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REN > Acid-Base regulation > Flashcards

Acid-Base regulation Flashcards

1
Q

What is pH?

A

A measure of the concentration of H ions

pH = -log10[H]

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2
Q

What is the circulation buffered by?

A

HCO3

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3
Q

What are the arterial pH, Hco3 and CO2 levels?

A 
pH = 7.4
HCO3 = 24
CO2 = 40
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4
Q

What are the venous pH, HCO3 and CO2 levels?

A 
pH = 7.35
HCO3 = 25
CO2 = 46
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5
Q

Why is there a difference between arterial and venous values?

A

Venous has a higher CO2 as it is removing the waste produced by tissues. CO2 is converted to HCO3 + H so pH is more acidic and there is a higher concentration of HCO3

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6
Q

Why is arterial blood used for a blood gas sample?

A

Venous blood is variable depending on which capillary bed is used

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7
Q

What is the equation for pH?

A

pH = pk + log10 x [Hco3] / (0.03 x PCO2)
Hco3 is the base
0.03 x PCO2 can also be replaced by acidic H2CO3

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8
Q

Why is pH maintenance in the kidney required?

A

To regulate levels of HCO3 for buffering the blood.

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9
Q

What is H a waste product of?

A

Hydrolysis of ATP
Lactate production in anaerobic respiration
Production of ketones
Ingestion of acids

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10
Q

How is H removed from the body?

A

Reacts with Hco3 to produce CO2 which can be exhaled.

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11
Q

What is the issue with H removal and how does the body compensate for this?

A

Removal of H leads to a loss of Hco3 so the kidney must reabsorb Hco3 being filtered or produce new.

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12
Q

What is pH proportional to?

A

[Hco3] / [H2CO3]

If Hco3 increases, pH increases

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13
Q

How is Hco3 absorbed in the PT?

A

Using an Na/H exchanger, Na moves down its concentration gradient and produces energy to allow H to cross the apical membrane in the opposite direction.
H reacts with HCO3 in the filtrate to produce neutral CO2 and H2O that can cross the membrane. Once inside the cell the neutral substances redissociate back into H and Hco3 via CA. H is recycled.
Hco3 reabsorption across the basal membrane drives the reabsorption of Na.

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14
Q

What produces the Na gradient in a PT cell?

A

Na/K ATPase pumps Na out of the cell and K in. K is recycled back into the intersitium for continuous production of the gradien.

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15
Q

What is the limit of Hco3 absorption?

A

It is freely filtered but Tm limited at 25mM. Its level varies depending on the amount of H in the tubule. Excess HCo3 will then be excreted to correct the plasma levels.

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16
Q

What happens if there is a loss of HCo3 in the body?

A

CO2 will be sourced from the vasa recta rather than the filtrate for HCo3 production inside the PT cell to reabsorb HCo3 levels to normal.
Luminal H is buffered by HPO4 instead to regulate plasma pH until HCo3 levels rise again.

17
Q

Why does new bicarb production not affect the pH?

A

Because H is produced alongside as CO2 and H2O dissociate, so there is no net change in pH, this is why HPO4 is required in the meantime.

18
Q

What prevents rejoining of H and HCO3?

A

HCO3 is reabsorbed and H is secreted into the filtrate

19
Q

What mechanism allows H secretion in the DT?

A

H secretion through primary active transport using apical H/K ATPase and H ATPase in the alpha intercalated cells of the DT. H is secreted into filtrate making urine acidic.

20
Q

How is excess H in the filtrate buffered to prevent acidic urine?

A

HPO4(2-) buffers as there is no HCO3 left in the filtrate after reabsorption. Phosphate is excreted through the kidney making it readily available.

21
Q

Where does filtrate buffering with HPO4 bring the pH?

A

pH = 6.8 as the buffering stops at the intermediate substance of H2PO4(-) as its pka value is the closest to normal pH, compared to H3PO4.

22
Q

What does the HPO4(2-) : H2POa(-) ratio show?

Ratio also seen as [HPO4] / [H2PO4]

A

Normally HPO4 predominates so the ration is >1. Under normal conditions it equals 4.
When urine is acidic the ratio is <1 as H2PO4 dominates due to the increase in H buffering.

23
Q

How is ammonium ion produced?

A

NH4+ is produced inside the PT cells by converting glutamine to glutamic acid and alphaKG.

24
Q

What is the function of ammonium ion?

A

NH4+ is at equilibrium with membrane permeable NH3 so NH4+ can reform in the filtrate using the excess H to produce a reservoir of H to reduce the acidity under extremely acidic conditions.

25
Q

What is the pH at the end of the PT?

A

6.9

26
Q

What is the pH and the DT?

A

Highly variable but around 4.5 depending on body’s acidic load

27
Q

What results from a metabolic change?

A

As HCO3 increases, pH increases

28
Q

What results from a respiratory change?

A

As CO2 increases, HCO3 and H increase so pH becomes more acidic. But the change is dependent on the starting level of the HCO3 reservoir

29
Q

What will correct an acid-base problem?

A

Metabolic and respiratory changes correct each other

30
Q

How does respiratory acidosis present, what is its cause and how is it corrected?

A

Caused by HYPOventilation.
Co2 levels rise so more H produced = fall in pH.
Presents with LOW pH and HIGH bicarb
Corrected by an increased HCO3 production in the kidney

31
Q

How does respiratory alkalosis present, what causes it and how is it corrected?

A

Caused by HYPERventilation and altitude.
CO2 levels fall so less H = pH rises
Presents with HIGH pH and LOW bicarb
The kidney responds by reducing HCO3 production

32
Q

How does metabolic acidosis present, what causes it and how is it corrected?

A

Caused be renal failure (no HCO3 production), lactic acidosis, ketoacidosis, poisoning.
H levels rise, Hco3 fall and pH falls.
Present with LOW pH and LOW bicarb
Corrected by an increased ventilation rate to remove CO2

33
Q

How does metabolic alkalosis present, what causes it and how is it corrected?

A

Caused by vomiting, contraction alkalosis.
H levels fall as Hco3 rises so pH rises.
Presents with HIGH pH and HIGH bicarb.
Corrected by a reduced ventilation to increase CO2 for more H production.

34
Q

What is an anion gap?

A

The difference between the cations and anions in the serum, plasma or urine. The sum of all the -ve and +ve charges should be EQUAL. [Na] - [Cl] - [HCO3]

35
Q

What is the cause of the anion gap?

A

If the gap is not equal then there are missing anions that have not been standard tested e.g. HPO4, proteins

36
Q

What makes the gap worse?

A

Divalent cations e.g. Mg2+

37
Q

What is the normal anion gap range?

A

3-11mmol.L

38
Q

What does an increased gap suggest and what conditions contribute to the increase?

A

A high concentration of anions that are not being counted. The gap is altered by METABOLIC ACIDOSIS.

  • Lactate (anaerobic)
  • Ketones (toxicity, DM)
  • Sulfates, phosphate, urate, hipppurate (renal failure)
  • Aspirin overdose

REN (14 decks)

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