360 - Acid-Base Balance Flashcards
pH of normal blood
7.4
7.35 to 7.45
alkalemia
pH above 7.45
acidemia
pH below 7.35
total CO2
The sum of the concentration of bicarbonate (HCO3-) and dissolved CO2 (dCO2)
dissolved CO2
The solubility coefficient α (0.0306 mmol/L/ mm Hg) multiplied by the partial pressure of CO2 (pCO2)
pCO2
the pressure exerted by CO2 in a gas mixture (partial pressure).
the four blood buffering systems
bicarbonate, hemoglobin, phosphate, and plasma proteins
the ratio of bicarbonate to dissolved CO2
20:1
The bicarbonate buffering system is the most important buffering system for three reasons:
- Carbonic acid dissociates into carbon dioxide and is eliminated in the lungs
- The lungs can modify the respiration rate and thus, the pCO2
- The kidneys can control bicarbonate reabsorption
regulation of CO2 in blood
- CO2 released by tissues
- diffuses into erythrocytes
- becomes H2CO3 in RBCs by carbonic anhydrase
- dissolves into bicarb and H+
- HCO3- moves into bloodstream; Cl- enters RBCs
- free H+ binds to deox Hb
CO2 regulation in lungs
- Hb binds oxygen and releases H+
- the H+ binds with HCO3- => H2CO3 which dissociates into CO2 and H2O
- CO2 diffuses into the alveoli and is exhaled
- lungs regulate the H2CO3 concentration by retaining or releasing CO2
hypoventilation
increases the amount of CO2 in the blood and decreases the pH
hyperventilation
decreases the amount of CO2 in the
blood and raises the pH
Ammonia is synthesized by the renal tubular cells by the
deamination of glutamine
primary cause of metabolic acidosis
a bicarbonate deficit
- the bicarbonate
concentration decreases and pCO2 remains normal
- the bicarbonate to total CO2 ratio is
decreased, and the blood pH decreases
causes of metabolic acidosis
increased endogenous and exogenous acids, inability to excrete acid, loss of bicarb
increased endogenous acids
o lactic acid: an increased anion gap is observed
o keto acids: an increased anion gap is observed
increased exogenous acids
o ethanol: metabolized to acetaldehyde which is metabolized to acetic acid; an increased anion and increased osmolal gap observed
o methanol: metabolized to formic acid; increases in the anion and osmolal gaps observed
o ethylene glycol: metabolized to glycolic and oxalic acid; increased amounts of calcium oxalate observed in urine
o salicylates*: an unmeasured anion; an increased anion gap is observed; stimulate the increased rate and depth of respiration =
decreasing in the pCO2 this results in a mixed metabolic acidosis/ respiratory
alkalosis
inability to excrete acid
o uremia/ renal failure
- decreased ammonia formation and Na+ - H+ exchange
- an increased anion gap is observed
o renal tubular acidosis
- a normal anion gap is observed
loss of bicarbonate
diarrhea
pancreatitis
intestinal fistula
normal anion gap
primary means of compensation for metabolic acidosis
hyperventilation
secondary compensation for metabolic acidosis
renal; relies on normal kidney function
primary cause of respiratory acidosis
excess carbon dioxide
causes of respiratory acidosis
- factors that directly depress the respiratory center
- mechanical obstruction of airway
- abdominal distention
- extreme obesity
- sleeping disorders
the immediate compensatory response to respiratory acidosis
blood buffer, hemoglobin, protein
primary cause of metabolic alkalosis
excess bicarb
causes of metabolic alkalosis
- hypochloremic alkalosis
- excess mineralocorticoids/corticoids
- excess administration/ingestion of bicarb
hypochloremic alkalosis
o The loss of chloride is the most common cause of metabolic alkalosis
o Prolonged diarrhea, vomiting or aspiration of gastric fluid leads to a loss of gastric HCl
o The loss of chloride leads to renal retention of bicarbonate
due to excess mineralocorticoids or corticoids, these two syndromes may affect the ability of the kidneys to regulate electrolyte balance
Hyperaldosteronism and Cushing’s syndrome
- sodium absorbed in distal tubules = hypokalemia
- correct the hypokalemia, potassium exits the cells and hydrogen enters
- movement of hydrogen decreases blood pH
causes of resp alkalosis
direct stimulatory effect on the respiratory system:
o Hysteria, fever, CNS infections, metabolic encephalopathy hypoxia
o Drugs: salicylates, nicotine
o Hypoxia: severe anemia, altitude sickness
factors that affect the pulmonary mechanism and lead to tissue hypoxia
o Pneumonia
o Pulmonary emboli,
o Congestive heart failure
primary compensation for respiratory alkalosis
renal
- kidney will try to decrease the reclamation of bicarb and increase reclamation of hydrogen
T or F. Exposure of blood samples to atmospheric air results in a false decrease in total and pCO2 and false increases in pH and O2
T!
