Acid base balance - C Flashcards
normal range for blood pH
7.35 - 7.45
normal blood pH
7.4
intracellular hydrogen ion concentration
50-100 mM
extracellular hydrogen ion concentration
40 mM
Stewart model: what three variables does the [H+] depend on?
- partial pressure of carbon dioxide (PCO2)
- strong ion difference (SID)
- total concentration of weak acids (Atot)
why does the pH in the body have to be maintained at a particular value?
pH must be kept within a very narrow range because the structure and function of large organic molecules is very sensitive to [H+]
what happens at 6.9 pH?
death
what happens at 7.0 pH?
cerebral palsy in the newborn, asphyxia
what happens at 7.1 pH?
blood vessels become calcified, bone is resorbed as hydrogen ions replace calcium ions
what happens at 7.2 pH?
reduced cardiac contractility
what happens at 7.3 pH?
hyperkalaemia - potassium ions move out of the cells and hydrogen ions move in
what happens at 7.4 pH?
normal pH
what happens at 7.5 pH?
tetany from low [Ca2+], fainting from low cerebral blood flow
what happens at 7.6 pH?
hypokalaemia, cardiac dysrhythmias
what happens at 7.7 pH?
haemolysis in dogs, death
what happens when pH moves from 7.4 to 7.35? (4points)
- hyperventilation (under 7.4)
- systemic vasodilation
- pulmonary vasoconstriction
- renal ammoniagenesis (7.35)
what happens when pH moves from 7.4 to 7.45? (4points)
- hypoventilation (over 7.4)
- systemic vasoconstriction
- pulmonary vasodilation
- renal bicarbonate secretion (7.45)
traditional approach emphasises
the intake and output of ‘acids’ that can ‘donate’ hydrogen ions, and buffers react with the hydrogen ions to take it out of the solution, especially bicarb and protein
what is the newer approach to acid base balance
it is controversial. it tries to account for the input and output for all substances that can affect hydrogen ions
PCO2
partial pressure of CO2, 40mmHg
SID
strong ion difference, 40mM
[HCO3-]
concentration of bicarbonate ions
[H+]
concentration of hydrogen ions
[protein]
19mM
diagram for shift in acid base balance
(diagram)
what does a bigger SID mean?
bigger SID means more A- and HCO3-and so less hydrogen ions to keep in equilibrium