Flashcards in acid base homeostasis Deck (117)
what is the total CO2 produced per day?
what is the total of unmetabolised acid produced per day?
50mmol/day and plasma [H+] is 40nmol/L
what does the maintenance of plasma H+ depends on when there is enormous turnover?
buffers, nitrogenous waste and carbon dioxide excretion
what is the cycle of metabolism in H+ maintenance?
metabolism feeds in as an input to the maintenance of normal H+ which then has buffers controlling it. The output then goes to the kidney as H+ and the lungs as CO2
where does H+ production come from?
incomplete metabolism of glucose - intermediary anaerobic process where glucose - 2 lactate + 2H+
incomplete triglyceride metabolism resulting in ketogenesis where triglycerides make free fatty acids and H+ and then free fatty acids make ketones and H+
amino acid metabolism (ureagenesis) where the metabolism of neutral amino acids generated H+
where does glucose metabolism occur?
mainly in the skeletal muscles and RBCs
where does triglyceride metabolism and ketogenesis occur?
triglyceride metabolism in the adipose tissue to make FFAs and to make ketones is in the liver
what is the H+ concentration like and why is it so tightly controlled?
it is low in relation to other concentrations of major ions and cannot be allowed to rise or fall by a lot because H+ will avidly bind to proteins changing their conformation and structure
what are the other major ions in the plasma and what are their concentrations?
Na+ = 140mmol/L
K+ = 4.5mmol/L
Cl- = 100mmol/L
HCO3 = 25mmol/L
what is the role of buffers?
they buffer H+ in mmol quantity but must keep it in nmol quantity
what are buffering systems?
they are solutions which resists change to pH when an acid or base is added and ensure that H+ can be transported and excreted without causing damage to physiological processes
what are the main buffering systems?
bicarbonate, ammonia, phosphate, haemoglobin and proteins
what are acids and bases and give example equations?
acids are proton donors - Hcl - H+ + Cl-
bases are proton acceptors - OH + H+ - H2O
what is pH?
it is the negative logarithm of the hydrogen ion concentration - pH = -log10[H+]
ph + log10(1/[H+])
why are logarithims used?
to make the wide range of H+ concentrations seen - more manageable
what is the normal range for pH and H+ in a patient?
pH from 7.35-7.45 and H+ from 35-45nmol/L
what is acidosis?
it is the abnormal processes or conditions that lower the arterial pH
what does a ph<7.35 mean?
the hydrogen concentration is >45nmol/L and the patient is acidaemic and vice versa for alkaemic
what is Ka and pKA?
in chemistry p means the negative logarithm of and therefore as the Ka is the acid dissociation constant the pKa is the negative logarithm of this
what are the values for pKa and Ka if the acid is strong?
the pKa is low and the Ka is high
if HA - A- +H+ then what does Ka equal?
Ka = ([A-][H+])/[HA]
A- is the conjugate base
in physiology why is CO2 an acid and HCO3 a base?
H2O + CO2 - H2CO3 - HCO3- + H+
what is the henderson hasslebalch equation?
it explains how acids and bases contribute to pH
pH = pKa + log10([base]/[acid])
how is CO2 an acid?
when dissolved in plasma it makes H2Co3 which is carbonic acid and then readily dissociates to H+
what is the pathway of HCO3-
it acts as a base - it accepts H+ to form carbonic acid and then is converted to CO2 for excretion from the lungs
what does blood pH depend on?
not the amounts of CO2 or HCO3 but the ratio between them
what is the concentration of CO2?
it is pCO2 (partial pressur of CO2) x solubility constant (a = 0.225 for CO2)
what will the pH of the blood be in a bicarbonate buffering is pKA is 6.1?
pH = 6.1 + log10([HCO3-]/(pCO2xa)) - Ph will be proportional to [HCO3-]/pCO2
why can HCO3- not buffer CO2?
because of the equation so would just result in more CO2 being produced - equilibrium of CO2 therefore relies on non bicarbonate buffers