Physiology 7+8: Acid Base Balance Flashcards
what is the pH of arterial blood
7.45
what is the pH of venous blood
7.35 (more acidic from CO2)
what affect does acidosis and alkalosis have on the CNS
acidosis = depression, alkalosis = over-excitability
what are sources of H+ from metabolic pathways
carbonic acid formation/ breakdown of nutrients to inorganic products/ organic acids from metabolism eg lactic acid
what endocrine condition can cause build up of H+
diabetes mellitus
how do strong and weak acids act in solution
weak acids partly dissociate and strong acids fully dissociate
what does a buffer system do
manages equilibrium of solution ie yields free H+ when [H] decreases and binds to H+ when [H] increases
what is the general buffer equation
HA H+ + A- (HA = acid, A = base).
what effect does adding acid to a solution have on a buffer
the A- base will mop up the H+ to form HA
what effect does decreasing H+ in a solution have on the buffer
more HA will dissociate to form H+
what is the buffer dissociation constant equation
K = ([H+] x [A-]) / [HA]
what is the buffer equation
pH = pKa + log([A-]/[HA])
what catalyses CO2 + H2O to H2CO3 (carbonic acid)
carbonic anhydrase
how does carbonic acid (H2CO3) work as a buffer in the body
dissociates to hydrogen ions and bicarbonate: H2CO3 H+ + HCO3-
which organ controls bicarbonate levels in the body
kidneys
which organ controls CO2 levels in the body
lungs
how is bicarbonate (HCO3-) reabsorbed from the filtrate (what does it bind too and what is it reabsorbed as)
binds to H+ to become H2CO3 then is reabsorbed as CO2 and H2O
what drives HCO3- reabsorption
H+ secretion (increased secretion = increased reabsorption)
why is reabsorption of HCO3- needed
prevent acidosis
what available buffers are also in filtrate if HCO3- not available
phosphate –> TA
ammonia –> ammonium
what is the normal concentration of HCO3
25 mmol/l
what is the normal arterial PCO2
40 mmHg
what is compensation of acid-base (AB) vs correction of AB
compensation = restore pH to 7.4 irrespective of what happens to HCO3 and PCO2 // correction = pH, HCO3, CO2 all restored
what are the 4 causes of AB disruptions
resp acidosis, resp alkalosis, metabolic acidosis, metabolic alkalosis
what is pH proportional to in terms of HCO3- and CO2
[HCO3-] / [CO2)
what is respiratory acidosis
retention of CO2 by body
what causes resp acidosis
HYPOVENTILATION, COPD, airway restriction (asthma, tumour), chest injury, resp depression
how does increased CO2 cause acidosis
CO2 + H20 H2CO3 H+ + HCO3- //// increased CO2 drives equilibrium to the right which increases H+ and HCO3-
what pH and PCO2 levels would indicate uncompensated acidosis
pH < 7.35 and PCO2 > 45 mmHg
how do the kidneys compensate for resp acidosis (3)
1) increased PCO2 drives H+ secretion 2) all HCO3 is reabsorbed to mop up H+ 3) TA and ammonium buffers are created
in compensated resp acidosis, what levels of pH, PCO2 and HCO3 would you expect
normal pH // PCO2 raised // HCO3 raised
how would correction of resp acidosis be achieved
normal ventilation to lower PCO2
what is respiratory alkalosis
excessive removal of CO2 by the body
what causes resp alkalosis
low inspired PO2 at altitude (hypoxia), hyperventilation (over breathing, fever)
how does decreased PCO2 cause alkalosis
CO2 + H20 H2CO3 H+ + HCO3- //// decreased CO2 drives equilibrium to the left which also decreased H+ and HCO3-
what levels of pH and PCO2 would be seen in uncompensated resp alkalosis
pH > 7.45 and PCO2 < 35 mmHg
how do the kidneys compensate resp alkalosis (3)
1) reduces H+ secretion 2) HCO3- is excreted into the urine 3) no ammonium or TA formed
what levels of pH, PCO2 and HCO3 are seen in compensated resp alkalosis
normal pH (increased H), decreased PCO2 and decreased HCO3
what does correction of resp alkalosis require
normal ventilation and increased PCO2
what is metabolic acidosis
increased H+ in the body (not from increased CO2)
what can cause metabolic acidosis
ingestion of acids, excessive metabolic production of H+ (exercise, DKA), excessive base loss (diarrhoea)
what happens to pH and HCO3- in metabolic acidosis
CO2 + H20 H2CO3 H+ + HCO3- /// increased pH and decreased HCO3- as not enough to mop up excess CO2
how do the lungs compensate metabolic acidosis
increased ventilation and more CO2 blown off
what levels of PCO2, pH and HCO3- are seen in compensated met acidosis
normal pH (H decrease) and low HCO3 and PCO2
how is metabolic acidosis correction achieved by kidneys (4)
HCO3- reabsorbed, H+ secreted and TA and ammonium can create new HCO3-, acid excreted, normal ventilation
what is metabolic alkalosis
excessive loss of H+ (nor as common as acidosis)
what can cause metabolic alkalosis
vomiting HCL from stomach, ingestion of alkali, aldosterone hyper-secretion (Na/H exchange)
what happens to pH, PCO2 and HCO3- in metabolic alkalosis
pH increased (decreased H+), increased HCO3-, normal PCO2
how do lungs compensate metabolic alkalosis
slow ventilation to increase CO2 –> H+
what happens to pH, PCO2 and HCO3- in compensated metabolic alkalosis
normal pH (increased H+), increased PCO2 and HCO3-
how do the kidneys correct metabolic alkalosis
no HCO3- reabsorbed, no TA or ammonium generated
