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Acid Base Regulation Flashcards

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1
Q

Define acid. Give an example.

A

Any chemical that can donate H+ (proton) e.g. HCL -> H+ + Cl-

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2
Q

Define base. Give an example.

A

Any chemical that can accept H+ e.g. NaOH -> Na+ + OH- which allows OH-+ H+ -> H2O

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3
Q

What is the difference between a strong and weak acid? Give examples.

A

Strong acid: completely dissociates in water releasing large amounts of H+ e.g. HCl -> H+ + Cl

Weak acids: incompletely dissociates in water + reaches equilibrium with its conjugate base forming a buffer pair that responds to changes in [H+] by reversibly binding H+ e.g. H2CO3 H+ + HCO3-

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4
Q

How do you measure acidity (pH scale)?

A

[H+] in mol/L but because there is a wide range of these values, you should take the negative logarithm to base 10 [H+] = pH range between 1-14

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5
Q

What is the relationship between pH and H+ concentration?

A

Inverse relationship where a 1 unit pH change is equivalent to a 10-fold increase in [H+] - as [H+] increases, pH decreases

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6
Q

What is the average pH of blood?

A

7.4 (7.36-7.44) = [H+] between 36-44 nanomoles/litre

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7
Q

Survival for short periods is possible at pH values ranging between?

A

6.8-8.0

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8
Q

Why is the regulation of H+ concentration more complex and tightly regulated than for other ions?

A

H+ is small + charged thus affecting protein function:

  • Alters protein activity especially enzymes; body wide effect where many physiological processes sensitive to small change in [H+]
  • Alters binding of other ions e.g. low [H+] increases Ca2+ binding to albumin
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9
Q

What processes are usually sufficient to maintain ion concentration?

A

Balance of intake, production + excretion to maintain homeostasis (kidney has a role)

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10
Q

What is acid-base regulation?

A

Control of [H+]

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11
Q

Why is it a bad thing if ion binding is altered in the body?

A

The body will think that the levels are different to what they are + try to correct this

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12
Q

What are the 2 sources of H+ in the body?

A
  1. Volatile acids (more easily vapourised)

2. Non-volatile (fixed/non-respiratory acids)

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13
Q

What is a volatile acid?

A

An acid that can leave solution + enter the atmosphere via lung excretion

H+ generated from aerobic metabolism + CO2 production by tissues (H2CO3)

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14
Q

What is a non-volatile acid?

A

Organics acids (H+) e.g. lactic or keto acids formed in certain circumstances from other metabolic processes + excreted by the kidneys

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15
Q

What are the 3 main mechanisms to maintain H+ concentration and thus, minimise changes in pH?

A
  1. Buffer systems: rapid chemical reaction that minimises sudden changes in pH (unable to change overall body H+)
  2. Lungs: RAPIDLY adjust excretion of CO2
  3. Kidneys: SLOWLY adjust urine excretion of H+ altering body HCO3- levels
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16
Q

Why are buffer systems only a good short-term mechanism to maintain pH?

A

They mop up H+ but cannot excrete it out of body so make pH appear maintained short-term but eventually will run out of ways to mop H+ up

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17
Q

What is a buffer? How does they work?

A

Any substance that reversibly binds H+ i.e. weak acid

Buffer + H+ HBuffer

So if H+ added, buffer binds it to form Hbuffer removing H+ however, if H+ removed, Hbuffer releases H+ adding H+

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18
Q

What are the 3 main buffer systems in the body?

A
  1. Bicarbonate (most important in EC): HCO3- + H+ H2CO3
  2. Phosphate (IC + urine): HPO42- + H+ H2PO4-
  3. Protein (mainly IC): Pr- + H+ HPr
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19
Q

What are the 3 types of protein buffer systems?

A
  1. Hb (RBC)
  2. AA (proteins)
  3. Plasma protein (albumin)
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20
Q

Explain the bicarbonate buffer system.

