Acid-Base Flashcards
Define acid and base
Acid = molecules that can release H+
Base = ion or molecule that can accept H+
What is the arterial blood pH?
7.35-7.45
What is urine pH and why does it range?
4.5 - 8
Ranges depending acid-base status of EFC
In order to tightly regulate body pH
What are the pH limits a person can live for a few hours?
6.8 - 8
Define acidosis
Arterial pH below 7
Define alkalosis
Arterial pH above 7.4
What systems regulate the body pH?
Kidneys
Lungs
Define a buffer
Substance that can bind or release H+ to keep pH of solution relatively constant despite addition of considerable acid or base
Name 4 buffers
H2CO3
H2PO4-
HProt
HHb
What does amino acid metabolism create?
Releases NH4+ and H2SO4 (sulfuric acid)
How does the kidney regulate acid-base balance?
Excretes acids
Conserves HCO3-
Where does H+ secretion and HCO3- reabsorption NOT occur?
THIN segment of loop of Henle
What effects do carbonic anhydrase inhibitors have?
Decrease proximal tubular H+ secretion»>Increase fluid excretion»>Increase loss of bicarbonate and Na+
What cells are found in the DCT?
Type A Intercataled cells
How is HCO3- reabsorbed in the DCT?
HCO3- / Cl- exchanger
How is H+ secreted in the DCT?
Mainly H+ ATPase mediated by ALDOSTERONE
H+/K+ ATPase
What happens when urine pH reaches 4.5?
Limiting pH = further H+ secretion is not possible
What is the role of buffering systems in terms of urine pH?
3 systems bind H+ in the urin
Allow more H+ secretion
Delay reaching limiting pH
What are the 3 buffering systems in urine?
Bicarbonate buffer system
Phosphate buffer system
Ammonia buffer system
Where does each buffering system in urine occur?
Bicarbonate = mostly PCT
Phosphate = DCT & CT
Ammonia = PCT & DCT
What is the ratio between HCO3- and phosphate?
New HCO3- is returned to the blood for each NaHPO4 rate reacts with a secreted H+
How does the ammonia buffer work?
Glutamine is taken up by the proximal tubular cell
It splits into 2HCO3- and 2NH4-
The NH4+ is secreted into tubular lumen by NH4- / Na+ exchanger
NH4+ joins with Cl-
What factors interfere with H+ secretion and HCO3- reabsorption?
CO2
Ang II
Aldosterone
Serum K+ levels
ECF volume
Why does high CO2 increase H+ secretion and HCO3- reabsorption?
Increases the carbonic acid levels = enhanced H+ secretion
How does increased aldosterone increase H+ secretion and HCO3- reabsorption?
Stimulates H+ secretion by Type A intercalated cells of the DCT
How does decrease in ECF volume increase H+ secretion and HCO3- reabsorption?
Activates RAAS -> increasing H+ secretion -> alkalosis
How does increase in Ang II increase H+ secretion and HCO3- reabsorption?
Ang II enhances the activity of the sodium-hydrogen exchanger (NHE3) located on the luminal membrane of PCT cells
Leading to increased secretion of H+
How does ventilation regulate acid-base balance?
Increase ventilation = eliminates CO2 = decrease in H+ concentration
How is bicarbonate lost and what does this cause?
Metabolic acidosis
Diarrhoea
Renal tubular acidosis type 2 (RTA2)
How is metabolic acidosis caused?
Ingestion of acidifying salts = NH4Cl and CaCl2
Decreased H+ excretion = renal failure or RTA1
Increased H+ production = diabetic ketosis and lactic acid generation
What are the causes of metabolic alkalosis?
Loss of H+ = vomiting & diuretics
Ingestion of HCO3- = ex-antacids
What are the causes of respiratory acidosis?
Decreased ventilation = due to lung diseases or neuromuscular problems (leading to respiratory muscle weakness)
Severe pneumonia / asthma
What are the causes of respiratory alkalosis?
Increased ventilation = due to hyperventilation of physiology
Physiology = high altitudes so low O2 level stimulates respiration
What happens in chronic acidosis?
Regardless of what type of acidosis = increased production of NH4+ which contribute to excretion of H+ and addition of new HCO3- to the extracellular fluid
What limits respiratory compensation of metabolic alkalosis?
Size of this compensation is limited by carotid and aortic chemoreceptor mechanisms
As pO2 should be maintained
What are other compensatory mechanisms for metabolic acidosis?
Decreased glomerular filtration of HCO3-
What are other compensatory mechanisms for metabolic alkalosis?
Decreased renal H+ secretion
Reduced HCO3- reabsorption
If levels are very high HCO3- can be excreted in urine
Why may compensation be complete or incomplete?
Compensatory mechanisms may not have time to form in severe acute disturbances
If acid-base disorder slowly develops = compensation will happen more effectively
