Lecture #19: Renal Acid-Base Regulation Flashcards Preview

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Flashcards in Lecture #19: Renal Acid-Base Regulation Deck (35)
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Distinguish between volatile and non-volativle acids and give examples.

> Volatile Acid -> excreted from lungs
- carbon dioxide
*product of cellular aerobic metabolism
*H2CO3 is a weak acid

> Non-volatile Acids (fixed acids) -> excreted from kidneys
- sulfuric acid (product of protein catabolism)
- phosphoric acid (product of phospholipid catabolism)
- ketoacids, lactic acid, salicylic acid


Define pH and know the normal pH range of venous and arterial blood.

arterial blood pH = 7.37 - 7.44

venous blood pH = 7.35 - 7.45


Define equilibrium constant for the dissociation reaction and explain what pKa refers to.

Ka is the equilibrium constant for the dissociation reaction. Ka = [H][A]/[HA]


Define acid and base.

Acid Definition -> compounds that release H+ ions.
- Strong Acids:
> dissociate completely
- Weak Acids (conjugate acid)
> do not dissociate completely
> dissociate into:
- hydrogen ions (H+)
- conjugate base

Bases -> compounds that accept H+ ions


List the major systems in the body that regulate pH.

> chemical acid/base buffer systems of the body fluids

> respiratory center

> kidneys


Define "buffer" and list the important buffer systems in the body.

A buffer is a substance that can reversibly bind H+.

> bicarbonate buffer system
> phosphate buffer system
> proteins as buffers (NOT covering)


Which buffer system is the most important extracellular buffer system?

Extracellular Buffer System

* This buffer system consists of:
- weak acid (H2CO3)
- bicarbonate salt (NaHCO3)

- bicarbonate concentration is regulated mainly by kidneys
- pCO2 is controlled by rate of respiration


Explain how the bicarbonate buffer system works when a strong acid or a strong base is added.

> add a strong acid to the system:

increase H + HCO3 -> H2CO3 -> CO2 + H20


What is the organ that primarily regulates the bicarbonate buffer system?

Bicarbonate concentration is regulated mainly by the kidneys.


Distinguish between metabolic acid/base disorders.

Metabolic Acid/Base Disorders:
- Result from primary change in bicarbonate concentrations in extracellular fluid.
> metabolic acidosis = decreased HCO3- (bicarbonate)
> metabolic alkalosis = increased HCO3- (bicarbonate)


Distinguish between respiratory acid/base disorders.

Respiratory acid/base disorders:
- Result from primary change in pCO2.
> respiratory acidosis = increased pCO2
> respiratory alkalosis = decreased pCO2


How does the normal operating pH point for the bicarbonate buffer system compare to its pKa?

normal operating point in body = 7.4 pH, and the pKa is 6.1
Thus, by examining figure 30-1 you can see that the normal operating point in the body is at the type range of the buffer capacity for bicarbonate.

*Note that pH of 6.1 occurs when concentrations of both bicarbonate ions and carbon dioxide are equal;

**Therefore, pH at this point = pKa of the buffer system.


Describe the phosphate buffer system and explain why it is more important as a buffer in the kidney tubular fluids.

> Plays major role in buffering renal tubular fluid and intracellular fluids.

> What area the two reasons for its importance as a buffer in kidney tubular fluids?
- usually becomes greatly concentrated in the tubules
- lower pH of the tubular fluid brings the operating range of the buffer closer to the pK of the buffer system.

> HCl + Ha2HPO4 -> Na H2PO4 + NaCl
- strong acid is replaced by an additional amount of weak acid and pH change is minimal.


What is the primary method for removing non-volatile acids?

Renal Excretion -> primary method for removing non-volatile acids.


True or False:

The kidneys can excrete either an acidic or basic urine?



What must happen before filtered bicarbonate is reabsorbed?

Almost all filtered bicarbonate is reabsorbed, but it must react with secreted hydrogen ion to form carbonic acid before it can be reabsorbed.

*must form carbonic acid before it can be reabsorbed.


How many mEq of hydrogen must be secreted each day by the kidneys?

4320 mEq of hydrogen ion must be secreted each day just to reabsorb the 4320 mEq of filtered bicarbonate.


What are the 3 mechanisms by which the kidneys regulate extracellular hydrogen ions?

1) Kidneys reabsorb filtered bicarbonate ions.
2) Kidneys can secrete hydrogen ions.
3) Kidneys produce new bicarbonate ions.


Review each of the below mechanisms for regulating hydrogen ion concentration ad study the below figures and accompanying information in the text book in detail for the exam!

