PHRM 825: Acid-Base Balance - Acid-Base Regulation Flashcards
Normal physiological pH
7.35-7.45
pH ___ is incompatable with life
<6.7 and >7.7
pH <7.35 = ______
acidemia
pH >7.45=______
alkalemia
The body regulates its pH via the _____ buffer system
Carbonic acid/Bicarbonate
Metabolic disorders involve changes in ________ levels, while respiratory disorders involve changes in _____ levels
H+ or HCO3- and CO2
The lungs compensate for ______ disorders
metabolic
The kidneys compensate for ______ disorders
respiratory
The Henderson-Hasselbach equation describes what
The relationship between pH and the concentrations of acid-base pairs in the buffer system
What is the Henderson-Hasselbach equation
pH = pKa + log(base/acid)
Carbonic anhydrase is a catalyst for what reaction?
H2CO3 CO2 + H2O
Most of the carbonic acid in plasma is in the form of _____
Carbon dioxide gas
Normal blood gas value of PaCO2
35-45 mmHg - Remember “40”
Normal blood gas value of HCO3
22-26 mEq/L - Remember “24”
Normal blood gas value of PaO2
95-100 mmHg
Normal blood gas value of SaO2
> 95%
______ is the best source for obtaining blood gas readings
Arterial blood
Acidemia ____ cardiac output (CO)
decreases
Acidemia causes ______ of cardiac contractility
impairment
Acidemia _____ pulmonary vascular resistance (PVR) and arrhythmias
increases
____ mEq/kg/day of acid consumed per day comes from oxidation of proteins and fats
~1
Aerobic metabolism of glucose produces _____ mmol of CO2 each day
15-20
Anaerobic metabolism produces ___ and ____
Lactic and pyruvic acid
Triglyceride oxidation produces ____ and _____
acetoacetic and beta-hydroxybutyric acid
Metabolism of sulfur-containing amino acids and phospholipids result in ____ and ___
sulfuric and phosphoric acids
What are 2 sulfur-containing amino acids
cysteine and methionine
____ mEq H+ from nonvolatile acids/kg of body weight must be excreted daily
0.8
Three standard mechanisms of acid regulation
Buffering, renal regulation, and ventilatory regulation
First line of defense in acid regulation
extracellular/intracellular buffering system
Buffer definition
Ability of a weak acid and its anion (base) to resist change in pH with addition of a strong acid or base
Buffers include
Bicarbonate/carbonic acid, phosphate, and protein
Principle buffer in the body
Bicarbonate
Bicarbonate has ____ onset with _____ capacity
Rapid; intermediate
HCO3- is present in largest concentrations _______
extracellularly
Bicarbonate’s supply of _____ is unlimited
CO2
In the bicarbonate/carbonic acid buffering system, acidity can be controlled by ____ or ____
HCO3-; pCO2
When acid is added to the carbonic acid/bicarbonate buffer system, ____ can be exhaled very rapidly
CO2
Phosphates have ____ onset and _____ buffering capacity
intermediate; intermediate
Extracellular inorganic phosphates have ____ buffering activity
limited
Calcium phosphates in bone are ______
relatively inaccessible
Albumin and hemoglobin have ___ onset and ____ buffering capacity
Rapid; limited
Proteins are more effective as buffers ____ than ____
Intracellularly; extracellularly
Kidneys serve 2 main purposes in acid regulation
Reabsorb filtered HCO3- and excrete H+ ions released from nonvolatile acids
______ mEq of HCO3- is filtered through kidneys daily
4000-4500
_____% of bicarbonate is reabsorbed by the _____ tubule
85-90%; proximal
10-15% of bicarbonate is reabsorbed via the ____ tubule or _____
distal; collecting duct
There is virtually no _____ in urine
HCO3-
Anything limiting H+ secretion into the proximal tubule lumen results in _____
urinary bicarbonate losses
H+ excretion takes place primarily in the ______
distal tubule
Distal tubular hydrogen ion secretion comprises ____% of net acid excretion
~50%