A

H+ + HCO3- (kidneys) H2CO3 (carbonic anhydrase/dehydratase) H2O + CO2 (lungs)

Connects the lungs control of [CO2] to kidneys control of [HCO3-] in acid-base balance -> shows how systems can compensate for each other

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21
Q

What is the Henderson-Hasselbalch (H-H) equation? What does it allow us to work out?

A

pH = pK + log10[HCO3-]/[CO2]

pK = constant
[HCO3-] = from kidneys
[CO2] = from lungs - measured from pCO2

Allows us to calculate pH based on measurements of [HCO3-] + [CO2] ratio (2 concentrations easily measured in arterial blood)

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22
Q

In arterial blood, what should ratio of HCO3- and CO2 concentration be roughly?

A

20:1

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23
Q

What are the 2 ways the body maintains pH?

A
  1. Functional ability of lungs to maintain [CO2] i.e. rapid response (mins-hrs) alters CO2 elimination via change in ventilation to restore pH
  2. Functional ability of kidneys to maintain [HCO3-] i.e. slow response (hrs-days) alters HCO3- production + H+ excretion to restore pH
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24
Q

pH is dependent on the __ of HCO3- and CO2 concentrations not the ___.

Study These Flashcards
A 
Ratio
Amounts (i.e. do not have be identical in concentration)
25
How can HCO3- and CO2 concentration change in order to decrease or increase pH?
Decreased pH: Increased [CO2] or decreased [HCO3-] or both Increased pH: Decreased [CO2] or increased [HCO3-] or both
26
How can the kidneys control acid-base balance and therefore, pH?
Control ECF pH via 2 mechanisms (both rely on kidneys ability to secrete H+): 1. Excretion of H+ (non-volatile acid production) in urine -> urine usually acidic (+ production of new HCO3- in turn) 1. Reabsorption of filtered HCO3- to avoid reduction in [HCO3-] H+ loss = HCO3- gain
27
Is there normally HCO3- in the urine? Why?
No | Because then less would be available to bind H+ in plasma, adding H+ to plasma and decreasing plasma pH
28
How much of the filtered HCO3- must be reabsorbed and where does this occur?
Must reabsorb 100% Majority of reabsorption occurs in proximal convoluted tubule (small amount in late distal + collecting tubules)
29
How is HCO3- reabsorbed from the tubular lumen of the kidneys?
1. HCO3- converted to H2CO3 (using secreted H+) + then CO2 + H2O (cannot be reabsorbed directly) 2. CO2 + H2O transported into tubular cells + converted back to H2CO3 via carbonic anhydrase 3. H2CO3 dissociates back into HCO3- + H+ -> H+ stays in cell to be secreted again whilst HCO3- co-transported with Na+ = no net gain/loss of H+ or HCO3- = no change in acid-base status despite H+ secretion as its just cycling round + reclaiming HCO3- that was already in blood
30
How is H+ secreted in the kidneys? Where does this occur?
Uses H+/K+ ATPase transporters in type A intercalating cells to pump H+ into tubular lumen = generates 800-fold H+ gradient + a min urine pH of 4.5 Late distal + cortical collecting tubules
31
Why are buffers needed in the urine?
Comfort Allow sufficient H+ to be excreted in urine to secrete all 70-100mmol of non-volatile H+ To stop H+/K+ ATPase switching off (stops working when there is high [H+])
32
What are the 2 main urinary buffers?
1. Phosphate | 2. Ammonia
33
Why is it important to generate new HCO3- in the kidneys?
Some is consumed buffering non-volatile acids produced each day but it needs to return to blood so H+ can bind it instead of H+ increasing + pH decreasing
34
How does the urinary phosphate buffer work?
Filtered phosphate has 2 forms that create a buffer pair in tubular fluid: monoprotic (HPO42-)+ diprotic (H2PO4) Excess of HPO42- can pick up excess secreted H+ in lumen excreting it in urine -> leads to HCO3- production which passes into blood HPO42- + H+ H2PO4-
35
In terms of the urinary phosphate buffer, what does H+ combine with when excreted? What process occurs at the same time?
NaHPO4- HCO3- passes into interstitial fluid
36
