Regulation of homeostasis by the kidney: acid base balance

Question 1

Role of the kidney in volume regulation

Answer 1

Fluid balance: the amount of water gained by the body each day equals the amount lost

Electrolyte balance: the ion gain each day equals ion loss

Question 2

Control of acid base balance by the kidneys

Answer 2

H+ gain is offset by H+ loss

Question 3

Buffers

Answer 3

Resist changes in pH

• when H+ added, buffer removes it
• when H+ removed, buffer replaces it

Question 4

pH homeostasis

Answer 4

Lungs excrete large amounts of CO2 (potential acid)

Kidneys secrete and excrete non- volatile acids which the lungs can’t excrete

Kidneys also reabsorb all filtered HCO3- (physiological buffer)

Question 5

Relationship between pH, CO2 and HCO3-

Answer 5

Blood pH: 7.4
Urine pH: 6

Blood [HCO3-]= 24mM
Blood pCO2= 40mmHg

Plasma osmolality: 285 mOsm/kg
Urine osmolality; 600 mOsm/kg

Question 6

Respiratory regulation of acid- base balance

Answer 6

CO2 reacts with water to form carbonic acid

Inverse relatiobship between pH and plasma concentration of CO2

Achieved via HCO3-/CO2 buffer system

Question 7

Renal regulation if acid- base balance

Answer 7

Most HCO3- in filtrate is reabsorbed, H+ secreted

If pH of ECF falls: more secretion of H+ into filtrate and reabsorption of HCO3- back into ECF so increase in pH

Secretion of H+ inhibited when urine pH falls below 4.5

If pH of ECF increases: secretion of H+ into filtrate and reabsorption of HCO3- declines

Question 8

Acidosis

Answer 8

pH of body fluids falls below 7.35

Too much H+

Solution: get rid of H+

• excrete via the lungs (CO2) and kidneys (H+)
• generate more buffer (HCO3-) in the kidneys

Question 9

Alkalosis

Answer 9

pH of body fluids climbs above 7.45

Too little H+

Solution: increase H+ levels

• reduce excretion of CO2 in the lungs
• increase excretion of HCO3- via kidneys
• increase generation of H+ by the kidneys

Question 10

Types of acidosis

Answer 10

Respiratory

• caused by inadequate ventilation
• can be acute or chronic

Metabolic

• results from all conditions other than respiratory
• always chronic

Question 11

How to gain H+

Answer 11

CO2 in blood (combines with H2O to form carbonic acid)

Non volatile acids from metabolism (e.g. lactic acid)

Loss of HCO3- in diarrhoea or non gastric GI fluids

Loss of HCO3- in urine

Question 12

Treatment of metabolic acidosis

Answer 12

Give IV isotonic HCO3-

Give IV lactate solution

Question 13

Treatment of respiratory acidosis

Answer 13

Restore ventilation

Treat underlying dysfunction or disease

Give IV lactate solution

Question 14

Types of alkalosis

Answer 14

Respiratory

• caused by hyperventilation
• can be acute or chronic

Metabolic

• results from all conditions other than respiratory
• always chronic

Question 15

How to lose H+

Answer 15

Use of H+ in metabolism of organic anions

Loss of H+ in vomit

Loss of H+ in urine

Hyperventilation

Question 16

Treatment of metabolic alkalosis

Answer 16

Give electrolytes to replace those lost

Give IV Vl- containing solution

Treat the underlying disorder

Question 17

Treatment of respiratory alkalosis

Answer 17

Treat underlying cause

Breathe into paper bag

Give IV CL- containing solution