Physiology 7 Flashcards
What is the normal pH and range?
pH = 7.4 range = 7.37 - 7.43
What should the ratio between bicarbonate and carbonic acid be?
20:1
What is unique about the bicarbonate buffer system?
It is an open buffer system, it includes gas which means the gas can be breathed off, meaning the equation won’t start pushing backwards.
How do we control carbon dioxide?
Via the respiratory system
How do we control bicarbonate?
Via the kidneys
what is the bicarbonate buffer system equation?
carbon dioxide + water = carbonic acid = Bicarbonate + H+ (proton)
How is the pH maintained in the extracellular fluid?
Via the bicarbonate buffer mainly
How is the pH maintained in the intracellular fluid?
Via importing H+ into cells (so its not free to contribute to pH) - this is done by swapping H+ for a K+ inside the cell, or by adding Cl- alongside H+.
What is a complication of acidosis?
hyperkalaemia - H+ is swapped for K+ which is now free in the plasma. Hyperkalaemia >5.5 and causes reduction in the resting membrane potential
What is the normal value of Bicarbonate?
24mmoles (22-26)
What is the normal value of PCO2?
40mmHg
What is a side effect of chronic renal failure?
Chronic acid load - the kidneys can’t remove the H+ so bicarbonate is increased by taking it from the bone.
When is intracellular buffering used?
In chronic acid loading.
When is the buffer system used?
the buffer system is used first to control pH levels, but it doesn’t REMOVE H+.
How do we remove H+ ions?
This is done using the kidneys. it is the definitive way to correct pH and occurs after buffering.
What is the point in buffering?
It maintains the pH until the kidney fixes it.
how is metabolic acid buffered?
43% in the ECF, 57% in the ICF.
How is respiratory acid buffered?
97% in cells (using haemoglobin)
3% in the plasma.
What controls bicarbonate?
The kidneys
What controls carbon dioxide?
The lungs
How does the kidneys reabsorb filtered bicarbonate?
Bicarbonate is filtered at the glomerulus and is in the tubule.
- hydrogen is transported out of the cell, sodium is transported into the cell to maintain the electrochemical gradient
- the hydrogen binds with the bicarbonate to create carbonic acid (via carbonic anhydrase)
- The carbonic acid dissociate into carbon dioxide and water
- the carbon dioxide is transported into the tubule cell where it binds with water again
- it creates carbonic acid - which dissolves into H+ and bicarbonate
- the H+ is secreted (to be reused again) and the bicarbonate is taken up into the blood
How does the kidney remove H+ and create new bicarbonate (initially)?
- using diphosphate
- carbon dioxide from the blood enters the tubule cell, it binds with water and uses carbonic anhydrase to become carbonic acid - it dissociates into bicarbonate (which is reabsorbed into the blood) and into H+ which is excreted into the tubule to be excreted
- diphosphate is in the tubule lumen - the sodium is absorbed into the tubule cell and Hydrogen is put out to maintain the electrochemical gradient
- the dibasic phosphate is excreted in the urine
Why can H+ not be removed on its own?
It would make the urine too acidic
What is the pH of the urine?
4.5-5.5 (Max 8)
How does the kidney excrete H+ and create bicarbonate (long term)?
The kidney takes 4-5 days to create glutamine
- carbon dioxide goes from the blood into the tubule cells, it binds with water and uses carbonic anhydrase to create carbonic acid - this dissociates into H+ and bicarbonate (which is reabsorbed in the blood), the H+ is used in the next step
- glutamine is broken down in the tubule cell into ammonia (NH3) and glutamate
- the NH3 is lipid soluble so it goes out into the tubule, it binds with a H+ to create NH4
- ammonium is insoluble so cannot cross back over the cell membrane - it is excreted in the urine
What does carbonic anhydrase do?
it is the enzyme in the reaction of building up and breaking down - carbonic acid into carbon dioxide and water - and vice versa
What does glutaminase do?
It converts glutamine into glutamate and ammonia
how is ammonia changed into ammonium in the distal tubule?
in the tubule lumen
How is ammonia changed into ammonium in the proximal tubule?
Inside the tubule cell (ammonium is insoluble so an ammonium transporter is needed to move it out into the tubule lumen) to be excreted
