regulation of homeostasis by the kidneys- acid base balance

Question 1

what is the role of the kidney in volume regulation? 2

Answer 1

• 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

Question 2

what is the control of acid-base balance by the kidneys?

Answer 2

• Acid base balance: H+ gain is offset by H+ loss

Question 3

what is the importance of pH control? 5

Answer 3

• 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

Question 4

what do buffers do?

Answer 4

resist changes in pH- replace and remove H+ when it is added or removed

Question 5

name 3 buffer systems? 3

Answer 5

• Carbonic acid/ bicarbonate
• Protein
• Phosphate

Question 6

describe the acid base balance? 3

Answer 6

• 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

Question 7

how is the acid-base balance maintained? 5

Answer 7

• 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

Question 8

average values?

• blood pH
• urine pH
• blood [HCO3-]
• blood pCO2
• plasma osmolality
• urine osmolality

Answer 8

• 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)

Question 9

what is the relationship between PH and plasma [CO2]?

Answer 9

inverse

When pCO2 increases, pH decreases

Question 10

describe respiratory regulation of acid-base balance? 4

Answer 10

• 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

Question 11

describe renal regulation of acid-base balance? 6

Answer 11

• 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

Question 12

what do we want to do in acidaemia? 2

Answer 12

• 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

Question 13

what is acidosis?

how do we deal with it? 2

Answer 13

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

Question 14

describe respiratory acidosis? 2

treatment? 3

Answer 14

• 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)

Question 15

describe metabolic acidosis? 2

treatment? 2

Answer 15

• 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)

Question 16

what states cause a marked change in HCO3-?

Answer 16

chronic

Question 17

how do we gain H+? 4

Answer 17

• CO2 in blood
• Non-volatile acids from metabolism
• Loss of HCO3- in diarrhoea or non-gastric GI fluids
• Loss of HCO3- in urine

Question 18

what is alkalosis?

how do we deal with it? 3

Answer 18

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

Question 19

what is respiratory alkalosis? 2

treatment? 3

Answer 19

• 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)

Question 20

what is metabolic alkalosis? 2

treatment? 3

Answer 20

• 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

Question 21

how do we suffer H+ loss? 4

Answer 21

• Use of H+ un metabolism of organic anions
• Loss of H+ in vomit
• Loss of H+ in urine
• Hyperventilation (blows off CO2)

Question 22

what conditions can cause respiratory acidosis? 5

Answer 22

• asphyxia
• hypoventilation
• advanced asthma
• severe emphysema
• reduced elimination of CO2 from bodily fluids

Question 23

what conditions can cause metabolic acidosis? 4

Answer 23

• 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

Question 24

what conditions can cause respiratory alkalosis? 2

Answer 24

• reduced CO2 levels in the extracellular fluid- hyperventilation
• decreased atmospheric pressure reduces oxygen levels and causes hyperventilation- high altitudes

Question 25

what conditions cause metabolic alkalosis? 2

Answer 25

• 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