Role of Ventilation in Acid-Base Balance Flashcards
What is the significance of maintaining pH?
Maintaining pH homeostasis is important for protein function (e.g. enzyme/receptor binding sites)
They’re dependent on specific secondary, tertiary and Quaternary structures achieved via inter- and intra-chain bonding
How are proteins denatured?
Various factors (pH, temperature etc) can denature proteins, by disrupting bonds and their structure - impairing function
Why is arterial pressure so tightly regulated?
As the circulatory system innervates all organs and tissues, arterial pH is tightly regulated to ensure effective protein function
How is the regulation of arterial pH achieved?
Due to the presence of buffering systems, and by regulating level of molecules associated with acid-base production
How is excess H+ dealt with?
Presence of buffers e.g. bicarbonate buffer system:
H₂CO₃ (weak acid) + HCO₃⁻ (conjugate base)
H⁺ + HCO₃⁻ ⇆ H₂CO₃
any H⁺ formed due to the addition of a strong acid, by reacting it with a conjugate base to form a weaker acid (H₂CO₃ ) maintains a stable pH
How are changes in pH regulated?
Buffers consisting of a weak acid and a conjugate base are used to resist sharp changes in pH
Name some intracellular buffer systems
- phosphate buffer system
- amino acids / proteins
- Hb in RBCs
Give some examples of extracellular buffer systems
- bicarbonate buffer system
- plasma proteins (e.g. albumin)
How does CO₂ affect the acid base balance?
The relationship between PCO₂ and [H₂CO₃] means that CO₂ transport is important in acid base balance
How does decreased [H⁺] lead to alkalosis and hyperventilation?
CO₂ + H₂O ⇆ H₂CO₃ ⇆ H⁺ + HCO₃⁻
←decreased [H⁺] = alkalosis
←decreased [H₂CO₃]
←Removal of CO₂ (hyperventilation)
How does increased CO₂ lead to acidosis?
CO₂ + H₂O ⇆ H₂CO₃ ⇆ H⁺ + HCO₃⁻
→accumulation of CO₂ (hypoventilation)
→increased [H₂CO₃]
→increased [H⁺] = acidosis
Explain the effect of CO₂ on pH
increased CO₂ = increased acidity
How do the lungs affect pH?
As the lungs play a role in regulating CO₂ levels, they also therefore contribute to acid-base balance
How can we diagnose respiratory distress syndrome?
signs of respiratory and metabolic distress can be diagnosed & interpreted from analysis of ABG and pH
How do the lungs and kidneys maintain pH?
The lungs and kidneys maintain blood pH homeostasis by regulating PaCO₂ and [HCO₃⁻] respectively
Explain the effects of PaCO₂ and [HCO₃⁻] on pH in the kidneys and lungs
↑PaCO₂ = ↓pH
(unless [HCO₃⁻] changes proportionally in opposite direction)
↓PaCO₂ = ↑pH
↑[HCO₃⁻] = ↑pH
(unless PaCO₂ changes proportionally in opposite direction)
↓[HCO₃⁻] = ↓pH
What causes excessive changes in blood pH?
As blood pH is proportional to the ratio of HCO₃⁻ to CO₂, excessive changes may result from respiratory (CO₂) or metabolic (HCO₃⁻) dysfunction
- Decreased pH = acidosis
- Increased pH = alkalosis
How can we differentiate between respiratory and metabolic acidosis?
pH < 7.35 indicates acidosis
if ↑ CO₂ = respiratory acidosis
if ↓ [HCO₃⁻] = metabolic acidosis
How can we differentiate between metabolic and respiratory alkalosis?
pH > 7.45 indicates alkalosis
if ↓ CO₂ = respiratory alkalosis
if ↑ [HCO₃⁻] = metabolic alkalosis
What are the causes of acidosis pH > 7.35?
Hypercapnia (hypoventilation) ↑ lactic acid (sepsis) ↑ ketone bodies (diabetes) ↓ kidney acid excretion (renal failure) ↓ HCO₃⁻ reabsorption (renal acidosis) HCO₃⁻ loss from gut due to diarrhoea
What are the effects of acidosis?
Tachypnoea
- muscular weakness
- headache
- confusion, coma
- cardiac arrhythmia
- hyperkalaemia (high K levels)
What compensatory mechanisms are induced due to acidosis?
Hyperventilation
- decreased PaCO₂, respiratory compensation
Renal compensation
- decreased HCO₃⁻ excretion
What are the causes of alkalosis > 7.45?
Hypocapnia (hyperventilation)
- vomiting: loss of H⁺ in HCl
↑ kidney acid excretion (diuretics)
↑ alkalotic agent consumption (antacids NaHCO₃)
What are the effects of alkalosis?
Bradypnoea
- muscle weakness, cramps, tetany
- Headache, nausea
- light-headedness, confusion, coma
- cardiac arrhythmia
- hypokalaemia
What compensatory mechanisms come into effect during alkalosis?
Hypoventilation
- increased PaCO₂, respiratory compensation
increased HCO₃⁻ excretion (renal compensation)
How does acidosis induce hyperkalaemia?
increased [H⁺] displaces K⁺ out of the cell into ECF
=> hyperkalaemia causes vasodilation of cerebral arteries
How does alkalosis cause hypokalemia?
Decreased CO₂ = decreased [H⁺] in cell so K⁺ moves into the cells to maintain balance
=> causes vasoconstriction of cerebral arteries
