Acid/Base I

Question 1

Describe whether H+ and CO2 are volatile or nonvolatile acids.

Answer 1

H+ - nonvolatile

CO2- volatile

Question 2

How is pH expressed? What is normal arterial pH?

Answer 2

-log[H+] or {H+]=10^-pH

normal arterial pH is 7.40

Question 3

How is the {H+} determined from pH 7.28 to 7.45? What happens over wider pH? (7-7.7)

Answer 3

[H+]= (7.8-pH) x 100 (log free expedient

over wider range pH 7-7.7 expedient loses accuracy
[H+]=24 x PaCO2/[HCO3-]

Question 4

Describe the regulation of extracellular and intracellular [H+].

Answer 4

regulation of intracellular [H+] of crucial importance (protein enzymes are located mostly intracellularly)

extracellular [H+] in the plasma that is operated on by the kidneys and lungs

regulation of extracellular [H+] helps regulate intracellular [H+]

Question 5

The regulation of extracellular [H+] helps regulate intracellular [H+].

Proton transfer from intracellular space to interstitial space is…

Proton transfer form IS space to P space is…

Proton transfer from P space to tubular space is…

Bicarb reabsorption from tubular space to P space…

Proton transfer (as CO2) from P space to alveolar air is …

Answer 5

Proton transfer from intracellular space to interstitial space is… slow

Proton transfer form IS space to P space is…fast

Proton transfer from P space to tubular space is…slow

Bicarb reabsorption from tubular space to P space…slow

Proton transfer (as CO2) from P space to alveolar air is … fast

Question 6

Draw and describe figure 1.

Answer 6

p 1 of h/o I

Question 7

What kind of acids induce strong shifts in K+?

Give examples.

Answer 7

mineral acids induce strong shifts in K+

HCl and KCl

Question 8

What kind of acids induce weak shifts in K+?

Give examples.

Answer 8

weak shifts in K+ induced by organic acids

lactic acidosis (metabolic acidosis)
hypercarbia (respiratory acidosis)
hypocarbia (respiratory alkalosis)

Question 9

Draw and describe figure 2 (H+ and K+ exchange with mineral and organic acids across the cell membrabe)

Answer 9

p 1

Question 10

What are three major systems for maintaining arterial plasma [H+]?

Answer 10

chemical buffering
renal system
respiratory system

Question 11

What are the main components of the chemical buffering system?

Answer 11

phosphate buffer system (effective in kidney)
protein buffers system (Hb, intracellular proteins)
bicarb buffer system

Question 12

Describe the renal system’s role in maintaining arterial plasma [H+]. Slow/fast? How much H+ is excreted a day (as what?) How much bicarb is reabsorbed?

Answer 12

slowly responding system

kidney excretes 50mmol H+ per day as H+, NH4+ an H2PO4-
(urine is acidic)

kidney reabsorbs 5,500 mmol HCO3- per day
([HCO3-] is at renal plasma threshold)

Question 13

Describe the respiratory system’s role in maintaining arterial plasma [H+]. Is it rapid/slow response? How much does lung ventillate a day? How does this compare to kidney?

Answer 13

rapidly responding system

lung ventilates off 13,000 mmol CO2 per day
(potential H+ via CO2 hydration reaction)

lung has 150x capacity of kidney
(13,000mmol-5,500mmol)/50mmol

Question 14

Describe the Bronsted-Lowry concept of acids and bases.

Acid, base?]

Answer 14

acid- (HA) proton donor

base (A-) proton acceptor

Question 15

Describe the dissociation constant Kd.

What does a small Kd mean? Large Kd?

Answer 15

dissociation constant Kd-

small Kd (weak acid)
large Kd (strong acid)

pKd=-log(Kd)

Question 16

How is pH computed?

Provide equation.

Answer 16

pH= pKd + log ([base]/[acid])
any increase or decrease of base can be balanced by an increase or decrease in acid

its the base/acid ratio that is critical, not absolute concentrations of acid/base

See figure 3

dissociation K= [H+][A-]/[HA]
pH=pK +log10 ([base]/[acid])

Question 17

Describe principles of titatration.

