[FMS] CBS - pH Flashcards
What is PH
Measure of hydrogen ion concentration - acidity or alkalinity of a solution
what does acidity depend on?
acidity depends only on free hydrogen ions
Not those still bound to anions.
what is the normal blood pH range?
Blood pH range: 7.35-7.45
when does acidosis and alkalosis happen?
- Acidosis: pH lower than 7
- Alkalosis: pH greater than 7.8
which 5 places does acids come from in the body?
food
protein breakdown
incomplete fats
glucose oxidation
loading and transport of CO2 in blood.
which 3 places in the body regulate the acid-base balance? which one is long terms and which one is short term?
- Kidney
- Lungs
- Chemical buffers
(where kidneys and lungs are longterm, and chemical buffers are short term)
what is buffering?
Buffers resist abrupt and large swings in the pH of body fluids by:
when pH increases, releasing H+ (acting as acids), OH- increases
When pH decreases, binding H+ (acting as bases), H+ increases
how many moles is pure water?
Pure water is a 55.6M solution
what is the value of ionic product of water
Ionic product of water: [H+] x [OH-] = 10^-14 M2
what is the ionic product of water at neutrality
Neutrality: [H+] = [OH-] = 10^-7M
what is the equation for pH
pH = -log[H+]
when [H+] is 10-2, then what is the value for [OH-]
Use equation for ionic product of water
where Kw = [H+][OH-]
Kw = 1x 10^-14
10^-14 = [10^-2][OH-]
rearrange and put in the calculator
then [OH-] is 10^12
when [H+] is 10-4, then what is the value for [OH-]
Use equation for ionic product of water
where Kw = [H+][OH-]
Kw = 1x 10^-14
10^-14 = [10^-4][OH-]
rearrange and put in the calculator
then [OH-] is 10^10
what is pKa equation?
pKa= -log Ka
what is Ka?
Ka is dissociation constant
what is pKa?
pKa is the pH at which the acid is half dissociated (equal amounts of undissociated acid and its conjugate base)
when pKa is low, is the acid strong or weak?
lower pKa = stronger acid
what is the henderson hasselbalch equation?
the lower the pKa the _____ the acid
The lower the pKa , the stronger the acid
at the ___ buffering is best
At pKa buffering is best
So, if you know the pKa of your acid, you know at what pH it will buffer best
what are the 4 physiologically important buffers?
H2CO3→HCO3- pKa 6.1
H2PO4- → HPO42- pKa 6.8
Protein → protein-
protein+ → protein
are amino acids good physiological buffers?
No - even if they are, they are caught in peptide bond = no dissociation
what complication does high carbonic acid (H2CO3) lead to?
respiratory acidosis
what complication does low bicarbonate (HCO3-) lead to?
metabolic acidosis (diabetic)
which amino acid groups dont dissociate?
anything with methyl ch3 group
what needs to be present in large numbers for Hb to be a good buffer?
histidine
what is the pKa of histidine
6
what affects the pKa of the histidine in Hb
it increases in proteins due to the ionic environment
of the side chains. As Hb changes shape, the pKa of histidine changes.
OxyHb pKa = 6.8
DeoxyHb pKa = 7.8
which is a better buffer, OxyHb or DeoxyHb?
DeoxyHb is a better buffer for H+ because it has a HIGHER PKA - therefore it is carrying more H+ at pH of blood
try the pH and buffers quiz on keats then come back
https://keats.kcl.ac.uk/mod/quiz/view.php?id=6694265
In what order are H+ lost from H3PO4
First Proton (H⁺) Loss: Phosphoric acid loses its first proton to form dihydrogen phosphate ion (H2PO4⁻).
H3PO4→H2PO4-
Second Proton (H⁺) Loss: Dihydrogen phosphate ion loses its second proton to form hydrogen phosphate ion (HPO4^2⁻).
H2PO4- →HPO42-
Third Proton (H⁺) Loss: Hydrogen phosphate ion loses its third proton to form phosphate ion (PO4^3⁻).
HPO42- →POA3-
What does a not steep titration curve mean
There is buffering
Why do most amino acids side-chains not buffer in physiological range
pKa outside range
amino acids involved in physiological buffering (state pKa)
Histidine (pKa 6)
How can histidine be involved in blood buffering when pKa below blood
range
pKa different in Hb than when free
A globular protein X found in blood can act as a buffer. If the pKa of the protein is increased because of conformational changes in that protein how will the buffering/ hydrogen ion binding properties be affected?
A) The protein will not be able to act as a physiological buffer
B) They will not be affected because the dissociating groups of the protein will still be the same
C) The protein will bind fewer Hydrogen ions
D)The protein will bind more Hydrogen ion
ANSWER = D, he protein will bind more Hydrogen ion
REMEMBER, IF THE PKA IS HIGHER THAN PH THEN IT WILL BIND MORE H+ IONS
What is respiratory acidosis caused by
HIGH H2CO3
What is metabolic acidosis caused by
LOW HCO3
