Acid/Base I Flashcards
Describe whether H+ and CO2 are volatile or nonvolatile acids.
H+ - nonvolatile
CO2- volatile
How is pH expressed? What is normal arterial pH?
-log[H+] or {H+]=10^-pH
normal arterial pH is 7.40
How is the {H+} determined from pH 7.28 to 7.45? What happens over wider pH? (7-7.7)
[H+]= (7.8-pH) x 100 (log free expedient
over wider range pH 7-7.7 expedient loses accuracy
[H+]=24 x PaCO2/[HCO3-]
Describe the regulation of extracellular and intracellular [H+].
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+]
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 …
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
Draw and describe figure 1.
p 1 of h/o I
What kind of acids induce strong shifts in K+?
Give examples.
mineral acids induce strong shifts in K+
HCl and KCl
What kind of acids induce weak shifts in K+?
Give examples.
weak shifts in K+ induced by organic acids
lactic acidosis (metabolic acidosis) hypercarbia (respiratory acidosis) hypocarbia (respiratory alkalosis)
Draw and describe figure 2 (H+ and K+ exchange with mineral and organic acids across the cell membrabe)
p 1
What are three major systems for maintaining arterial plasma [H+]?
chemical buffering
renal system
respiratory system
What are the main components of the chemical buffering system?
phosphate buffer system (effective in kidney)
protein buffers system (Hb, intracellular proteins)
bicarb buffer system
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?
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)
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?
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
Describe the Bronsted-Lowry concept of acids and bases.
Acid, base?]
acid- (HA) proton donor
base (A-) proton acceptor
Describe the dissociation constant Kd.
What does a small Kd mean? Large Kd?
dissociation constant Kd-
small Kd (weak acid) large Kd (strong acid)
pKd=-log(Kd)
How is pH computed?
Provide equation.
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])
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?
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
Describe buffer power, buffer range, and buffer capacity.
When is resistance to changes in H+ greatest?
What is strength of buffering directly related to?
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…)
Describe figure 5.
Figure 5, see h/o
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?
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
What are the pKd values for the following important physiological buffers?
protein
phosphate
bicarb
protein- pKd =7
phosphate- pKd =6.8
bicarb- pKd=6.1
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?
-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
What is the most important site of protein buffering?
Describe the pKd ranges.
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)
Describe the phosphate buffer system.
What is the pK?
Is this a weak or strong buffer system? why?
Where is it stronger?
(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
