Katz: Acid Base Flashcards
What is pH?
-log [H] = pH
What is a normal pH
7.4 (40 nm)
What is the isohydric principle?
Multiple acid/base pairs in solution will be in equilibrium with one another, tied together by their common reagent: the hydrogen ion and hence, the pH of solution.
CHANGE IN H LEADS TO A CHANGE IN IONIZATION
What is Le Chatelier’s Principle?
- increase in right side of the eqtn
- left shift
- increase in H
What is the most important extracellular buffer system? How does the buffer work when there’s acidosis?
C02 + H20 > H2C03 > H + HC03
- Increase in H
- Left shift
- Decrease in H (attenuated the rise in H)
Where does compensation occur? What does it do?
It occurs SLOWLY and return pH to NORMAL.
Lungs, kidney (liver)
How long does it take the lungs and kidneys to compensate?
lungs- minutes
kidneys- days
How does renal compensation respond to acidosis?
Acidosis stimulates the Na/H antiporter in the proximal tubule and increases proximal ammonium production.
H is added to the proximal lumen (much of it riding on NH3 as NH4), so the acid is TRAPPED in the lumen and excreted in the urine.
What is urine pH usually during acidosis?
It can be as low as 4-4.5 with 100mM NH4
How is plasma H reduced?
Plasma H is reduced by adding bicarbonate to the blood.
Why are renal ammonia production and renal H secretion often increased to compensate for an acidosis?
As acid builds up the cell becomes better at getting rid of acid and actually becomes MORE efficient.
What are the three cells involved in renal compensation to acid base disturbance?
- Proximal tubule cell (Secretes H/NH4, reabsorbs HCO3)
- Alpha intercalated cell (secretes H, reabsorbs K)
- Type B intercalated cell
Where are alpha intercalated cells located?
Distal tubule
Collecting ducts
What does an alpha intercalated cell do?
Reabsorbs K and secretes H
What is the primary urinary buffer in alpha intercalated cells? How much H rides on H2PO4 and how much on NH4+?
HPO4-/H2PO4 (1/2 of urinary H)
NH4 (2/3 of urinary H)
*you can excrete maybe 100 mM total H on these carriers per day, but urine pH range is from 4-8 (only a tiny amt of H is freely dissolved)
Why is alpha intercalated cell H secretion often increased as a compensation for acidosis?
Plasma H is reduced by adding bicarbonate to the blood. This creates more free H which leads to an increase in the H that is secreted.
Why is acidosis often accompanied by hyperkalemia?
As you stimulate the K/H ATPase to get rid of H, you simultaneously reabsorb more K. K can’t leave the cell via the luminal side, but there are many transporters on the basolateral side so MORE K is reabsorbed.
How does a beta intercalated cell compare do an alpha intercalated cell?
It has REVERSE polarity
Beta cells increase HCO3 secretion during alkalosis.
Why is alkalosis often accompanied by hypOkalemia?
As H is reabsorbed to counteract alkalosis, more K is secreted into the lumen along with bicarb. This leads to hyp0kalemia
What compensates for respiratory acidosis and alkalosis?
Respiratory acidosis/alkalosis are due to RESPIRATORY PROBLEMS so the KIDNEY must compensate. (slowly hours to days)
What compensates for metabolic acidosis/alkalosis?
Both are caused by non-respiratory metabolic problems so are dealt with by the LUNGS with some help from renal mechanisms if possible. Alveolar ventilation is a means to keep plasma pH near 7.4 during a metabolic disturbance.
What compensates faster, lungs or kidneys?
Lungs- w/in minutes, very fast!
What happens when H increases in plasma? (acidosis)
Peripheral chemoreceptors (carotid bodies) directly sense this change and mediate a rapid increase in alveolar ventilation (increased breathing) thereby lowering H.
Increased breathing:
- Lowers pCO2
- Increases pO2
How does a decrease in C02 (caused by rapid breathing) combat acidosis (decrease H)?
C02 + H20 < > H2CO3 < > H + HCO3
Breath more>
Decrease in C02>
left shift>
Decrease H
