Lecture 19: Renal acid-base Regulation-Exam 3

Question 1

pH range in venous and arterial

Answer 1

Arterial blood pH=7.37-7.44

Venous blood pH= 7.35-7.45

Question 2

Systems regulating [H+]

Answer 2

Chemical acid base buffer systems of the body fluids
Respiratory center
Kidneys

Question 3

Buffer

Answer 3

Substance that can irreversibly bind H+

Consists of a weak acid (conjugated acid)

Question 4

Buffer Systems

Answer 4

Bicarbonate buffer system
Phosphate buffer system
Proteins

Question 5

Bicarbonate buffer system

Answer 5

Most important extracellular buffer system
Consists of a weak acid (H2CO3) and a bicarbonate salt (NaHCO3)
CO2 + H2OH2CO3 speed up by carbonic anhydrase
H2CO3H+ + HCO3-
NaHCO3 HCO3- + Na+

Question 6

Effects of strong acid and strong base on bicarbonate system

Answer 6

Addition of a strong acid leads to formation of a weak acid

addition of a strong base leads to formation of a weak base

Question 7

Regulation

Answer 7

Increased levels of HCO3- can be excreted via the kidneys
Net result is a tendency for the CO2 levels in the blood to decrease
Decrease CO2 levels—> Decrease respiration rate—>CO2 expiration
PCO2 controlled by rate of respiration

Question 8

Metabolic acid Base disturbances

Answer 8

results from primary change in bicarbonate concentration
Metabolic acidosis= decrease in HCO3-
Metabolic alkalosis= Increase in HCO3-

Question 9

Respiratory acid base disturbance

Answer 9

Results from primary change in pressure of CO2 (PCO2)
Respiratory acidosis= increase in PCO2
Respiratory alkalosis= Decrease in PCO2 ( caused by hyperventilation)

Question 10

Relation between pH, [HCO3-], [CO2]

Answer 10

[HCO3-]=[CO2]==>pH=6.1

pH=6.1= pKa of the buffer

Question 11

Phosphate buffer system

Answer 11

Plays major role in buffering renal tubular fluid and intracellular fluid
Phosphate is greatly concentrated in the tubules
Lower pH of the tubular fluid brings operating range of buffer closer to the PK
Main elements are H2PO4-, HPO4–
HCl + Na2HPO4—->NaH2PO4 + NaCl
Strong acid is replaced by an additional amount of a weak acid and pH change is minimal

Question 12

Overall mechanism

Answer 12

Kidneys cab excrete an acidic or basic urine
Non volatile acids are excreted through renal excretion
All filtered bicarbonate is reabsorbed

Question 13

Regulation of extracellular H+

Answer 13

Bicarbonates reabsorbed via proximal tubule(85%), ascending tubule (10%), distal tubule (4%)
Minimal bicarbonates excreted (1%)
Kidneys can secrete H+ by primary active transport
Kidneys produce new bicarbonate ions via CO2 from body and water
CO2+ H2O–>H2CO3—>H+ + HCO3-

Question 14

Limitation of amount of free H+ excreted

Answer 14

Only small part of the excess H+ is secreted due to the lower limit of pH that can be achieved in normal kidneys=4.5
[H+]= 0.03 mEq/L
80 mEq H+ secreted so for the body to get rid of all that would require 2667 L (80/0.03) of urine
Buffer allow larger amounts of hydrogen to be excreted without requiring large amount of urine.

Question 15

Compensatory mechanisms in acidosis

Answer 15

Primary compensatory response in respiratory acidosis is an increase in plasma bicarbonate ion due to addition of new bicarbonate by the kidney.
Primary compensatory response in metabolic acidosis is an increased ventilation rate and renal compensation by addition new bicarbonate ions to extracellular fluid

Question 16

Compensatory mechanisms in alkalosis

Answer 16

Compensatory response in respiratory alkalosis is done by a reduction in plasma bicarbonate ion concentration due to renal excretion of bicarbonate ion
Compensatory response in metabolic alkalosis is done by a decrease in ventilation and an increase renal bicarbonate ion excretion

Question 17

Types of acid

Answer 17

Volatile acid (CO2) excreted from lungs
Non volatile acid (fixed acids) excreted from kidneys (sulfuric acid, phosphoric acid, lactic acid)