Acid-base Balance:- Part 1 – Introduction to the Acid-Base Balance

May 30, 2022Chemical pathologyLab Tests

Acid-base Balance

Definition of acid-base balance:

1. This regulation of the extracellular fluid environment involves the ratio of acid to base, measured clinically as pH.
   1. Physiologically all positively charged ions are called acids, and all negatively charged ions are called bases.
      

      Acid-base definition and explanation

      Distribution of the various anions/cations in body fluids:

      Anions	Extracellular fluid (ECF)	Intracellular fluid (ICF)
      Chloride	104 meq/L	4 meq/L
      Bicarbonate	24 meq/L	12 meq/L
      Phosphate	2 meq/L	40 to 95 meq/L
      Protein	16 meq/L	54 meq/L
      Other anions	8 meq/L	31 to 85 meq/L
      Cations
      Potassium	5 meq/L	156 meq/L
      Sodium	142 meq/L	10 meq/L
      Calcium	5 meq/L	4 meq/L
      Magnesium	2 meq/L	26 meq/L

   2. The regulation of intracellular and extracellular electrolytes concentration depends on the following factors:
      1. There is a balance between the intake of substances in a diet containing electrolytes and the electrolytes’ output in feces, urine, and sweating.
      2. It also depends upon the transport of fluids and electrolytes between ECF and ICF.
2. Acid-base balance is essential for life.
3. Physiological changes in the concentration of H⁺ ions in the blood lead to acid-base balance.
4. A systemic increase in the H⁺ ions concentration is called acidosis (acidemia).
   

   Acid-base Imbalance and acidemia

5. A systemic decrease in the H⁺ ions is called alkalosis (alkalemia).
   

   Acid-base imbalance and alkalemia

6. Must regulate acid-base balance within a narrow range for the body to function normally.
   1. A very slight change in the pH will affect the body.
   2. A very slight change in the H⁺ ions can bring changes in the cell and tissue.

For normal body functions, the pH range is very narrow and needs to be maintained within these limits.
pH significance in our life:

The pH of different body fluids:

H⁺ ions are needed for:

1. To maintain the integrity of the membrane.
2. Speed of the metabolic reactions.
3. Any change in the pH will lead to more harmful effects than other diseases.
4. The symbol pH represents the power of H⁺.
5. When pH changes one unit like 7.0 to 6.0 = [H⁺] [H⁺] = H⁺ ions concentration changes 10 folds.

Body acids are formed from end products of:

1. Metabolism of proteins.
2. Metabolism of Carbohydrates.
3. Metabolism of fats.
4. This must be balanced by the number of basic substances in the body to maintain the normal pH.
   1. Lungs, kidneys, and bones are the major organs involved in the regulation of acid-base balance.

Body acids are of two types:

1. Volatile acids:
   1. Carbonic acid (H2CO₃) is a weak acid, and it does not easily release the H⁺ ions.
   2. The presence of carbonic anhydrase enzyme can eliminate CO 2 gas and water H2O.
   3. CO 2 is eliminated through the lungs.
2. Nonvolatile acids:
   1. These are sulfuric acid, phosphoric acid, and other organic acids that are eliminated through the kidneys.
   2. These are strong acids and readily give up their H⁺ ions.
   3. Nonvolatile acids are secreted into the urine by the renal tubules.
   4. These acids are about 150 meq/L of H+ ions per day or about 1 meq/kg body weight.

Buffer systems of the acid-base balance:

The buffer systems become active in response to changes in the pH of the body as acid-base balance.

Functions of the buffer system:

1. Prevent the significant change in pH.
2. Buffer can absorb the excess of the H⁺ ions (acid).
3. Buffer system can absorb OH^– ions, Hydroxyl (base).
4. The buffer system is present in the intracellular fluid (ICF) and extracellular fluid (ECF).
5. The most common buffer systems are:
   1. Carbonic acid-bicarbonate system.
   2. Hemoglobin-oxyhemoglobin system.
   3. Phosphate and protein are the most important intracellular buffers (ICF).

Summary of the different buffer systems in acid-base balance:

Renal buffering system:

1. The distle tubule of the kidneys regulates acid-base balance by secreting the H⁺ ions in the urine and reabsorbs the HCO3^–.
2. Dibasic phosphate (HPO4^—) and ammonia (NH3) are two important renal buffer.
3. The renal buffering of H+ ions requires CO2 and water (H2O) to form the H₂CO3.
4. The enzyme carbonic anhydrase catalyzes the reaction.
5. H+ ions are secreted from the tubular cells and buffer in the lumen by PO4^— and NH3 = H2PO^–3 + NH4⁺.
6. The rest of HCO3^– is reabsorbed.
   

   Kidneys role in the acid-base balance

7. If a respiratory Disease causes acidosis or alkalosis, then the kidney becomes active and responds by changing H⁺ and HCO3^– ions to return the pH to normal.
   1. Renal compensation starts in hours to days after respiratory alteration in the pH.
   2. There is a delay, but the renal buffer system is powerful.
   3. In acidemia (acidosis) Kidney excrete an excess of the H+ ions, and these may combine with PO4 (phosphate) or NH3 (ammonia) to form titratable acids in the urine.
   4. The net outcome is to raise the concentration of the HCO3^– ions in the ECF and restore the acid-base balance.
   5. In alkalemia (alkalosis), kidneys excrete HCO3^–  ions, usually with Na⁺ ions.
   6. The net result is to decrease the concentration of the HCO3- ions in the ECF and restore the acid-base balance.

Carbonic acid-bicarbonate buffering system:

1. This buffer system operates both in the lungs and kidneys.
2. This is the major extracellular buffer system.
3. Lungs can decrease the carbonic acid by blowing out the CO2 and leaving water behind.
4. Kidneys can reabsorb HCO3- or regenerate new HCO3- from CO 2 and water.
5. Normal bicarbonate (24 meq/L) and normal carbonic acid (1.2 meq/L), produce a 20:1 relation and maintain the pH of 7.4
6. Both the systems are very efficient because:
   1. HCO3^– is easily reabsorbed or regenerated by the kidneys.
   2. The lungs adjust acid concentration.
7. Compensation for the pH is done as:
   1. The respiratory system compensates for pH by decreasing or increasing CO2 by changing the rate of respiration.
   2. The renal system produces more acidic or more alkaline urine.

Protein buffering system:

1. Hemoglobin (Hb) is the best intracellular buffer system, and it combines with H⁺ and forms HHb and CO2, forming the HHbCO2 complex.
2. When Hb combines with H⁺ ions becomes weak acid.
3. Venous blood Hb is a better to buffer system than arterial blood Hb.

Acid-base control by the various organs of the body

Pulmonary role in the acid-base balance:

1. In case of acidosis or alkalosis resulting from metabolic or renal diseases, the respiratory system regulates the respiratory rate to restore the pH to normal.
2. In acidemia (acidosis), there is an increased respiratory rate and depth to eliminate CO2.
3. In alkalemia (alkalosis), there is decreased respiratory rate and depth to retain the CO2.

Various Buffer systems and their role in the acid-base system:

Role of various organs as a buffer and their role in acid-base balance:

Role of various anions in the acid-base balance:

Panic values:

Summary of the parameters needed for the acid-base balance: