Acid Base Balance

ACID-BASE BALANCE

Fatima Tasneem Jimlok Mohammad Sali FEU – Institute of Nursing BSN003 / Group 11

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Normal function of body cells depends on regulation of the hydrogen ion (H+) concentration within very narrow limits. Acid-Base imbalances are frequently diagnosed with Arterial Blood Gas.

Regulation of Acid-Base balance 

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The symbol pH refers to the negative logarithm of the H+ concentration. A pH of 7.0 is neutral; an acidic solution has a pH less than 7.0; and an alkaline solution has a pH greater than 7.0 Normal serum pH is 7.35-7.45

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Three physiologic systems act interdependently to maintain a normal serum pH Chemical buffering of excess acid or base by buffer systems in the blood plasma and in cells. Excretion of acid by the lungs Excretion of acid or regeneration of base by the kidneys.

Modulation of serum pH by buffer systems  

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Chemical buffers are solutions that resist changes in pH A buffer is made up of a weak acid and its conjugate base. The most important extracellular buffer is the HCO3 −/H2CO3 system, described by the equation: H+ + HCO3 − ↔H2CO3 ↔ CO2 + H2O

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The organic acids formed during cellular energy metabolism are strong acids. Example of buffering reactions Strong acid buffered: HCL + (H2CO3/NaHCO3) → H2CO3 + NaCl Strong base buffered: NaOH + (H2CO3/NaHCO3) →NaHCO3 + H2O

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Proteins such as hemoglobin in RBCs and albumin in the plasma are quantitatively the most important blood buffers. Negatively charged ions, such as phosphate within body cells and carbonate within bones, are important intracellular buffers. Buffer systems act instantly to minimize the impact of adding strong acids or bases to body fluids.

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The concentrations of bicarbonate ions and of carbonic acid are controlled by two independent physiological systems. Carbonic acid concentration is controlled by the lungs while bicarbonate ions is through the lungs.

Regulation of volatile acids by the lungs  

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Volatile acids are acids that can be converted to gases. During normal ventilation (breathing), the lungs exhale large quantities of “potential” acid in the form of CO2 CO2 diffuses from body cells into the blood, where it may combine with water to form H2CO3 , which then dissociates into its component ions: H+ and HCO3-. This hydrolysis reaction, which is reversible, is shown as follows: H2O + CO2 ↔H2CO3 ↔ HCO3- + H+

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The law of mass action states that the rate of a chemical reaction is directly proportional to the molecular concentrations of the reacting substances. The rate and direction of the hydrolysis reaction are determined by (1) the addition of substrate or (2) the removal of end product. In the lungs, CO2 diffuses along its concentration gradient from the plasma to the alveoli, from which it is exhaled.

Regulation of fixed acids and bicarbonate by the kidneys 

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Fixed acids are acids that cannot be converted to gases, thus should be eliminated in the urine. These fixed acids include the ff: Sulfuric, phosphoric, ketones, lactic acid and occasionally, ingested toxins such as salicylates, drugs and methanol. The kidneys regulate serum pH by secreting H+ into the urine and by regenarating HCO3- for reabsorption in the blood.

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URINARY BUFFER SYSTEMS The three principal buffer systems in renal tubules are the bicarbonate, ammonia and phosphate (titratable acid) systems. Bicarbonate buffer Ammonia buffer Phosphate buffer

Bicarbonate Buffer  

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H+ is secreted into the tubular lumen by tubular cells in countertransport with sodium. The combination of H+ with filtered bicarbonate regenerates CO2 in a reversal of the hydrolysis reaction. This CO2 is reabsorbed into tubular cells, where hydrolysis proceeds.

GLOMERULUS

2

HCO3+ 3 H+

1 Na+

Na+

H2CO3

H+ +

5 H20+C02 4 TUBULAR FLUID

CO2+H20

H2C03

6 HCO3-

HCO3-

RENAL TUBULAR CELLS

PERITUBULAR CAPILLARY

Ammonia Buffer 

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Depends on the generation of ammonia (NH3) from amino acids in renal tubular cells. NH3 diffuses into the tubular lumen, where it may combine with secreted H+ to form ammonium (NH4+) NH4+ is excreted in the urine in combination with Clfrom NaCl

GLOMERULUS Cl-

1 3

H+ + NH3

2 Cl-+NH4

NH3

Glutamine

4 NH4Cl

TUBULAR FLUID

RENAL TUBULAR CELLS

PERITUBULAR CAPILLARY

Phosphate Buffer 

Results in the formation of weak acids that are excreted in the urine.

GLOMERULUS

2

HPO42-

Na+

HPO42- + H+

1

3

H2PO4- + Na+

4

NaH2PO4

TUBULAR FLUID

RENAL TUBULAR CELLS

PERITUBULAR CAPILLARY