ACID BASE BALANCE

                         ACID BASE BALANCE

A hydrogen ion is a single free proton released from a hydrogen atom

Acids.. Molecules containing hydrogen atoms that can release hydrogen ions in solutions

   -hydrochloric acid (HCl) ,carbonic acid (H2CO3)

A base…. an ion or a molecule that can accept an H+

   -HCO3-,HPO4=,The proteins ,hemoglobin

Strong and Weak Acids and Bases

·         A strong acid ..rapidly dissociates and releases large amounts of H+ in solution….HCl

·         Weak acids ..less tendency to dissociate their ions … is H2CO3

·         A strong base … reacts rapidly and strongly with H+ and quickly removes these from a solution…OH-

·         A typical weak base is HCO3-

·         Most of the acids and bases in the extracellular fluid that involved in normal acid-base regulation are weak acids and bases

Types of Acids in the body

• Volatile acids:

–        Can leave solution and enter the atmosphere.

–        H₂C0₃ (carbonic acid).

               Pco₂ is most important factor in pH of body tissues

• Organic Acids:

–        Byproducts of aerobic metabolism, during anaerobic metabolism and during starvation, diabetes.

               Lactic acid, ketones

Normal Hydrogen Ion Concentration and pH of Body Fluids

• the blood H+ concentration is normally maintained within tight limits around a normal value of about 0.00004 mEq/L (40 nEq/L)

Ph= log 1/H= -log [H]

Ph=7.4

Defenses Against Changes in Hydrogen Ion Concentration

Defenses Against Changes in Hydrogen Ion Concentration

There are three primary systems that regulate the H+ concentration

(1)    the chemical acid-base buffer systems of the body fluids

        (2) the respiratory center

        (3) the kidneys

Buffer Systems

• Chemical buffer system

–        Combination of weak acid and weak base

–        Binds to H⁺ as H⁺ concentration rises

–        Releases H⁺ as H⁺ concentration falls

–        Can restore normal pH almost immediately

–        Three major chemical buffer systems

•          Bicarbonate system

•          Phosphate system

•          Protein system

BODY BUFFER SYSTEMS

–        bicarbonate/carbonic acid

•          major plasma buffer

–        phosphate: H2PO4- / HPO42-

•          major urine buffer

–        ammonium: NH3 / NH4+

•          also used to buffer the urine

–        proteins: important in ICF

–        Hb: is the main buffer against CO2 changes

BICARBONATE BUFFER SYSTEM

• Carbonic acid (H₂CO₃)

–        Weak acid

• Bicarbonate ion (HCO₃^-)

–        Weak base

• CO₂ + H₂0 ó H₂CO₃ ó H⁺ + HCO₃^-
• Works along with respiratory and urinary system

–        These systems remove CO₂ or HCO₃^-

§  NaOH  + H2CO3               H2O  +  Na HCO3

§  HCl  +  Na HCO3               NaCl   +   H2CO3

• pK 6.1
• the concentrations of CO2 and HCO3 not great.
• the most powerful extracellular buffer in the body
• the two elements of the buffer system are regulated by the kidneys and the lungs

PHOSPHATE BUFFER SYSTEM

• Dihydrogen phosphate ion (H₂PO₄^-)
• Weak acid
• Monohydrogen phosphate ion (HPO₄^2-)
• Weak base
• H₂PO₄^- ó H⁺ + HPO₄^2-
• More important in buffering kidney filtrate than in tissue

The main elements of the phosphate buffer system are H2PO4- and HPO4

NaOH  +  NaH2PO4           H2O+ Na2HPO4

HCl +  Na2HPO4             NaCl + NaH2PO4

• pK 6.8

• 8 % of the concentration of the bicarbonate buffer
• the total buffering power less than that of the bicarbonate buffering system.

PROTEIN BUFFER SYSTEM

• Proteins are more concentrated than bicarbonate and phosphate buffers
• Accounts for ~75% of all chemical buffering of body fluids
• Buffering ability due to certain functional groups of amino acid residues
• the pKs of many of these protein systems close to 7.4.

Isohydric buffer system

The buffer system buffers each other by shifting hydrogen from buffer to other

2. Respiratory mechanisms

• Exhalation of carbon dioxide
• Powerful, but only works with volatile acids
• Doesn’t affect fixed acids like lactic acid
• CO₂  +  H₂0  ↔ H₂CO₃  ↔    H⁺  + HCO₃^-
• Body pH can be adjusted by changing rate and depth of breathing

3.Renal Control of Acid-Base Balance

•          Alkalosis
→↑urinary HCO3-

•          Acidosis
→↓urinary HCO3-
     new HCO3- production

                        

                        Acid-Base Imbalances

•         pH< 7.35 acidosis

•         pH > 7.45 alkalosis

Compensation for Metabolic Acidosis

•          Increased ventilation

•          Renal excretion of hydrogen ions if possible

•          K⁺ exchanges  with excess H⁺ in ECF

•          ( H⁺ into cells, K⁺ out of cells)

Analysis of Acid-Base Disorders

SUBMITTED TO :                                                      SUBMITTED BY :

Dr V ASHOK                                                              RV/07-70

ASST PROFESSOR                                                     RV/07-71

DEPT OF VBC                                                             RV/07-72

                                                                                     BATCH-B