The renal system plays an important role in maintaining pH balance in the body. The kidneys regulate hydrogen ion concentration by secreting hydrogen ions into the urine and reabsorbing bicarbonate ions into the blood. This process occurs primarily in the proximal convoluted tubules of the nephron. When blood becomes too acidic, the kidneys remove excess hydrogen ions and excrete them in urine, lowering the pH of blood and making urine more acidic. Conversely, in alkalosis the kidneys reduce hydrogen ion secretion and excretion to raise blood pH. Through these mechanisms, the kidneys are able to keep blood pH within a narrow range to support normal enzymatic bodily functions.

1. RENAL MECHANISM
FOR MAINTAINANCE OF H+
IN BODY FLUIDS
VETERINARY PHYSIOLOGY – II
SUBMITTED TO:-DR ABDUL JABBAR
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2. INTRODUCTION:-
Hydrogen ions determine the acidity of a
solution which ultimately means the PH of a solution. PH is maintained by the
kidneys and whole renal system in our body.
It is similar to the regulation of other ions by homeostasis and a balance must
be maintained between intake or production and the net removal.
WHY IS THE REGULATION IMPORTANT ?
The regulation of concentration is important because all the enzymatic
reactions taking place in our body requires a specific PH to function normally.
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3. WHAT ACTUALLY IS A HYDROGEN ION?
A single proton released from a hydrogen atom is called a hydrogen ion. And
it is the measure of PH or acidity of a solution.
NORMAL PH AND H+ CONCENTRATION
OF BLOOD:-
 The normal blood hydrogen ion concentration is maintained at
0.00004 mEq/L but it may vary from 0.00003mEq/L to 0.00005 mEq/L.
 The normal PH of arterial blood is 7.4 whereas the PH of venous blood and
interstitial fluids is 7.35 because of CO2 which forms HCO3 in tissues.
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4. PRODUCTION OF HYDROGEN IONS:-
 During glycolysis.
 During Ketogeneses.
 Other metabolic processes.
PRODUCTION OF HCO3 IONS:-
HCO3 ions are produced when the CO2 reacts with water to form carbonic
acid in the tissues.
This carbonic acid is broken down in lungs to first produce HCO3 and then
releasing the carbon dioxide into alveoli.
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5. WAYS TO MAINTAIN H+
CONCENTRATION:-
 Production or reabsorption of Bicarbonate(HCO3) ions.
 Excretion of Hydrogen (H+) ions inside cells.
 Production of protein buffer in the cells.
Out of these processes only two are done by the renal system itself i.e. the
production of HCO3 and excretion of H+. While the production of protein
buffer occurs inside the cell.
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6. PROTEIN BUFFER FOR PH
REGULATION:-
BUFFER:-
“A buffer is a chemical substance that resists changes in PH.”
The body has several different buffering systems that temporarily bind or release
free H+ ions when the pH is changed.
BASIC BUFFER:-
“Buffer having PH more than 7”
If an acidic solution is added to this buffer solution, the buffer will combine
with the extra H+ ions and help to maintain the PH.
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7. ACIDIC BUFFER:-
“A buffer having PH less than 7 is called an acidic buffer”
If a basic solution is added to a buffer solution, the buffer will release H+ ions
to help maintain the PH.
EXAMPLE OF BUFFER SYSTEM:-
An example of a buffer system is carbonic acid-bicarbonate buffer system.
When CO2 diffuses into the blood, it reacts with water (H2O) in the plasma to
produce carbonic acid (H2CO3). This unstable acid then breaks down into
hydrogen ions and bicarbonate ions (HCO3– ). Chemical equation for this
reaction is given below;
CO2 + H2O <===> H2CO3 <===> H+ + HCO3
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8. If the amount of carbon dioxide is increased, i.e. during exercise, it will cause
the equilibrium to shift to the right, thus increasing the amount of H2CO3
(carbonic acid), H+ and HCO3– (bicarbonate ions). The increase in H+ leads to
a decrease in pH (that is, the blood becomes more acidic).
If the amount of CO2 is decreased, the reaction can run in reverse. That is, the
HCO3– binds the free H+ ions to produce carbonic acid and convert it into
CO2. The blood becomes more alkaline.
This process is used to maintain the PH of blood in a specified range.
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9. SECRETION OF H+ IONS AND
REABSORPTION OF HCO3:-
 Hydrogen ion secretion and bicarbonate ion reabsorption occurs in all
parts of the nephron except the loop of Henle.
 80% to 90% of the reabsorption and secretion occurs in the proximal
convoluted tubules.
 A very small amount of HCO3 is reabsorbed in the distal convoluted tubule
and collecting ducts. This makes 10% of the total amount.
H+ and Sodium ion concentration are maintained by COUNTER CURRENT
MULTIPLIER. By this process urine becomes more and more concentrated
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10. HOW THE RENAL SYSTEM WORKS:-
When blood becomes too acidic, the kidneys remove excess H+ ions from the
body and excrete them in urine.so the high PH of blood lowers and urine
becomes more acidic.
This is done by the reabsorption and giving up of some substance inside the
renal medulla.
For studying this in detail we need to study the renal system’s structure at
first.
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11. STRUCTURE OF RENAL SYSTEM:-
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Renal system consists
of kidneys, ureters,
bladder and urethra.
But the main role is of
the kidneys themselves.
The main functional part
of the kidney is the renal
medulla.

