Acid-Base Physiology Flashcards
(116 cards)
1
Q
Acid-base balance is concerned with maintaining?
A
a normal hydrogen ion concentration in the body fluid
2
Q
How is normal acid-base balance achieved?
A
- by utilization of buffers in ECF and ICF
- by respiratory mechanisms that excrete CO2
- by renal mechanisms that reabsorb bicarbonate and secrete hydrogen ions
3
Q
The hydrogen ion concentration of the body fluids is extremely ____.
A
low
4
Q
As H+ concentration increases, pH _____.
A
decreases
5
Q
Do equal changes in pH reflect equal changes in H+ concentration? Why or why not?
A
No, because the relationship between the 2 is logarithmic
6
Q
What is normal pH range?
A
7.37 - 7.42
7
Q
When arterial pH is less than 7.37 it is called what?
A
acidemia
8
Q
When arterial pH is greater than 7.42 it is called what?
A
alkalemia
9
Q
What are the 3 mechanisms that contribute to maintaining pH in the normal range?
A
- buffering of H+ in both ECF and ICF
- respiratory compensation
- renal compensation
10
Q
Is arterial pH slightly acidic or alkaline?
A
alkaline (7.4)
11
Q
What are the 2 forms of blood acid?
A
- CO2 (volatile acid)
- fixed (nonvolatile)
12
Q
Why is CO2 considered a volatile acid?
A
Because it easily combines with H2O to form H2CO3 which can then be dissociated into H+ and HCO3 and travel through the blood.
In the lungs it occurs in reverse, CO2 is regenerated and then expired
13
Q
What results in the production of fixed acid?
A
Catabolism of proteins and phospholipids
14
Q
What type of acid is produced when proteins are metabolized?
A
sulfuric acid
15
Q
What type of acid is produced when phospholipids are metabolized?
A
phosphoric acid
16
Q
What are the 7 fixed acids that can be produced in certain pathophysiologic states?
A
- β-hydroxybutyric acid
- acetoacetic acid
- lactic acid
- formic acid
- salicyclic acid
- glycolic acid
- oxalic acid
17
Q
Both β-hydroxybutyric acid and acetoacetic acid are produced in what pathology?
A
diabetes mellitus
18
Q
When is lactic acid produced?
A
During strenuous exercise or when the tissues are hypoxic
19
Q
How are salicyclic acid, glycolic acid, and oxalic acid introduced into the body?
A
They are ingested
20
Q
The overproduction or ingestion of fixed acids causes what?
A
metabolic acidosis
21
Q
What is the major difference between volatile and nonvolatile acids?
A
- volatile acids do not have to be buffered
- nonvolatile acids must be buffered in the body fluids until they can be excreted by the kidneys
22
Q
What is a buffer?
A
A mixture of a weak acid and its conjugate base or a weak base with its conjugate acid
23
Q
A buffer solution resists a change in what?
A
pH
24
Q
What equation is used to calculate the pH of a buffered solution?
A
the Henderson-Hasselbalch equation
25
What is the Henderson-Hasselbalch equation?
pH = pK + log ([A-] / [HA])
26
What is [A-]?
the concentration of the base form of buffer
27
What is [HA]?
the concentration of the acid form of buffer
28
What is pK?
A characteristic value for a buffer pair.
It equals -log of the equilibrium constant (K)
29
Strong acids (HCl) are more dissociated into H+ and A-, therefore they have ____ equilibrium constants (K) and ____ pKs.
high
low
30
Weak acids (H2CO3) are less dissociated into H+ and A-, therefore they have ____ equilibrium constants (K) and ____ pKs.
low
high
31
______ curves are graphic representations of the Henderson-Hasselbalch equation.
Titration
32
At low pH (acidic) a buffer exists primarily in what form?
HA
33
At high pH (alkaline) a buffer exists primarily in what form?
A-
34
What pH equals pK what are the concentrations of HA and A-?
they are equal to each other
35
What is the significance behind the sigmoidal shape of the titration curve?
It signifies that when inside the buffering range, pH changes are minimal whereas once outside of the effective buffering range pH changes drastically when small amounts of H+ are added or removed
36
What are the major buffers of the ECF?
Bicarbonate and Phosphate
37
What is the A- form and the HA form for bicarbonate?
A- form is HCO3-
| HA form is CO2
38
What is the A- form and the HA form for phosphate?
A- form is HPO4-
| HA form is H2PO4-
39
What is the most important extracellular buffer?
HCO3-/CO2
40
The preeminence of HCO3-/CO2 as an ECF buffer is due to what 3 things?
1) The concentration of HCO3-, is high at 24mEq/L.
2) The pK of the HCO3−/CO2 buffer is 6.1, which is fairly close to the pH of ECF.
3) CO2, the acid form of the buffer, is volatile and can be expired by the lungs
41
Describe the reaction that occurs when HCl is added to the ECF
H+ combines with some of the HCO3- to form H2CO3. H2CO3 then dissociates into CO2 and H2O, both of which are expired by the lungs. The result is that blood pH does not decrease as drastically.
