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Renal System > Renal Regulation of Acid-Base Balance > Flashcards

Renal Regulation of Acid-Base Balance Flashcards

1
Q

Why is pH regulation so tightly controlled and important?

A

Βecause metabolic reactions are highly sensitive to the H+ concentration of the fluid in which they occur

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2
Q

Why are metabolic reactions so sensitive to H+ concentration?

A

Due to the influence that H+ has on the tertiary structure of proteins, such as enzymes, such that their function can be altered

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3
Q

How can hydrogen regulation be viewed?

A

Matching gains and losses

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4
Q

What happens when loss exceeds gain in hydrogen ion regulation?

A

The arterial plasma H+ concentration decreases, and the pH exceeds 7.4, this is known as alkalosis

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5
Q

What is the relationship between H+ and pH?

A

The greater the H+ concentration –> the lower the pH

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6
Q

What happens if gain exceeds loss in hydrogen ion regulation?

A

The arterial plasma H+ concentration increases and the pH is less than 7.4, that is known as acidosis

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7
Q

The total-body balance of H+ is a result of what?

A

Both metabolic production of H+ ions and net gains or losses via the respiratory system, gastrointestinal tract, and urine.

A stable balance is achieved by regulation of urinary losses

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8
Q

What are the sources (gains) of H+?

A
  1. Generation of H+ from CO2
  2. Production of nonvolatile acids from the metabolism of proteins and other organic molecules
  3. Gain of H+ due to loss of HCO3- in diarrhea or other nongastric GI fluids
  4. Gain of H+ due to loss of HCO3- in the urine
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9
Q

What are the losses of H+?

A
  1. Utilization of H+ in the metabolism of various organic anions
  2. Loss of H+ in vomitus
  3. Loss of H+ in the urine (primarily in the form of H2PO4- and NH4+)
  4. Hyperventilation
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10
Q

Why is there a loss of H+ during vomiting?

A

Expelling HCl

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11
Q

How does hyperventilation lead to the loss of H+?

A

CO2 exhalation > CO2 production

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12
Q

What is buffering? How do they achieve that?

A

A means of minimizing changes in H+ concentration by combining these ions reversibly with anions such as HCO3- and intracellular proteins

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13
Q

What is the general form of buffering reaction?

A

Buffer + H+ –> HBuffer, H+ ions do not get eliminated but they instead bund them so that they are not free.

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14
Q

What happens when the H+ concentration increases?

A

The reaction is forced to the right, and more H+ is bound by the buffer to form HBuffer

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15
Q

What happens when the H+ concentration decreases?

A

The loss of H+ or the addition of alkali, the reaction proceeds to the left ad H+ is released from the HBuffer.

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16
Q

What is the major extracellular buffering system?

A

CO2/HCO3- system:
CO2 + H2O <–> H2CO3 <–> HCO3- + H+

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17
Q

What is the major intracellular buffer?

A

Phosphate and proteins, for instance: hemoglobin

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18
Q

What helps the reversible conversion of CO2 + H2O –> H2CO3?

A

Carbonic anhydrase (CA)

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19
Q

What systems work together to regulate hydrogen ion concentrations?

A

Kidneys and respiratory

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20
Q

What is the organ that achieves body H+ balance?

A

The kidneys

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21
Q

What does a decrease in arterial plasma H+ concentration cause?

A

Reflex HYPOventilation, which increases arterial PCO2, and hence, increases plasma H+ concentration toward normal (pH decreases)

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22
Q

What does an increase in plasma H+ concentration cause?

A

Reflex HYPERventilation, which decreases arterial PCO2 and, hence, decreases plasma H+ concentration towards normal (pH increases)

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23
Q

When do buffers work?

A

Within seconds

24
Q

When does ventilation (respiratory buffers) work?

A

Within minutes to hours

25
Q

When does renal buffer system work?

A

WIthin hours to days

26
Q

What happens if the respiratory system is the actual cause of the H+ imbalance?

A

Then the kidneys are the sole homeostatic responder

27
Q

What happens if malfunctioning kidneys create an H+ imbalance by eliminating too little or too much H+ from the body?

A

Respiratory response is the only one in control

28
Q

What is the renal mechanism like?

A

The kidneys eliminate or replenish hydrogen ions from the body by altering plasma bicarbonate concentration

29
Q

What is the kidneys’ response to plasma H+ ion concentration decreasing ?

A

During alkalosis, the kidneys’ homeostatic response is to excrete large quantities of HCO3-

This increases plasma H+ concentration towards normal

30
Q

What is the kidneys’ response to plasma H+ concentrations increasing?

A

During acidosis, the kidneys do not excrete HCO3- in the urine rather, kidney tubular cells produce new HCO3- and add it to the plasma.

This decreases the H+ ion concentration towards normal, increases pH

31
Q

What happens to HCO3- when H+ is secreted into the lumen and combined with filtered HCO3-?

A

HCO3- is reabsorbed when the H+ generated from tubular cells is secreted and combined with filtered HCO3-

The secreted H+ is NOT excreted in this situation

32
Q

What happens to the H+ that is generated in the tubular cells that is not secreted?

