Lecture 11 - Regulation of Blood pH Flashcards
What does pH mean?
Measure of plasma [H+] => [H+] = 10(-pH) mol/L (aka M)
Plasma [H+] when pH = 7.4? How does this compare to plasma [Na+] or [K+]?
4 x 10^(-8) = 40 nM
Much much smaller
Normal range of plasma [H+]?
35-45 nM
What amount of H+ is dumped into the ECF on a daily basis? What does this mean?
40-80 mmol (millions more than what is supposed to be in there for the pH to be normal)
That is the amount that the kidney will need to excrete everyday and in the process, the kidney will generate new buffer
Range of pH compatible with human life?
7-7.7
pH of urine?
4.5-7
pH of saliva?
6.5
Plasma [H+] when pH = 7?
100 nM
Plasma [H+] when pH = 7.7?
20 nM
Normal pH range?
7.35-7.45
What makes a good buffer?
Weak acids because they only dissociate partially, so there is both HA and A- in solution:
- When you add a strong acid, the A- reacts with it to produce water: very small pH change
- When you add a strong base the HA reacts with it to produce water: very small pH change
They are optimal at a pH equal to their pKa (within a 1 pH unit range) because the acid has released 50% of its protons at the pKa: [HA] = [A-]
Which blood ion has a pKa of 7.4?
NONE
Which blood ion has a pKa CLOSEST to 7.4? Why is it not used as the main blood buffer?
H2PO4-/HPO42- => pKa = 6.8
Not use as main plasma buffer, because plasma [HPO42-]= 1mM => not enough of it
What is the Henderson-Hasselbach equation? What does it mean?
pH = pKa + log [A-]/[HA]
Means that when you have more dissociation than not, pH>pKa
What is the Henderson-Hasselbach equation for blood?
pH = 6.1 + log [HCO3-]/0.03xPCO2
0.03 = solubility coefficient
What is the Henderson-Hasselbach equation when phosphate is the buffer?
pH = 6.8 + log [HPO42-]/[H2PO4-]
What is the blood buffer? pKa? Plasma concentration? What to note?
HCO3-
pKa = 6.1
[HCO3-] = 24 mEq/L
Some buffering by plasma proteins: Pr- + H+ <=> HPr
What are mM = to?
mEq/L
Blood buffer reaction?
Dissolved CO2 + H2O <=> H2CO3 <=> H+ + HCO3-
0.03 x 40 mmHg = ?
1.2
24 mEq/L / 1.2 =>
20
What people do not form H+ with their diet?
STRICT vegans
Describe the body’s response to an acid load? Include the timing.
Acid load => titrate intracellular buffers + titrate extracellular buffers (both in minutes) => increased respiration (hours) to decrease PCO2 + kidney excretes extra H+ and in the process generates additional bicarbonate to replace that which was initially lost in buffering (days)
Main intracellular buffers?
- H2PO4-/HPO42-
2. Proteins
Describe the impact of intracellular buffering of acid. What to note?
ACIDOSIS:
- H+ moves into the cells
- Na+ and K+ leave the cells (more K+ though)
ALKALOSIS:
- H+ comes out of the cells
- Na+ and K+ enter the cells (more Na+ though)
Overall changes wouldn’t be more than 0.5 mEq/L
Does buffering happen mainly intracellularly or extracellularly?
Intracellularly (57%)
Extracellular plasma buffering of non volatile acid:
- Buffers and %?
- % of total buffering?
- Timing?
- Bicarbonate (92%), plasma proteins (8%), and inorganic phosphate
- 13%
- Seconds
Extracellular interstitial fluid buffering of non volatile acid:
- Buffers and %?
- % of total buffering?
- Timing?
- Bicarbonate (99%+), inorganic phosphate
- 30%
- Minutes
Intracellular RBC buffering of non volatile acid:
- Buffers and %?
- % of total buffering?
- Timing?
- Bicarbonate (30%), Hb (60%), plasma proteins and inorganic phosphate (10%)
- 6%
- Seconds
Intracellular fluid and bone buffering of non volatile acid:
- Buffers and %?
- % of total buffering?
- Timing?
- Inorganic phosphate and proteins
- 51%
- Hours
Do most cells contain HCO3-?
NOPE - RBC is special
Can the bicarbonate system buffer volatile acid, aka CO2? What do we call this? Explain how this is done.
NOPE
Respiratory acidosis, buffered by:
- ECF (5%): proteins
- ICF (95%): rapid equilibration occurs as CO2 (lipid soluble) diffuses into cell compartments to be buffered by Hb, proteins, and inorganic phosphate
How do we call non volatile acid load?
Metabolic acidosis
Can a buffer buffer itself? What is this called?
NOPE => the isohydric principle
Are humans open or closed systems?
OPEN
Describe the closed and open system responses to adding 10 mmol/L of a strong acid to the body?
- Steady state before adding:
- {HCO3-] = 24 mEq/L
- Dissolved [CO2] = 1.2
- pH = 7.40 - Closed system response - intracellular and extracellular buffering:
- {HCO3-] = 14 mEq/L
- Dissolved [CO2] = 11.2
- pH = 6.20 - Open system response - remove CO2 by lungs:
- {HCO3-] = 14 mEq/L
- Dissolved [CO2] = 1.2
- pH = 7.17 - Open system response - remove excess CO2 due to hyperventilation:
- {HCO3-] = 14 mEq/L
- Dissolved [CO2] = 0.9
- pH = 7.29 - Open system response - kidneys add bicarb to blood and excrete H+:
- {HCO3-] = 24 mEq/L
- Dissolved [CO2] = 1.2
- pH = 7.40
Sources of daily acid load?
- Metabolism of ingested food
- Secretions by GIT (base loss)
- De novo generation of acids and bases from metabolism of stored fat and glycogen
- Changes in the production of CO2
Describe the closed and open system responses to adding 10 mmol/L of a strong base to the body?
- Steady state before adding:
- {HCO3-] = 24 mEq/L
- Dissolved [CO2] = 1.2
- pH = 7.40 - Closed system response - intracellular and extracellular buffering:
- {HCO3-] = 34 mEq/L
- Dissolved [CO2] = 0
- pH = 6.20 - Open system response - retain CO2 by lungs:
- {HCO3-] = 34 mEq/L
- Dissolved [CO2] = 55 mmHg
- pH = 7.2 - Open system response - kidneys decrease bicarb reabsorption:
- {HCO3-] = 24 mEq/L
- Dissolved [CO2] = 40 mmHg
- pH = 7.4