42
Inorganic ______ also serves as a buffer.
phosphate
43
What is the pK for HCO3-/CO2?
6.1
44
The linear portion of the titration curve for HCO3-/CO2 extends from ___ - ___.
5.1 - 7.1
45
What is the pK for HPO2/H2PO4?
6.8
46
The linear portion of the titration curve for HPO2/H2PO4 extends from ___ - ___.
5.8 to 7.8
47
Despite inorganic phosphate's effective buffering range is closer to 7.4 than bicarbonate. What are the 2 reasons what bicarbonate is the more effective buffer?
1) HCO3- is in much higher concentration
| 3) CO2 is volatile and can be expired by the lungs
48
In order to utilize organic phosphates and proteins as ICF buffers what must happen first?
H+ must cross the cell membrane
49
What are the 3 mechanisms by which H+ crosses the cell membrane?
1) in conditions where there is an excess or a deficit of CO2, CO2 can cross the cell membranes
2) In conditions where there is an excess or deficit of fixed acid, H+ can enter or leave the cell with an organic anion
3) H+ exchanges with K+ to preserve electroneutrality in other cases of excess or deficit of fixed H+
50
Although they are not present in ICF, plasma _____ also buffer H+.
proteins
51
What is the relationship between plasma proteins and Ca2+?
Negatively charged groups of plasma proteins bind to Ca2+
52
In academia, there is an excess of H+ in blood. This results in ____ H+ bound to plasma proteins, ____ Ca2+ bound, which produces a(n) _____ in free Ca2+ concentration.
increased
decreased
increase
53
In alkalemia, there is a deficit of H+ in blood. This results in ____ H+ bound to plasma proteins, ____ Ca2+ bound, which produces a(n) _____ in free Ca2+ concentration.
less
more
decrease
54
What are the 5 organic phosphates in the ICF?
- ATP
- ADP
- AMP
- glucose-1-phosphate
- 2,3-diphosphoglycerate
55
What is the pK range for the organic phosphates of the ICF?
6.0 to 7.5, which is ideal for effective physiologic buffering
56
How do intracellular proteins serve as buffers?
Becasue they contain a large number of acidic or basic groups such as −COOH/−COO- or −NH3+/−NH2
57
What is the most significant intracellular buffer?
hemoglobin
58
What are the 2 forms of hemoglobin in the blood?
oxyhemoglobin and deoxyhemoglobin
59
Which form of hemobglobin is the more effective buffer? Why?
Deoxyhemoglobin, because it has a pK of 7.9; whereas oxyhemoglobin has a pK of 6.7
60
What are the 2 major roles the kidneys play in the maintenance of normal acid-base balance?
- excretion of H+
| - reabsorption of filtered HCO3-
61
What are the 2 forms in which H+ is excreted?
1) as a titratable acid
| 2) as NH4+
62
Excretion of H+ by either mechanism is accompanied by what?
synthesis and reabsorption of new HCO3-
63
What is the purpose of the new HCO3-?
to replenish the HCO3- stores that were used for buffering
64
Describe the mechanism of HCO3- reabsorption in the proximal tubule
1) as Na+ moves from the lumen into the cell H+ moves from the cell into the lumen
2) this H+ combines with filtered HCO3- to form H2CO3
3) H2CO3 decomposes into CO2 and H20
4) CO2 and H20 readily cross the luminal membrane into the cell
5) CO2 and H2O then recombine to form H2CO3 which is converted back to H+ and HCO3-
6) the H+ is secreted by the Na+-H+ exchanger to aid in the reabsorption of another filtered HCO3- and HCO3- is transported into the blood via 2 cotransport exchangers (Na+ and Cl-)
65
The process of HCO3- reabsorption in the proximal tubule results in the reabsorption of what 2 things?
Na+ and HCO3-
66
Does the process of HCO3- reabsorption in the proximal tubule result in net secretion of H+?
No, remember the H+ is recycled across the luminal membrane to reabsorb more filtered HCO3-
67
Does the process of HCO3- reabsorption in the proximal tubule produce a change in tubular fluid pH?
Very little changes, because there is no net secretion of H+
68
In a normal person, approximately __ mEq of fixed H+ is produced daily.
The kidneys excrete ___% of this fixed acid; __% as titratable acid and __% as NH4+
50
100
40
60
69
In persons with diabetic ketoacidosis, fixed acid production is greatly ______, at __ mEq/day.
increased
500
70
To account for this increased acid production, the excretion of both titratable acid and NH4+ increases. With the greatest increase being ____ excretion.
NH4+
71
In persons with chronic renal failure, acid production is normal at 50 mEq/day. However, there is a ______ in the amount of titratable acid and NH4+ excreted.
reduction
72
______ is an increase in H+ concentration and a decrease in pH
Acidemia
73
_____ is a decrease in H+ concentration and an increase in pH
Alkalemia
74
Disturbances of blood pH can be caused by what 2 things?
