Week 8 - Acid-Base Balance

State the 2 overall types of systems that regulate pH of the blood

• Chemical Buffer

• Physiological Buffer

State the 2 types of physiological buffer systems

• Respiratory

• Renal

Give an example of a strong acid, weak acid and weak base

• Strong Acid - H+ ions

• Weak Acid - Carbonic Acid (H2CO3)

• Weak Base - Bicarbonate (HCO3-)

Explain how the bicarbonate buffer system brings pH back up to normal when the blood is acidic

• High concentration of H+ in the blood

• Bicarbonate (weak base) ties up excess H+ (strong acid) and forms carbonic acid (weak acid) that lowers acidity and increase pH

Explain how the respiratory physiological buffer system regulates pH

H+ ions and bicarbonate form carbonic acid which is broken down into carbon dioxide and water in the bloodstream and eliminated during exhalation.

Explain how the renal physiological buffer system regulated pH

The kidneys will retain H+ ion or bicarbonate ions by increasing its reabsorption into the blood while increasing excretion of the other ion into urine.

Explain how the respiratory buffer system deals with hypercapnia

• Hypercapnia (excess CO2) stimulates the respiratory centre

• The respiratory system increases respiratory rate and the depth of breathing

• This increases the amount of CO2 eliminated via exhalation, decreasing H+ concentration in the blood to prevent respiratory acidosis

Explain how the respiratory buffer system deals with hypocapnia

• Hypocapnia (low CO2) inhibits the respiratory centre

• The respiratory system then decreases respiratory rate and the depth of breathing

• This decreases the amount of CO2 eliminated via exhalation, increasing H+ concentration in the blood to prevent respiratory alkalosis.

State the indicators of respiratory acidosis

• Blood pH < 7.35

• PCO2 > 45 mmHg

• Normal blood bicarbonate levels

State causes of respiratory acidosis

Respiratory conditions that impair gas exchange or ventilation:

• Emphysema

• Asthma

• COPD

• Brainstem trauma

When there is respiratory impairment explain how respiratory acidosis is resolved

• The renal buffer system kicks in

• The kidneys increase the amount of H+ ions excreted in urine, decreases the amount in the bloodstream.

• Additionally the kidneys will increase the reabsorption of bicarbonate ions into the bloodstream that bind to excess H+ ions to form carbonic acid and further decrease acidity

Explain symptoms

State the indicators of respiratory alkalosis

• Blood pH > 7.45

• PCO2 < 35 mmHg

• Normal blood bicarbonate levels

State the causes of respiratory alkalosis

Increase in ventilation or gas exchange from:

• Anxiety

• Pain

• High altitudes

• Aspirin

When there is respiratory impairment explain how respiratory alkalosis is resolved

• The renal buffer system kicks in

• The kidneys increase the amount of bicarbonate ions excreted in urine to bring down blood pH

• Additionally the kidneys will increase the amount of H+ ions reabsorbed into the bloodstream to bind to excess bicarbonate and form carbonic acid that further reduces blood pH to normal.

Explain symptoms

State the indicators of metabolic acidosis

• Blood pH < 7.35

• HCO3- (Bicarbonate) < 22 mEq/L

• PCO2 is normal

State and explain the causes of metabolic acidosis

• Increased alcohol consumption (metabolises into acetic acid)

• Diabetic ketoacidosis, malnutrition and starvation (fatty acid metabolism leads to ketone formation breakdown increases blood acidity)

• Diarrhoea (loss of bicarbonate ions)

• Kidney disorders

When there is renal impairment explain how metabolic acidosis is resolved

• The respiratory buffer system kicks in

• The respiratory centre in the brain is stimulated increasing respiratory rate and depth of breathing

• This increases the amount of CO2 eliminated via exhalation, therefore increasing H+ removal from the blood to increase pH to normal

Explain symptoms

State the indicators of metabolic alkalosis

• pH > 7.45

• HCO3- (Bicarbonate) > 26 mEq/L

• PCO2 is normal

State some of the causes of metabolic alkalosis

• Vomiting (acid removal)

• Sodium bicarbonate IV and baking soda (excess base intake)

• Blood transfusions

• Hypokalaemia (H+ is then moved into cells swapping with K+ to increase blood levels)

• Diuretics

When there is renal impairment explain how metabolic alkalosis is resolved

• The respiratory buffer system kicks in

• The respiratory centre in the brain is inhibited decreasing respiratory rate and depth of breathing

• This decreases the amount of CO2 eliminated via exhalation and therefore decreases the removal of H+ from the bloodstream, increasing its concentration and therefore lowering pH to normal.

Explain symptoms