A

It combines with the lumen with a filtered HCO3- and generates CO2 and H2O, both of which can diffuse into the cell and be available for another cycle of H+ generation

33
Q

What is the kidneys’ normal response to HCO3-?

A

In all cases, except of alkalosis, the kidneys reabsorb all filtered HCO3- and thereby prevent its loss in the urine

34
Q

What is the mechanism in the case of metabolic acidosis? (H+ ions)

A

H2O + CO2. –> H2CO3
H2CO3 is broken down into H+ and HCO3-
H+ binds to the HCO3- which is filtered in the tubular lumen to form H2CO3 and break it further down into H2O and CO2
The whole point is to decrease the H+ concentration

35
Q

What happens when secreted H+ combines with filtered phosphate ions or other non-bicarbonate buffers?

A

It is excreted and the kidneys contribute to new HCO3- added to he blood

36
Q

What are examples of non-bicarbonate buffers?

A

HPO4-

37
Q

When do H+ ions combine with filtered non-bicarbonate buffers?

A

Only after the filtered HCO3- has virtually all been reabsorbed, the reason for this is that there is such a large load of filtered HCO3- competing for the secreted H+

38
Q

What is the mechanism in the case of severe acidosis?

A

There is no bicarbonate
H2O + CO2 –> H2CO3
H2CO3 –> H+ and HCO3-
The H+ attaches to the HPO4 2- which is filtered into the tubular lumen
HPO4 2- + H+ –> H2PO4- which is then excreted in the urine, and this way, you decrease the H+ ion concentration, neutralizing the pH

39
Q

When do the kidneys contribute new HCO3- to the blood?

A

When they produce and excrete ammonium

40
Q

When is ammonium used as a non-bicarbonate buffer and why?

A

If the phosphate is not enough, phosphate is not formed in the body so there is a limited supply of it

41
Q

What is the mechanism of ammonium as a non-bicarbonate buffer like?

A

Glutamine and sodium enter from the tubular lumen into the tubular epithelial cells
Glutamine is then broken down into NH4+ and HCO3-
The new HCO3- is added to the plasma
The NH4+ is moved into the tubular lumen whilst Na+ is reabsorbed back into the epithelial cells
The NH4+ is then excreted in the urine

42
Q

What are the classifications of alkalosis/acidosis?

A

Respiratory or metabolic

43
Q

What causes respiratory acidosis?

A

The retention of carbon dioxide (increased CO2)

44
Q

What causes respiratory alkalosis?

A

Excessive elimination of carbon dioxide (decreased CO2)

45
Q

What is the difference between metabolic and respiratory?

A

In metabolic, it is the reflection of gain or loss of H+ from a source OTHER than CO2

46
Q

What are the renal responses to acidosis?

A
  1. Sufficient H+ is secreted to reabsorb all filtered HCO3-
  2. Still more H+ is secreted, and this contributes new HCO3- to the new plasma as the H+ is excreted bound to non-bicarbonate urinary buffers such as HPO4 2-
  3. Tubular glutamine metabolism and ammonium excretion are enhanced, which also contributes new HCO3- to the plasma.
    Result: More HCO3- added than usual to the blood and plasma HCO3- is increased, thereby compensating for acidosis. The urine is highly acidic (lowest attainable pH = 4.4)
47
Q

What are the renal responses to alkalosis?

A
  1. The rate of H+ secretion is inadequate to reabsorb all the filtered HCO3-, so significant amounts of HCO3- are excreted in the urine and there is little or no excretion of H+ on non-bicarbonate urinary buffers.
  2. Tubular glutamine metabolism and ammonium are decreased so that little or no new HCO3- is contributed to the plasma from this source
    Result: Plasma HCO3- concentration is decreased, compensating for alkalosis. The urine is alkaline (pH >7.4)
48
Q

What are the changes in the arterial concentrations of H+, HCO3- and CO2 in respiratory acidosis?

A

H+ –> high
HCO3- –> high
CO2 –> high

49
Q

What is the cause of HCO3- change in respiratory conditions?

A

Renal compensation

50
Q

What is the cause of CO2 change in respiratory conditions?

A

Primary abnormality

51
Q

What are the changes in the arterial concentrations of H+, HCO3- and CO2 in respiratory alkalosis?

A

H+ –> low
HCO3 –> low
CO2 –> low

52
Q

What are the changes in the arterial concentrations of H+, HCO3- and CO2 in metabolic acidosis?

A

H+ –> high
HCO3- –> low
CO2 –> low (compensatory)

53
Q

What are the changes in the arterial concentrations of H+, HCO3- and CO2 in metabolic alkalosis?

A

H+ –> low
HCO3- –> high
CO2 –> high (compensatoy)

54
Q

What is the cause of HCO3- change in metabolic conditions?

A

Primary abnormality

55
Q

What is the cause of CO2 change in metabolic conditions?

A

Reflex ventilatory compensation

56
Q
A

Renal System (24 decks)

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