Discuss the relative importance of respiratory systems and kidney in regulating pH


Discuss the relative importance of respiratory systems and kidney in regulating pH

pH is a very tightly controlled parameter in the body 7.35-7.45
It is important to maintain pH to allow functioning of enzymes and ion channels (other proteins e.g haemoglobin bohr effect)

Maintenance
Buffers
Carbonic anhydrase
CO2 + H2O <-----> H2CO3 <-----> HCO3-  + H+
Respiration and affects CO2
Kidney excretes and produces HCO3-
Kidney excretes H+
H+ can come from metabolism and diet. It varies greatly in diets e.g in vegans low H+ is while in meat eaters there is a high H+
pKa of the buffer system is 6.1 but desired pH is 7.4 so minute by minute control by lungs are required. The HCO3/0.03PCO2 must be set to 20.

Repiration
so pH changes are detected by the central and peripheral chemo receptors (more central) and altered signals are sent to the medulla to alter respiratory rate
Show link between alveolar resp rate and pACO2 (CO2 can also be carried by proteins and inorganic phospates as well as affecting pH)

Kidney
In PCT H+ ATPase and NHE acidifies the lumen driving the HCO3- into CO2 (Via CA) so it can diffuse in and then is taken up by either CL- antiporter or NBC1 co transporter.
In DCT (TYPE A INTERCALATING CELLS) K+ H+ ATP antiporters are used instead and CL- antiporter is on the basolateral membrane
IN TYPE B INTERCALATING CELLS produce HCO3- and NH4+ from Glutamine
The urine is buffered with ammonia in ammonia trapping

Control of Kidney
In the long term pH is controlled by the kidney this is controlled intrinsically and also by four hormones (hormones don’t really do much more intrinsic nature of kidney):
-cortisol – Increases transcription of NHE and NBC
-PTH- Promotes acid secretion and reduces phosphate reabsorption
-Angiotensin II – stimulates Na+/H+ exchange
-Aldosterone – stimulates K+/H+ ATPase in type A intercalated cells
Points to get across overall:
Kidney long term control and more important
Respiration short term minute by minute control

Diseases to consider
Metabolic alkalosis (Emesis)/ Metabolic acidosis (Ketoacidosis) – corrected by respiratory compensation
Respiratory Acidosis (COPD) / Alkalosis (Hyperventilation at altitude) – corrected by renal compensation

Written by Elizabeth Starling

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