Acid-Base balance

outline

• Definition & types of acid and base• Sources of acid• Why regulation is important?• Defences against change in {H+}• Acid base disorders• Compensation• Diagnosis• Treatment

Acid-base balance…

• Definition of an acid and a base

• Types of acids and bases

based on different criteria• Is the precise regulation of free(unbound) hydrogen

ion concentration in the body fluids

Sources of H+ in the Body

• Carbonic acid formation

• Inorganic acids produced during breakdown of nutrients sulfuric acid and phosphoric acid…

• Organic acids resulting from intermediary metabolism lactic acid,fatty acids…

Why regulation is important?

• Changes in excitability of nerve and muscle cells acidosis - depression of the central nervous system

(CNS) alkalosis- overexcitability of the nervous system

• Exerts a marked influence on enzyme activity• Influence K+ levels in the body• Even to death

(1) chemical buffer systems,

(2) respiratory mechanism of pH control,and

(3) renal mechanism of pH control

Defense Against Change in [H+]

chemical buffer systems

• Is a mixture in a solution of two chemical compounds that minimize pH changes when either an acid or a base is added to or removed from the solution• by converting strong acids and bases into weak

acids and weak bases with in fractions of a second• It is the first line of defense

Types of buffer

• Protein buffer system is the most abundant buffer in intracellular fluid(Hb)

and blood plasma(albumin)Approximately 60 to 70 percent of the total chemical

buffering of the body fluids is inside the cells, and most of this results from the intracellular proteins

COOH as an acid and NH2 as a base

1a.

b.

Hb in RBC

• Phosphate buffer system Uses dihydrogen phosphate and monohydrogen

phosphate It plays a major role in buffering renal tubular fluid

and intracellular fluids

As an acid

As a base

• Carbonic Acid–Bicarbonate Buffer Systemis based on the bicarbonate ion(HCO3) and carbonic

acid(H2CO3)

Can not protect against pH changes due to respiratory problems in which there is an excess or shortage of CO2

As a base

As an acid

Exhalation of Carbon Dioxide(Lung)

• As a second line of defense• Through its ability to alter pulmonary ventilation and

consequently to alter excretion of H+-generating CO2• Doubling the ventilation increases pH by about 0.23 units,

from 7.4 to 7.63• Reducing ventilation to one-quarter of normal lowers the

pH by 0.4 units, from 7.4 to 7.0.• one to two times as much acid or base can normally be

buffered by this mechanism as by the chemical buffers

Changes in either pulmonary ventilation or the rate of CO2 formation by the tissues can change the extracellular fluid Pco2

Not only does the alveolar ventilation rate influence H+ concentration by changing the Pco2 of the body fluids, but the H+ concentration affects the rate of alveolar ventilation

Renal regulation

is third line of defense Uses (1) H+ excretion, (2) Reabsorption of filtered HCO3– (3) ammonia (NH3) secretion (4) filtered phosphate Ammonia and phosphate mechanism produce new

bicarbonate

Hydrogen and Bicarbonate ion

ammonia (NH3) secretion

Phosphate buffer

Acid–Base Disoders

• Either simple or combined

Use of the Acid-Base Nomogram for Diagnosis

Renal and respiratory compensation

• Respiratory compensation Is only for metabolic acidosis and alkalosis For metabolic acidosis - hyperventilation For metabolic alkalosis – hypoventilation

• Renal compensation For both metabolic and respiratory For acidosis – absorb bicarbonate For alkalosis - excrete bicarbonate

How can we treat acidosis and alkalosis

• For acidosissodium bicarbonatesodium lactate sodium gluconate

• For alkalosisammonium chloridelysine monohydrochloride

References

• Guyton,12e

• Principles of ANATOMY &PHYSIOLOGY,13e

• Ganong’s Review of Medical Physiology,23e

• Fundamentals of Human Physiology,4e

• Kaplan

Thank U