Acid - Base Balance Flashcards
(34 cards)
Acid Base Balance
Acid-base balance is carefully regulated to maintain a normal pH via multiple mechanisms
pH
- Inverse logarithm of the H+ concentration
- If the H+ are higher in number, the pH is low (acidic); if the H+ are lower in number, the pH is high (alkaline)
pH (cont’d)
The pH scale ranges from 0 to 14: 0 is very acidic, 14 is very alkaline
Each number represents a factor of 10
- If a solution moves from a pH of 6 to 5, the H+ have increased 10 times
pH (cont’d)
Acids are formed as end products as protein, carbohydrate, and fat metabolism
To maintain the body’s pH (7.35- 7.45) the H+ must be neutralized or excreted
The bones, lungs, and kidneys are the major organs involved in the regulation of the acid and base balance
Buffering Systems
A buffer is a chemical that can bind excessive H+ or OH- without a significant change in pH
A buffering pair consists of a weak acid and its conjugate base
The most important plasma buffering systems are the carbonic acid - bicarbonate pair
- CO2 + H2O H2CO3 H + HCO3
Carbonic Acid - Bicarbonate Pair
Operates in the lung and the kidney
The greater the partial pressure of carbon dioxide, the more carbonic acid is formed
- At a pH of 7.4 the ratio of bicarbonate to carbonic acid is 20:1
- Bicarbonate and carbonic acid can increase or decrease, but the ratio must be maintained
Carbonic Acid - Bicarbonate Pair (cont’d)
If the amount of bicarbonate decreases, the pH decreases, causing a state of acidosis
The pH can be returned to normal if the amount of carbonic acid also decreases
- This type of pH adjustment is referred to as compensation
Carbonic Acid - Bicarbonate Pair (cont’d)
The respiratory system compensates by increasing ventilation to expire carbon dioxide or by decreasing ventilation to retain carbon dioxide
The renal system compensates by producing acidic or alkaline urine
Other Buffering Systems
Protein buffering (hemoglobin)
- Proteins have negative charges, so they can serve as buffers for H+
Renal buffering
- Secretion of H+ in the urine and reabsorption of HCO3-
Ion exchange (between ICF and ECF)
- Exchange of K+ for H+ in acidosis and alkalosis
Acid- Base Imbalances
Normal arterial blood pH
- 7.35-7.45
- Obtained by ABG sampling
Acidosis
- Systemic increase in H+ concentration or decrease in bicarbonate
Alkalosis
- Systemic decrease in H+ concentration or increase in bicarbonate
Bicarbonate
HCO3: anion electrolyte Normal: 21-28 mmol/L Regulated by the kidney Combines with H+ Neutralizes (buffers) acidity - 28 too much bicarb or note enough acid
Carbonic Acid
A weak acid
The primary blood buffer
Neutralizes H+, maintains pH
Forms either H+ and HCO3, or H2O and CO3
Carbon Dioxide
Normal 35-45 mm Hg A gas exhaled by the lungs Diffuse easily across the alveoli Elimination directly related to ventilation - 45 hypoventilation - retaining acid
Acidosis and Alkalosis
Four categories of acid-base imbalances
- Respiratory acidosis: elevation of pCO2 as a result of ventilation depression
- Respiratory alkalosis: depression of pCO2 as a result of alveolar hyperventilation
- Metabolic acidosis: depression of HCO3- or an increase in non carbonic acids
- Metabolic alkalosis: elevation of HCO3- usually caused by an excessive loss of metabolic acids
Acidosis and Alkalosis (cont’d)
Four categories of acid-base imbalances
- Metabolic acidosis: depression of HCO3- or an increase in non carbonic acids
- Metabolic alkalosis: elevation of HCO3- usually caused by an excessive loss of metabolic acids
Anion Gap
Used cautiously to distinguish different types of metabolic acidosis
By rule, the concentration of anions (-) should equal the concentration of cations (+); not all normal anions are routinely measured
Anion Gap (cont’d)
Normal anion gap:
Na+ + K+ = Cl- + HCO3 + 10 to 12 mEq/L (other miscellaneous anions [the ones we don’t measure]: phosphates, sulfates, organic acids, etc.)
Respiratory System
Regulates carbonic acid by eliminating or retaining carbon dioxide
Increase in carbon dioxide or hydrogen ions stimulates the respiratory centre in the brain to increase rate and depth of respirations
- Eliminates carbon dioxide, carbonic acid levels falls, and pH levels become normal
Respiratory System
Alkalosis depresses the respiratory centre
- Causes rate and depth of respirations to decrease
- Carbon dioxide is retained
- Retained carbon dioxide combines with water
- Carbonic acid levels fall, and pH levels become normal
Renal System
Regulates bicarbonate levels in extracellular fluid to excrete or retain hydrogen ions
Excessive hydrogen ions causes pH levels to fall
- Kidneys excrete hydrogen ions and retain bicarbonate
Renal System
Excessive bicarbonate levels cause the kidneys to retain hydrogen ions and excrete bicarbonate to restore acid-base balance
Example:
The primary acid-base imbalance moves the pH away from normal limits
If pCO2 is increased, and pH is below normal … Respiratory acidosis
Example:
The primary acid-base imbalance moves the pH away from normal limits
If HCO3 is increased, and pH is above normal … Metabolic alkalosis
Example:
pH : 55 - acidosis
HCO3: 24 - normal
Respiratory Acidosis
