Acid-Base (Don's class) Flashcards
Acid-base physiology is all about……..
H+ ion concentrations
Normal ECF H+ concentration is…..
~ 40nEq/L
An acid is a proton (H+) _____.
donor
A base is a proton (H+) ______.
acceptor
A weak acid or base _______ donates or accepts a proton
reversibly
A weak acid the equation looks like this:
HA <=> H+ + A-
The Henderson–Hasselbalch equation describes the relationship between _____,_____and______.
pH, PaCO2, and serum bicarbonate.
the solubility coefficient for CO2 is:
is 0.03 mmol/mm Hg at body temperature.
This means that 0.03 millimole of H2CO3 (carbonic acid)is present in the blood for each mm Hg PCO2measured.
Buffers are most efficient when:
pH=pKa
Body Buffers: (5)
Bicarbonate (H2CO3 / HCO3)
Hemoglobin
Intracellular proteins
Phosphate (H2PO4- /HPO42-)
Ammonia (NH3/NH4)
Buffer systems do not eliminate H+from or add H+to the body but only…..
keep them tied up until balance can be re-established.
The three primary systems that regulate H+ concentration in the body fluids to prevent acidosis or alkalosis:
- Chemical acid-base buffer system
2.Respiratory center (regulate CO2 removal and therefore H2CO3- from the ECF)
3.The kidneys (excrete acid or alkaline urine) MOST POWERFUL
Bicarbonate Buffer System Equation:
H2O + CO2 <=> H2CO3 <=> H+ + HCO3-
CO2 combines with water to form H2CO3 which rapidly dissociates into H+ and HCO3-
(H2CO3= Carbonic acid)
Hydration of CO2 is catalyzed by _____ _____.
Carbonic anyhdrase
The bicarbonate buffer is effective against _______ but not ________ acid-base disturbances
metabolic
NOT respiratory
The pKa of bicarbonate is:
6.1
The bicarbonate Buffer System is the…..
the most powerful extracellular buffer in the body.
How do the kidneys compensate during Acidosis?
Increased HCO3- re-absorbtion:
-CO2 combines with water to form H2CO3 which rapidly dissociates into H+ and HCO3-
H+ is secreted into the proximal tubule and ________ is reabsorbed to blood (renal compensation of acidosis)
bicarbonate
H+ in the tubule combines with filtered HCO3- to form carbonic acid
Carbonic anhydrase hydrolyzes this to water and CO2 which goes into the cell replacing the original CO2
For for each________ reabsorbed, a ______must be secreted.
HCO3−
H+
The epithelial cells of the proximal tubule, the thick segment of the ascending loop of Henle, and the early distal tubule all…….
secrete H+into the tubular fluid by sodium-hydrogen counter-transport,
______ of filtered bicarbonate is reabsorbed in the _______ _______.
10-20% reabsorbed in the ______ ______.
80-90%
proximal tubule
distal tubule
*In the distal tubule a______ ______exists which can establish a steep gradient for _______ urine
H+ pump
acidifying
Intercalated Cells of Collecting Duct do what job?
Reabsorption & Secretion of Bicarbonate
Type A intercalated cells are especially important in eliminating_____ _______ while reabsorbing ______ in acidosis.
hydrogen ions
bicarbonate
Type B cells secrete _______ into the tubular lumen while reabsorbing _______ ______ in alkalosis
bicarbonate
hydrogen ions
H+ secreted in tubule lumen can combine with HPO42- to form H2PO4- that is……
not re-absorbable and becomes trapped in urine.
HPO4/2—hydrogen phosphate
H2PO4—dihydrogen phosphate
Phosphate has pK of ___ which in acidic urine allow to be more effective buffer
6.8
The total buffering power of the_____ _____in the extracellular fluid is much less than that of the _________buffering system.
phosphate system
bicarbonate
The phosphate buffer is especially important in the tubular fluids of the kidneysfor two reasons:
(1)phosphateusually becomes greatly concentrated in the tubules, thereby increasing thebuffering power of thephosphatesystem.
(2) the tubular fluid usually has a considerably lower pH than the extracellular fluid does, bringing the operating range of thebuffercloser to the pK (6.8) of thesystem.
Tubular Buffer =
Ammonium (NH4) Production & Secretion
Ammonium (NH4):
Important tubular fluid buffer that works in the ___, ___, and _____.
PT, TAL, & DT
Bicarbonate generated in synthesis process
Ammonium is synthesized from _____
glutamine.
Collecting Tubules: ____ combines with _____ to form _____ which is excreted.
