renal physiology part 2 - acid base balance Flashcards
1
Q
what is the pH of arterial blood
A
7.45
2
Q
what is the pH of venous blood
A
7.35
3
Q
what is the average pH of blood
A
7.4
4
Q
why is venous blood more acidic than arterial blood
A
due to presence of CO2
5
Q
what is considered acidotic
A
below 7.35
6
Q
what is considered alkalotic
A
above 7.45
7
Q
what is the equation for pH using log and [H+]
A
log(1/[H+])
8
Q
an increase in [H+] does what to the pH
A
lowers the pH
9
Q
small change in pH reflect ____ changes in [H+]
A
large
10
Q
acidosis can lead to ____ of the CNS
A
depression
11
Q
alkalosis can lead to ____ of the peripheral and later the central nervous system
A
overexcitability
12
Q
what are some examples of changes in the nervous system due to alkalosis
A
pins and needles (sensory) muscle spasms (motor) - fatal if respiratory
13
Q
change of pH of bodily fluids will alter the ______ of proteins causing a knock on effect on ____
A
secondary structure
enzymes
14
Q
increased plasma [H+] ______ K+ secretion in renal tubules
A
decreases
15
Q
what are the 3 ways in which H+ is added to the bodily fluids
A
carbonic acid formation
inorganic acids produced during breakdown of nutrients
organic acids resulting from metabolism e.g. lactic acid
16
Q
what is a strong acid
A
dissociates completely in solution
17
Q
what is a weak acid
A
partially dissociates in solution
18
Q
what is the first line defence to any change in pH
A
buffer systems
19
Q
what does a buffer system consist of
A
one substance can yield a H+ ion if [H+] decreases
one substance can bind to H+ if [H+] increases
20
Q
what is the equation of a buffer solution
A
HA H+ + A-
21
Q
what is the base in the buffer solution
A
A-
22
Q
what is the undissociated acid in the buffer solution
A
HA
23
Q
what is the proton in the buffer solution
A
H+
24
Q
if H+ is added to a buffer system equilibrium shifts to the ….
why?
A
left
H+ is mopped up by A- leading to formation of more HA
[HA] rises, [A-] falls
25
if base B- is added to a buffer system, equilibrium shifts to the....
why?
right
base is tied up by combining with H+ allowing more HA to dissociate
[HA] falls, [A-] rises
26
at equilibrium what is the equation for K (dissociation constant) of a weak acid
[H+]{A-}/[HA]
27
what is the henderson hasselbach equation
pH = pK + log[A-]/[HA]
28
what is the most important physiological buffer system in the body
CO2 - HCO3 buffer
29
what enzyme converts CO2 + H20 --> H2CO3 (carbonic acid)
carbonic anhydrase
30
what does carbonic acid dissociate to
H+ + HCO3-
31
what is the pK for carbonic acid
6.1
32
what is normal arterial PCO2
40mmHg
33
what is normal [HCO3-]
24mmol/L
34
what controls [HCO3-]
kidneys
35
what controls PCO2
lungs
36
how can the kidneys control HCO3- (2 ways)
| what do both these processes depend on
variable reabsorption of filtered HCO3
and kidneys can add new HCO3 to the blood
- both depend on H+ secretion into the tubule
37
true/false
| the concentration of bicarbonate can be higher in the renal vein than in the renal artery
true
38
where is bicarbonate reabsorbed
PCT
39
what is needed in order to reabsorb bicarbonate ions
hydrogen ions
40
how is bicarbonate reabsorption started
H2O and CO2 in the epithelial cell of the PCT form carbonic acid which then dissociates into HCO3- and H+
41
how does the bicarbonate get from the epithelial cell into the interstitial fluid
Na+/HCO3- co transporter
42
where does the H+ ion (the other dissociate) go and how
goes into the filtrate via the Na+/H+ antiporter
43
what happens to this H+ ion when it goes into the tubular fluid
binds with a bicarbonate already in the filtrate to form carbonic acid
44
how does this carbonic acid formed get back into the epithelial cell
breaks down to form CO2 and H20 which diffuses across apical membrane into cell
45
what drives the secretion of H+ through the apical membrane
CO2 partial pressure
