Acid-Base Balance

Question 1

majority of CO2 in blood

Answer 1

HCO3 - (90%) of total CO2 in whole lood

Question 2

proteins that can bind CO2

Answer 2

• carbamino CO2 (plasma proteins) = 3%

- carbamino CO2 (Hb) = 2-10%

Question 3

maintenance of normal plasma pH

Answer 3

- first defense: blood buffers
second defense: lungs blow off CO2(gas)
- third defense: kidneys
 > reclaim HCO3-
 > generate new HCO3-
 > excrete all excess H+

Question 4

the role liverp lays in HCO3- retention

Answer 4

• urea cycle eliminates nitrogen from protein catabolism; urea = ammonia and bicarb
• in acidosis, urea cycle slows down to conserve HCO3-

Question 5

how does the kidney generate new bicarbonate?

Answer 5

glutamine is catabolized to produce new HCO3-

Question 6

how do kidneys excrete acid?

Answer 6

• Na+/H+ exchange
• H+-ATPase pumps out H+ from formation of carbonic acid
• secreted H+ reacts with:
  > filtered bicarb to reclaim bicarb
  > filtered fixed acids to eliminate acid in urine
  > secredted ammonia to eliminate acid in urine

Question 7

T or F. weak acids do not fully dissociate in H2O

Answer 7

• T

- they can buffer H+ generated from cell metabolism

Question 8

___ determines buffer eqm and __ on response to a change in concentration of salt or _____

Answer 8

pka, pH, acid

Question 9

what determines pH of a buffer solution?

Answer 9

RATIO (not indiv values) of salt/acid
> Henderson-Hasselbach eqn

• acid form is dissolved CO2; alpha = solubility coefficient of CO2 gas; P = pressure ; in denominator
• normal ratio is 20/1

Question 10

pH range compatible with life

Answer 10

6.8 to 8.0

20/1 applies to 7.35 to 7.45

Question 11

Hb buffer

Answer 11

• major red cell buffer (essentially hides acids in cells before it gets to lungs)
• globin chain has one histidine residue that is normally liganded to the heme iron in oxyHb (HbO2)
• histidine pKa = 6.7 in HbO2
  = 7.9 in deoxy Hb

Question 12

how do we move H+ in and out of red cells

Answer 12

isohydric shift; shifting H+ from Hb to bicarbonate within RBC
- between Hb and bicarb buffer

Question 13

other RBC buffers

Answer 13

• HP4O2-
• Hb-
• protein buffers work best at their pI
• blood buffers are efficient
  > vneous blood pH only 0.02 < arterial blood pH

Question 14

metabolic acidosis

Answer 14

• renal prob

- decrease bicarb

Question 15

respiratory acidosis

Answer 15

• lung prob

- increase in dissolved CO2 (denominator)

Question 16

compensation for primary disturbances in aci-base balance

Answer 16

• attempt to normalize pH by normalizing the ratio of [HCO3-]/dCO2]
• if successful = ratio will return to 20:1 and pH = 7.4 but [HCO3-] and [dCO2] will be abnormal