H+
NH3
NH4
Bicarbonate also generated in synthesis process
With chronic acidosis, the dominant mechanism by which acid is eliminated is excretion of ___
NH4 (Ammonium)
This process also provides the most important mechanism for generating new bicarbonate during chronic acidosis
Ammonium Production & Secretion (tubular buffer)
The _____is secreted into the tubular lumen by a _____-_______ _____ in exchange for sodium, which is reabsorbed.
NH4+
counter-transport mechanism
The HCO3−is transported across the basolateral membrane, along with the reabsorbed Na+, into the interstitial fluid and is taken up by the peritubularcapillaries.
Metabolic alkalosis is mainly possible in 2 situations:
- Na+ depletion: more sodium is reabsorbed in the PT (Cl- moves with it to preserve electroneutrality) HCO3- must be reabsorbed (contraction alkalosis)
- Increased aldosterone (mineralocorticoid) activity increases Na+ reabsorption and H+ secretion in the distal tubule
Base excess is defined as the amount of acid or base that must be added to return blood pH to 7.4 with PaCO2 = 40 mmHg and temp 37o C
Positive value indicates _______.
Negative value indicates _______.
metabolic alkalosis
metabolic acidosis
Metabolic Alkalosis: Causes
- Loss of acid from the extracellular space:
-loss of gastric fluid
-acid loss in urine (hyperaldosteronism) K+ deficiency
-loss of acid in stool - Excessive HCO3- loads:
-oral or parenteral Bicarb
-NaHCO3- dialysis
Factors That Maintain Metabolic Alkalosis:
-decreased GFR
-Hypokalemia
-volume contraction (HCO3 reabsorption)
-Hypochloremia
-Aldosterone
Metabolic Alkalosis:
1. PaCO2increases ∼___-___ mmHg per 1 mEq/L increase in [HCO3−]
- The last two digits of the pH should approximate the [HCO3−] + ___.
0.5-0.6 mmHg
15
Elevated Anion Gap Metabolic Acidosis:
3 diseases:
Toxins:
Three diseases:
Uremia
Ketoacidosis
Lactic acidosis
Toxins:
Methanol
Ethylene glycol
Salicylates
Paraldehyde
NormalAnion Gap Metabolic Acidosis: Causes
Renal tubular acidosis
Diarrhea
Carbonic anhydrase inhibition
Ureteral diversions
Early renal failure
Hydronephrosis
HCl administration
Saline administration
Potassium increases ___ mEq/L for each 0.1 unit decrease in pH
0.6
Physiologic effects of acidosis:
A rightward shift is seen in the oxy-hemoglobin dissociation curve
Cardiac contractility is decreased
There is decreased responsiveness to catecholamines
Potassium increases 0.6 mEq/L for each 0.1 unit decrease in pH
Treating Metabolic Acidosis: (3)
-Treat underlying cause (e.g. hypovolemia, anemia, cardiogenic shock
-NaHCO3 (Do not give to patient with respiratory failure as CO2 will go up
-Refractory acidosis may require dialysis
Treating alkalosis:
-IV HCl is used in rare cases
-Spironolactone if increased mineralocorticoid activity
-Diuretics are the cause of chloride sensitive metabolic alkalosis
-Diuretics are the cause of chloride sensitive _____ ______.
metabolic alkalosis
Hypokalemia will also augment_____ ________.
H+ secretion
Halving minute ventilation _____ PaCO2 and _____ cerebral blood flow.
doubles and doubles
Respiratory alkalosis may be a sign of……
pain, anxiety, hypoxemia, central nervous system disease, or systemic sepsis.
In metabolic acidosis, an excess of H+over HCO3−occurs in the tubular fluid primarily because of decreased _____ _____ ____.
filtration of HCO3−.
Anion Gap calculation:
[Na+] - ([Cl-] + [HCO3-])
Normal value 140 - (104 +24) = 12 mEq/L
Usually 7-14 mEq/L
Respiratory acidosis: Acute compensation
1 mEq/L INCREASE in HCO3- for every 10 mmHg increase in CO2 (usually from 40 mmHg
Respiratory Acidosis: Chronic compensation
expect a 4 mEq/L INCREASE in HCO3- for every 10 mmHg increase in CO2
Metabolic Acidosis: CO2 DECREASES ____ X the decrease in HCO3- (Usually from 24 mEq/L)
CO2 DECREASE 1.2 times the decrease in HCO3-
Acute Respiratory Alkalosis Compensation:
2 mEq/L DECREASE in HCO3- for every 10 mmHg DECREASE in CO2
Chronic Respiratory Alkalosis Compensation:
4 mEq/L DECREASE in HCO3- for every 10 mmHg DECREASE in CO2
Metabolic Alkalosis Compensation:
CO2 INCREASE by 0.7 X the INCREASE in HCO3-
