Regulation of Acid Base Balance

Regulation of acid-base balance
- The term acid–base balance refers to the precise regulation of free hydrogen ion
(H+) concentration in the body fluids.
- pH represents Hydrogen ion concentration.
- Hydrogen ion concentration is very low, so it is expressed in logarithm scale.
• pH = log 1/ H+ = - log (H+ )
- PH = - log (0.00000004) = 7.4
- Low pH corresponds to a high hydrogen ions concentration (acidosis)
- High pH corresponds to a low hydrogen ions concentration (alkalosis).
- Normal PH in arterial blood = 7.40
- Normal PH in venous blood = 7.35 (due to excess CO2).
- PH compatible with life = 6.8 to 7.8
- Body is under constant threat of acidosis because of the production of large amount
of acids. Generally, two types of acids are produced in the body:
1. Volatile acids
2. Non-volatile acids.
1. Volatile Acids: are derived from CO2. Large quantity of CO2 is produced during
the metabolism of carbohydrates and lipids. This CO2 is not a threat because it is
almost totally removed through expired air by lungs.
2. Non-volatile Acids: are produced during the metabolism of other nutritive
substances such as proteins. These acids are real threat to the acid-base status of the
body. For example, sulfuric acid is produced during the metabolism of sulfur
containing amino acids such as cysteine and metheonine; hydrochloric acid is
produced during the metabolism of lysine, arginine and histidine.
- It is very essential to regulate pH to maintain:
• Normal/optimal enzyme activities
• Normal metabolism
• Normal Coordination
• Normal Health
• Hormones and ion distribution.
• pH also affects excitability of Nerve & Muscle cells (↓ pH →↓ excitability&
↑ pH → ↑ excitability)
- The body has three different mechanisms to regulate acid-base status:
I- First line of defense, blood buffer system (chemical buffers); react very
rapidly (within less than a second)
II- Second line of defense, respiratory mechanism; react rapidly (within
seconds to minutes).
III- Third line of defense, renal mechanism; react slowly; (minutes to hours)
I. Regulation of acid-base balance by acid-base buffer system:
- It is the combination of a weak acid and its conjugated base (the salt).
- The buffer system is most effective when pH of the solution = pk of the buffer.
pK of the buffer is the pH at which equal amounts of buffer exist as acidic and
base forms.
- Types of Buffer Systems:
A. Bicarbonate buffer system, HCO3-/H2CO3 (20:1 at 7.4 pH)
B. Phosphate buffer system, HPO4--/NaH2PO4 (4:1 at 7.4 pH)
C. Protein buffer system, Na-Protein/H-Protein
D. Hemoglobin Buffer
A. Bicarbonate Buffer System:
- It is present in ECF (plasma).
- It consists of the weak acid, carbonic acid (H2CO3) and a weak base [HCO3 – (in
the form of sodium bicarbonate, NaHCO3].
Mechanism of action of bicarbonate buffer system
- It prevents the fall of pH in a fluid when a strong acid like hydrochloric acid (HCl)
is added.
- Normally, when HCl is mixed with a fluid, pH of that fluid decreases quickly
because the strong HCl dissociates into H+ and Cl–. But, if bicarbonate buffer
system (NaHCO3-) is added to the fluid with HCl, the pH is not altered much.
HCl + NaHCO3 → H2CO3 + NaCl
↓
CO2 + H2O
- Bicarbonate buffer system also prevents the increase in pH in a fluid to which a
strong base like sodium hydroxide (NaOH) is added.
- Normally, when a base (NaOH) is added to a fluid, pH increases. It is prevented
by adding H2CO3.
NaOH + H2CO3 → NaHCO3 + H2O
NaHCO3 is a weak base and it prevents the increase in pH by the strong NaOH.
• Alkali reserve is represented by the concentration of HCO3- in the blood.

