Flashcards in Renal Acid Base Regulation Deck (50):
What is a base?
A compound that accepts hydrogen ions.
What is a volatile acid, and what organ is it excreted from?
carbon dioxide is a volatile acid. It is a product of aerobic respiration and is excreted from the lungs.
What is a nonvolatile acid, and where is excreted from?
sulfuric acid, phosphoric acid, ketoacids, lactic acid, salicylic acid. It is excreted from the kidneys.
What is pH?
You take a blood sample from a healthy patient. What do you expect the pH of the blood (arterial and venous) to be?
arterial: 7.37 - 7.44
Venous: 7.35 - 7.45
What is the equilibirum constant for the dissociation reaction?
K = [H+][A-]/[HA]
When determining the pH of blood, what does the pKa value represent?
the dissociation constant of carbonic acid in water (6.1).
You take a blood sample from a healthy patient. What do you expect the pH of their blood pressure to be?
What three major systems regulate [H+]?
Chemical acid-base buffer systems of body fluids
What is a buffer?
A substance that can reversibly bind H+.
What are the three important buffer systems in the body?
Which buffer system is the most important extracellular system?
bicarbonate buffer system.
When a strong acid is added to the bicarbonate buffer system, what is formed?
A weak acid.
When a strong base is added to the bicarbonate buffer system, what is formed?
A weak base.
What organ primarily regulates the bicarbonate buffer system?
As carbon dioxide decreases in the biccarbonate buffer system, what subsequently decreases?
Respiration and carbon dioxide expiration.
You encounter a patient who is experiencing metabolic acidosis. What ion is most likely affected?
bicarbonate; it is LOW in the extracellular fluid.
You encounter a patient who is experiencing metabolic alkalosis. Do you expect extracellular bicarbonate levels to be low or high?
You encounter a patient who is suffering from respiratory acidosis. Do you expect levels of carbon dioxide to be low or high?
You encounter a patient who is suffering from respiratory alkalosis. Do you expect their carbon dioxide levels to be low or high?
You encounter a patient who has a respiratory disorder. You note that they have a low pCO2 value. Are they suffering from respiratory acidosis or alkalosis?
How does the normal operating pH point for the bicarbonate buffer system compare to its pKa?
The normal operating point has a higher pH (7.4) and has a greater level of buffer (HCO3). The buffer has a much lower pH (6.1) and has equal amounts of carbonic acid, bicarbonate and carbon dioxide.
The phosphate buffer system plays a major role in buffering what fluid?
Renal tubular fluid.
The phosphate buffer system is important because phosphate usually becomes greatly concentrated in the tubules. What is another reason why the phosphate buffer system is important in the kidneys?
The phosphate buffer system lowers the pH of tubular fulid, bringing the operating range of the buffer closer to the pKa of the buffer system.
What is the primary method for removing nonvolatile acids?
Through renal excretion.
What must happen before bicarbonate is reabsorbed?
It must react with secreted hydrogen ion to form carbonic acid before it can be reabsorbed.
How much of the hydrogen ion must be secreted to reabsorb 4320 mEq of filtered bicarbonate?
What are the three mechanisms by which the kidneys regulate extracellular hydrogen ions?
Kidneys reabsorb filtered bicarbonate ions
Kidneys can secrete hydrogen ions
Kidneys produce new bicarbonate ions.
Where in the kidney tubules does hydrogen ion secretion and bicarbonate reabsorption occur?
The majority of bicarbonate reabsorption occurs in the proximal convoluted tubule.
Hydrogen ion secretion via secondary active transport occurs in all parts of the tubules except the descending and ascending limbs of the loop of Henle.
How is a bicarbonate ion reabsorbed?
It is initially broken down in the lumen (becomes carbon dioxide and water) and diffuses across the tubular cells.
The carbon dioxide then reacts with water in the cell to make bicarbonate before it is actively transported (via a symporter) into the interstitial fluid.
What role does carbonic anhydrase play in reabosrbing bicarbonate?
It is necessary for the formation of carbonic acid from carbon dioxide and water.
Why is the bicarbonate ion returned to the extracellular fluid not the same as that filtered idnto the tubular lumen?
The bicarbonate dissociates in the lumen and reforms in the tubular cells.
How is the bicarbonate ion normally titrated against hydrogen ions?
Each time a hydrogen ion is formed in the tubular epithelial cells, a bicarbonate ion is also formed and released back into the blood.
How is incomplete titration used to correct acidosis?
A new bicarbonate ion is added to the extracelular fluid.
How is incomplete titration used to correct metabolic alkalosis?
bicarbonate ions are removed from extracelular fluid by renal excretion.
What is the role of intercalated cells in hydrogen ion transport, and where are these cells found?
They use primary active transport to secrete hydrogn ions into the lumen. They are found in the late distal renal tubules.
What is the lower limit of pH that can be achieved in normal kidneys?
Wha is the 2-step process of hydrogen ion secretion in intercalated cells?
Dissolved carbon dioxide in intercalated cells combines with water to form carbonic acid.
The carbonic acid dissociates into bicarbonate, which is rapidly reabsorbed into the blood, and hydrogen ion, which is secreted ino the tubular lumen via hydrogen-ATPase transporters.
How are excess hydrogen ions generated?
They are produced from nonvolatile acids. They are removed via renal excretion.
What limits the amount of free hydrogen ion that can be excreted?
The minimal urine pH, which is about 4.5.
What buffers are important in allowing larger amounts of hydrogen ion 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?
Hydrogen ions combine with other buffers in the tubular lumen. This allows excess bicarbonate ion to be created.
How does the renal system handle excess base?
The kidneys will not reabsorb all the filtered bicarbonate ion. This is the same as adding hydrogen ion to the extracellular fluid, and the pH of the extracellular fluid returns to normal.
How can the respiratory system produce acidosis?
Acidosis occurs when the ratio of bicarbonate ion to carbon dioxide in extracellular fluid decreases.
A decrease in bicarbonate ion occurs during metabolic acidosis, and an increase in carbon dioxide occurs in respiratory acidosis.
How can the respiratory system produce alkalosis?
Alkalosis occurs when there is an increase in the rate of bicarbonate to hydrogen ion concentration.
It is corrected by excreting excess bicarbonate in the urine. This adds hydrogen ions to extracellular fluid.
What is the primary compensatory response of respiratory acidosis?
Increase in plasma bicarbonate ion due to addition of new bicarbonate by the kidney.
What is the primary compensatory response of metabolic acidosis?
Increased ventilation rate
new bicarbonate is added to the extracellular fluid.
How does the respiratory system compensate for decreased carbon dioxide concentration?
There is a reduction in plasma bicarbonate ion concentration caused by renal excretion of bicarbonate ion.
How does the respiratory system comopensate when there is metabolic alkalosis?
There is decreased ventilation and increased renal bicarbonate ion excretion.