- a primary disturbance of HCO3- concentration
| - a primary disturbance of PCO2.
75
Disturbance of acid-base balance are described as either _____ or ______.
metabolic or respiratory
76
What are the 4 simple acid-base disorders?
- metabolic acidosis
- metabolic alkalosis
- respiratory acidosis
- respiratory alkalosis
77
Metabolic acid-base disturbances are primary disorders involving what?
HCO3-
78
Metabolic acidosis is caused by a(n) _____ in HCO3- concentration.
decrease
79
Metabolic acidosis is can also be caused by ____ of fixed H+ in the body
gain
80
What is the respiratory compensation for metabolic acidosis?
hyperventilation
81
What is the renal correction for metabolic acidosis?
increased HCO3- reabsorption
82
Metabolic alkalosis is caused by a(n) _____ in HCO3- concentration.
increase
83
Metabolic alkalosis can also be caused by ____ of fixed H+ in the body.
loss
84
What is the respiratory compensation for metabolic alkalosis?
hypoventilation
85
What is the renal correction for metabolic alkalosis?
increased HCO3- excretion
86
Respiratory acid-base disturbances are primary disorders involving what?
CO2
87
Respiratory acidosis is caused by ___ventilation, which results in CO2 _____, ______ PCO2, and ______ pH.
hypoventilation
retention
increased
decreased
88
What is the renal compensation for respiratory acidosis?
increased HCO3- reabsorption
89
Respiratory alkalosis is caused by ___ventilation, which results in CO2 _____, ______ PCO2, and ______ pH.
hyperventilation
loss
decreased
increased
90
What is the renal compensation for respiratory alkalosis?
decreased HCO3- reabsorption
91
What is a measurement that is useful in the diagnosis of acid-base disorders?
the anion gap of plasma
92
What is the cation that is measured in an anion gap of plasma?
Na+
93
What are the 2 anions that are measured in an anion gap of plasma?
HCO3- and Cl-
94
What produces the anion gap?
The Na+ concentration is greater than the sum of the HCO3- concentration and Cl- concentration
95
Since electroneutrality is never violated what must the plasma contain to make up for this "gap"?
unmeasured anions
96
The unmeasured anions include...
- plasma proteins
- phosphate
- citrate
- sulfate
97
Metabolic ___dosis results from an increased anion gap
acidosis
98
What are 6 examples of increased anion gap metabolic acidosis?
- diabetic ketoacidosis
- lactic acidosis
- salicylate poisoning
- methanol poisoning
- ethylene glycol poisoning
- chronic renal failure
99
These 6 types of increased gap metabolic acidosis are caused by what?
excessive production or ingestion of fixed H+
100
What are 2 forms of metabolic acidosis in which no organic anion is accumulated (normal anion gap)?
- diarrhea
| - renal tubular acidosis
101
Both diarrhea and renal tubular acidosis are caused by what?
a loss of HCO3-
102
Metabolic alkalosis is caused by a(n) ______ HCO3- concentration in the blood.
increased
103
Metabolic alkalosis results in ______ pH, bicarbonate concentration, and PCO2 in arterial blood.
increased
104
Metabolic alkalosis is the result of what 3 things?
- loss of fixed H+ from the GI tract
- gain of HCO3-
- ECF volume contraction
105
What are 2 examples in which H+ is lost from the GI tract?
- vomiting
| - hyperaldosteronism
106
HCO3- is gained in metabolic alkalosis due to what 2 mechanisms?
- ingestion of NaHCO3
| - Milk-alkali syndrome
107
ECF volume contraction causes metabolic alkalosis via what 2 diuretics?
loop or thiazide
108
Respiratory acidosis is caused by ____ventilation, which results in what?
hypoventilation, which results in CO2 retention
109
CO2 retention can be caused what 3 things?
- inhibition of the medullary respiratory center
- paralysis of respiratory muscles
- airway obstruction
- failure to exchange CO2 between pulmonary capillary blood and alveolar gas
110
Respiratory acidosis results in ______ pH and _____ bicarbonate concentration and PCO2 in arterial blood.
decreased
increased
111
What 3 events occur in the generation of respiratory acidosis?
1) CO2 retention
2) buffering of the excess CO2
3) increased H+ excretion and reabsorption of new HCO3-
112
Respiratory alkalosis is caused by ____ventilation, which results in what?
hyperventilation, which results in excessive loss of CO2
113
What 3 things can cause hyperventilation?
1) direct stimulation of the medullary respiratory center
2) bypoxemia
3) mechanical ventilation
114
Respiratory alkalosis results in ______ pH and _____ bicarbonate concentration and PCO2 in arterial blood.
increased
decreased
115
What 3 events occur in the generation of respiratory alkalosis?
1) loss of C02
2) buffering in the ICF
3) decreased H+ excretion and reabsorption of new HCO3-
116
What are the respiratory compensations for respiratory acidosis and alkalosis?
There are none because respiration is the cause of the disorder
