3.1 Acid Base Balance

Question 1

What is the Bronstead-Lowry concept?

Answer 1

An acid is a substance that can donate protones, a base is a substance that can accept protons

Question 2

What is a weak acid?

Answer 2

Partially dissociates into HA, H+, A-

Question 3

What is a strong acid?

Answer 3

Fully dissociates into conjugate base and H+

Acid conc = 0

Question 4

pH = ?

Answer 4

pH = -log[H+]

Question 5

What does pH measure?

Answer 5

Acidity = free [H+] ions

Question 6

What does pKa measure?

Answer 6

A measure of the strength of an individual acid or its ‘acidity’

Question 7

pKA = ?

Answer 7

pKa = -log[Ka]

Question 8

What is Ka?

Answer 8

Ionisation constant or dissociation constant for HA

(HA ⇋ H+ + A-)
Large Ka = strong acid
Small Ka = weak acid
Small pKa = more acidic

Question 9

Ka = ?

Answer 9

Ka = [H+][A-] / [HA]

Question 10

What is the Henderson-Hasselbach equation?

Answer 10

pH = pKa + log([A-]/[HA])

Question 11

What is a healthy pH?

Answer 11

7.35-7.45

Question 12

What is a buffer?

Answer 12

A solution that ‘mops up’ or ‘donates’ [H+] to minimise pH changes. It is a weak acid and its conjugate salt/base.

Question 13

What happens when a strong acid is added to a buffer solution?

Answer 13

Dissociated H+ binds to conjugate base

Free [H+] change minimised

pH change is minimised

Question 14

How does bicarbonate-carbonic acid act as a buffer?

Answer 14

CO2 + H2O ⇋ H2CO3 ⇋ H+ + HCO3-

CO2 removed by lungs, buffer keeps [CO2] relatively constant (PaCO2=40mmHg)

Question 15

When does buffering work best?

Answer 15

pH = pKa ± 1-2pH

Question 16

How do phosphates work as a buffer?

Answer 16

H2PO4- ⇋ H+ + HPO4 2-

Question 17

How do proteins work as a buffer?

Answer 17

Protein (n)- ⇋ H+ + Protein (n+1)-

• dissociable side groups buffer
• Albumin important
• Haemoglobin important

Question 18

Respiratory acidosis

Answer 18

pH < 7.35
Hypovetilation
↑PCO2
Compensation = ↑HCO3

Question 19

Respiratory alkalosis

Answer 19

pH > 7.45
Hyperventilation
↓PCO2
Compensation = ↓HCO3

Question 20

Metabolic acidosis

Answer 20

pH < 7.35
↓HCO3
Compensation = ↓PCO2

Question 21

Metabolic alkalosis

Answer 21

pH > 7.45
↑HCO3
Compensation = ↑PCO2

Question 22

How is alveolar ventilation controlled?

Answer 22

Sensors - peripheral and chemoreceptors detect changes in pH and CO2
↓ (signal sent to brain)
Neural controller act to alter resp. rate and depth
↓ (to lungs)
Resp. motor output - muscles of breathing

Question 23

Regulation of blood pH by kidneys

Answer 23

Regulate [H+] production

Reabsorb nearly all filtered HCO3-

Excrete acid in urine

Regenerate HCO3- and replenish that lost in buffering