Physiology 7 Flashcards
normal blood pH?
7.35-7.45
venous blood = 7.35 due to higher CO2 concentration
small changes in pH reflect large changes in [H+], true or false?
true
why is blood pH important?
acidosis can depress CNS
alkalosis can overexcite the peripheral NS and later the CNS
[H+] affects enzyme activity and K+ levels in the body
- high H+ secretion = low K+ secretion = potassium retention
H+ is continuously added to the body via what 3 sources?
carbonic acid formation
inorganic acids produced during breakdown of nutrients
organic acids resulting from metabolism (fatty acids, lactic acid etc)
how is diabetes mellitus related to [H+]?
sufferers metabolise fat instead of glucose which produces ketoacids
strong vs weak acids in solution?
strong = dissociate completely in solution weak = only dissociate partly in solution
what is a buffer system and what does it consist of?
first line of defence for pH change
compensates for change in pH of body fluids
consists of a pair of substances
- one which yields free H+ as [H+] decreases
- other binds free H+ when [H+] increases
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what happens if base is added to buffer system?
base it tied up by combining with H+, allowing more HA to dissociate
[HA] falls and [A-] falls
- i.e ……
dissociation constant=?
K = [H+][A-] / [HA] pK = -logK
how is pH calculated from pK?
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most important buffer I the body?
CO2 - HCO3 buffer
CO2 + H2O <> H2CO3 <> H+ + HCO3
- catalysed by carbonic anhydrase
CO2 and HCO3 concentrations are controlled by what?
CO2 = lungs HCO3 = kidneys pH = pK + log kidneys/lungs?
describe the role of the kidneys in control of [HCO3]
variable reabsorption of filtered HCO3
kidneys can also add new HCO3 into the blood (more HCO3 in renal vein than renal artery)
both are driven by H+ secretion into the tubule
why is reabsorption of HCO3 important?
counteracts acid
if none was reabsorbed, would be like adding 4 L of 1M HCl to the body every day
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more hydrogen ions are secreted than bicarbonate is reabsorbed, true or false?
true
when is this not true?
when HCO3 being used to buffer an acidosis, needs to be replenished
when HCO3 is low due to reabsorption, H+ then combines with phosphate instead (as its the 2nd most plentiful)
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how can titration be used?
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3 functions of H+ secretion?
drives bicarbonate ion reabsorption
drives formation of acid phosphate (can be measured as titratable acid which allows formation of 1 bicarbonate into blood)
drives formation of ammonia which also allows formation of new bicarbonate into the blood
secretion of how many H+ ions equates to production/reabsorption of 1 HCO3 or production of 1 acid phsopahte or 1 ammonium?
1
daily summary?
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