Renal Regulation of Plasma pH

Question 1

Normal range of pH of fluids in body ?

Answer 1

ECF: 7.35-7.45
ICF: 7.2

acidosis = less than 7.35
Alkalosis = more than 7.45

Question 2

How do we correct acidosis in renal system

Answer 2

Too much H+ in filtrate
HCO3 +H–>H2CO3–>H2O+CO2 which diffuse into tubular epithelium
The H2O and CO2 turn into H2CO3 and then HCO3 , H+ is formed
HCO3 is reabsorbed
H+ EXCRETED but cant react again —as all HCO3 has been used up hence it is just excreted

Question 3

Differences between chemical and physiological buffers

Answer 3

Buffers = binds to H+ , removing it from solution
protein buffer system = can take , release H+
Bicarbonate buffer

physiological buffers : stabilise the pH by controlling output of:
1- Acids , bases = renal
2- Volatile acids CO2 in respiratory system

Renal = takes hours to a day
Respiratory = only CO2 but within minutes If ONE breaks down then the other can compensate !

Question 4

How does the renal system contribute to the regulation of body fluid pH ?

Answer 4

-Filtrate => HCO3 + H+ –>H2CO3–>H2O+ CO2, these can both diffuse across the tubular membrane and convert back to HCO3 and H+
(these are both charged molecules to they cant just diffuse )
- HCO3–> reabsorbed into the blood
- H–> transported back into the filtrate via Na/H+ pump
-then the H+ in filtrate binds again with HCO3 and cycle starts again

IN CONCLUSION :
H+ is secreted and HCO3 is reabsorbed
mainly in PCT
HCO3 is not lost

Question 5

The role of Ammonia in buffering H+ excretion in urine

Answer 5

For H+ secretion the H+ gradient needs to be maintained
when pH is below 4.5 in filtrate, H+ will stop being secreted from tubular cells
SO
- NH3 is secreted by tubular cells
- They go into the filtrate and react with the H+ to form NH4+ , which reduced the free H+ ( increasing pH) so that the gradient is maintained and H+ can still be excreted

Question 6

Acidosis :

• physiology
• Causes of acidosis RAAADD

Answer 6

• Dropping pH= more H+ = higher affinity to the albumin = so ca20 cant bind to the albumin–>Free ca2+ increases = blocks Na+ Channels = reduced AP = lower RMP = Vascular depression , bradycardia , systole , coma
  1) Respiratory acidosis = severe ventilatory defects ( asthma, COPD, pulmonary oedema )

2) Metabolic Acidosis:
- Renal injury
- Aspirin overdose= hyperventilation = acidosis
- Addisons disease = Hypoaldosteronism = na/h pump function is decreases so H+ secretion goes down
- Alcoholism = kidney damage
- Diarrhoea = loss of Na+ in filtrate means less H+ secreted
- DKA= increased ketones

Question 7

Alkalosis:

a) Physiology ca2+ wise
b) Causes

Answer 7

• Ca2+ binds to albumin , so it doesn’t bind to Na+ channel = they open = more excitability
• Many AP occur —> confusion , skeletal muscle spasms , death

Causes:
Respiratory alkalosis
-Hyperventilation ( paCO2, HCO3 decreased)

Metabolic alkalosis :

• Bicarbonate overdose
• Hyperaldosteronism ( more H+ lost)
• Vomiting = loss of gastric acid

Question 8

What would you expect to see biochemically in the blood in acidosis ?
(3)
what kind of breathing

Answer 8

1) Low ECF HCO, Low pH
2) Normal PaO2, slightly decreases paCO2
3) Compensatory deep breathing = Kussmaul’s breathing

Question 9

what is the counter current flow in kidney

4

Answer 9

1- Blood + filtrate in different directions
2- Filtrate moves from descending limb( water moved out )
3- Na+ pumped out in ascending limb => so blood is hypertonic ( lots of sodium )
This causes water to move via osmosis out of the descending limb into the blood= re absorbs the water into the blood
Hence we keep in water in the vasa recta