In the distal tube ____ combines with ___ in the presence of _____ to form ____, which breaks down to ___ and ____
CO2; water; carbonic anhydrase; H2CO3; H+ and HCO3-
H+ is transported back into the tubular lumen of the kidney via ____
ATPase
_____ freely crosses the distal tubular membrane and enters the _____ for absorption
HCO3-; peritubular capillary
Ventilatory acid regulation has a ____ onset and ___ capacity
rapid; very large
During ventilatory acid regulation ____ detect an increase in the ____ and ___ the rate and depth of ventilation
Chemoreceptors; PCO2 levels; increase
Where are peripheral chemoreceptors located
carotid arteries and aorta
What activates peripheral chemoreceptors
Arterial acidosis, hypercapnia, and hypoxia
Hypercapnia meaning
High CO2
Where are central chemoreceptors located
Medulla
What activates central chemoreceptors
CSF acidosis
CSF meaning
Cerebrospinal fluid
Oxidation of proteins generates what
HCO3- and NH4+
____ can be eliminated via urea synthesis or renal ammoniagenesis
NH4+
Equation for urea synthesis
HCO3- + NH4+ –> Urea + CO2 + H2O
If liver diminishes hepatic urea synthesis, _______ may occur or ____ will be coorected
Metabolic alkalosis; an acidotic state
An increase or decrease in the urea cycle will affect the _____ pool
HCO3-
____ compensation is very rapid
Respiratory
____ compensation takes 3-5 days for max effect
Renal
Adverse consequences of acidemia on the cardiovascular system
- Decreased cardiac output
- Impairment of cardiac contractility
- Increased pulmonary vascular resistance (PVR) and arrhythmias
Adverse consequences of acidemia on the metabolism
- Insulin resistance
- Inhibition of anaerobic glycolysis
- Hyperkalemia
Adverse consequences of acidemia on the CNS
Coma or altered mental status
Adverse consequences of acidemia on the respiratory system
- Decreased respiratory muscle strength
- Hyperventilation –> compensation feature
- Dyspnea
Adverse consequences of alkalemia on the cardiovascular system
- Decreased coronary blood flow
- Arteriolar constriction
- Decreased anginal threshold
- Arrhythmias
- Risk of heart attack
Adverse consequences of alkalemia on metabolism
-Decreased K+, Ca, and Mg
Adverse consequences of alkalemia on the CNS
- Decreased cerebral blood flow
- Seizures
Adverse consequences of alkalemia on the respiratory system
Decreased respirations
What is the primary change of metabolic acidosis and what is it’s compensation?
Decreased HCO3-; Decreased PaCO2
What is the primary change of metabolic alkalosis and what is it’s compensation?
Increased HCO3-; Increased PaCO2
What is the primary change of respiratory acidosis and what is it’s compensation?
Increased PaCO2; Increased HCO3-
What is the primary change of respiratory alkalosis and what is it’s compensation?
Decreased PaCO2; increased HCO3-
In metabolic acidosis, what should the body do to compensate?
PaCO2 should fall 1 to 1.5 times the fall in plasma HCO3-
In metabolic alkalosis, what should the body do to compensate?
PaCO2 should increase by 0.4 to 0.6 times the rise in plasma HCO3-
In acute respiratory acidosis, what should the body do to compensate?
The plasma HCO3- should rise by 0.1 times the increase in PaCO2 plus or minus 3
In chronic respiratory acidosis, what should the body do to compensate?
The plasma HCO3- should rise by 0.4 times the increase in PaCO2 plus or minus 4
In acute respiratory alkalosis, what should the body do to compensate?
The plasma HCO3- should fall by 0.1 to 0.3 times the decrease in PaCo2 but usually not to less than 18 mEq/L
In chronic respiratory alkalosis, what should the body do to compensate?
The plasma HCO3- should fall by 0.2 to 0.5 times the decrease in PaCO2 but usually not to less than 14 mEq/L