L12: pH measurement®ulation

pH:influences most enzymes within body

physiological pH=7.4= -log[H+]=0.00004mEq/L or 40nEq/L : varry:10-160

pH regulation: 3 mechanisms:

1(seconds) Chemical ACID-BASE BUFFER system of body fluids

buffer+H+ ↔HBuffer

• Bicaronate buffer system

CO2+H2O↔↓H2CO3↔↑H+ +↑CO3-

Ionizes almost completely Na+

↑Acidosis: If Add acid: CO2 stimulates respiration removes it from system
↑Alkalosis: If Str.Base: ↓respiration to reserve CO2, ↑renal excretion: HCO3

H-H Eqn: pH=^.1+log HCO3-/(0.03*PCO2)

METABOLIC A-B DISORDERS:

M. Acidosis: ↓HCO3

M. Alkalosis: ↑HCO3

RESPIRATORY A-C DISORDERS:

R.Acidosis: ↑PCO2

R.Alkalosis: ↓PCO2

• Phosphate buffer system: important in TUBULAR system of kidneys

A: HCl + Na2HPO4 ↔ NaH2PO4 + NaCl

B: NaOH+ NaH2PO4 ↔ Na2HPO4 +H2O

• MAINLY: Cellular Protein buffer system

slow reaction, take several hrs to buffer changes in extracellular fluid due to slow movement of bicarbnate+ protons across plasma membr. (with exception of RBCs)

2 (minutes): Respiratory centre-regulation of pH

control of extracellular fluid: PO2

↑ [H+]->↑ alveolar ventilation-> ↓ PO2 (-feedback to [H+]) ↓ ventilation->↑ PO2

Abnormalities in respiration-> change in A-B balance&alter extracellular pH

e.g. emphysema: ↓ ability eliminate CO2-> build CO2->extracellular pH becomes acidic-> R.ACIDOSIS

3 (hrs-days) Kidneys-Renal Control ->pH regulation: regulation of extracellular fluid: [H]: 3 ways:

• Reabsorption of 85% HCO3 -->>contributes to:
• Generation of new HCO3 inside tubule cells
• Secretion of H+

if person suffering ACIDOSIS additional buffering can be gained with new bicarb. ions synthesized in the tubule cells, as long as a sink for H+ (HPO4-2) is available.

2nd way: from catalysis of a.a. glutamine

ACIDOSIS/ALKALOSIS:

better look handwritten notes