• Alkali reserve concentration (HCO3-) determines the strength of buffering action
towards added H+ ions by acids.
• More the concentration of Alkali reserve, more is the buffering action and vice a
versa.
Importance of bicarbonate buffer system:

- Bicarbonate buffer system is not powerful like the other buffer systems
because of
- Its pK is 6.1 far away from blood pH.
- Its concentration is less than protein buffer.
- But this buffer system is important in maintaining the pH of body fluids than
the other buffer systems. It is because the concentration of two components
(HCO3– and CO2) of this buffer system is regulated separately by two
different mechanisms.
- Concentration of HCO3– is regulated by kidney and the concentration of CO2
is regulated by the respiratory system.
- These two regulatory mechanisms operate constantly and simultaneously,
making this system more effective.
2. Phosphate Buffer System:
- This system consists of a weak acid, (NaH2 PO4) and the conjugate base (Na2
HPO4 ).
- Phosphate buffer system is useful in the renal tubules because:
• It is concentrated in renal tubules.
• Suitable pH. (Its pK is 6.8)
- Inspite of its pK is nearer to plasma pH, it is a weak buffer in blood due to its
low plasma level (HCO3- = 24 mEq/L & PO43- = 1.5 mEq/L i.e. 1/12th the
level of bicarbonate).
- Mechanism of phosphate buffer system:
• On adding acid:
HCl + Na2HPO4 → NaCl + NaH2PO4 (weak acid)
These acid phosphates then excreted out through kidneys as acidic urine.
• On adding alkali:
NaOH +NaH2PO4 → Na2HPO4 +H2O (alkaline phosphate)
This alkaline phosphate is excreted in urine making it alkaline urine.
3. Protein Buffer System:

• Proteins are the most plentiful buffer in the body.
• Proteins are excellent buffers because they contain both acidic and basic
groups that can give up or take up H+.
• including the intracellular proteins and the plasma proteins.
• Most of intracellular buffering actions are done by intracellular proteins.
• Plasma proteins represent 15% of buffering power of the blood because of
their high concentration in plasma and because of their pK being very close
to 7.4.
• b) Haemoglobin:
- High concentration (15 gm/dl). It is the most effective protein buffer and the
major buffer in blood. Due to its high concentration than the plasma proteins.
- Act inside RBCs.
- Carboxyl group gives up H+
- Amino Group accepts H+
- The deoxygenated hemoglobin is a more powerful buffer than oxygenated
hemoglobin because of the higher pK. When a hemoglobin molecule becomes
deoxygenated in the capillaries, it easily binds with H+, which are released
when CO2 enters the capillaries. Thus, hemoglobin prevents fall in pH when
more and more CO2 enter the capillaries.
- Hb buffers H+ ions formed inside RBCs when CO2 is added from tissues.
-It also buffers CO2 directly to form carbaminoHb.
II- Regulation of acid-base balance by respiratory mechanism

- The respiratory system plays an important role in acid–base balance through
its ability to alter pulmonary ventilation and consequently to alter
excretion of CO2.
- When metabolic activities increase, more amount of CO2 is produced in the
tissues and the concentration of H+ increases.
- ↑ arterial [H+] and CO2 as the result of a metabolic cause → stimulate the
peripheral and central chemoreceptors → stimulation of the respiratory
center → increase rate & depth of breathing →CO2 is washed → ↓H+
concentration →↑ pH up to normal.
- ↓ CO2 (in hyperventilation) →↑ pH → ↓ alveolar ventilation → retention of
CO2 → ↑ H+ concentration → ↓ pH down to normal.
III- Role of Kidney in regulation of acid-base balance:
See renal physiology

Regulation of Acid Base Balance

Uploaded by

Copyright:

Available Formats

Regulation of Acid Base Balance

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Regulation of Acid Base Balance

Uploaded by

Copyright:

Available Formats

Regulation of acid-base balance

• Alkali reserve is represented by the concentration of HCO3- in the blood.

Importance of bicarbonate buffer system:

3. Protein Buffer System:

II- Regulation of acid-base balance by respiratory mechanism

You might also like