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

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what does the acid-base balance regulate?

Only free unbound hydrogen ions


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

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


what is it called when pH drops below 7.35?



what is it called when pH rises above 7.45?



what do small changes in pH reflect?

Large changes in H+ ion


what can acidosis lead to?

depression of the CNS


what can alkalosis lead to?

over excitability of the peripheral NS and later the CNS


what effect can [H+] have?

-marked influence of enzyme activity
-influence K+ levels in the body


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

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


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

-Strong acids dissociate completely in solution
-Weak acids dissociate partially in solution


what does a buffer system consist of?

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


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

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


what happens if base are added to the system?

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


what is the equation for the dissociation constant?

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


what is the henderson-hasselbalch equation?

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


what is the most important physiological buffer system?

CO2 - HCO3 buffer


what is the equation for the Co2 - HCO3 buffer?

CO2 + H2O --> H2CO3--> H+ + HCO3-


what catalysises the production of H2CO3 from CO2 and H2O?

carbonic anhydrase


why is this buffer system so important?

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


how do the kidneys control the [HCO3-]?

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


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

-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


How is new HCO3- formed?

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)


How can the amount of H+ excreted be measured?

titratable acid


how can ammonia act as a tubular buffer?

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


how can NH4+ be measured?

a separate ammonium ion determination


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

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


what does the excretion of TA and NH4+ do?

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