Acid-Base-balance complete notes, Exams of Nursing

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Acid Base balance

Content

• Buffer systems and its efficiency
• Requirement of maintenance of acid base balance
• Causes of acid base imbalances
• Regulation of acid base balance
  • Renal
  • Respiratory

Case report 2

• A man suffering from untreated diabetes mellitus is admitted to the hospital. Glucose and acetoacetate are present in his urine and he exhibits shallow breathing. Analysis of his blood indicates [HCO3-] =16 mM and PCO2=
• The most likely pH of blood is

Relationship of pH to hydrogen ion concentration

• What is pH?
• Negative logarithm of H+ concentration in a solution
• pH Scale:
• Ranges from 0 to 14
• What is pKa?
• Negative logarithm of dissociation constant
• The pH at which an acid is half dissociated, existing as equal proportions of acid and conjugate base.

What is buffer

• A buffer is a mixture of a weak acid and a salt of its conjugate base that resists changes in pH when a strong acid or base is added to the solution .
• Functions of a buffer depends on:
• pH
• pK
• Salt to acid ratio

Requirement of maintenance of acid base balance

• For optimum function of biomolecules : Enzymes, transport molecules, nucleic acid
• To avoid disruption of structure and function of cells
• Several serious health consequences: Acidosis, alkalosis

Buffer systems

• 1. Bicarbonate/Carbonic acid buffer systems
  • Extra cellular buffer
  • pK=6.
  • cHCO3-/cdCO2=?
• 2. Phosphate buffer
  • pK= 6.
  • cHPO4-/H2PO4-=
  • Intracellular buffer
• 3. Plasma protein and Hemoglobin: Imidazole group of histidine: pK=7.

Partial pressure of oxygen and carbon di oxide

Respiratory Response to Acid-Base

Perturbations

• responds immediately to a change in acid -base status
• several hours may be required for the response to become maximal
• in the early stage plasma pH decreases
• H+ ions equilibrate slowly across the blood -brain barrier, the pH in CSF remains nearly normal
• Stimulated peripheral chemoreceptor induces hyperventilation: Plasma pCO2 decreased

Role of

RBC and

Hb

Role of RBC and Hb

1. Na+-H+ exchange :

2. Reclamation of HCO3-