46
why is the reabsorption of HCO3 known as unorthodox reabsorption
the same HCO3- doesn't cross the epithelium
47
what does secreted H+ bind to when bicarbonate concentration in tubular fluid is low
phosphate - the next most plentiful buffer
48
how does excretion of titratable acid (phosphoric acid) and ammonia increase the pH of plasma
H+ has been excreted with a net gain of a new bicarbonate ion
49
for every hydrogen ion secreted, how many new bicarbonate ions are made and absorbed into blood
one
50
if 40mmol of titratable acid was passed out in the urine, how much new bicarbonate has been created
40mmol
51
how do you see how much [H+] has been secreted
titrating H+ excreted as phosphoric acid against a strong base
52
if a patient is very acidotic what happens
H+ binds to ammonia to form an ammonium ion which is excreted
53
what is the chemical from the liver that is broken down to give ammonia in acidotic conditions
glutamine
54
how does ammonia get into the tubular fluid from the epithelial cell
diffusion - it is a gas
55
what is the enzyme that breaks down glutamine
glutaminase
56
can H+ excreted as ammonium ions be titrated and therefore measured
no
57
for every ammonia acid created how many new bicarbonate ions are generated
1
58
what 3 things does H+ secretion do
drives the reabsorption of bicarbonate ions
forms acid phosphate
makes an ammonium ion
59
what regenerates buffer stores and rids the body of an acid load
excretion of titratable acid and ammonium ions
60
what is the range of [HCO3-]
23-27 (close to 25)
61
what is the range of PCO2
35-45 (close to 40)
62
what is compensation
restoration of pH irrespective of what happens to the plasma concentration of bicarbonate and PCO2
63
what is correction
restoration of pH and the PCO2/bicarbonate back to normal
64
what happens first in acid base disturbance
compensation
65
what 2 processes are involved in the immediate buffering of a pH change
immediate dilution of the acid or base in the ECF
| buffers present in the blood and ECF
66
what buffers are present in the blood
Hb and HCO3-
67
what buffers are present in the ECF
HCO3-
68
deoxygenated blood has a higher/lower affinity for H+
higher
69
acidosis will ____ the plasma levels of bicarbonate
reduce
70
what happens when the stores of buffer are depleted (happens quickly)
up to the kidney to replete the stores
71
using the HH equation, a blood gas analyser can measure the __ and ___ allowing the conc of ____ to be measured and the results are shown on a ____
pH and PCO2
bicarbonate ions
davenport diagram
72
what causes respiratory acidosis
retention of CO2 in the body - hypoventilation
73
give 5 conditions that would result in respiratory acidosis
```
chronic bronchitis
chronic emphysema
airway restriction
chest injury
respiratory depression - morphine/GA
```
74
CO2 retention drives the equilibrium to the
right
75
acute retention of CO2 causes levels of H+ to ___ and levels of HCO3- to ____
both rise
76
what would indicate uncompensated respiratory acidosis
pH < 7.35
| PCO2 > 45
77
true/false
there is virtually no extracellular buffering in respiratory disorders. since the cause is respiratory the kidneys must compensate
true
78
CO2 retention stimulates what
H+ secretion into the filtrate
79
are any bicarbonate ions excreted in the urine in acidosis
no - all filtered HCO3- is reabsorbed as H+ is secreted into the urine
80
what happens as H+ continues to be secreted
TA and NH4+ are generated which means new bicarbonate ions are added to the blood and acid is excreted out in the urine
81
why does [HCO3-]plasma rise in respiratory acidosis
the condition itself - shifting the equation to the right due to high levels of CO2
and as a result of renal compensation introducing new bicarbonate into the blood
82
what is involved in correction of respiratory acidosis
lowering the PCO2 by restoration of normal ventilation
