Acid base balance 1 Flashcards
What is the pH equation?
pH = log 1/hydrogen
pH is a measure of what?
Unbound hydrogen ions and thus the acidity or alkalinity of a solution
Which is more acidic venous or arterial blood and why?
Venous blood due to the presence of carbonic acid
What is the normal pH range of blood?
7.35-7.45
Big changes in pH reflect big changes in hydrogen ion concentration. T/F
False - small changes in pH reflect big changes in hydrogen ion concentration
Why is it important to regulate hydrogen ion (i.e pH) levels?
Hydrogen ions affect:
- Enzyme activity
- Nerve activity
- Potassium levels
How does nerve activity change with differing levels of hydrogen ions?
Increased hydrogen - depression of CNS
Decreased hydrogen - overexcitibility of peripheral NS (–> CNS)
Hydrogen is continually added to the body via three main mechanisms. List them
Carbonic acid formation
Inorganic acids from nutrient breakdown (e.g meat protein)
Organic acids from metabolism
How can diabetes mellitus cause an acid base imbalance?
Glucose cannot be broken down so must switch to fat metabolism >
Increased production of ketoacids >
Decreased pH
Weak acids dissolve partially in solution. Write this equation
Undissociated weak acid –> hydrogen ion/proton + base
Explain a buffer system
Pair of substances where one dissociates to give hydrogen (in deficit) and the other combines with hydrogen (in excess)
If acid is added to a buffer system which way does equilibrium shift?
Acids provide hydrogen which combines with the base to form an undissociated acid (thus equilibrium shifts to the left)
If base is added to a buffer system which way does equilibrium shift?
Base combines with hydrogen forcing more undissociated acid to dissociate (thus equilibrium shifts to the right)
What is the dissociation constant pK? What is it’s equation?
pH at which equilibrium is reached. pK = -log K (where K is the right part of the buffer system over the left)
Write the henderson hasselbach equation
pH = pK + log [base/acid]
What is the most important physiological buffer system?
Carbon dioxide and bicarbonate
Which enzyme is responsible for converting carbon dioxide and water into carbonic acid?
Carbonic anhydrase
What version of the henderson hasselbach equation do we use with regard to physiological buffers?
pH = pK + log [bicarb/(solubility coefficient x partial pressure of carbon dioxide) ]
What makes the carbon dioxide and bicarbonate buffer system so important?
Bicarb is controlled by the kidneys
Carbon dioxide is controlled by the lungs
Interplay allows for precise control
By which two methods does the kidney control bicarbonate levels?
Changes in reabsorption of filtered bicarbonate
Addition of “new” bicarbonate to the blood (i.e higher concentration of bicarb in the renal veins than in renal arteries)
What is the kidney control of bicarbonate levels dependent on?
Hydrogen ion secretion into the kidney tubules
How is bicarbonate reabsorbed in the proximal tubule?
It must be indirectly reabsorbed:
Carbon dioxide (from interstitium) and water (from tubular fluid) combine within the tubular cells to form carbonic acid >
Carbonic acid dissociates into bicarbonate and hydrogen >
Bicarbonate already within the tubular cell leaves at the basolateral membrane via the sodium bicarbonate cotransporter >
Hydrogen ions secreted into the tubular fluid via sodium hydrogen exchanger >
Bicarbonate in tubular filtrate combines with the hydrogen ions to form carbonic acid >
Carbonic acid dissociates into water and carbon dioxide and water enters the tubular cells
Hydrogen ion secretion is driven by the partial pressure of carbon dioxide. T/F
True - increase in partial pressure causes increase in hydrogen secretion
What do hydrogen ions combine with when bicarbonate in the tubular fluid is low?
Phosphate (next most plentiful buffer)
Which primary active transport mechanisms are present in the collecting ducts?
Hydrogen potassium ATPase
Hydrogen ATPase
Sodium-hydrogen exchanger
How does phosphate act as a tubular buffer?
Hydrogen ions which are being pumped from the tubular cell via the sodium hydrogen exchanger combine with phosphate >
Formation of dihydrogen phosphate ion >
Acidic ion is excreted >
Net gain of two “new” bicarbonate ions
What is titratable acid? How is titratable acid measured?
Hydrogen excreted as the dihydrogen phosphate ion.
Measure the amount of strong base needed to bring the pH of the urine back to normal
How does ammonia act as a tubular buffer? When does ammonia start being used as a buffer?
Glutamine from the liver is broken down to ammonia by glutaminase >
Ammonia enters the tubular fluid >
Hydrogen ions which have been pumped from the tubular cell via the sodium hydrogen exchanger combine with ammonia >
Ammonium is formed >
Ammonium is excreted >
Net gain of two “new” bicarbonate ions
When all the phosphate has been used up
Is ammonium a titratable acid?
No
What does hydrogen secretion from the kidney tubules do?
Drives reabsorption of bicarbonate
Forms acid phosphate (dihydrogen phosphate ion)
Forms ammonium ion
Excretion of TA and NH4 simultaneously rids the body of acid and regenerates buffer stores. T/F
True - remember buffer equation
