The document discusses the regulation of acid-base balance in the kidneys, highlighting how metabolic processes produce acids that are excreted as hydrogen ions in urine. It explains metabolic acidosis and alkalosis, including their causes and treatments, and emphasizes the importance of urine acidification for preventing renal stones and promoting antibacterial action. Key mechanisms and conditions affecting bicarbonate levels and pH regulation in the body are detailed.

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.