12. NEPHRON:-
Renal medulla consists of tiny functional units called Nephrons.
These nephrons have tubular structure which is essential for maintenance of
ionic concentration and reabsorption.
The nephron consists of;
 Glomerulus.
 Proximal convoluted tubule.
 Loop of Henle.
 Distal convoluted tubule.
 Collecting ducts.
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13. Diagram showing structure of a nephron.
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14. FUNCTIONING OF A NEPHRON:-
 Blood passes from the glomerulus (which is a system of closely packed
blood vessels) and is converted into glomerular filtrate.
 This filtrate passes from PCT and here some of the hydrogen ions are
removed from glomerular filtrate.
 In the loop of Henle water is reabsorbed along with some salts.
 In the last part i.e. the collecting duct, secretions are released such as urea
and creatinine. In this stage more hydrogen ions are released to balance
blood PH.
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15. TRANS-MEMBRANE CARRYING IN
KIDNEYS:-
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 In the interstitial
space bicarbonate
reacts with H+ form
H2O an Co2, these
go through an
Enzymatic chain
and by action of
ATP are converted
to hydrogen ions
which are absorbed
Into urine.

16. REGULATION OF RENAL TUBULAR
HYDROGEN ION CONCENTRATION:-
 In ALKALOSIS, tubular secretion of H+ must be reduced to a level that is too
low to achieve complete HCO3 reabsorption enabling kidneys to increase
HCO3 excretion.in this condition titratable acid and ammonia are not excreted
because there is no excess H+ available to combine with non bicarbonate
buffers therefore there is no new HCO3 added to the urine in alkalosis.
 In ACIDOSIS, the tubular H+ secretion must be increased sufficiently to
reabsorb all the filtered HCO3 and still have enough H+ left over to excrete
large amounts of NH4+ and titratable acid, thereby contributing large
amounts of new HCO3 to the total body extracellular fluid. The most
important stimuli for increasing H+ secretion by the tubules in acidosis are;
1. Increase in PCO2 of the extracellular fluid.
2. Increase in H+ concentration of the extracellular fluid hence a decreased PH.
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17.  The tubular cells respond directly to an increase in PCO2 of blood as
occurs in respiratory acidosis, with an increase in The rate of H+ secretion
as;
1. The increased PCO2 raises the PCO2 of the tubular cells causing increased
formation of H+ in the tubular cells which in turn stimulates the secretion
of H+.
2. The 2nd factor that stimulates H+ secretion is increase of extracellular
fluid H+ concentration
 Extracellular fluid voulume depletion stimulates sodium reabsorption by
the renal tubules and increases H+ secretion and HCO3 reabsorption
through multiple mechanisms including
1. Increased angiotension II levels which directly stimulate the activity of Na
+ - H+ exchanger in th renal tubules.
2. Increased aldosterone levels which stimulate H+ secretion by the
intercalat3d cells of the cortical collecting tubules therefore extracellular
fluid volume depletion tends to cause alkalosis due to excess H+
secretion and HCO3 reabsorption.
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18.  Changes in plasma potassium concentration can also influence H+
secretion HYPOKALEMIA stimulating and HYPERKALEMIA inhibiting H+
secretion in proximal tubules.
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19. DETECTION OF ALKALOSIS AND ACIDOSIS:-
There are diagnostic tests which can be used to detect these acid and base
back flushes. Some of them are given below:
 Blood PH (level chart given below)
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20.  Blood PCO2 levels.(numerical values below)
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21.  Blood Bicarbonate levels (lab sampling results given below).
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22. CAUSES OF METABOLIC ACIDOSIS:-
DIARRHEA:-
Severe diarrhea may lead to acidosis. The cause for
this is loss of excess Bicarbonate ions in feces. And this may lead to severe
consequences.
INGESTION OF ACIDS:-
Sometimes ingestion of acids or
an acidic food may lead to acid flush and then metabolic acidosis.
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23. DIABETES MELLITUS:-
Diabetes mellitus is caused by the lack of
insulin secretion by pancreas or by insufficient insulin secretion to
compensate for decreased sensitivity to the effects of insulin. In the absence
of sufficient insulin the normal use of glucose for metabolism is prevented.
With severe DM acetoacetic levels can rise causing metabolic acidosis.so to
compensate for this large amount of acid is released in urine as much as
500mmol/day.
CHRONIC RENAL FAILURE:-
In case of chronic renal
failure, acids build up in the body, Also potassium and NH4 cant be excreted
and bicarbonate is not reabsorbed to the body fluids so it may lead to severe
metabolic acidosis.
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24. CAUSES OF METABOLIC ALKALOSIS:-
VOMITING OF INTESTINAL CONTENTS:-
Vomiting of gastric contents would cause loss of acid and a tendency towards
alkalosis because stomach secretions are highly acidic in nature.
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25. TREATMENTS FOR ACIDOSIS AND
ALKALOSIS:-
 The best treatment for acidosis or alkalosis is to correct the condition that
caused it.
 To Neutralize excess acid, drugs with higher concentration of SODIUM
BICARBONATE may be administered. This will get reabsorbed from the
gastrointestinal tract to blood and bring down the acid levels
 For alkalosis, AMMONIUM CHLORIDE may be administered by mouth
which gets into blood then travels to liver which forms urea. This reaction
liberates HCL which reacts with buffers and PH normalizes.
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26. FACTS ABOUT THE TOPIC:-
 The minimum achievable urine pH is roughly 4.5.
 Lungs also help maintain Acid-Base Balance of body fluids.
 Most of the acids produced in our body are Non-Volatile.
 Urine makes about 1% of the glomerular filtrate.
 Most of the blood i.e.25% is supplied to the kidneys.
 Velocity of blood in kidneys is roughly 1.2 - 1.3 L/min in a 70-kg adult
male.
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