Physiology 6 - Acid Base Flashcards

1
Q

What are hte major sources of H+?

A

Respiratory Acid (CO2+H2O -> Carbonic acid)

Metabolic Acid (Inorganic e.g. sulphuric acid from Amino acids or organic e.g. fatty acids/lactic acid)

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2
Q

What is the normal arterial pH?

A

7.4 RANGE= 7.37-7.43

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3
Q

What is the normal concentration of bicarbonate/

A

[HCO3-] = 24mmoles/l Range=22-26

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4
Q

What are the major H+ buffer systems of the body?

A

1) Bicarbonate
2) Plasma proteins
3) Dibasic -> Monobasic phosphate (HPO4 {2-} + H{+} -> H2PO4{-} )
4) Intracellular buffers
5) Bone carbonate

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5
Q

Whats the consequence of using intracellular buffers?

A

H+ ions moved into the cells must either come with Cl- or be exchanged with K+ to maintain electrical equilibrium.
In acidosis this can cause Hyperkalemia –> Vfib & death

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6
Q

Whats the consequence of using bone carbonate as a buffer?

A

Occurs mainly in chronic renal failure when H+ can’t be excreted.
Causes bone wasting due to the chronic acid load

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7
Q

How much H+ do you take in a day?

A

50-100mmoles/day

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8
Q

BY what mechanisms do the kidneys regulate acid/base balance?

A

1) Reabsorption of Bicarbonate
2) Excretion of H+ as titratable acids
3) Excretion of H+ with ammonium

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9
Q

Explain the process of HCO3- reabsorption?

A

1) H+ ions actively secreted into proximal tubule (coupled to passive Na+ Reabsorption)
2) H+ & filtered bicarbonate form carbonic acid
3) dissociates to CO2/H2O which are then reabsorped
4) forms carbonic acid again in proximal tubule cell
5) dissociates to H+ & bicarbonate
6) bicarbonate is reabsorped and H+ secreted again for the same purpose

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10
Q

How is H+ excreted as a titrable acid?

A

Excess (Exceeding Tm) dibasic PO4{2-} ions reach distal tubule.
H+ secreted into distal tubule (coupled to passive Na+ reabsorption) and binds to dibasic phosphate
Making monobasic phosphate (HPO4{-})
Which is then excreted

This process is dependant on blood PaCO2

Also works with uric acid and creatinine

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11
Q

What else is produced when H+ ions are excreted as titratable acids?

A

New bicarbonate.
Blood CO2 is absorbed into distal tubule cells
+water –> Carbonic acid
Then dissociates to H+ (for secretion) and HCO3- (absorped into blood)

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12
Q

Whats different about ammonium excretion compared to other methods of regulating Acidity?

A

It is variably active.
Normally it excretes 30-50mmoles H+/day but during a chronic acid load the kidneys can synthesize new proteins over 4–5 days and up that to 250mmoles/day

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13
Q

How does ammonium excretion work in the distal tubule?

A

Ammonium (NH3) is lipid soluble but ammonia (NH4+) is not.
Distal Tubule:
1) Renal glutaminase deaminates amino acids producing NH3
2) NH3 moves into lumen, combines with H+ –> NH4+ and is excreted

The H+ ions are secreted from the distal tubule cells after being produced from blood CO2 (So this process is also reliant on PaCO2)

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14
Q

How does ammonium excretion work in the proximal tubule?

A

Almost the same as in the distal.

But H+ and NH3+ combine in the cell and are actively excreted using a NH4+/Na+ exchanger

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15
Q

What else is produced during ammonium excretion?

A

HCO3- is produced when you make H+ from blood CO2 to secrete. The bicarbonate is then reabsorped into the blood

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16
Q

Summary of renal regulation:

A

1) HCO3- reabsorption # No new HCO3- # No net excretion of H+ # Proximal tubule
2) H+ excretion as titrable acids # New HCO3- produced # Net loss of H+ as monobasic phosphate # Distal tubule
3) Ammonium excretion # New HCO3- # Net loss of H+ as NH4+ # Proximal and distal tubule

17
Q

Describe the blood gasses of Respiratory Acidosis?

A

High PaCO2 = Directly
High HCO3- = Kidney’s regulating pH
Slightly acidic pH

18
Q

What could cause respiratory alkalosis?

A

Acute- aspirin or high altitude

Chronic - Low PaO2 or high altitude

19
Q

Describe the bloods of respiratory alkalosis?

A

Low PaCO2 = directly
Low HCO3- = because less H+ means less secretion which means less HCO3- reabsorption/production
Slightly raised pH

20
Q

What can cause metabolic acidosis?

A

Excess H+ or loss of HCO3-:

1) Increased H+ production e.g. DKA
2) Decreasd H+ excretion e.g. renal failure
3) Decreased intestinal HCO3- reabsorption e.g. Diarrhoea

21
Q

Describe the bloods of metabolic acidosis?

