T3 L8 Regulation of homeostasis in the kidney: acid-base balance Flashcards
What is the definition of renal dysfunction?
Inability to maintain salt and water balance & acid-base balance
What is the role of the kidney in volume regulation?
Fluid balance - amount of water gained by the body = amount lost
Electrolyte balance - ion gain = ion loss
Why is pH control important?
Alterations outside the normal range can cause coma, cardiac failure & circulatory collapse
pH < 6.0 or >8.0 leads to death
What do acids do?
Release H+ into solution
What do bases do?
Remove H+ from solution
What is pH?
Potential of hydrogen
Specifies the acidity or basicity of an aqueous solution
What are buffers?
Resist changes in pH
When H+ is added, the buffer removes it
When H+ is removed the buffer replaces it
What are some types of buffers?
Carbonic acid / bicarbonate
Protein
Phosphate
What is the acid-base balance reaction?
CO2 + H2O H2CO3 H+ + HCO3-
Why is carbonic acid volatile?
It can be converted to CO2
What is the pH of human blood?
7.4
What is the pH of urine?
6.0
Slightly more acidic as you get rid of acids through the urine
What does urine osmolality depend on?
The hydration status
What is the relationship between pH and bicarbonate/CO2?
pH is inversely proportional to (HCO3-) / (pCO2)
HCO3- is a physiological buffer regulated by the kidney
pCO2 is a potential acid that is regulated by the lungs
What happens to pH when pCO2 increases?
pH decreases as the extra CO2 reacts with water to form carbonic acid
What detects changes in pH?
Peripheral chemoreceptors which act on the respiration centres in the brain to adjust respiration rates
What is the most effective regulator of body fluid pH?
Renal system
When does renal tubular acidosis occur?
When the kidneys don’t effectively reabsorb HCO3- and secrete H+
What happens if the pH of the extracellular fluid increases?
Alkalaemia –> secretion of H+ into filtrate & reabsorption of HCO3- decreases –> extracellular pH decreases
What happens if the oH of the extracellular fluid falls?
Acidaemia –> more secretion of H+ into filtrate & reabsorption of HCO3- back into the extracellular fluid –> causes pH to increase
What is acidosis?
When the pH of the body fluid falls below 7.35
Too much H+
What is the solution to acidosis?
Get rid of H+ out of the body
Excreted via the lungs as CO2 or via the kidneys as H+
Generate more buffer in the kidneys
What is alkalosis?
pH of body fluids goes above 7.45
What the solution to alkalosis?
Increase H+ levels in the body
Reduce excretion of CO2 via the lungs to increase blood CO2
Increase excretion of HCO3- buffer via the kidneys
Increase generation of H+ by the kidneys
What is respiratory acidosis?
Caused by inadequate ventilation
Acute or chronic
What is the treatment for respiratory acidosis?
Restore ventilation
Treat underlying dysfunction or disease
Give IV lactate solution which is converted to HCO3- buffer in the liver
What is metabolic acidosis?
Results from all conditions that decrease pH apart from respiratory
Always chronic
What is the treatment for metabolic acidosis?
Give IV isotonic HCO3-
Give IV lactate solution - converted to. HCO3- buffer in liver
What are some ways to gain H+?
CO2 in the blood - combines with H2O to form carbonic acid
Non-volatile acids from metabolism such as lactic acid
Loss of HCO3- in diarrhoea or non-gastric GI fluids
Loss of HCO3- in urine
What is respiratory alkalosis?
Caused by hyperventilation
Acute or chronic
What is the treatment for respiratory alkalosis?
Treat underlying cause
Breathe into paper bag to increase pCO2
Give IV Cl- containing solution which increases HCO3- excretionn
What is metabolic alkalosis?
Results from all conditions that increase pH apart from respiratory
Always chronic
What is the treatment for metabolic alkalosis?
Give electrolytes to replace those lost
Give IV Cl- containing solution
Treat underlying disorder
What are the reasons for a loss of H+?
Use of H+ in metabolism of organic anions
Loss of H+ in vomit
Loss of H+ in urine
Hyperventilation
