pH, bicarbonate, and alk/acidosis

Question 1

pH of blood:

Answer 1

7.4

Question 2

pH of cells:

Answer 2

7.0

Question 3

Normal HCO3- concentration

Answer 3

23-25 mosmol/L

Maintained at 24 in kidneys.

Question 4

How does the kidney regulate bicarbonate levels?

Answer 4

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.

Question 5

Bicarbonate production:

Answer 5

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.

Question 6

Acidosis

Answer 6

pH<7.35

Question 7

alkalosis

Answer 7

pH>7.45

Question 8

Respiratory vs metabolic Alk/acidosis

Answer 8

Respiratory: Primary defect is a change of paCO2
Metabolic: Primary defect is a change of HCO3-

Question 9

Causes of metabolic acidosis

Answer 9

Excess acid production:
-keto-acid produced in diabetes mellitus
-ketones
Diarrhea (loosing bicarb)
Renal failure (failure to produce/reabsorb bicarb).

Question 10

Compensatory response to metabolic acidosis:

Answer 10

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+.

Question 11

Cause of respiratory acidosis

Answer 11

decreased respiratory rate

- opiates, codeine
- COPD
- Lung damage (embolism, edema)

Question 12

Effects of acidosis

Answer 12

• CNS-confusion
• K+ plasma concentration
• osteomalacia (demineralization of bones).

Question 13

causes of alkalosis

Answer 13

• Vomiting
• ingesting antacids
• reduced blood volume (causes increased Na absorption and K secretion)
• hyperventilation

Question 14

Compensation for alkalosis

Answer 14

• decreased breathing
• decreased HCO3- reabsorption
• decreased secretion of titratable acid and NH4+

Question 15

Hypokalaemic tetany

Answer 15

Hyperventilation leads to alkalosis, less free calcium, tetany.