83
what causes respiratory alkalosis
excess removal of CO2 from the body - hyperventilation
84
give some examples of when respiratory alkalosis might occur
fever
panic/hysterical overbreathing
low inspired PO2 at high altitude leading to hyperventilation
brainstem damage
85
excessive CO2 removal drives equilibrium to the
left
86
excess removal of CO2 from the body causes levels of H+ to ____ and levels of HCO3- to ___
both fall
87
what would indicate uncompensated respiratory alkalosis
pH > 7.45
| PCO2 < 35
88
how does the kidney compensate for respiratory alkalosis
lack of CO2 in the plasma causes a decrease in H+ secretion meaning [H+] goes up
and further lowers the amount of bicarbonate in the plasma
89
is bicarbonate secreted in the urine in respiratory alkalosis
yes - secretion of H+ into the tubular fluid is insufficient to reabsorb all of the bicarbonate so even though it is lower in level than normal some is excreted and the urine is alkaline
90
what does correction of respiratory alkalosis require
restoration of normal ventilation
91
what is the most common of the acid base imbalances
metabolic acidosis
92
what causes metabolic acidosis
excess H+ from any source other than CO2
93
what are some examples of causes of metabolic acidosis
ingestion of acids or acid producing food
excessive production of H+ e.g. lactic acid during exercise
excessive loss of base e.g. diarrhoea
94
what does metabolic acidosis do to the levels of [H+] and [HCO3-] in the body
increases [H+]
| decreases [HCO3-]
95
why is [HCO3-] decreased in metabolic acidosis
either due to loss from the body
| or depleted as a result of buffering excess
96
what indicates uncompensated metabolic acidosis
pH < 7.35
| HCO3- low
97
what is involved in the compensation of metabolic acidosis
respiratory compensation - decrease in plasma pH stimulates peripheral chemoreceptors to increase ventilation and blow off CO2
98
blowing off CO2 moves the equilibrium to the
left
99
respiratory compensation by blowing off CO2 causes H+ to ____ and HCO3- to ____
both decrease
100
what is involved in correction of metabolic acidosis
filtered HCO3 is very low and readily reabsorbed
H+ secretion continues and produces TA and NH4+ generating new HCO3-
kidneys lose H+ and gain HCO3-
101
correction of metabolic acidosis by the kidneys causes the urine to become ___
acidic - acid load is excreted
102
why is respiratory compensation essential in metabolic acidosis
acid load cannot be excreted immediately
103
how is metabolic alkalosis caused
excessive loss of H+ from the body
104
give some examples of situations that would cause metabolic alkalosis
loss of HCl from stomach e.g. vomiting
ingestion of alkali or alkali producing food e.g. antacids
aldosterone hypersecretion
105
metabolic alkalosis causes [H+] to ____ and [HCO3-] to ____
H+ fall
| HCO3- to rise
106
how does metabolic alkalosis cause HCO3- to rise
either due to loss of H+ or addition of base
107
what would indicate uncompensated metabolic alkalosis
pH > 7.45
| HCO3- high
108
how does increased pH from a metabolic source cause respiratory compensation
peripheral chemoreceptors detect increased pH and slow ventilation to retain CO2 (PCO2 rises)
109
CO2 retention shifts the equilibrium to the
right
110
CO2 retention causes [H+] to ____ and [HCO3-] to ____
H+ rises
| HCO3- also rises
111
what does renal correction for metabolic alkalosis involve
filtered HCO3- load is so large compared to normal that not all of the filtered HCO3- is reabsorbed so is excreted
no TA or NH4+ is generated, no new bicarbonates are formed
[HCO3-] of blood returns to normal
112
renal correction of metabolic alkalosis causes urine to be ....
alkaline - bicarbonate is excreted
113
what is harder to compensate for: respiratory acidosis or metabolic acidosis
respiratory acidosis - renal compensation takes longer than respiratory compensation