What happens if acid and base conc. are identical?

When does system work best?

What happens if you add H ion in a buffered system, how is base and acid affected? How does pH change?

Describe slope further away from pK, what does this mean?

Answer 17

Figure 4. (relisten?)

if acid and base conc. are identical then log of 1 =0 so pH=pKa - this is shown at point A (this is pK)

system works best when environmental pH centered on pK for that system

raise H, eat up more base, have CH3COOH but only free proton conc. contributes to pH

further from pK slope is less, means as you change proton conc. you don’t protect against as well bc slope is shallow…buffer range

Question 18

Describe buffer power, buffer range, and buffer capacity.

When is resistance to changes in H+ greatest?

What is strength of buffering directly related to?

Answer 18

buffer power- resistance to changes in [H+] is greatest when operating pH matches pKd

buffer range -buffering ability still persists within one pH unit on either side of pKd

buffer capacity- strength of buffering is directly related to conc. of buffer components. (+/-1 pH unit on either side of pK bc you still have some slope here…)

Question 19

Describe figure 5.

Answer 19

Figure 5, see h/o

Question 20

Compare titration curves for acids with different pKd values (Figure 6).

If pK of system is below environmental pH will most of it be found in its acid or base form?

What substance is mostly found in acidic form?

Answer 20

each system has its own unique pK
undissociated acid form (HA) favored when operating pH is less than pKd

undissociated base form (A-) is favored when pH is greater than pKd

balance between acid and base forms when operating pH=pKd

if pK of system is below environmental pH, more is found in the BASE form
Exception: ammonium- since pK above plasma pH, most found in acid form

Question 21

What are the pKd values for the following important physiological buffers?

protein
phosphate
bicarb

Answer 21

protein- pKd =7
phosphate- pKd =6.8
bicarb- pKd=6.1

Question 22

Describe the most important blood borne protein buffer.

Which protein has highest conc. for any protein in blood?

Is this protein classified as extracellular or intracellular?

Answer 22

-large fraction of all chemical buffering is attributed to intracellular proteins

-Hb is the most important blood borne protein buffer
(Hb has the highest conc. for any protein in the blood)
(Hb is classified as extracellular despite its intracellular location within RBCs

Question 23

What is the most important site of protein buffering?

Describe the pKd ranges.

Answer 23

the imidazole group of histadine residues is the most significant site of protein buffering of H+ (HbH+ to H+ and Hb)

pKd values of diff imidazole groups vary from 5.3 to 8.3

many imidazole groups have pKd values within physiological range (pKd=7.4 +/- 1)

Question 24

Describe the phosphate buffer system.

What is the pK?

Is this a weak or strong buffer system? why?
Where is it stronger?

Answer 24

(weak)
H2PO4- to H+ and HPO42-

pKd=6.8 (within physiological range of pH =7.4)

weak buffer system in the plasma since the buffer capacity is low
-low plasma conc. of HPO42-

stronger buffer system in kidney (bc in kidney its counter current multipied)
renal environment is more acidic (pH is less than 7.4)
higher conc. of HPO42-

*is countercurrent multipied, changes capacity

Question 25

Describe the bicarbonate buffer system. (Figure 7)

Answer 25

Figure 7.
CO2 is the acid bc it hydrates to free proton and bicarb base.

Henderson H-
pK+ log 10 ([HCO3-]/[CO2]

Question 26

Is the bicarb buffer system open or closed?

How is CO2 and H+ connected to the environment?

Answer 26

bicarb system imp. not bc pK in bad position but bc bicarbonate buffer system is an open system (open nature of bicarb buffer system more than compensates for its low pKd (as ventilate CO2 goes into environment)

CO2 directly linked to environment via the lungs (ventilation)
H+ is directly linked to the environment via the kidneys (excretion, urination)

steady state balance