The body's balance between acidity and alkalinity is referred to as acid-base balance. The blood's acid-base balance is precisely controlled because even a minor deviation from the normal range can severely affect many organs. The body uses different mechanisms to control the blood's acid-base balance.

1. REGULATION OF ACID BASE BALANCE WITH
REFERENCE TO THE KIDNEY
METABOLIC ACIDOSIS & ALKALOSIS
IMPORTANCE OF ACIDIFICATION OF URINE
FATIMA WAHID MANGRIO
fatimawahid1234@gmail.com

2. ACID BASE BALANCE WITH
REFERENCE TO THE KIDNEY
• Metabolic reactions produce acids.
• The only way to eliminate this huge acid load is
to excrete H+ in the urine.
• Given the magnitude of these contributions to
acid–base balance, it’s not surprising that renal
failure can quickly cause death.

3. • Cells in both the proximal convoluted tubules
(PCT) and the collecting ducts of the kidneys
secrete hydrogen ions into the tubular fluid.
• In the PCT, Na+ – H+ antiporters secrete H+ as
they reabsorb Na+.

6. • Even more important for regulation of pH of
body fluids, however, are the intercalated cells
of the collecting duct.
• The apical membranes of some intercalated cells
include proton pumps (H+ ATPases) that secrete
H+ into the tubular fluid.
• HCO3- produced by dissociation of H2CO3-
inside intercalated cells crosses the basolateral
membrane by means of Cl- HCO3- antiporters
and then diffuses into peritubular capillaries.

7. • The HCO3- that enters the blood in this way is
new (not filtered).
• For this reason, blood leaving the kidney in the
renal vein may have a higher HCO3-
concentration than blood entering the kidney in
the renal artery.

9. • Some H+ secreted into the tubular fluid of
the collecting duct is buffered, but not by
HCO3- most of which has been filtered and
reabsorbed.
• Two other buffers combine with H+ in the
collecting duct.
• The most plentiful buffer in the tubular fluid
of the collecting duct is HPO42
(monohydrogen phosphate ion).
• In addition, a small amount of NH3 (ammonia)
also is present.

10. • H+ combines with HPO42- to form H2PO4
(dihydrogen phosphate ion) and with NH3
to form NH4+ (ammonium ion).
• Because these ions cannot diffuse back
into tubule cells, they are excreted in the
urine.

12. Metabolic Acidosis
• In metabolic acidosis, the systemic arterial
blood HCO3- level drops below 22 mEq/liter.
• Such a decline in this important buffer causes
the blood pH to decrease. Three situations may
lower the blood level of HCO3-

13. • (1) actual loss of HCO3- such as may occur with
severe diarrhea or renal dysfunction;
• (2) accumulation of an acid other than carbonic
acid, as may occur in ketosis
• (3) failure of the kidneys to excrete H+ from
metabolism of dietary proteins.

14. • If the problem is not too severe,
hyperventilation can help bring blood pH into
the normal range (respiratory compensation).
• Treatment of metabolic acidosis consists of
administering intravenous solutions of sodium
bicarbonate and correcting the cause of the
acidosis.

15. Metabolic Alkalosis
• In metabolic alkalosis, the systemic arterial
blood HCO3- concentration is above 26
mEq/liter. A nonrespiratory loss of acid or
excessive intake of alkaline drugs causes the
blood pH to increase above 7.45.
• Excessive vomiting of gastric contents, which
results in a substantial loss of hydrochloric
acid, is probably the most frequent cause of
metabolic alkalosis.

16. • Other causes include gastric suctioning, use of
certain diuretics, endocrine disorders,
excessive intake of alkaline drugs (antacids),
and severe dehydration.
• Respiratory compensation through
hypoventilation may bring blood pH into the
normal range.
• Treatment of metabolic alkalosis consists
ofgiving fluid solutions to correct Cl-, K+, and
other electrolyte deficiencies plus correcting
the cause of alkalosis.

17. Importance Of Acidification Of Urine
• To promote antibacterial action of
methenamine in urine:
• Below pH 5.5, methenamine releases
formaldehyde, which is antibacterial.
Acidifying agents are given with
methenamine to lower urinary pH.
•

18. • Prevention of calcium phosphate renal
stones: An alkaline pH favors the
crystallization of calcium- and phosphate-
containing stones hence acidification of
urine will prevent the formation of these
stones.