Urinary System 7 - Acid base regulation Flashcards
List the possible metabolic changes that can cause acidosis or alkalosis
- Acidosis can be caused by H+ gain and HCO3- loss
- Alkalosis can be caused by H+ loss and HCO3 gain
What is the normal plasma proton concentration?
- 49nmol/L
What is the normal arterial bicarbonate?
22-26mEg/l
Compare the range for normal blood pH to the range for normal urine pH
- Normal blood pH ranges between 7.35-7.45
- Normal urine pH regulates between 5-8, as it is a regulator
Describe the absorption of bicarbonate throughout the kidney
- 80% reabsorbed PCT
- 10% reabsorbed ascending loop of henle
- 6% reabsorped DCT
- 4% reabsorbed collecting duct
Why is bicarbonate important?
- It is a high capacity chemical buffer that can respond to changes in metabolic acid and be produced from respiratory acid
Write the henderson hasslebach equation with normal values substituted
pH=pK + log10(HCO3-/CO2)
pH = 6.1 + log10(24/1.2)
pH = 7.4
What is the davenport diagram?
- A graphical respresentation of the association between pH, bicarbonate and carbon dioxide in the blood
- Plasma bicarbonate on the y axis, pH and [H=] on the x axis, and pCO2 on a bent axis in the right hand corner
Explain what the deviations mean on the davenport diagram
- Slight increase in plasma bicarbonate and low pH is due to acute respiratory acidosis
- Slight decrease in plasma bicarbonate and high pH due to acute respiratory alkalosis
- Metabolic acidosis recongised by low bicarbonate, low pH
- Metbolic alkalosis low pH and high bicarbonate
- Chronic respiratory acidosis is similar to acute but with very high plasma bicarbonate and a more normal pH
- Chronic respiratory alkalosis is slightly high pH and very low base excess
Describe the process of bicarbonate reabsorption in the PCT
- Carbonic anhydrase converts bicarbonate to H2O and CO2. CO2 moves into the cell and is converted back to bicarbonate ions and protons
- Protons diffuse into filtrate via a H+ ATPase and the sodium proton exchanger
- Bicarbonate diffuses into the blood through the chloride bicarbonate exchanger, and bicarbonate sodium exchanger (3bicarb to 1Na)
- Chloride also diffuses into the blood through its channels
What are the two types of intercalating cells and what are their functions?
- Alpha cells (acid-secreting)
- Beta cells (bicarbonate secreting)
Describe the process in alpha intercalating cells
- Bicarbonate remade in the cytoplasm via CA
- Protons pumped into tubular fluid via hydrogen potassium ATPase and sodium proton antiporter
- Bicarbonate diffuses into blood via chloride bicarbonate exchanger, and chloride via channels
Describe the process in beta intersticalating cells
- In the cytoplasm, CO2 and H2O used to make bicarbonate and protons
- Protons pumped into the blood (H+ ATPase, H+/Na+ antiporter and H+/K+ ATPase)
- Bicarbonate enters the tubular fluid via chloride bicarbonate exchanger, and chloride diffuses back into tubular fluid via its channels
Describe the process of HCO3- generation by cells
- Glutamate enters the cell through SGLT-1
- Glutamate converted to NH4+ and HCO3-
- HCO3- enters blood (HCO3/CL- exchanger, HCO3/Na+ cotransporter, Na+/K+ ATPase)
- Ammonium leaves the cell through a NH4/Na+ antiporter to enter the filtrate
- Can also be produced using carbonic anhydrase and H2O/CO2
What is the compensatory mechanism for respiratory acidosis?
- Decrease acid increase bicarbonate
- Intracellular buffering, bicarbonate generation and ammonium excretion
