Acid-base balance Flashcards
1
Q
define pH:
A
-ve log of H+ conc (mol/L)
pH = -log [H+]
[H+] = 10 ^ -pH
2
Q
normal ECF values:
A
~7.4
cell values at 7.2
(60 nM)
3
Q
arterial blood pH:
A
7.4
4
Q
venous blood pH:
A
7.36
5
Q
normal arterial pH maintained btw:
A
7.35 - 7.45
6
Q
acidotic and fatal pH:
A
<7.35 acidotic
<6.8 is fatal
7
Q
alkalotic and fatal pH:
A
> 7.45 alkalotic
>8 is fatal
8
Q
reactions increasing net body acid: list (5)
A
- aerobic metabolism of carbs, fats, neutral aa to
- sulphur w aa
- aa w cationic side groups
- phospholipids, phosphorylated proteins
- incomplete metabolism of carbs during anaerobic exercise
9
Q
reactions increasing net body acid: aerobic metabolism of carbs, fats, neutral aa to produce-
A
CO2 in CAC
10
Q
reactions increasing net body acid: sulphur w aa produce-
A
produced H2SO4
11
Q
reactions increasing net body acid: aa w cationic side groups produce-
A
produce urea and H+
12
Q
reactions increasing net body acid: phospholipids, phosphorylated proteins produce-
A
H2PO4-
13
Q
reactions increasing net body acid: incomplete metabolism of carbs during anaerobic exercise produce-
A
produce lactate and H+
14
Q
major fuel source in diabetics:
A
- fats for ATP prod
- acetoacetic acid, ß-hydroxybutyric acid (ketoacids aka ketone bodies) also produced
- true in starvation
15
Q
reactions increase net body base: list (2)
A
- breakdown aa w anionic side groups
- metabolism of organic anions (eg. citrate, ascorbate)
16
Q
reactions increase net body base: breakdown aa w anionic side groups produce-
A
- consumes H+
17
Q
reactions increase net body base: metabolism of organic anions (eg. citrate, ascorbate) produce-
A
- produces HCO3-
18
Q
base/acid excess: diet rich in meat/protein vs. vegetarian
A
protein: excess acid (non-carbonate, non-volatile)
veggie: slight base excess
19
Q
loss of: vomiting
A
loss of HCl (acid)
20
Q
loss of: diarrhoea
A
loss of NaHCO3 (base)
21
Q
pH homeostasis: maintained by list (3) and time taken
A
- immediate neutralisation of added base/acid by buffers (secs)
- continuous controlled removal of CO2 by lungs (mins)
- maintenance of ECF [HCO3-] by kidneys (hrs to days)
22
Q
pH homeostasis: long term features
A
- homeostatic control of ECF pH requires balancing endogenous (from aerobic respiration)
- exogenous (food) input of acid and base w their output from body
- instantaneous pH regulation vital
- physiological processes take time
- chemical buffering is interim measure to ensure pH remains in narrow range
23
Q
buffering: acids defined as
A
H+ donors
24
Q
buffering: bases defined as
A
H+ acceptors
25
conjugate acid base equation:
acid base + H+
26
buffering: what acts as pH buffers
conjugate acid/base pairs of weak acids
27
acid dissociation constant (equilibrium constant) equation
Ka= [base] x [H+] ÷ [acid]
28
ECF buffers: list (3)
- HCO3-/ CO2
- proteins esp haemoglobin, albumin
- H2PO4-/ HPO42-
29
which buffer accounts for 90% of ECF's buffering capacity btw pH 7.2-7.6
HCO3-/ CO2
30
ECF buffers: haemoglobin sig
- next most important after HCO3-/ CO2
- histidine residues act as buffers in haemoglobin
- 36 in each haemoglobin
- buffers btw pKa values of 6.5
- haemoglobin buffers acid derived from CO2
- therefore CO2 produced by cellular metab buffered by haemoglobin while being transported by blood to lungs for excretion
31
bicarbonate buffering sys: what is buffered in this sys
H+ from non-carbonate acids
32
bicarbonate buffering sys: equation
H2O + CO2 H2CO3 HCO3- + H+
33
bicarbonate buffering sys: HCO3-/ CO2 sys highly effective coz (2)
- conc of HCO3- in plasma is high (24mM)
| - operates as regulated open sys, kidney controlling [HCO3-] and respiratory sys controlling plasmaCO2
34
controlled removal of CO2:
- by respiratory sys
| - within body pCO2 controlled by resp sys in response to arterial (eventually CSF) pH
35
pH stabilisation in body: continued input of acid
- HCO3- continually consumes to buffer non-carbonic acids
36
pH stabilisation in body: role of kidney list (3)
- HCO3- filtered into kidney tubules reabsorbed, not lost to body
- additional HCO3- molecules created by kidney tubule cells, transported into plasma to replenish alkaline store
- non-carbonate acids r excreted
37
pH stabilisation in body: to increase body HCO3- lvls
- organic anions (bases) added to body r metabolised to HCO3-
38
pH stabilisation in body: excess HCO3- removed by
- allowing appropriate amount of HCO3- filtered into kidney tubule to be excreted
39
reabsorption of filtered HCO3-: conc of HCO3- higher in plasma or ECF?
