SM 200a/201a - Acid Base Flashcards
What is Pendrin?
Which cells contain it?
Pendrin is an HCO3-/Cl- exchanger on the apical membrane of beta-intercalated cells of the collecting duct (secrete bicarb), and the basolateral membrane of alpha-intercalated cells of the collecting duct (reabsorb bicarb)
It functions to get HCO3- out of the cell, and Cl- into the cell
What is the effect of angiotensin II on HCO3- reabsorption and acid excretion?
Angiotensin II stimulates bicarbonate reabsorption and acid excretion
Angiotensin II -> kidney works to increase pH
(Angiotensin II is secreted in response to signals that indicate low volume; low volume -> hypoperfusion -> lactic acidosis -> decreased serum pH; kidney reacts by retaining bicarb and excreting acid)
What is citrate?
What is its role in acid-base balance?
Citrate is an organic anion
Citrate reabsorption is equivalent to base retention
- Main urinary base
- Reabsorbed and converted to CO2 and H2O
- This consumes H+ and generates OH-
- Chelates Ca2+
- Prevents precipitation with phosphate and oxalate ->
- *prevents kidney stones**
How does NH3 get across the membranes of the kidney tubule?
Diffusion
- Proximal convluted tubule
- Diffuses into the lumen
- Binds to H+ and becomes trapped
- Reabsorbed and recycled in the Loop of Henle
- Medullary collecting duct
- Diffuses into lumen
- Binds to H+ and becomes trapped and excreted
What is the differential for anion-gap metabolic acidosis?
MUDPILES: Acid add-on state
- Methanol
- Uremia
- Diabetic ketoacidosis (any ketoacidosis)
- Phenformin, paracetamol/acetaminophen, paraldehyde
- Iron, Isoniazid, Inborn errors of metabolism
- Lactic acidosis
- Ethanol/Ethylene glycol
- Saliclates/ASA/Aspirin
What is the Henderson-Hasselbach Equation for Biarbonate/Carbonic acid?
What acid-base transporters in the cell membrane protect the cell from changes in pH?
-
Na+/H+ exchanger
- Main mechanism
- Na+ dependent
- Cl-/HCO3- exhcanger
- Na+ independent
- Na+,HCO3-/H+,Cl- exchanger
- Na+ dependent
What is the effect of hypokalemia on HCO3- reabsorption and acid excretion?
Hypokalemia stimulates bicarbonate reabsorption and acid excretion
Hypokalemia -> kidney works to increase serum pH
In which tubules of the kidney is bicarbonate reabsorption driven by the Na+/H+ exhchanger?
Proximal tubule
Thick ascending limb of LOH
(Not the collecting tubule, although Na+ indirectly affects H+ secretion in the CT)
Where in the kidney tubule is NH4+ reabsorbed?
Loop of Henle
What is the equation for urine anion gap?
How do you use it?
[Na+] + [K+] + [NH4+] = [Cl-]
Useful in in ruling in/out RTA as a cause of hyperchloremic (non-AG) metabolic acidosis
- If [Na+] + [K+] > [Cl-], then there is no NH4+ in the urine
- If this is true while the patient is acidemic, the kidney tubules are not properly acidifying the urine
- If [Na+] + [K+] -], then there is NH4+ in the urine
- This is an indication of acid excretion, which means the metabolic acidosis is not likely to be caused by RTA
Why might does amiloride cause metabolic acidosis?
Amiloride blocks Na+ reabsorption in the collecting duct
- Decreased Na+ reabsorption
- -> Decreased Na+/H+ exchange
- -> Decreased H+ secretion
- -> Metabolic acidosis
Describe the pathophysiology of diabetic ketoacidosis
Lack of insulin
- -> Lipolysis and release of fatty acids
-
-> Accumulation of ketone bodies
- Acetoacetatic acid and beta-hydroxybutyric acid
-
-> Accumulation of ketone bodies
What is Type A lactic acidosis?
Increased lactic acid generation
- Due to tissue hypoxia
- Severe hypotension
- Cardiac arrest
- Sepsis
(Type B = decreased utilization of lactic acid)
A state of _______________ leads to the formation of glutamine in the liver
A state of metabolic acidosis leads to the formation of glutamine in the liver
What is the most frequent and severe cause of H+ build up in the circulation?
Lactic acidosis
Describe the transport of NH4+ (ammonia) in the kidney tubule
-
Glutamine –> NH4+ in the proximal tubule
- Glutamine into PCT epithelial cell through the basolateral membrane
- Glutamine –> NH4+ –> NH3 + H+
- H+ is secreted into the tubule via H+/Na+ exchanger
- NH3 diffuses into the tubule
- In the tubule, NH3 + H+ –> NH4+
-
NH4+ is reabsorbed in the Loop of Henle
- NH4+/K+ exchanger
- Na+/NH4+/Na+ exchanger
- NH4+ channel
-
NH3 diffuses into the medullary collecting duct, binds to H+ and is trapped as NH4+
- Acid (H+) secreted by collecting duct epithelial cells binds to NH3 and becomes trapped as NH4+
- This is how the body secretes acid while retaining bicarb
What is the differential for non-anion gap (hyperchloremic) metabolic acidosis?
USED CARS: Bicarb loss
- Uretrosigmoidostomy
- Saline administration (NaCl)
- In the face of renal dysfunction
- Endocrine (addison’s), Ethanol
- Diarrhea
- Carbonic anhydrase inhibitors
- Ammonium chloride
- Renal tublar acidosis
- Spironolactone
Meatabolic Acidosis is a primary disturbance characterized by _________________
Meatabolic Acidosis is a primary disturbance characterized by
a fall in blood bicarbonate levels
This leads to decreased pH
Why do you see hypokalemia in Distal RTA?
DRTA = the distal tubule (alpha-intercalated cells) cannot secrete H+
- Lumen is negatively charged due to Na+ reabsorption
- Pulls + charge in
- K+ is secreted instead