Disturbances of Acid-Base Balance

Question 1

What organs are involved in acid-base balance and how do they achieve this?

Answer 1

• Lung: retain or blow off CO2
• Kidney: Excrete acid, make more HCO3, Prevent loss of HCO3
• Liver: Metabolism results in titration HCO3

Question 2

What is an alkalosis?

Answer 2

pH rising leading to alkalaemia (pH above 7.45)

Question 3

What is an acidosis?

Answer 3

pH falling leading to acidaemia (pH below 7.35)

Question 4

How is CO2 involved in acid-bas balance disturbances?

Answer 4

• CO2 is an acid
• Hyper- or Hypoventilation
• Hyper = fast breathing rate and large breath size = less CO2 = more basic and vice versa
• Chemoreceptors detect changes in pH depending on whether pH has increased or decreased the message sent to respiratory centre will cuase hypo or hyperventilation changing CO2 levels and therefore, pH

Question 5

What happens when a fall in CO2 is detected in the blood?

Answer 5

Respiration is depressed increasing the levels of CO2 as well as the levels of H2CO3 to decrease the pH back to normal

Question 6

How does the kideny regulate acid-base balance?

Answer 6

• Regulates daily H+ production and H+ in disease
• They regulate acid base balance by:
  1. Reabsorbing nearly all filtered bicarbonate
  2. Excreting acid in the urine
  3. Regenerate bicarbonate that would have been lost by buffering via excretion of ammonium salts and phosphate salts

Question 7

6 Steps

How is re-absorption of bicarbonate achieved?

Answer 7

Bicarrbonate passes through glomeruli into the tubules, to prevent acidaemia kidneys reabsorb the bicarbonate.
1. Bicarbonate filtered by glomerulus
2. Carbonic anhydrase converts carbonic acid to CO2 and H2O in tubular lumen
3. CO2 diffuses into tubular cells
4. CO2 combines with H2O to form carbonic acid
5. H+ passes into the lumen in exhange with Na+, combining with bicarbonate forming H2CO3
6. HCO3 reabsorbedwith Na into blood

Question 8

Phosphate 5 steps

How is excretion of acid in the urine achieved?

Answer 8

1. HPO42- is filtered into tubule
2. H+ is moved into tubule in exhange for Na+ combines with HPO42- forming H2PO4-
3. H2PO4- excreted in urine with Na+
4. Carbonic anhydrase combines the CO2 with H2O to form H2CO3 - this dissociates into H+ and HCO3
5. HCO3- in the tubule passes into the blood with Na+

Question 9

6 steps

How is excretion of acid via ammonia achieved?

Answer 9

Ammonia generated via metabolism
1. CO2 diffuse into tubule form blood or lumen
2. H2CO3 dissociates into H+ and HCO3
3. H+ passes into the lumen in exchange for Na+
4. NH3 produced from metabolism in the tubular cells is able to diffuse into the lumen accepting the H+ forming NH4+
5. NH4+ cannot pass back as it is charged , excreted in urine with anion from the glomerular filtrate
6. HCO3- in tubular cell passes into the blood together with Na+

Question 10

How do Metabolic Acidosis and Alkalosis occur?

Answer 10

Changes in bicaronate levels and changes in base excess
Metabolic Acidosis = Low bicarbonate and more negative BE
Metabolic Alkalosis = High bicarbonate and more positive BE

Question 11

How do Respiratory Acidosis and Alkalosis occur?

Answer 11

Changes in CO2
Respiratory Acidosis = High CO2
Respiratory Alkalosis = Low CO2

Question 12

What is Base Excess/Base Deficit?

Answer 12

The amount of acid (base excess) or base (base deficit) that must be dded to a sample of oxygenated blood to restore pH to 7.4 at 37 degress and at a pCO2 of 40 mmHg

Question 13

What are the compensatory responses to pH changes? Mention overcompensation

Answer 13

• Lungs hypo- or hyperventilation happens within minutes
• The kidneys are slower - starts within hours, maximum effect in 4-5 days
• Overcompensation does not occur