A

Low PaCO2 = kussmauls respiration blows off CO2 to lower H+
Low HCO3- = Directly (either lost or used up buffering extra H+)
pH slightly low

22
Q

What can cause metabolic alkalosis?

A

H+ ion loss in vomit
Excess aldosterone –> Na+ reabsorption in exchange for H+ –> More H+ excretion and also less H+ available for HCO3- reasborption.
Excess HCO3- administration in the renally impaired
Massive blood transfusions (contain citrate for anticoagulation)

23
Q

Describe the bloods of metabolic alkalosis?

A

High PaCO2 = to raise acidity
High HCO3- = Directly
Slightly high pH

24
Q

What is the anion gap?

A

A measure of the difference between the principle cations (Na+/K+) and anions (Cl-/HCO3-).
Usually about 14-18mmoles/l more cations than anions.

25
Q

When is the anion gap a useful measurment?

A

In acidosis
It increases when bicarbonate is used up by lactic acidosis/DKA

It stays the same when HCO3- is lost in the gut as its compensated by extra Cl-

26
Q

Patient with pH = 7.32, [HCO-3]= 15 mM, PCO2 = 30mmHg (4kPa)
What Acid/base disturbance is this?

A

Metabolic acidosis

pH low = Acidosis
HCO3- & PaCO2 are low = metabolic acidosis

27
Q

Patient with pH = 7.32, [HCO-3]= 33 mM, PCO2 = 60mmHg (8kPa)

What acid/base disturbance is this?

A

pH low = Acidosis
PaCO2 high = Respiratory acidosis
High HCO3- = Chronic

Crhonic because more H+ means more HCO3- production and reabsorption.
In the acute form HCO3- would not be elevated

28
Q

Patient with pH = 7.45, [HCO-3] = 42 mM, PCO2 = 50mmHg (6.7kPa)

What they got?

A

high pH = alkalosis

High HCO3- & PaCO2 = metabolic

29
Q

pH = 7.45, [HCO-3]= 21 mM, PCO2 = 30mmHg (4kPa)

What they got?

A

high pH = alkalosis
Low PaCO2 = Respiratory
Normal HCO3- = acute (chronically it would adjust downward)

30
Q

Patient with pH = 7.31, PCO2 = 7.7.kPa, (58mmHg), [HCO3-] =36mmoles/l.
Which of the following is true:
1. It is likely that he has renal disease.
2. He may have an acute respiratory infection.
3. It is possible that he may have chronic bronchitis.
4. There will be a decrease in his excretion of ammonium ions.
5. His plasma potassium will be reduced.

A

3!!

1) He’s acidotic but his HCO3- is still raised so hes not losing to renal disease
2) Hes in respiratory acidosis, we know its not acute due to the high HCO3- so it not a resp infection
3) His High HCO3- indicates it a chronic respiratory acidosis as its compensating with more HCO3-
4) False it will increase
5) False it will go up as H+ is exchanged into cells for K+ in order to be buffered

31
Q

The following acid/base values were obtained:
pH = 7.25, [HCO3-] = 12mmoles/l, PCO2 = 3.3kPa (25mmHg)

Which of the following are true?

1) They are indicative of a respiratory acidosis
2) The reduction in Pco2 is a result of under-breathing
3) The subject has probably been taking bicarbonate of soda
4) It could be related to impaired renal function
5) The subject may have been vomiting very badly

A

4!! They’re in metabolic acidosis

1) Low HCO3- and PaCO2 indicates its metabolic
2) False, you hyperventilate in response to acidosis
3) Why would their bicarbonate be so low
4) True, thats where the HCO3- might be going
5) that would cause alkalosis (So a high pH)

32
Q

Normal pC02

A

pCO2: 40mmHg Range=36-44
pCO2: 5.3kPa. Range=4.8-5.9

33
Q

What is Pk of arterial blood and what is this useful in?

A

H2CO3  H+ + HCO3-
pH=pK+log⁡〖([〖HCO〗_3^-])/(〖[H〗_2 〖CO〗_3])〗
Ph= 7.4
Pk=6.1

SO: 1.3 = log 20
The ratio of [HCO3-]/[ H2CO3] in blood at 7.4 is 20:1

34
Q

What does the conc of H2CO3 in the blood depend on?

A

The amount of C02 in the plasma: its solubility and pco2

35
Q

What would happen if H+ was not buffered

A

Blood pH of 1.2 to 2.4 which is not sustainable with life.

36
Q

What would happen in a patient that was experiencing both hypovolumia and metabolic alkalosis

A

Hypovolumia= loss of h20 and nacl
The kidneys compensate by releasing aldosterone which stimulates the relase of Na+ in exchange for H+

Metabolic alkalosis: high HC03-, low H+
Due to the aldosterone response even more H+ are lost so the metabolic alkalosis is exacerabated.

Shows that regulation of volume is more important than alkalosis.
Once you have restored volume and given NaCl then alkalosis will be resolved.

37
Q

What does liquorice contain?

A

glycyrrhizic acid, which is very similar to aldosterone, so that excess ingestion  metabolic alkalosis.