Acid-base Balance

Question 1

What are the three blood buffering systems?

Answer 1

Bicarbonate, phosphate and protein

Question 2

What is an effective range?

Answer 2

The range a buffer works in

Question 3

Where is a buffers effective range?

Answer 3

1 pH either side of its pK

Or a factor of 10 either side

Question 4

What is pK?

Answer 4

The equilibrium constant of a reaction

Question 5

What relationship does plasma [CO2] have to pCO2 in plasma?

Answer 5

Proportional

Question 6

How do you convert pCO2 to [CO2]?

Answer 6

0.03

Question 7

How can you measure blood pH?

Answer 7

Arterial blood gases

Question 8

What is the normal [HCO3 -]: [CO2]?

Answer 8

20:1

Question 9

When do buffer solutions resist pH change?

Answer 9

When [base]=[acid]

Question 10

Why is bicarbonate buffering bad?

Answer 10

pK is 6.1 which isn’t anywhere near the desired plasma pH of 7.4

Question 11

Why is bicarbonate buffering good?

Answer 11

The body is constantly creating CO2 and we can control both parts of the Henderson hasselbalch equation (through kidneys and lungs)

Question 12

What are the renal mechanisms for controlling acid- base levels?

Answer 12

Reabsorption and secretion of HCO3 -
Formation of new HCO3 -
Secretion of [H+] into tubular fluids

Question 13

What buffer systems react with the secreted H+?

Answer 13

HCO3 -: H2CO3
HPO4 2-: H2PO4 -
NH3: NH4 +

Question 14

What is carbonic anhydrase activity dependant on?

Answer 14

[H+] in the ECF

Question 15

How much of the filtered bicarbonate is reabsorbed in the proximal tubule?

Answer 15

85-90%

Question 16

When does H+ react with other buffers in the intercalated cells of the late DCT and collecting duct?

Answer 16

[HCO3 -] is low

Question 17

Why is the phosphate buffer very effective?

Answer 17

pK = 6.8, which is close to filtrate pH

Question 18

How does the phosphate buffer work?

Answer 18

HPO4 2- reacts with H+ to form H2PO4 - which is excreted in the urine

Question 19

How are bicarbonate ions removed from the cell?

Answer 19

Chloride antiporter

Question 20

What does the tubular epithelium produce from glutamine?

Answer 20

NH3 and alpha ketoglutarate

Question 21

How much does urinary excretion of ammonium salts increase during metabolic acidosis?

Answer 21

30-50 mMol/day to 300-500 mmol/day

Question 22

What part of the brain senses blood pH changes?

Answer 22

Medulla oblongata

Question 23

How does the medulla oblongata sense changes in pH?

Answer 23

CO2 passes the blood brain barrier, where it reacts with water to form H2CO3 which then dissociates into H+ and HCO3 -

Question 24

What are the two possible ways you can have metabolic acidosis?

Answer 24

Increased ECF [H+] or decreased ECF [HCO3 -]

Question 25

What can cause metabolic acidosis?

Answer 25

• Severe sepsis or shock (-> lactic acid)
• Uncontrolled diabetes -> overproduction of 3-OH- butyric acid and other keto acids
• diarrhoea -> loss of HCO3 - from GIT

Question 26

What are the two possible ways you can get metabolic alkalosis?

Answer 26

Characterised by high pH caused by increased ECF [HCO3 -] or decreased ECF [H+]

Question 27

What can cause metabolic alkalosis?

Answer 27

Excessive thiazide use
Vomiting - loss of H+ from GIT
Ingestion of alkaline antacids
Hypokalaemia