Acid base balance

Question 1

What is the normal pH of arterial blood?

Answer 1

7.45

Question 2

What is the normal pH of venous blood?

Answer 2

7.35

Question 3

What can acidosis lead to?

Answer 3

CNS depression

Question 4

What can alkalosis lead to?

Answer 4

Over excitation of PNS and CNS

Question 5

What generates H+ in the body?

Answer 5

Metabolism

Question 6

What is the difference between a strong and weak acid?

Answer 6

Strong acid dissociates fully in solution

Question 7

What is a buffer system?

Answer 7

Two substances of which one can absorb free H+ and one can donate it

Question 8

What happens if more H+ is added to a system?

Answer 8

A- mops it up to generate more HA (conjugate acid). Buffering.

Question 9

What happens if more base is added to a system?

Answer 9

More HA dissociates leading to an increase in H+. Buffering.

Question 10

How do you calculate the pH of a substance?

Answer 10

pK + log[A-]/{HA]. [A-]=base, [HA]=acid

Question 11

What is the most important physiological buffer system?

Answer 11

CO2-HCO3 buffer

Question 12

Describe the CO2-HCO3 buffer system

Answer 12

H2O+CO2 H2CO3 H+ + HCO3-

Question 13

What is the acid and base in the CO2-HCO3 buffer system?

Answer 13

Acid- H2CO3

Base- HCO3-

Question 14

What role do the kidneys play in the CO2-HCO3 buffer system?

Answer 14

Variable reabsorption of HCO3

Add new HCO3 to the system

Question 15

How is HCO3 reabsorbed at the luminal membrane?

Answer 15

Changed back to H2O and CO2 then reabsorbed.

Question 16

What happens to HCO3 once it’s in the epithelial cells?

Answer 16

Converted from H2O and CO2 back to HCO3

Question 17

How does HCO3 get out of the epithelial cells?

Answer 17

NaHCO3 cotransporter.

Question 18

How can the kidneys generate more HCO3?

Answer 18

By allowing free H+ to combine with phosphate and being excreted when HCO3 is low thus allowing excretion of H+ without HCO3 loss.

Question 19

How much acid is excreted a day combined with phosphate?

Answer 19

40mmol/day

Question 20

What other molecule can be used as a buffer for H+?

Answer 20

Ammonia

Question 21

What parameters need to be filled for someone to be near normal acid base balance?

Answer 21

Plasma pH close to 7.4 (7.35-7.45)
HCO3- close to 25mmol/l (23-27)
Arterial pCO2 close to 40mmHg (35-45)

Question 22

What is the difference between compensation and correction?

Answer 22

Compensation- restore pH to 7.4 at detriment of HCO3 and pCO2
Correction- Restore all three to normal

Question 23

What are the four disturbances that can affect the acid-base balance?

Answer 23

Resp acidosis
Resp alkalosis
Met acidosis
Met alkalosis

Question 24

What is immediate buffering?

Answer 24

Buffering of change immediately with HCO3 in the blood etc.

Question 25

How long can immediate buffering last for?

Answer 25

Not very long

Question 26

What can cause resp acidosis?

Answer 26

Retention of CO2 in the lungs

Question 27

What happens in resp acidosis?

Answer 27

Equal increase in H+ and HCO3-

Question 28

What indicates uncompensated resp acidosis?

Answer 28

pH<7.35 and pCO2>45

Question 29

How is resp acidosis compensated for?

Answer 29

Excretion of H+ with P in urine and all HCO3 reabsorbed

Question 30

What causes resp alkalosis?

Answer 30

Excessive removal of CO2

Question 31

What happens in resp alkalosis?

Answer 31

Both H+ and HCO3 fall

Question 32

What indicated uncompensated resp alkalosis?

Answer 32

pH>7.4 and pCO2<35

Question 33

How is resp alkalosis compensated for?

Answer 33

Decreased H+ secretion and increased HCO3 secretion

Question 34

What causes met acidosis?

Answer 34

Excessive H+ from any source other than resp: Exercise (lactic acid) Loss of base (diarrhoea)

Question 35

What indicated uncompensated met acidosis?

Answer 35

pH<7.35 and HCO3 very low

Question 36

How is met acidosis compensated for?

Answer 36

Increase ventilation which removes CO2 thus losing H+ and HCO3. HCO3 reabsorbed from urine and H+ secreted to produce new HCO3.

Question 37

What causes met alkalosis?

Answer 37

Hacessive loss of H+ from the body: Vomiting Aldosterone hypersecretion

Question 38

What indicated met alkalosis?

Answer 38

pH>7.45 and HCO3 very high

Question 39

How is met alkalosis compensated for?

Answer 39

Ventilation decreased giving rise to both H+ and HCO3. Lots of HCO3 filtered and most not reabsorbed.

Question 40

How long does extracellular buffering of H+ take to start working in met disturbances?

Answer 40

Immediatly

Question 41

How long does resp buffering of H+ start to take working in met disturbances?

Answer 41

Minutes

Question 42

How long does intracellular buffering (proteins etc) of H+ start to take working in met disturbances?

Answer 42

2-4 hours

Question 43

How long does renal buffering of H+ take to start working in met disturbances?

Answer 43

Days-weeks

Question 44

How long does extracellular buffering take to start to start working in resp disturbances?

Answer 44

Immediately but not very effective.

Question 45

How long does renal buffering take to start working in resp disturbances?

Answer 45

Hours to days