Renal Acid-Base Balance Flashcards
Why is venous blood slightly more acidic than arterial blood?
Presence of waste gases such as CO2
How much blood enters the kidneys per minute?
1200 mL / min
What is the only artery in the body which carries de-oxygenated blood?
Pulmonary artery
Which vessel contains more waste products, the renal artery or the renal vein?
Renal artery
What pH is blood in for it to be acidic?
Less than 7.35
What pH is blood in for it to be alkaline?
Greater than 7.45
What three ways is blood pH regulated?
- Chemical buffers (fastest)
- Respiratory centres
- Renal system (slowest)
Ketone bodies are formed via the breakdown of?
Anaerobic metabolism of fatty acids
What are the two buffering systems used to regulate pH the quickest?
Bicarbonate buffer system
Protein buffer system
Outline the chemical equation of the Bicarbonate buffer system
CO2 + H2O = H2CO3 = HCO3- + H+
Why does the PCT have a high level of mitochondria?
Ion / amino acid / glucose exchange relies heavily on ATP
What are the two main cell types found within the Proximal Convoluted Tubule?
Principal cells
Intercalated cells
What is the primary role of the Principal cells of the PCT?
H2O and Na+ balance
What is the primary role of the Intercalated cells of the PCT?
Acid-base balance
ADH acts on which cells of the Collecting Duct? How and what is the effect?
Principal cells, which causes an increase of aquaporin transcription on their cell membrane to reabsorb more water
Explain how H+ is filtered out into the urine and HCO3- is reabsorbed in the PCT of the kidneys
- H+ and HCO3- is freely filtered by the glomerulus and forms H2CO3 in the PCT tubule lumen
- H2CO3 dissociates into H2O and CO2 by Carbonic anhydrase IV and moves into intercalated cell
- Carbonic anyhdrase II converts this into H+ and HCO3- again
- HCO3- is exchanged for Cl- (from the capillary) into the capillary and is resorbed back into circulation
- H+ moves from the intercalated cell into the tubule lumen again via ATP / proton pump
- Other free Na+ filtered by the glomerulus is exchanged into the intercalated cell for H+ which is pumped out as well
When does H+ secretion into the urine cease? What happens then?
When urine pH falls to 4.5. Any additional H+ is neutralised in the filtrate and HCO3- is generated
Once H+ is successfully pumped from the intercalated cell wall into the tubule lumen, how is secreted out into the urine?
It can bind to HOP42- to form H2OP4-
How is new HCO3- generated in the PCT? In the instance where there is a dramatic fall in pH due to increased circulating H+
- Glutamine moves from the tubule lumen into the intercalated cell wall, where it is metabolised into NH4+ and HCO3-
- NH4+ is shuttled back into the tubule lumen via a Na+/H+ exchanger, which moves Na+ into the intercalated cell
- Finally, HCO3- enters the capillaries
What are the two reasons for acidaemia?
Metabolic acidosis
Respiratory acidosis
What are the two reasons for alkalaemia?
Metabolic alkalosis
Respiratory alkalosis
Why does respiratory acidosis occur?
Build up of CO2 (hypercapnia) due to hypoventilation
Mainly due to pulmonary problems i.e. pneumothorax, emphysema, chronic bronchitis, asthma
Why does metabolic acidosis occur?
Increased production of metabolic acids i.e. lactic acid or disturbances in ability to excrete acid via kidneys i.e. renal tubular acidosis
Why does respiratory alkalosis occur?
Hypocapnia due to hyperventilation
Why does metabolic alkalosis occur?
Caused by repeated vomiting, resulting in a loss of stomach acid HCl. Also caused by severe dehydration and alkali consumption
What population of patients are at a greater risk of acid-base abnormalities?
Infants and aged people
