Acid balance / dental courses

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ACID-BASE BALANCEACID-BASE BALANCE
INDIAN DENTALACADEMY
Leader in continuing Dental Education

ACID-BASE BALANCE:ACID-BASE BALANCE:
The normal PH
of the blood is maintained in the narrow range of 7.35-7.45 that is
slightly alkaline.
Maintenance of blood PH
is an important homeostatic mechanism of the body.
In normal circumstances, the regulation is so effective that the blood PH
varies
very little.
Production of acids by the body:Production of acids by the body:
The metabolism of the body is accompanied by an overall production of acids.
These include the volatile acids like carbonic acid or non-volatile acids such as
lactic acid, sulfuric acid and phosphoric acid..
Carbonic acid is formed from the metabolic product CO2 and lactic acid is
produced in anaerobic metabolism.
These acids add up H+
ions to the blood.
A diet rich in animal proteins results in more acid production by the body that
ultimately leads to the excretion of urine, which is profoundly acidic

Production of bases by the body:Production of bases by the body:
The formation of basic compounds in the body, in the normal
circumstances, is negligible.
Some amount of bicarbonate is generated from the organic
acids such as lactate and citrate.
A vegetarian diet has a tendency for a net production of
bases.
For this reason a vegetarian diet has an alkalizing effect on
the body.

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Maintenance of Blood PH:Maintenance of Blood PH:
The body has developed three lines of defense to
regulate the body’s acid base balance and maintain the blood
PH
around 7.4
1). Blood buffers
2). Respiratory mechanism
3). Renal mechanism

Blood buffers:Blood buffers:
A buffer may be defined as a solution of a weak acid (HA)
and its salt (BA) with a strong base.
The buffers resists the change in PH
by the addition of acid or
alkali and the buffering capacity is dependent on the absolute
concentration of salt and acid.
It should be borne in mind that the buffer cannot remove H+
ions from the body.
It temporarily acts as a shock absorbent to reduce the free H+
ions.
The H+
ions have to be ultimately eliminated by the renal
mechanism www.indiandentalacademy.com

The blood contains 3 buffer systemsThe blood contains 3 buffer systems:
1). Bicarbonate buffer
2). Phosphate buffer
3). Protein buffer

Bicarbonate buffer system:Bicarbonate buffer system:
Sodium bicarbonate and carbonic acid is the most
predominant buffer system of the extra cellular fluid,
particularly the plasma.
Carbonic acid dissociates into hydrogen and bicarbonate ions.
The blood PH
and the ratio of HCO3-
to H2CO3:
The plasma concentration is around 24mmol/l.
Carbonic acid is a solution of CO2 in water.
In concentration is given by the product of Pco2 and the
solubility constant of CO2
Thus H2CO3= 40 X 0.03=1.2 mmol/l.

At a blood PAt a blood PHH
7.4 the ratio of bicarbonate to carbonic acid is7.4 the ratio of bicarbonate to carbonic acid is
20: 120: 1
Thus the bicarbonate concentration is much higher thanThus the bicarbonate concentration is much higher than
carbonic acid in the blood.carbonic acid in the blood.
This is referred to as alkali reserve and is responsible for theThis is referred to as alkali reserve and is responsible for the
effective buffering of Heffective buffering of H++
ions, generated in the body.ions, generated in the body.
In normal circumstances the concentration of bicarbonateIn normal circumstances the concentration of bicarbonate
and carbonic acid determines the Pand carbonic acid determines the PHH
of blood.of blood.

Phosphate buffer systemPhosphate buffer system:
Sodium dihydrogen phosphate and disodium hydrogen
phosphate constitute the phosphate buffer.
It is mostly an intracellular buffer and is of less importance in
plasma due to its low concentration.
Protein buffer system:Protein buffer system:
The plasma proteins and hemoglobin together constitute the
protein buffer system of the blood.
The buffering capacity of proteins is depends on the PK
of
ionizable groups of amino acids.

Respiratory mechanism for PH
regulations.
Respiratory system provides a rapid mechanism for the
maintenance of acid base balance.
This is achieved by regulating the concentration of carbonic
acid in the blood.
The large volumes of CO2 produced by the cellular metabolic
activity endanger the acid base equilibrium of the body.
But in normal circumstances all of this CO2 is eliminated from
the body in the expired air via the lungs,
H2CO3 CO2 + H2O

The rate of respiration is controlled by a respiratory center,
located in the medulla of the brain.
This center is highly sensitive to changes in the PH
of blood.
Any decrease in the blood PH
causes hyperventilation to blow
off CO2 there by reducing the H2CO3 concentration.
Simultaneously the H+ ions are eliminated as H2O.

Renal mechanism for PRenal mechanism for PHH
regulation:regulation:
The role of kidneys in the maintenance of acid base balance
of the body is highly significant.
The renal mechanism tries to provide a permanent solution to
the acid base disturbances.
The kidneys regulate the blood PH
by maintaining the alkali
reserve, besides excreting or reabsorbing the acidic or basic
substances, as the situation demands.

Urine PUrine PHH
normally lower than the blood Pnormally lower than the blood PHH
::
The PH
of the urine is normally acidic.
This clearly indicates that the kidneys have contributed to the
acidification of urine.
When it is formed from the blood plasma.
In the other words, the H+
ions generated in the body in the
normal circumstances are eliminated by acidified urine.

