Session 5 - Acid-Base Balance

Question 1

What is the normal range for plasma pH?

Answer 1

7.35-7.45

Question 2

What is a plasma pH greater than 7.45 known as?

Answer 2

Alkalaemia

Question 3

What is a plasma pH less than 7.35 known as?

Answer 3

Acidaemia

Question 4

How does alkalaemia increase neuronal excitability? What does it therefore lead to?

Answer 4

Alkalaemia lowers free calcium by causing Ca2+ ions to come out of solution. This therefore increases neuronal excitability and can lead to paraesthesia and tetany.

Question 5

What effect does acidaemia have on plasma potassium ion concentration?

Answer 5

Acidaemia increases plasma potassium concentration (hyperkalaemia). This effects excitability, particularly of cardiac muscle, leading to arrhythmias.

Question 6

What is the reaction in the CO2/HCO3- buffer system?

Answer 6

CO2 + H2O H+ + HCO3-

Question 7

Plasma pH depends on what ratio?

Answer 7

Ratio of [HCO3-] to pCO2. More CO2 drives the reaction to produce H+, more HCO3- drives the reaction to remove H+.

Question 8

What two organs work together to control plasma pH?

Answer 8

Lungs and kidneys

Question 9

How do the kidneys control pH?

Answer 9

Variable recovery of bicarbonate and active secretion of hydrogen ions.

Question 10

How to the lungs control pH?

Answer 10

Control of pCO2 and pO2.

Rate of ventilation controlled by chemoreceptors.

Question 11

How does acidosis cause hyperkalaemia?

Answer 11

High concentration of H+ in blood.
Increase in movement of H+ into cells.
Therefore an increase in K+ movement out of cell (reciprocal cation shift).
Decreased potassium excretion in the distal nephron.
Hyperkalaemia.

Question 12

How does alkalosis cause hypokalaemia?

Answer 12

Decreased H+ concentration in plasma. 
More H+ ions move out of cells.
More K+ ions move into cells. 
Enhanced excretion of potassium in distal nephron.
Hypokalaemia.