Renal Acid-Base Regulation Flashcards
What is the basic definition of acid
Compounds that release H+ ions
What is the basic definition of a base?
Compounds that accept H+ ions
What is a volatile acid?
excreted from the lungs
Carbon dioxide; carbonic anhydrase
What is a nonvolatile acid?
a fixed acid; excreted from the kidney
sulfuric, phosphoric, and lactic and salicylic acids
What is the pH of arterial blood
7.4
What is the pH of the venous blood
7.35
Define pH
-log[H+]
What is the Henderson Hasselbach equation?
pH= pKa + log ([A-]/[HA])
What are the 3 major systems that regulate H+?
- Chemical acid base buffer systems of the body fluids
- Respiratory center
- Kidneys
Define buffer
substance that reversibly binds to H+
consists of a weak acid or a conjugate acid
What are examples of buffer systems?
Bicarbonate buffer system
phosphate buffer system
proteins as buffers
Describe the bicarbonate buffer system
-consists of a weak acid and a bicarbonate salt (H2CO3 and NaHCO3)
If a strong acid is added you create a weak acid, if a strong base is added, you create a weak base
bicarbonate concentration is regulated mainly by the kidneys
pCO2 is controlled by the rate of respiration
MOST IMPORTANT EXTRACELLULAR BUFFER SYSTEM
What happens to the respiratory rate if the CO2 levels decrease?
It will decrease as well so that you retains much CO2 as possible
Describe metabolic acid base disorders
Result from the change in the bicarbonate concentrations in the extracellular fluid
decreased bicarb= metabolic acidosis
increased bicarb= metabolic alkalosis
Describe the respiratory acid-base disorders
Result from a primary change in pCO2
increased pCO2 is respiratory acidosis
Decreased pCO2 is respiratory alkalosis
What is the pH if the concentrations of Co2 and bicarb are equal?
6.1
Describe the phosphate buffer system
-MAJOR ROLE in buffering the renal tubular fluid
WHY?
1. greatly concentrated in the tubules
2. lower pH of the tubular fluid brings the operating range of the buffer closer to the pK
-main elements are H2PO4- and HPO4–
Describe what happens when the kidneys secrete a basic urine?
Large numbers of bicarbonate ions are filtered into the tubule and this in turn removes the bases from the blood and puts it into the urine
Describe what happens when the kidneys secrete acidic urine
Large numbers of hydrogen ions are secreted into the tubular lumen
What is the primary method for removing non-volatile acids?
renal excretion
How is bicarbonate reabsorbed in the kidneys?
most react with carbonic acid so that it can be reabsorbed
carbonic anhydrase
What are the mechanisms for regulating the extracellular H+?
- Kidneys can reabsorb filtered bicarb ions
- kidneys can secrete hydrogen ions
- kidneys can produce new bicarb ions
Where in the kidney tubules does hydrogen ion secretion and bicarbonate reabsorption occur?
-hydrogen ion secretion happens via secondary active transport in all of the tubules except for the ascending and descending thin loops of Henle
Primary active hydrogen secretion begins in the late distal tubules in the intercalated cells with a H+ ATPase
80-90% of bicarb reabsorption is in the proximal tubules
Describe the reabsorption of bicarbonate
- initialted in the tubules between the bicarbonate ion filtered at the glomerulus and the hydrogen secreted by the tubular cells
- forms carbonic acid
- CO2 into tubular cells where it combines with water to create a carbonic acid molecule
- dissociates to bicarb ion and hydrogen ion
- bicarb ion diffuses through the basolateral membrane into the intersititial fluid and into the blood
Describe what happens in bicarbonate reabsorption when the body is in metabolic acidosis
A new bicarbonate ion is added to the extracellular fluid
Describe what happens in bicarbonate reabsorption when the body is in metabolic alkalosis
bicarbonate ions are removed from the extracellular fluid by renal excretion
Describe the tubular secretion of H+
-active transport via intercalated cells in the late distal renal tubules
What are the 2 steps that are involved in the hydrogen ion secretion of intercalated cells?
- dissolved CO2 in intercalated cells combines with water to form carbonic acid
- carbonic acid dissociates into bicarbonate, which is absorbed into the blood and the hydrogen ion which is secrete into the lumen via H+ ATPase
Describe tubular secretion of H+ in the proximal tubule
secondary sodium-hydrogen counter transport in the apical membrane
sodium potassium ATPase are in the basal membranes
What is the lower limit of pH that can be achieved in normal kidneys?
4.5
What are the limitations on the amount of free H+ that is secreted?
The fact that only a small part of the excess hydrogen can be excreted via the renal system because it is not able to keep up and it has a limit of a 4.5 pH
What are the buffer systems that are important in allowing larger amounts go H+ to be excreted?
- phosphate buffer system
2. Ammonia buffer system
Define the “new bicarbonate ion”
If hydrogen ions are combining with other buffers in the tubular lumen, then the bicarbonate ions are able to be returned to the blood which is referred to as a “NEW” ion
Describe what the kidneys do during alkalosis
they fail to reabsorb all of the filtered bicarbonate ions which is similar to adding hydrogen to the extracellular fluid
If the body has a decrease in the bicarbonate ion concentration, it is in???
Metabolic acidosis
If the body has an increase in carbon dioxide, it is in??
Respiratory acidosis
What is the primary compensatory response to respiratory acidosis?
Increase in the plasma bicarbonate ion due to an addition of the new bicarb of the kidney
What is the primary compensatory response to metabolic acidosis?
Increased ventilation rate
kidneys add new bicarbonate ions to the extracellular fluids
If a person is hyperventilating, what state will their body likely be in?
Respiratory alkalosis
What is the compensatory response to respiratory alkalosis?
reduction int he plasma bicarb by renal excretion of bicarb
What is the primary compensatory response to metabolic alkalosis?
decreased ventilation and increased renal bicarb ion excretion
If the pH is elevated and the bicarbonate ion concentration is also elevated, the body will be in what state? this will be compensated via….
Metabolic alkalosis
Respiratory compensation
If the pH is elevated but the bicarbonate ion concentration is decreased, the body is in what state? This will be compensated via…
Respiratory alkalosis
Renal compensation
If the pH of the body is decreased and the bicarb ion concentration is also decreased, the body is in which state? This will be compensated via…
Metabolic acidosis
Respiratory compensation
If the pH of the body is decreased and the bicarbonate ion concentration is increased, the body is in what state? This is compensated via…
Respiratory acidosis
Renal compensation