Carbonic anhydrase and renal regulation of PCarbonic anhydrase and renal regulation of PHH
::
The enzymes carbonic anhydrase is of central importance in the renal
regulation of PH, which occurs by the following mechanisms.
1). Excretion of H1). Excretion of H++
ionsions
Kidney is the only route through which the H+
ions can be eliminated
from the body.
An H+
excretion occurs in the proximal convoluted tubules and is
coupled with the regeneration of HCO3
-
.
Carbonic anhydrase catalyses the production of carbonic acid from
CO2 and H2O in the renal tubular cells.
H2CO3 dissociates to H+
ions are secreted into the tubular lumen in
exchange for Na+ in association with HCO3- is reabsorbed in to the
blood. www.indiandentalacademy.com

Excretion of titrtable acid:Excretion of titrtable acid:
Titrable acidity is a measure of acid excreted into urine by the
kidney.
This can be estimated by titrating urine back to the normal PH
of blood.
In quantitative terms, titrable acidity refers to the number of
milliliters of N/10 NaOH required to titrate 1 liter of urine to
PH
7.4.
Titrable acidity reflects the H+
ions excreted into urine, which
resulted in a fall of PH
from 7.4.
That excreted H+
ions are actually buffered in the urine by
phosphate buffer. www.indiandentalacademy.com

Disorders of ACID-BASE balance:Disorders of ACID-BASE balance:
The human body developed an efficient system for the
maintenance of acid – base equilibrium with a result that the PH
of blood is almost constant.
The blood PH
compatible to life is 6.8 - 7.8 beyond which life
cannot exist.
For a better underst6anding of the disorders of acid – baser
balance, the Henderson – Hasselbalch equation must be
frequently consulted.
[HCO3-]
PH
= pKa + log
[H2CO3]

Acid-base disorders are mainly classified as:Acid-base disorders are mainly classified as:
1). Acidosis --------- a decline in blood PH
a). Metabolic acidosis – due to a decrease in bicarbonate
b). Respiratory acidosis-due to an increase in Carbonic
acid

2). Alkalosis – a rise in Blood P2). Alkalosis – a rise in Blood PHH
a). Metabolic alkalosis- due to an increase in bicarbonate
b). Respiratory alkalosis- due to increase in carbonic acid.
The four acid base disorders referred above are primarily
due to alterations in either bicarbonate or carbonic acid.
It may be observed that the metabolic acid –balance
disorders are caused by direct alterations in bicarbonate
concentration while the respiratory disturbances are due to a
change in carbonic acid level.

Compensation of acid - base disorders:Compensation of acid - base disorders:
To counter the acid – base disturbances, the body gears up its
homeostatic mechanism and makes every attempt top restore
the PH
to normal level.
This is referred to as compensation, which may be partial or
full.
Sometimes the acid – base disorders may remain
uncompensated.
The principal acid-base disturbances, along with the blood
concentration of HCO3- and H2CO3.

Anion gap:Anion gap:
The total concentration of cations and anions is equal in the body
fluids.
This is required to maintain electrical neutrality.
The commonly measured electrolytes in the plasma are Na+
, K+
together constitute about 95% of the plasma cations.
Cl-
and HCO3-
are major anions, contributing to about 80% of the
plasma anions..
The remaining 20% of plasma anions include proteins,
phosphate, sulfate, urate and organic acids.
Anion gap is defined as the difference between the total
concentration of measured cations and that of measured anion.

The anion gap in fact represents the unmeasured anions in
the plasma, which may be calculated as follows, by
substituting the normal concentration of electrolytes.
The anion gap in a healthy individual is around 15mEq/l.
Acid – base disorders are often associated with alterations in
the anion gap.

Metabolic acidosis:Metabolic acidosis:
The primary defect in metabolic acidosis is a reduction in
biocarbonate concentration, which leads to a fall in blood PH
.
The bicarbonate concentration may be decreased due to
utilization in buffering H+
ions, loss in urine or gastrointestinal
tract or failure to be regenerated.
The most important cause of metabolic acidosis is due to an
excessive production of organic acids, which combine with
NaHCO3-
and deplete the alkali reserve.
NaHCO3-
+ organic acids Na salts of organic acids + CO2.
Metabolic acidosis is commonly seen in severe uncontrolled
diabetes mellitus, which is associated with excessive
production of acetoacetic acid and β-hydroxy butric acid.www.indiandentalacademy.com

Compensation of metabolic acidosis:Compensation of metabolic acidosis:
The acute metabolic acidosis is usually compensated by
hyperventilation of lungs.
This leads to an increased elimination of CO2 from the body
but respiratory compensation is only short – lived.
Renal compensation sets in with in 3 - 4 days and the H+
ions
are excreted as NH 4+
ions.

Respiratory acidosis:Respiratory acidosis:
The primary defect in respiratory acidosis is due to retention of
CO2 there may be several causes for respiratory acidosis
which include depression of the respiratory center, pulmonary
disorders and breathing air with high content of CO2.
The renal mechanism comes for the rescue to compensate
respiratory acidosis.
More HCO3 is generated and retained by the kidneys, which
adds up to, the alkali reserve of the body.

Metabolic alkalosis:Metabolic alkalosis:
The primary abnormality in metabolic alkalosis is an increase
in HCO3-
concentration.
This may occur due to excessive vomiting or an excessive
intake of sodium bicarbonate for therapeutic purposes.
The respiratory mechanism initiates the compensation by
hypoventilation to retain CO2.
This is slowly taken over by renal mechanism, which
excretes, more HCO3-
and retains H+
.

Respiratory Alkalosis:Respiratory Alkalosis:
The primary abnormality in respiratory alkalosis is a decrease
in H2CO3 concentration.
This may occur due to prolonged hyperventilation resulting in
resulting in increased exhalation of CO2 by the lungs.
Hyperventilation is observed in conditions such as hysteria,
hypoxia, raised intracranial pressure, and excessive artificial
ventilation and the action of certain drugs that stimulate
respiratory center.
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education

Acid balance / dental courses

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