pH, bicarbonate, and alk/acidosis Flashcards
pH of blood:
7.4
pH of cells:
7.0
Normal HCO3- concentration
23-25 mosmol/L
Maintained at 24 in kidneys.
How does the kidney regulate bicarbonate levels?
Most all bicarbonate in the plasma is reabsorbed in the PT (80%). 20% in the CD.
Bicarbonate that is lost to buffering is compensated for by production in the CD.
Bicarbonate production:
Method 1: Carbonic anhydrase can produce H2CO3 in the intercalated cells of the CD. But what is to be done with the H+ that disassociates? It is pumped into the lumen and binds to a different buffer, mainly phosphate or creatine.
Method 2: NH4+ trapping.
Acidosis
pH<7.35
alkalosis
pH>7.45
Respiratory vs metabolic Alk/acidosis
Respiratory: Primary defect is a change of paCO2
Metabolic: Primary defect is a change of HCO3-
Causes of metabolic acidosis
Excess acid production:
-keto-acid produced in diabetes mellitus
-ketones
Diarrhea (loosing bicarb)
Renal failure (failure to produce/reabsorb bicarb).
Compensatory response to metabolic acidosis:
ECF:
- Buffering by HCO3-, P-, plasma proteins.
- Bone: Ca2+ is released from bone as calcium carbonate, and H+ moves into the bone to take the place of Ca+.
ICF:
-H+ titrated by HCO3-, P-, proteins, and histamine groups on proteins.
Respiratory: increase in respiration, reducing paCO2 below normal levels to compensate.
Renal compensation: H+ excreted bound to P and creatine buffers, or trapped by NH4+.
Cause of respiratory acidosis
decreased respiratory rate
- opiates, codeine - COPD - Lung damage (embolism, edema)
Effects of acidosis
- CNS-confusion
- K+ plasma concentration
- osteomalacia (demineralization of bones).
causes of alkalosis
- Vomiting
- ingesting antacids
- reduced blood volume (causes increased Na absorption and K secretion)
- hyperventilation
Compensation for alkalosis
- decreased breathing
- decreased HCO3- reabsorption
- decreased secretion of titratable acid and NH4+
Hypokalaemic tetany
Hyperventilation leads to alkalosis, less free calcium, tetany.
