12 pH SCALE pH refers to Potential Hydrogen Expresses hydrogen ion concentration in water solutions. Water ionizes to a limited extent to form equal amounts of H+ ions and OH- ions H2OH+ + OH- H+ion is an acid OH-ion is a base
25 SOURCE OF HYDROGEN ION CO2 + H2O H2CO3 H+ + HCO3- H+ H2CO3 HCO3-
26 Regulation of Acid Base Balance Two types of acids are produced in the body:
Volatile acids :CO2 produced
during the metabolism of carbohydrates and lipids
Non-volatile acids:metabolism of
protein e.g. sulphuric acids
Compensatory mechanisms 1)Chemical Buffers
React very rapidly(less than a second)
Reacts rapidly (seconds to minutes)
Reacts slowly (minutes to hours)
4) Intracellular Shifts of Ions 27
Acid-base buffer system
Maintains the pH by binding with free hydrogen ions.
Combination of weak acid and a base (unprotonated compound).
Three major chemical buffer systems
29 BICARBONATE BUFFER SYSTEM This system is most important because the concentration of both components can be regulated:
Carbonic acid by the respiratory system
Bicarbonate by the renal system
H2CO3H+ + HCO3-
Hydrogen ions generated by metabolism or by ingestion react with bicarbonate base to form more carbonic acid
31 BICARBONATE BUFFER SYSTEM H+
Equilibrium shifts toward the formation of acid
Hydrogen ions that are lost (vomiting) causes carbonic acid to dissociate yielding replacement H+ and bicarbonate
32 BICARBONATE BUFFER SYSTEM H+ HCO3- H2CO3 H2O CO2 + + Addition of lactic acid Exercise Loss of HCl Vomiting
33 PHOSPHATE BUFFER SYSTEM Na2HPO4 + H+ NaH2PO4+ Na+
Most important in the intracellular system
Na2HPO4 + H+ + Na+ NaH2PO4
34 PHOSPHATE BUFFER SYSTEM
Regulates pH within the cells and the urine
Phosphate concentrations are higher intracellular and within the kidney tubules.
More phosphate ions
are found in tubular fluids
More powerful than
bicarbonate buffer system HPO4-2
35 PROTEIN BUFFER SYSTEM Proteins are excellent buffers because they contain both acid and base groups that can give up or take up H+ Proteins are extremely abundant in the cell The more limited number of proteins in the plasma reinforce the bicarbonate system in the ECF
Hemoglobin buffers H+ from metabolically produced CO2 in the plasma only
As hemoglobin releases O2 it gains a great affinity for H+
H+ O2 O2 Hb O2 O2
37 H+ generated at the tissue level from the dissociation of H2CO3 produced by the addition of CO2 Bound H+ to Hb(Hemoglobin) does not contribute to the acidity of blood H+ O2 O2 Hb O2 O2
38 As H+Hb picks up O2 from the lungs the Hb which has a higher affinity for O2 releases H+ and picks up O2 Liberated H+ from H2O combines with HCO3- HCO3-H2CO3CO2(exhaled) O2 O2 H+ Hb O2 O2
39 RESPIRATORY CENTRE Pons Respiratory centers Medulla oblongata
40 CHEMOSENSITIVE AREAS
Chemo sensitive areas of the respiratory center are able to detect blood concentration levels of CO2 and H+
Increases in CO2 and H+ stimulate the respiratory center
The effect is to raiserespiration rates
But the effectdiminishes in1 - 2 minutes
CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2
41 cell production of CO2 increases CO2 + H2O H2CO3 H2CO3 H+ + HCO3- H+ acidosis; pH drops H+ stimulates respiratory center in medulla oblongata rate and depth of breathing increase CO2 eliminated in lungs pH rises toward normal RESPIRATORY CONTROL OF pH
42 RENAL RESPONSE The kidney compensates for Acid - Base imbalance within 24 hours and is responsible for long term control The kidney in response: To Acidosis Retains bicarbonate ions and eliminates hydrogen ions To Alkalosis Eliminates bicarbonate ions and retains hydrogen ions
Increased loss of CO2 from the lungs at a rate faster than it is produced
Decrease in H+
CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2 CO2
55 RESPIRATORY ALKALOSIS Can be the result of: 1) Anxiety, emotional disturbances 2) Respiratory center lesions 3) Fever 4) Salicylate poisoning (overdose) 5) Assisted respiration 6) High altitude (low PO2)
CLINICAL EVALUATION OF DISTURBANCES IN ACID BASE STATUS 74
ANION GAP The term anion gap (AG) represents the concentration of all the unmeasured anions in the plasma. The negatively charged proteins account for about 10% of plasma anions. Reference range is 8 to 16 mmol/l. 75 Anion gap = [Na+] - [Cl-] - [HCO3-] AG = [Na+] + [K+] - [Cl-] - [HCO3-]
Major Clinical Uses of the Anion Gap
To signal the presence of a metabolic acidosis and confirm other findings.
Help differentiate between causes of a metabolic acidosis.
To assist in assessing the biochemical severity of the acidosis and follow the response to treatment .
General Factors affecting Acid-Base Balance in Infants
Low Bicarbonate depends
on Gestational Age
lower renal threshold
lower capacity to reabsorb HCO3-
Very low birth weight babies: bicarbonate levels of 12-16 mmoles/l
Term babies : levels of 20-22 mmol/l.
78 The rate of metabolism in infants is twice as great in relation to body mass as in adults Twice as much acid is formed which leads to a tendency toward acidosis Functional development of kidneys is not complete until the end of the first month Renal regulation of acid base may not be optimal.
Low Reserve to excrete an Acid Load
Term infants, acid excretion is working near maximum capacity and there is little reserve to deal with acidosis.
Preterm babies less capacity than a term neonate to buffer an acid load.
80 Other Factors Growth results in deposition of base in new bone as the calcium salts in bone are alkaline salts. On a weight basis, fixed acid production is higher than in adults. Neonates and children < 12 months fixed acid production is 2 to 3 mmol/kg/day).
Infantile Metabolic Acidosis
Different inborn errors of metabolism cause a metabolic acidosis:
organic acidosis (enzyme defect resulting in accumulation of acidic metabolic intermediates)
Feeding difficulties often in association with tachypnoea
Lactic acidosis : enzyme defects and present during childhood.
not an isolated finding as these children have serious dysfunctions of organ systemsesp. affecting brain, liver and muscle. 82
Other Acid-Base Disorders in Children Insulin dependent diabetes mellitus usually presents during childhood or adolesence. Poisoning in children may cause an acid-base disorder 83
REFERENCES Fundamentals of physiology: a human perspective:Lauralee Sherwood; Fluid and acid base balance; page:453-61 Essentials of medical physiology: K Sembulingam; Acid base balance:36-47 Ganong’s Review of Medical Physiology: Renal physiology: 679-682 84
THANK YOU Presented by: Dr. Ruby Kharkwal 1st year postgraduate student Department of Pedodontics 85