reabsorbed occur constantly and are
20% water not under any hormonal regulations.
reabsorbed
• Still a large volume (~ 180 L x 15% = 27
L) is remained to be reabsorbed in the
rest of the nephron tubules (distal
convoluted tubules and collecting
ducts).

6. Counter current multiplier system
Ascending limb of
Descending limb of loop of Henle ~ 100 mOsm
loop of Henle goes to distal
convoluted tubules
and collecting duct.
< 300
> 300 > 300 mOsm/L
> 300
Water NaCl NaCl
Capillary

7. Water reabsorption in distal convoluted
tubules and collecting duct
Distal CT ADH
100 mOsm
300 300
400 400
water Collecting Duct
600
600
NaCl
800
800

8. Vasa recta and countercurrent exchange

9. The role of urea in the concentration of the urine

10. Plasma concentration and antidiuretic hormone ADH

11. The final products of the process
Composition of the plasma, glomerular filtrate, and the urine:
Solute Plasma Filtrate Final urine % reclaimed
Urea + + + 50%
Glucose + + - 100%
Amino acids + + - 100%
Total inorganic ions* + + + 95.5%
Protein + + - -
Organic toxins + + ++ 0%
* mainly Na+ and Cl-

12. Renal plasma clearance
Renal clearance of inulin

13. Renal clearance of Inulin
measurement of GFR
• Inulin is not produced by our cells and it is not metabolized. Also it is
fully filtered and neither secreted nor reabsorbed.
- Inulin clearance depends on GFR.
Inulin filtered = inulin excrected
Inulin Filtered = GFR (ml/min) x P (mg/ml)
Glomerular Filteration Rate Plasma concentration of Inulin
Inulin excreted = V (ml/min) x U (mg/ml)
Rate of urine formation Inulin concentration in urine
GFR x P = V x U
V (ml/min) x U (mg/ml)
GFR (ml/min) =
P (mg/ml)

14. Renal Plasma Clearance of Solutes
Clearance of a solute is the volume of plasma that is completely cleared
from that solute in one minute.
Clearance of inulin (ml/min) = GFR (ml/min)
V (ml/min) x U (mg/ml)
Clearance (ml/min) =
P (mg/ml)
- A substance that is filtered and reabsorbed has
clearance < GFR or inulin
- A substance that is filtered and secreted has
clearance > GFR or inulin

15. Clearance of Urea
-Urea is filtered like inulin but also partially
reabsorbed.
-So how clearance of urea is compared to GFR?
UREA CLEARNCE (ml/min) ?
< GFR (ml/min)

16. Clearance of Para-aminohippuric Acid (PAH)
PAH is filtered like inulin but in addition it is also
secreted.
-So how clearance of PAH is compared to GFR?
PAH (ml/min) >
? GFR (ml/min)
PAH is used to measure renal plasma flow.

17. Renal control of electrolyte and
acid-base balance
In the region of the late distal tubule
and the cortical collecting duct,
reabsorbtion of Na+ results in
secretion of K+ and H+.
In case of hyperacidity H+ is
secreted at the expense of K+
this is why hyperacidity is
associated with increase in
blood K+.
On the other hand hyperkalemia
results in secretion of K+ at the
expense of H+ causing hyperacidity
in the blood.
Reabsorption of Na+ and
secretion of K+ are regulated by
aldosterone.

18. Homeostasis of plasma Na+

19. Urine formation
Filtration is the process of flow
of water and dissolved solutes from
the blood plasma to the capsule.
Reabsorption is the back uptake of
water and NaCl, glucose, and amino
acids from the tubular fluid to the
blood.
Secretion is the addition of some
substances from the blood capillaries
directly into the tubules.
Excretion is the elimination of water
and some solutes in form of urine.

20. Kidney Disease
• Glomerulonephritis
• It is the inflammation of the glomeruli, or small blood vessels in the
kidneys. It may present with isolated hematuria and/or proteinuria
(blood or protein in the urine).
• Acute Renal Failure
• Acute: Sudden onset. Rapid reduction in urine output-usually
reversible.
• This may be due to infection, drugs, traumatic injury, major surgery,
nephrotoxic poisons.
• Emergency dialysis may be needed until the situation resolves and the
kidneys begin functioning again.
• Chronic Renal Insufficiency (CRI)
• Slow distruction of the filtering capacity of the kidney.
• It is irreversible.
• 75% of function can be lost before it is noticeable.