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
What is the compensatory mechanism for respiratory alkalosis?
- Intracellular buffering
- Decreased bicarbonate reabsorption and decreased ammonium excretion
What is the compensatory mechanism for metabolic alkalosis?
Hyperventillation
What is the compensatory mechanism for metabolic acidosis?
Hypoventilation
What is the blood pH compatable for life?
6.8-8 - critically ill
What is the normal venous bicarbonate?
22-29mmol/L