> kidneys reabsorb filtered bicarbonate ions.
- figures 30-4 and 30-5
> kidneys can secrete hydrogen ions
- figures 30-5 and 30-6
> kidneys produce new bicarbonate ions
- figures 30-7 through 30-9

Dr. Anderson said to know this.


Where in the kidney tubules does hydrogen ion secretion and bicarbonate reabsorption occur?

H+ Secretion -> almost all parts of the tubules via secondary active transport (coupled with sodium ion transport) except the descending and ascending thin limbs of the loop of Henle

Primary active hydrogen secretion begins in late distal tubules in intercalated cells and involves a hydrogen-transporting ATPase.

Bicarbonate Reabsorption -> about 80-90% of bicarbonate reabsorption occurs in the proximal tubule


Describe the mechanism by which bicarbonate ion is reabsorbed.

Bicarbonate is joined with H+ and dissolves into CO2 + H20 in the tubular lumen. The CO2 + H20 diffuse (reabsorbed) into the cell and are turned back into carbonic acid by carbonic anhydrase. Carbonic Acid dissolves into bicarbonate and hydrogen ion and the bicarbonate ion is reabsorbed into renal interstitial fluid by a sodium/bicarbonate symporter.


What role is played by carbonic anhydrase?

Turns CO2 + H20 in the cell into carbonic acid so that bicarbonate can be regenerated.


Explain why the bicarbonate ion returned to the extracellular fluid is not the same as that filtered into the tubular lumen.

Because the bicarbonate in the tubular lumen dissociates into CO2 + H20 to diffuse back into the cell. Those reactants are then turned into carbonic acid via carbonic anhydrase, which then dissociates into bicarbonate and hydrogen ion. This is the bicarbonate that is then returned to the extracellular fluid.


Explain how bicarbonate ion is normally titrated against hydrogen ion and how incomplete titration can be used to correct acidosis or alkalosis.

> Use of incomplete titration to correct acidosis or alkalosis:
- normally each time a H+ is formed in tubular epithelial cells, a bicarbonate ion is also formed and released back into the blood.
- in metabolic acidosis new bicarbonate ion is added to the extracellular fluid
- in metabolic alkalosis, bicarbonate ions are removed from extracellular fluid by renal excretion.

**talking about incomplete titration to correct acidosis or alkalosis. It is not a 1:1 process.


What is the role of intercalated cells in hydrogen ion transport, and where are these cells found?

Active transport resulting in hydrogen ion secretion is carried out by intercalated cells.

Found -> only in late distal renal tubules

2-step process of H+ secretion in intercalated cells:
- dissolved CO2 in intercalated cells combines H20 to from carbonic acid.
- carbonic acid then dissociates into bicarbonate, which is rapidly reabsorbed into the blood, and hydrogen ion, which is secreted into the tubular lumen by means of the hydrogen-ATPase transporters.


What is the lower limit of pH that can be achieved in normal kidneys?

pH =4.5


Explain how excess hydrogen ion is generated.

> each day the body produces about 80 mEq of non-volatile acids, mostly from the metabolism of proteins. Because these are non-volatile acids, they cannot be excreted by the lungs. They are primarily removed via renal excretion.

> Note also that loss of bicarbonate ions is the same as adding hydrogen ions to the extracellular fluid.


What limits the amount of free hydrogen ion that can be excreted?

> only a small part of the excess H+ secreted in excess of the filtered bicarbonate ion can be excreted in ionic form in the urine.
- this is because the minimal urine pH is about 4.5

> to excrete the 80 mEq of non-volatile acid formed by metabolism per day, about 2667 L of urine would have to be excreted if all the excess H+ remained free in solution.

***Buffers are important in allowing larger amounts of H+ to be excreted *** (phosphate buffer system and ammonia buffer system)


What buffers are important in allowing larger amounts of H+ to be excreted?

Phosphate Buffer System

Ammonia Buffer System


How does the excretion of excess hydrogen ions lead to the formation of new bicarbonate ions?

Bottom Line: if H+ are combining with other buffers in the tubular lumen, then excess bicarbonate ion is available to be returned to the blood. This bicarbonate ion is referred to as "new bicarbonate ion".

> Excess H+ are eliminated through binding with phosphate or ammonia ions.
- this means that the bicarbonate ions formed when carbon dioxide combines with water in the tubular cells and then dissociates into H+ and bicarbonate ions can be returned to the extracellular fluid and blood, while the H+ are buffered with the phosphate and ammonia buffer systems.