How does the urinary ammonia buffer work?
Ammonia + ammonium form a buffer pair: NH3 + H+ NH4+ NH3 secreted mainly in collecting duct + picks up excess secreted H+ excreting it in urine as NH4+ (in turn HCO3- is produced + goes into interstitial fluid then blood)
37
How is ammonium (NH4+) synthesized? What then happens to it?
From glutamine via glutaminase in PCT cells Broken down to glutamate + then α-ketoglutarate
38
How is the urinary ammonia buffer regulated?
Responds to body's acid-base status -> decrease in pH stimulates renal glutamine metabolism leading to increased H+ excretion (+ vice versa)
39
Why are renal responses to pH slower than in the lungs?
Because the kidneys response requires protein synthesis + breakdown
40
What 4 factors stimulate H+ secretion in the kidneys?
1. Increased pCO2 in ECF 2. Decreased pH of ECF 3. Increased aldosterone 4. Hypokalaemia
41
Define acidosis.
Any process that results in blood becoming more acidic than normal i.e. lower pH via addition if acid/loss of alkali Can have respiratory or metabolic causes
42
Define alkalosis.
Any process that results in blood becoming more alkaline than normal i.e. higher pH via addition of alkali/loss of acid Can have respiratory or metabolic causes
43
What will happen if a disease alters the ratio of HCO3- concentration to CO2 concentration?
Change in pH i.e. acidosis or alkalosis (signify underlying disease)
44
What is a metabolic problem?
Primary problem affecting [HCO3-]
45
What is a respiratory problem?
Primary problem affecting CO2 excretion
46
What is compensation?
When a change in either [HCO3-] or [CO2] is compensated by via the other parameter changing in order to minimise the change in pH attempting to restore it back to normal
47
If a disease is compensated for, what will you see in terms of HCO3- and CO2 concentration?
Both [HCO3-] AND [CO2] will lie outside normal ranges in same direction i.e. both will be raised/lowered
48
What can cause a respiratory acidosis?
Any disorder affecting lungs, chest wall, nerves, muscles or CNS leading to inappropriate reduction in ventilation thus, increasing [CO2]
49
What can cause a respiratory alkalosis?
Any disorder leading to inappropriate increase in ventilation e.g. anxiety + hyperventilation or high altitude leading to decreasing [CO2]
50
What can cause a metabolic acidosis?
Addition of exogenous acid e.g. methanol or endogenous acid e.g. lactic/keto acids Failure of H+ secretion e.g. decreased kidney function Loss of HCO3- e.g. severe prolonged diarrhoea -> decreasing [HCO3-]
51
What can help narrow the underlying differential diagnosis of a metabolic acidosis?
Anion gap
52
What can cause a metabolic alkalosis?
Addition of alkali Excess loss of H+ e.g. severe prolonged vomiting Excess aldosterone e.g. due to dehydration - stimulates H+ secretion in distal tubule -> increased [HCO3-]
53
How can you treat metabolic acid-base disorders?
1. Treat + correct underlying problem whenever possible most importantly 2. Use substances to neutralise acid or base OCCASIONALLY e.g. sodium bicarbonate to treat acidosis or ammonium chloride for alkalosis
54
How should you interpret acid-base changes?
1. Look at pH 2. Look at [HCO3-] + pCO2 3. Look for compensation evidence
55
What does it mean if HCO3- + CO2 concentration are both out of range but in OPPOSITE directions?
Mixed metabolic and respiratory disorder
56
What will a blood gas show in a respiratory acidosis? What if its compensated for?
Increased pCO2 Compensation: increased pCO2 + increased [HCO3-]
57
What will a blood gas show in a respiratory alkalosis? What if its compensated for?
Decreased pCO2 Compensation: decreased pCO2 + decreased [HCO3-]
58
What will a blood gas show in a metabolic acidosis? What if its compensated for?
Decreased [HCO3-] Compensation: decreased [HCO3-] + decreased pCO2
59
What will a blood gas show in a metabolic alkalosis? What if its compensated for?
Increased [HCO3-] Compensation: increased [HCO3-] and increased pCO2

Block 2 (45 decks)

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