Renal Regulation of Acid-Base Balance Flashcards

1
Q

What is the effect and cause of rhabdomyolysis?

A

It is due to the release of myoglobin into the bloodstream

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2
Q

In order to control pH what is secreted and what must be replenished?

A

H+ will be secreted and the kidneys must prevent the loss of HCO3- in the urine as it is used to neutralize much of the acid.

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3
Q

What is the pH of urine around?

A

It is usually low due to the secretion of H+ so therefore it is acidic

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4
Q

How do the kidneys secrete a large amount of H+ if they can only secrete urine with a pH of 4.0 - 4.5?

A

They must excrete H+ alongside buffers like Pi

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5
Q

What term is used to refer to the urinary buffers?

A

Titratable Acids

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6
Q

Besides the excretion of H+ as a titratable acid what other mechanisms contribute to the maintenance of the acid-base balance?

A

It is done through the synthesis and excretion of ammonium (NH4+)

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7
Q

Where does most of the HCO3- reabsorption occur?

A

In the proximal tubule (80%)

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8
Q

What is the predominant buffer in the proximal tubule?

A

HCO3- because the CO2 hydration reaction predominates due to presence of carbonic anhydrase in the border.

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9
Q

What is the level of net H+ secretion in the proximal tubule?

A

Net H+ secretion of H+ is low due to the neutralization of H+ with HCO3- during HCO3- ion reabsorption

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10
Q

What are the main buffers in the distal tubule and the collecting duct?

A

Phosphate and ammonium ions dominate due to the scarcity of carbonic anhydrase

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11
Q

What is the net secretion of H+ in the distal tubule and the collecting duct?

A

It is very high due to strong proton pumping and buffering with Pi and NH4+

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12
Q

What is Type I-Renal Tubular Acidosis?

A

It is distal tubule RTA and is the failure of the distal nephron to secrete H+ which leads to increased back-leaking of H+ and may be caused by H+ pump failure.

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13
Q

What is Type II-Renal Tubular Acidosis?

A

It is proximal tubule RTA and is the failure of the proximal nephron to recycle H+ due to low carbonic anhydrase and decreased HCO3- reabsorption.

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14
Q

What is the [HCO3-] that HCO3- is regulated at?

A

It is regulated at a concentration near the renal plasma threshold

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15
Q

What processing of HCO3- occurs in the PT?

A

80% reabsorption

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16
Q

What processing of HCO3- occurs in the DT and CD?

A

20% reabsorption

17
Q

How does the GFR regulate HCO3- reabsorption?

A

Reabsorption rate of the HCO3- is matched to changes in the filtered load via GT balance

18
Q

How does the systemic acid-base balance regulate HCO3- reabsorption?

A

Respiratory acidosis and increase in arterial PCO2 or metabolic acidosis and decreased [HCO3-] will lead to the acidification of the ICF.

This causes the insertion of the apical H+-ATPase that leads to increased H+ secretion and decreased HCO3- reabsorption.

19
Q

How does aldosterone regulate HCO3- reabsorption?

A

Increased aldosterone will lead to increased H+ secretion in the intercalated cells of CD.

Increased aldosterone will increase Na+ reabsorption and lead to increased H+ secretion.

20
Q

How does arterial [K+] regulate HCO3- reabsorption?

A

Increased K will increase K+-H+ exchange and lead to extracellular acidosis -> hyperkalemic metabolic acidosis

Decreased K will lead to hypokalemic metabolic alkalosis.

21
Q

How does the arterial [Cl-] regulate HCO3- reabsorption?

A

Increased [Cl-] will decrease HCO3- reabsorption and decreased will cause the opposite

22
Q

How does the extracellular fluid volume regulate HCO3- reabsorption?

A

During expansion of ECF, HCO3- reabsorption will be inhibited to to dilution of plasma [HCO3-]

23
Q

How does the Na+ balance regulate the HCO3- reabsorption?

A

Retaining Na+ will decrease HCO3- reabsorption and losing Na+ will increase HCO3- reabsorption

24
Q

What is the minimal urinary pH around and how does it reach such impressively low levels?

A

It is around a pH of 4.4 and it demonstrates the ability of the distal nephron to secrete H+ against a strong acid gradient.

25
Q

What are sources of free H+ in the urine?

A

Fixed acids - H2SO4

Titratable acids - H3PO4

26
Q

What acid is not a source of free H+ in the urine?

A

Carbonic acid

27
Q

What is the role of HPO4(2-) as a titratable acid?

A

It can combine with secreted H+ ions and make H2PO4- and the negatively charged anion is lipid insoluble so there is no back diffusion.

28
Q

What is the role of diffusion trapped ions and how do they “trap?”

A

NH3 reacts with secreted H+ to form NH4+ and NH4+ is charged and lipid impermeable, which traps the H+. NH3 is made from deamination reactions and it is freely permeable across tubular cells.

29
Q

What happens to NH4+ in chronic acidosis?

A

NH3 production increased in acidosis which allows for increased H+ secretion as an adaptation to the acidosis

30
Q

How is HCO3- and H+ balanced through NH4+?

A

For each secreted molecule of NH4+ a new molecule of HCO3- is added to the ECF