Acid-base balance 1: Renal mechanisms involved in regulation of [H+]plasma

Question 1

what does the acid-base balance regulate?

Answer 1

Only free unbound hydrogen ions

Question 2

what are the pH’s of arterial/venous and the average blood?

Answer 2

pH of arterial blood = 7.45
pH of venous blood = 7.35
Average pH of blood = 7.40

Question 3

what is it called when pH drops below 7.35?

Answer 3

Acidosis

Question 4

what is it called when pH rises above 7.45?

Answer 4

alkalosis

Question 5

what do small changes in pH reflect?

Answer 5

Large changes in H+ ion

Question 6

what can acidosis lead to?

Answer 6

depression of the CNS

Question 7

what can alkalosis lead to?

Answer 7

over excitability of the peripheral NS and later the CNS

Question 8

what effect can [H+] have?

Answer 8

• marked influence of enzyme activity

- influence K+ levels in the body

Question 9

[H+] is continually added to body fluids from what 3 sources?

Answer 9

1) Carbonic acid formation
2) Inorganic acids produced during breakdown of nutrients
3) Organic acids resulting from metabolism

Question 10

what is the difference in dissociation rates between strong and weak acids?

Answer 10

• Strong acids dissociate completely in solution

- Weak acids dissociate partially in solution

Question 11

what does a buffer system consist of?

Answer 11

a pair of substances –
one can yield free H+ as the [H+] decreases
the other can bind free H+ when [H+] increases

Question 12

what happens if H+ ions are added to the system?

Answer 12

Protons are “mopped-up” by A- leading to formation of more HA - equilibrium shifts to the left

Question 13

what happens if base are added to the system?

Answer 13

Base is “tied-up” by combining with H+, allowing more HA to dissociate and so equilibrium shifts to the right

Question 14

what is the equation for the dissociation constant?

Answer 14

K = [H+] [A-]/ [HA]

Question 15

what is the henderson-hasselbalch equation?

Answer 15

pH = pK + log [A-]/[HA]

Question 16

what is the most important physiological buffer system?

Answer 16

CO2 - HCO3 buffer

Question 17

what is the equation for the Co2 - HCO3 buffer?

Answer 17

CO2 + H2O –> H2CO3–> H+ + HCO3-

Question 18

what catalysises the production of H2CO3 from CO2 and H2O?

Answer 18

carbonic anhydrase

Question 19

why is this buffer system so important?

Answer 19

[HCO3-] is controlled by the kidneys & PCO2 is controlled by the lungs

Question 20

how do the kidneys control the [HCO3-]?

Answer 20

1) Variable reabsorption of filtered HCO3-
2) Kidneys can add “new” HCO3- to the blood
i. e. [HCO3-]renal vein > [HCO3-]renal artery

Question 21

what is the mechanism of [HCO3-] reabsorption in the proximal tubule?

Answer 21

• bicarbonate cannot be transported from the tubular fluid
• H+ ions are secreted by cells in the proximal tubule and transported across the apical membrane( Na comes in)
• using the H+ ions , bicarbonate ions are made in the epithelial cells and released into the interstitial fluid and eventually into the blood

Question 22

How is new HCO3- formed?

Answer 22

H+ ions bind with phosphate to make acid phosphate which is excreted in the urine but a bicarbonate ion is generated by renal tubular cells so there is a net gain of bicarbonate (this is H+ dependant)

Question 23

How can the amount of H+ excreted be measured?

Answer 23

titratable acid

Question 24

how can ammonia act as a tubular buffer?

Answer 24

ammonia (from glutamine) binds with a H+ ion to make an ammonium ion which is excreted in urine and bicarbonate is generated

Question 25

how can NH4+ be measured?

Answer 25

a separate ammonium ion determination

Question 26

what 3 things does H+ secretion by the tubule do?

Answer 26

A) Drives reabsorption of HCO3-
B) Forms acid phosphate
C) Forms ammonium ion

Question 27

what does the excretion of TA and NH4+ do?

Answer 27

simultaneously rids the body of acid load and regenerates buffer stores (alkalinizes the body)