3 - Acids and Bases Flashcards
What is an alkali?
Another word for a base
Molecule formed by an alkaline metal and a highly basic ion like hydroxyl
What are the alkali metals
Farthest left column of the periodic table
lithium, sodium, potassium
How does an alkali or base react with free H+?
The base portion of the molecules bind with H+ and remove it from the solution
What is a strong acid?
Give an example
rapidly dissociates and releases especially large amounts of H+ in a solution
Hydrochloric Acid (HCl)
What is a weak acid?
Give an example
Less likely to dissociate their ions, and release H+ much more slowly
Carbonic Acid (H2CO3)
What is a strong base?
Give an example
Reacts rapidly and strongly with H+ and quickly removes it from a solution
Hydroxide (OH-)
OH- reacts with H+ to form ______
water
What is a weak base?
Give an example
Binds weakly with H+
Bicarbonate (HCO3-)
At a normal pH of 7.4, what is the [H+]?
40 nEq/L
What are the upper and lower limits of pH in humans?
6.8 - 8.0
What is the pH of gastric HCl?
0.8!
Acid base regulation occurs in what three places?
The blood (buffers)
The lungs (respiration)
The kidneys (excretion of bicarb and H)
What is the function of the buffer system?
Do not effect the total amount of H+ in the body
They keep the H+ tied up until balance can be restored
What is the definition of a buffer?
Any substance that can reversibly bind H+
How is carbonic acid (H2CO3) formed?
CO2 + H2O ⇔ H2CO3
Carbonic anhydrase increases the speed of reaction
Where is carbonic anhydrase especially abundant?
Aveolar Walls
Renal Tubule Walls
In the buffering system, what is the primary reason the [H+] is so low?
H2CO3 is a very weak acid, so it holds onto almost all the
H+ it binds to
In buffering systems, what is K’ ?
The dissociation constant
The concetration of the acid relative to its dissociated ions
What is the calculation of K’ of H2CO3?
K’ = (H x HCO3) / (H2CO3)
The amount of CO2 dissolved in the blood is directly proportional to the amount of ______________
undissociated H2CO3
What is pK?
-log K
What is the Henderson-Hasslebach Equation?
What does it calculate?
pH = 6.1 + log [(HCO3)/(0.03 x PCO2)]
the pH of a solution if the molar concentration of HCO3 and the PCO2 are known
Any metabolic acid-base disorder is caused by
a primary change in the ECF [HCO3]
What is the pK of of the bicarb buffer system?
6.1
In the bicarb buffer system, if the pK is equal to the pH, what does that mean?
each of the components (HCO3 and CO2) are present in equal amount
50% of the total concentration of the system is HCO3
50% of the total concentration of the system is CO2
Given that the pKa of the bicarb buffer system is 6.1, why are the kidneys and lungs so important?
A system is most effective within 1 pH unit above or below the pKa
Since the pH of the ECF is about 7.4, the bicarb buffer system is operating outside of its optimal effect
The difference is made up by the lungs and kidneys
Where does the phosphate buffer system play a primary role?
Where does it not?
Renal tubular fluid and intracellular fluid
extracellular fluid
What is the pK of the phosphate system?
6.8
Why is the phosphate buffer system important in the kidneys?
- There’s an increase concentration of phosphate in the tubules
- the pH of the tubules is nearer 6.8
Why is the phosphate buffer system important in the ICF?
The intracellular [PO4] is much highert than in the ECF
It takes a long time for H+ and HCO3 to diffuse across a cell membrane, except in ________ cells
RBCs
What percentage of chemical buffering occurs inside cells?
60-70%
What is the isohydric principle?
A change in the balance of one buffer system effects the other
Buffer systems actually buffer one another by shifting H+ back and forth between them
What is the relationship between CO2 and H?
Increased CO2 expulsion decreases H by mass effect
Which is more effective: respiratory response to a low pH or a high pH?
low pH. Lungs don’t respond that much to increased pH
How effective is respiratory control in moderating [H]?
about 50-75% effective
If the pH falls from 7.4 to 7, the respiratory control can increase the pH to about
7.2 or 7.3
Which is more effective: blood buffering or respiratory buffering?
Respiratory, but about 1-2x
What are nonvolatile acids?
Non-carbonic acids that cannot be excreted by the lungs
Why does the body produce nonvolatile acids?
Metabolism of proteins
How are nonvolatile acids removed from the ECF?
THe kidneys
What are the three mechanisms of kidney [H] regulation?
- secretion of H
- Reabsorption of HCO3
- Production of new HCO3
In the kidneys, for each HCO3 that is reabsorbed, _________ must be secreted
Hydrogen
Where does 90% of HCO3 reabsorption occur?
Proximal tubule
What happens in the tubules if there is more H than HCO3?
All of the bicarb is reabsorbed, and the excess H if buffered and sent into the urine
What happens in the tubules if there is more HCO3 than H?
Excess HCO3 cannot be reabsorbed, so it is left in the tubules and excreted by the urine
How is the excretion of large amounts of H in the urine accomplished?
Combining H with buffers in the tubular fluid, usually phosphate and ammonia
How is new bicarb synthesized in the tubules?
when H binds with phosphate or amoonia HCO3 is reabsorbed
What happens when CO2 is combined with H2O in the tubule?
Forms carbonic acid, which is a weak acid and dissociates into H + HCO3.
The hydrogen is expelled from the cell and the HCO3 is reabsorbed
In the setting of chronic acidosis, how do the kidneys make more HCO3?
Increased [H+] stimulates renal gulatime metabolism, increasing formation of NH4, which increases the amount of HCO3 that can be formed
What are the most important stimuli for increasing H secretion by the tubules in acidosis?
- An increase in ECF PCO2 (respiratory)
- An increase in [H+] of the ECF (resp and metabolic)
What happens to H secretion when Angiotensin II is increased?
Decreased?
Increased
Decreased
What happens to H secretion when PCO2 is increased?
Decreased
Increased
Decreased
What happens to H secretion when Aldosterone is increased?
Decreased?
Increased
Decreased
What happens to H secretion when ECF volume is increased?
Decreased?
Decreased
Increased
What happens to H secretion when K is increased?
Decreased?
Decrease
Increase
Factors that stimulate Na reabsoprtion will have what effect of H and HCO3?
increase H secretion and HCO3 reabsorption
Hyperkalemia decreases ________ and tends to cause _________
H secretion and HCO3 reabsorption
acidosis
What is renal tubular acidosis?
impairment of HCO3 reabsorption
OR
inability of renal tubular H secretion to establish normal acidic urine
What are some causes of renal tubular acidosis?
chronic renal failure
Addison’s Disease (insufficient aldosterone secretion)
Fanconi Syndrome
Diarrhea is the most common cause of metabolic _______.
Why?
acidosis
GI secretions contain large amounts of bicarb, and motility is too rapid they can’t be reabsorbed
Why does chronic renal failure cause acidosis?
- Buildup of nonvolatile acids
- Reduced excretion of phosphates and ammonia reduce amount of HCO3 produced
What is the real anion gap in the plasma?
Zero!
The anion gap is only a diagnostic concept
Causes of Increased Anion Gap Acidosis
Ketoacidosis
Uremia
Salicylate
Starvation
Methanol
Lactic Acidosis
Causes of Normal Anion Gap Acidosis
Diarrhea
Renal tubular acidosis
carbonic anhydrase inhibitors
Addison Disease