plasma
| - 24mM
40
reabsorption of filtered HCO3-: how much filtered HCO3- reabsorbed?
almost completely
41
reabsorption of filtered HCO3-: depends on? and locations
- from tubular fluid active transport of H+ into tubular fluid
- LUMINAL Na/H antiport in proximal tubule and luminal H+ pump in collecting duct
42
reabsorption of filtered HCO3-: most of reabsorption occurs in
proximal tubule
43
excretion of titratable (non-carbonic) acid/ HCO3- regeneration: how is H+ transported into lumen
- actively transported
| - bound by basic form of non-carbonate buffers (mainly HPO4 2-)
44
excretion of titratable (non-carbonic) acid/ HCO3- regeneration: HCO3- generated in cell?
- to produce H+ for export = net increase in HCO3-
| - 'new' HCO3- ion transported into blood
45
excretion of titratable (non-carbonic) acid/ HCO3- regeneration: HCO3- reabsorption, location
- tranporter on LUMINAL membrane
- Na/H antiport in proximal tubule
- also proton pump in collecting duct
46
excretion of titratable (non-carbonic) acid/ HCO3- regeneration: luminal Na/H antiport only secrete at?
- against modest pH grad so tubular fluid (proximal tubule) not fall below 6.8
47
excretion of titratable (non-carbonic) acid/ HCO3- regeneration: H+ pump can produce tubular fluid pH low as, where?
4.5 in collecting duct
48
excretion of titratable (non-carbonic) acid/ HCO3- regeneration: titratable acids have pKa values btw, sig?
- 4.5-7.4 (pH of glomerular filtrate)
| - effective buffers at pH of urine
49
excretion of titratable (non-carbonic) acid/ HCO3- regeneration: list titratable acids (4) and key
- urate
- creatine
- beta-hydroxybutarate
- HPO4 2-
will bind to H+ in tubular fluid
50
excretion of titratable (non-carbonic) acid/ HCO3- regeneration: pKa- urate
5.8
51
excretion of titratable (non-carbonic) acid/ HCO3- regeneration: pKa- creatine
5
52
excretion of titratable (non-carbonic) acid/ HCO3- regeneration: pKa- betahydroxybutarate
4.8
53
excretion of titratable (non-carbonic) acid/ HCO3- regeneration: pKa- HPO4 2-
6.8
54
excretion of ammonium (NH4+)/ HCO3- regeneration: glutamine features
- made from liver, mm and gut
- taken up from blood into proximal tubule
- neutral aa w 2 nitrogenous side groups
55
excretion of ammonium (NH4+)/ HCO3- regeneration: glutamine converted into
- å ketoglutarate (AKG2-) w 2x NH4+ produced -> glucose (will consume a H+ in this step)
56
excretion of ammonium (NH4+)/ HCO3- regeneration: glutamine products excreted
- NH4+ ions excreted in urine
| - 2x HCO3- (which provided H+ ends up in blood)
57
excretion of ammonium (NH4+)/ HCO3- regeneration: sig of excreting NH4+
- or will be converted into urea in liver= releasing 2x H+ cancelling out HCO3- gained by ECF
58
excretion of ammonium (NH4+)/ HCO3- regeneration: NH4+ is it titratable? and pKa
- NH4+ not titratable acid, v weak acid
| - pKa= 9
59
regulation of kidney function: how
- active secretion of H+ into tubular fluid
- drives HCO3- reabsorption and regeneration is increased by sys acidosis
- glutamine uptake by tubular cells increased at acidic pH
60
control of cell pH: how does cells maintain pH ~7.2 despite acid producing metabolic processes? list (3)
- rapid efflux of CO2, end product of ox phos
- intracellular buffering mainly by HCO3-, cellular proteins, organic phosphates (eg. ATP), lesser extent: inorganic phosphates (H2PO4-/ HPO4 2-)
- exporting H+ via H/Na exchanger
61
summary: (3)
- resp sys reg so daily CO2 prod excreted in expired air (lungs), constant pCO2 is maintained
- H+ liberated from non-carbonic acids instantly buffered, eventually by HCO3-
- HCO3- used up replaced in kidney
- kidney also excretes some acids such as H2PO4-
- resp and renal sys both maintain body pH by holding ratio of [HCO3-]/[CO2] constant rate
