Acid-Base balance I Flashcards
What is pH?
pH = log 1/H
What is the pH of arterial blood?
7.45
What is the pH of venous blood?
7.35
What is the pH of the ECF controlled close to?
7.4
What can acidosis do?
lead to depression of CNS
What can alkalosis do?
over-excitability of peripheral NS or later the CNS
What does H influence?
enzyme activity and K levels in the body
How is H continually added to the body fluids?
metabolic activity
carbonic acid formation
inorganic acids from breaking down nutrients
organic acids from metabolism
What is the dissociation constant for acids and bases?
K = [H][A]/HA
What is pK equal to?
pK=-logK
What is the henderson-hasselbach equation?
H = K x HA/A
OR
pH = pK + log [A]/[HA]
What are some physiological buffers?
HCO3-CO2
Why is the HCO3-CO2 buffer so important?
HCO3 is controlled by kidneys, PCO2 is controlled by lungs
How does the HCO3-CO2 buffer influence physiological pH?
pH = pK + log [HCO3]/pCO2 x 0.03 solubility coefficient
Normal conditions HCO3 = 24 mmol, pCO2 is 40 mmHg
pH = 6.1 + log 24/40.0.03 = 7.4
What is the role of the kidney in control of HCO3?
variable reabsorption of filtered HCO3
Kidneys can add new HCO3 to the blood
What does the kidneys control of HCO3 depend upon?
H secretion into the tubule
How much HCO3 is filtered per day?
4320 mmol/day
How does HCO3 get back into the interstitial fluid?
Doesn’t do it as an ion
takes H from NHE -> H2CO3 which is converted to CO2 which diffuses into epithelial cell where converted back to HCO3 which goes to interstitial fluid via Na/HCO3 cotransporter
How does the kidney form new HCO3 when HCO3 is low?
secreted H binds with next most plentiful buffer in filtrate - phosphate
How does phosphate act as a buffer?
binds H and HPO4 to make H2PO4 which is an acid that is excreted so there is a net gain of HCO3
What is titratable acid?
the amount of H excreted as H2PO4 can be measured
What is the maximum amount of titratable acid that can be excreted per day?
40mmol/day
What happens if 40mmol/day is added as titratable acid then how much HCO3 is gained by the circulation?
40mmol/day
How does ammonia act as a tubular buffer?
NH3 binds H to make ammonium ion that is excreted causing net gain of HCO3
How is ammonia secreted into the tubule?
glutamine from the liver -> glutaminase -> NH3 in tubule
What is the usual excretion of NH4?
20mmol/day
What may happen in acidosis?
NH4 excretion increases to 5-600mmol/day
What are the three actions of H?
drives HCO3 reabsorption - 4300mmol/day
Forms acid phosphate 20 mmol/day
Forms ammonium ion - 40 mmol/day
What is the total H secretion per day?
sum of all the HCO3 reabsorption and TA and NH4 excretion - 4360mmol/day
What is the total H excretion per day?
sum of Ta and NH4 excretion - 60 mmol/day
What is the total amount of new HCO3 generated a day?
60mmol/day
