Acid-base regulation

Question 1

Physiological pH: recall the normal plasma pH and the limits compatible with life

Answer 1

Regulator (blood pH) is more important in distinguishing normality/abnormality in urine

Question 2

Buffering: explain the bicarbonate buffer system, recall the normal value for plasma bicarbonate, recall and apply the Henderson-Hasselbach equation, and explain renal mechanisms to alter/maintain serum bicarbonate concentration (reabsorption and secretion)

Answer 2

Bicarbonate

• HIGH CAPACITY CHEMICAL BUFFER
• can respond rapidly to changes in
• METABOLIC ACID
• can be produced from VOLATILE RESPIRATORY ACID

Most bicarbonate is absorbed in Proximal Convoluted Tubule - 80%

Ascending limb reabsorb most of what is left - 10%

Distal convoluted tubule - 6%

Collecting duct 4%

Useful buffering mechanism – we want all of it reabsorbed

pH=pK+〖log〗_(10 ) ([〖HCO〗_3^-])/(〖[CO〗_2])

Question 3

Davenport diagram

Answer 3

Horizontal line – normal bicarb

Vertical line – normal H+

PCO2- 5.4 kPa

1. TOP RIGHT QUADRANT:

• Metabolic alkalosis
• pH will increase
• Bicarb increases
• Migration along the green line because pCO2 not necessarily changes

2. metabolic acidosis

(less steep than alkalosis)

3. acute respiratory alkalosis
4. Chronic respiratory alkalosis
5. Chronic respiratory acidosis
6. Acute respiratory acidosis

Acute conditions go sideways because not much time is given to the body to accommodate change

Question 4

Phosphate, ammonium and protons: explain the mechanisms involved in the excretion of phosphate, ammonium salts and hydrogen ions

Answer 4

1. Proximal convoluted tubule

• Carbonic anhydrase combines with bicarbonate -> co2 and H20
• C02 goes into the cell
• Inverse carbonic anhydrase enzyme remakes bicarbonate from CO2 and H2P
• Bicarbonate reabsorbed in capillaries by:
  
  1. Sodium bicarbonate cotransporter
  2. Chloride bicarbonate exchanger

(Cl- re-pumped outside of the cell and Na is removed through Na+K+ ATPase)

• ATPases pump the H+ outside the cell
• Bicarb is saved in the cell

2.

• Acid-secreting cell (alpha cell) (same mechanism with the one above)
• Bicarbonate-secreting cells (beta cell; same mechanism but exactly the opposite -> sends bicarbonate into filtrate and H into the interstitium
  
  • significance: If we are trying to reduce H we increase bicarb which allows more bicarb and h to come together –> battle acidosis

3

• we don’t only save the bicarb but we can manufacture it
• glutamine – getting rid of the ammonium (leverage amino acids) to create bicarb
• that creates a titratable redox reaction

see images

Question 5

Acid-base disturbance: recall and explain disturbances in acid-base balance (including respiratory acidosis, metabolic acidosis, respiratory alkalosis and metabolic alkalosis), and explain respiratory and metabolic compensation

Answer 5

fully compensation BE and pco2 abnormal in the same direction