regulation of homeostasis by the kidneys- acid base balance Flashcards
what is the role of the kidney in volume regulation? 2
- Fluid balance: the amount of water gained by the body each day equals the amount lost
- Electrolyte balance: the ion gains each day equals ion loss
what is the control of acid-base balance by the kidneys?
- Acid base balance: H+ gain is offset by H+ loss
what is the importance of pH control? 5
- The pH of the ECF remains between 7.35 and 7.45
- If plasma levels fall below 7.35- acidosis results
- If plasma levels rise above 7.45, alkalosis results
- Alterations outside of these boundaries affects all body systems- can result in coma, cardiac failure and circulatory collapse
- <6/8 or >8 can cause death
what do buffers do?
resist changes in pH- replace and remove H+ when it is added or removed
name 3 buffer systems? 3
- Carbonic acid/ bicarbonate
- Protein
- Phosphate
describe the acid base balance? 3
- The kidneys are essential for maintaining acid-base balance
- This is important because all biochemical processes must occur within an optimal pH window
- The kidneys do this in conjunction with the cardiovascular and respiratory systems
how is the acid-base balance maintained? 5
- The lungs excrete a large amount of CO2- this is a potential acid formed by metabolism (CO2 reacts with water to form carbonic acid)
- The kidneys also secreted and excrete non-volatile acids produced from normal metabolism- lactic acid, which the lungs can’t excrete
- However, to maintain acid-base balance, the kidneys must also reabsorb virtually all filtered HCO3-
- This is important as HCO3- acts as a physiological buffer
- This control of acid-base balance prevents acidosis or alkalosis
average values?
- blood pH
- urine pH
- blood [HCO3-]
- blood pCO2
- plasma osmolality
- urine osmolality
- Blood pH= 7.4
- Urine pH= 6.0
- Blood {HCO3-} = 24mM
blood pCO2= 40mmHg - Plasma osmolarity= 285 mOsm/kg water
- Urine osmolality= 600 mOsm/kg water (depends on hydration status)
what is the relationship between PH and plasma [CO2]?
inverse
When pCO2 increases, pH decreases
describe respiratory regulation of acid-base balance? 4
- Respiratory regulation of pH is achieved via the HCO3-/CO2 buffer system
- As pCO2 levels increase, pH decreases
- As pCO2 levels decrease, pH increases
- Changes in pH levels are detected by peripheral chemoreceptors which then act on respiration centres in the brain to adjust respiration rates
describe renal regulation of acid-base balance? 6
- The kidneys are the most effective regulator of body fluid pH
- Most HCO3- in filtrate is reabsorbed, H+ is also secreted.
- Renal tubular acidosis may occur is the kidneys don’t do this effectively which can cause renal failure
- If pH of ECR falls there is more secretion of H+ into filtrate and reabsorption of HCO3- back into ECF to cause the pH to increase
- Secretion of H+ is inhibited when urine pH falls below 4.5
- If pH of ECF increases, secretion of H+ into filtrate and reabsorption of HCO3- declines so the ECF pH decreases
what do we want to do in acidaemia? 2
- we want to increase H+ secretion into and HCO3- reabsorption from the proximal tubules
- We want to increase H+ secretion and HCO3- reabsorption and HCO3- generation in the distal tubule and intercalated cells
what is acidosis?
how do we deal with it? 2
Acidosis= pH of body fluid falls below 7.35 due to too much H+.
- Excrete H+ via the lungs as CO2 and the kidneys as H+
- Generate more buffer (HCO3-) in the kidneys
describe respiratory acidosis? 2
treatment? 3
- Caused by inadequate ventilation
- Can be acute or chronic
- Treatment:
- Restore ventilation
- Treat underlying dysfunction of disease
- Give lactate solution IV (converted into HCO3- buffer in the liver)
describe metabolic acidosis? 2
treatment? 2
- Results from all other conditions than respiratory that decrease pH
- Always chronic
- Treatment:
- Give IV isotonic HCO3-
- Give IV lactate solution (Ringer’s lactate or Hartmann’s solution- converted to HCO3- buffer in the liver)
what states cause a marked change in HCO3-?
chronic
how do we gain H+? 4
- CO2 in blood
- Non-volatile acids from metabolism
- Loss of HCO3- in diarrhoea or non-gastric GI fluids
- Loss of HCO3- in urine
what is alkalosis?
how do we deal with it? 3
Alkalosis= pH of body fluid climbs above 7.45
- Reduce excretion of CO2 via the lungs (increase blood CO2)
- Increase excretion of HCO3- buffer via the kidneys
- Increase generation of H+ by the kidneys
what is respiratory alkalosis? 2
treatment? 3
- Caused by hyperventilation
- Can be acute or chronic
- Treatment:
- Treat underlying cause
- Breathe into paper bag- increases pCO2
- Give IV Cl- containing solutions (increase HCO3- excretion)
what is metabolic alkalosis? 2
treatment? 3
- Results from all other conditions other than respiratory that increase pH
- Always chronic
- Treatment:
- Give electrolytes to replace those lost
- Give IV Cl- containing solution
- Treat the underlying disorder
how do we suffer H+ loss? 4
- Use of H+ un metabolism of organic anions
- Loss of H+ in vomit
- Loss of H+ in urine
- Hyperventilation (blows off CO2)
what conditions can cause respiratory acidosis? 5
- asphyxia
- hypoventilation
- advanced asthma
- severe emphysema
- reduced elimination of CO2 from bodily fluids
what conditions can cause metabolic acidosis? 4
- elimination of large amounts of HCO30 resulting from mucus secretion (diarrhoea vomiting)
- direct reduction of the bodily fluid pH as acid is absorbed
- production of large amounts of fatty acids and acidic metabolites- diabetes mellitus
- inadequate O2 delivery tp tissue resulting in anaerobic respiration and lactic acid build up-exercise, heart failure, shock
what conditions can cause respiratory alkalosis? 2
- reduced CO2 levels in the extracellular fluid- hyperventilation
- decreased atmospheric pressure reduces oxygen levels and causes hyperventilation- high altitudes
what conditions cause metabolic alkalosis? 2
- elimination of H+ and reabsorption of HCO3- in the stomach or kidney- vomiting or acidic urine formation due to excess aldosterone
- ingestion of alkaline substances- large amounts of sodium bicarbonate
