Regulatory functions of the kidney
1-Regulation of water balance.
2-Regulation of electrolyte balance .
3-Regulation of acid –base balance.
Regulation of water balance
Anti-diuretic hormone (A.D.H) influence permeability of distal
convoluted tubule, collecting tubules
-Stimulus for Secretion of A.D.H
1-Decrease blood volume as in hemorrhage leads to ↑ADH secretion ( through
stimulation of volume receptor in big veins)
2-Increase osmotic pressure of blood (osmolarity) ,stimulation of osmoreceptor
of hypothalamus leads to increase ADH
3- IF their excess water in the body no stimulation of ADH .SO excess water
pass in urine .
Water balance depend upon balance between water gain & water loss
Regulation of electrolyte balance
Sodium is present mainly outside cells ,so it is essential for
maintenance of osmotic of the pressure of plasma and
extracellular fluids, Potassium is presents mainly inside the
cells and it is responsible for most of intracellular osmotic
In proximal convoluted tubuleIn proximal convoluted tubule;
85% OF na+ reabsorption leads to reabsorption of HCO3-,PO4
100% of K+ is actively absorped from renal tubule.
85% of H2O is obligatory reabsorped .
In distal convoluted tubulesIn distal convoluted tubules;;
The remaining 15% of Na+ Is reabsorbed in exchange with K+ ,H
( k+ is controlled by aldosterone)
K+ & H+ Compete for exchange with na+.
The reabsorption of H2o in DCT Is controlled by ADHIs controlled by ADH .
Regulation of acid base balanceRegulation of acid base balance
It is regulated through secreting acidic urineacidic urine down to PH 4 by direct excretion of acids like
phosphoric ,beta hydroxy butyric ,creatinine ,other organic acids ,also the kidney maintenance
acids base balance by preserving the alkali reserve of the bloodby preserving the alkali reserve of the blood
The bicarbonate (HCO3) is the main alkali reserve of the blood and available for
neutralization of acids
Reduction of alkali reserve is called acidosis .if accompany with change in ph called academiaacademia
.Increase in alkali reserve is called alkalosis ,if accompany with change in ph called alkalemiaalkalemia.
Renal stabilization of bicarbonate occurs byRenal stabilization of bicarbonate occurs by;;
1-Complete reabsorption of bicarbonate in glomerular filtrate .
2- Excretion of any excess of bicarbonate in the body. .
3-renewing of the depleted reserve by the process of hydrogen ion and ammonia excretion.
This mechanism is determined by the nature of the buffer in the tubular urine at a site of
exchange (H+ excretion & na+ reabsorption ).
A- Buffer isA- Buffer is
If the buffer is mainly bicarbonate (HCO3),
the exchange of hydrogen for sodium form
carbonic acids in the tubular fluids.
H+NaHCO3→ Na+ +H2CO3.
This carbonic acid is change to CO2& H2O
CO2 diffuse into tubular cells
In the tubular cell CO2 is hydrated to reform
CO2 + H2O→HHCO3
This cellular carbonic acids is the source of
both the hydrogen ions secreted into the
tubular fluids ,and of the bicarbonate returned
to the blood in association with na+ .
B- buffer is mainlyB- buffer is mainly
If the major buffer in the urine is
phoshate po4, the exchange of
hydrogen ions for sodium ions
converts the filtered dibasic
phoshate (Na2Hpo4)to an
The hydrogen ion are excreted
as titratable monobasic acid
The carbonic acids which is the
source of the cellular hydrogen
ions exchange for Na + ions,is
derived in part from CO2
produced in cellular metabolism
and in part from CO2 brought to
the cell in peritubular blood .
CO2+ H2O→H+ +HCO3.
Buffer is mainlyBuffer is mainly
If little buffer is present in the tubular
urine ,the exchange of H2 for sodium
decrease because of the accumulation
of free unbuffered hydrogen block the
Under these condition ,low bicarbonate
,low phosphate in tubular urine ,the
free base NH3 is formed in
glutamine→glutamic acid+ NH3
The NH3 formed diffuses into the acidic
urine ,buffer hydrogen ion ,and prevent
their accumulation in high concentration
Removal of NH3 used in buffering the
excess hydrogen ion occurs in the form
To summarize the process of exchange of
hydrogen excretion with na absorption the
Most of sodium ions are absorbed and combine with bicarbonate
.simultaneously the hydrogen ions combine with bicarbonate to form
carbonic acid, in the tubular lumen. this acids dissociate to form CO2& H2O
When HCO3- is not sufficient the hydrogen combine with na2hpo4
to convert it into nah2po4.
If phosphate is not sufficientIf phosphate is not sufficient the hydrogen ions combine with the
synthesized ammonia to form NH4
If acidity is still excessive the NH4 combine with chloride to be
excreted as NH4CL.
In all these process the bicarbonate is formed in tubular cells to combine with
absorbed Na+ or K+ to keep the bicarbonate at normal blood concentration.