Block 4: Acid-Base Physiology Flashcards
What is acid-base balance?
Regulation hydrogen ion (H+) concentration in body fluids → for normal cell/organ function and survival
How does the H+ influence acid-base balance?
Highly reactive where concentration is precisely regulated within a narrow normal range
What is the function of H+ concentration?
- Alters distribution of electrolytes
- Alters activity of enzymes involved in ATP production
How do lungs contribute to acid-base balance?
Regulate the elimination of CO2, a source of carbonic acid
How do kidneys contribute to acid base balance?
Eliminate H+ and HCO3-
What is tissue perfusion?
Ensures delivery of O2 and nutrients → Maintaining aerobic metabolism
Decreased perfusion → anaerobic metabolism and accumulation of lactic acid
What are volatile acids? Example?
Can dissociate forming a gas eliminated by the lungs
Carbonic acid (H2CO3)
How leads to CO2 production?
- Formed during aerobic metabolism
- Combines with water to form carbonic acid
- H2CO3 dissociates into H+ and bicarb
What happens if there is an accumulation of CO2?
↑ Carbonic acid → ↓ pH
What are nonvolatile acids?
Not gases → cannot be eliminated from the lungs; eliminated primarily by kidneys
How does nonvolatile acid differ from volatile gases?
Lower production → takes longer to reach comparable degree of acidity in kidney failure than respiratory failure
What causes fluctuations of H+?
- Daily ingestion
- Metabolic production
- Utilization of acids and bases
What are the types of buffer systems?
- Chemical
- Respiratory
- Renal
What is the function of chemical buffers?
Intracellular and extracellular buffers that neutralize excess acids and bases
What is the function of respiratory buffers?
eliminates carbonic acid (H2CO3) in the form of CO2 in exhaled air
What is the function of renal buffers?
regulates the excretion of bicarbonate (HCO3-) and H+ from nonvolatile acids
What is important for local acid-base balance?
Good tissue perfusion
What are components of chemical buffers?
- Consist of a weak acid and a weak base.
- Convert strong acids/bases to weak ones.
How long does chemical buffer take to buffer?
Max efficiency with an hour after imbalance
React almost immediately
What are the types of chemical buffers?
- Bicarbonate buffer system
- Phosphate buffer system
- Intracellular and extracellular proteins
How do you calculate pH of a buffer system?
Henderson–Hasselbalch equation
Describe the chemical regulation of bicarb buffer system?
The ratio of bicarbonate (HCO3-) to carbonic acid (H2CO3) is 20:1
What is pKa?
Dissociation constant of weak acid
What is the ideal buffer system?
pKa = pH of solution
What is the purpose for bicarbonate buffer system?
pKa=6.1 (and blood pH=7.4) → still an important ECF buffer because:
1. Lungs can regulate the level of carbonic acid
2. Kidneys can regulate the level of bicarb
How does the bone contribute to acid and base balance?
- H+ ions move into bone to be buffered by hydroxyapatite and carbonates → release of Ca and phosphate from bone
- Prolonged ↑ H+ → activate osteoclasts → bone resorption
- Electrolyte loss and resorption → bone demineralization and increased risk of fractures
How does respiration regulate acid-base balance?
- CO2 diffuses from pulmonary capillaries into alveoli and is then eliminated in exhaled air
- If CO2 accumulates, then the concentration of H+ in body fluids increases
How control respiratory reg?
Brainstem respiratory center → feedback mechanism between it and the lungs
H+ excess trigger a neural reflex
How does ↑ H+ neural reflex?
- ↑ rate and contraction of respiratory muscles
- ↑ breathing rate and depth
- Eliminate CO2 → ↓ carbonic acid → ↑ pH
How does the respiratory system compensate for extreme acidosis?
Hyperventilation ceases
Reflex fails
How does the respiratory system compensate for extreme alkalosis
Ventilation is depressed, leading to:
1. Accululation of CO2 → ↑ carbonic acid → ↓ pH
What is compensatory hypoventilation?
Lungs retain CO2 → more carbonic cid
How is hypoventilation not really noticed?
Subsequent hypoxemia and hypercapnia stimulate respiration
How long does it take for respiratory reg compensate?
Maximal compensation takes 24-48 hours
Chemoreceptors detect H+ changes
What may cause a delay is respiratory reg?
- Transporting blood
- Initiating a relex response
What are the respiratory compensation limitations?
- If lungs are source of acidosis or alkalosis.
- Diminished stimulus to respiratory center
- Lung disease
- Neuromuscular disease
How does the renal regulate acid-base?
Regulates bicarbonate and nonvolatile acids
What is normal pH of urin?
Usually acidic
4-8, average: 6
What are the mechanisms of renal reg?
- Conservation of bicarbonate by tubular reabsorption.
- Secretion of H+ into urine; synthesis of new bicarbonate.
- Excretion of H+ buffered by ammonia
How does it take longer for the renal system to regulate acid-base?
8-12 hours – begin to have effect
4-6 days – maximum effectiveness
Slowest yet most effective → H+ and HCO3- can be excreted if need → capable of completely retuning pH to normal
How causes disruption to renal reg?
- Kidney impariment
- They are a source of the imbalance
Describe how the renal system conserves bicarb ions?
Describe how the renal system secrete H+ in the urine and creates new HCO3-?
What is the difference between compensation and correction?
Compensation: Chemical buffers, renal or respiratory function return pH within normal range → Underlying disease
Correction: Condition responsible for imbalance is controlled or no longer present → pH is within normal range
What is intracellular pH?
- Major impact on cell function
- Affected by changes in both the H+ concentration and ECF
- Varies with different cell types
- Clinical pHi measurement is not feasible
What are the mechanism for regulating pHi?
- buffers
- HCO3-
- Transporters
What are the simple acid-base imbalances? Distinguish the types?
- Respiratory acidosis
- Respiratory alkalosis
- Metabolic acidosis
- Metabolic alkalosis
What is the difference between respiratory and metabolic imbalances?
R: Due to alteration in CO2 elimination by lungs
M: Due to alterations in the level of nonvolatile acids or bases HCO3
How are the clinical manifestation of acid-base imbalances?
- Effects of acidosis or alkalosis on cell functions.
- Effects of underlying disease process causing acid-base imbalance.
- Manifestations of respiratory or renal compensation.
What is the normal ratio of bicarb to carbonic acid?
20:1
What ions control neuromuscular function?
Hydrogen and calcium ions that bind to negative charged plasma intracellular proteins and
How is neuromuscular function affected by acidosis?
Reduced NM excitability by ↑ levels of calcium that blocks sodium channels in nerves and muscles → decreases neuromuscular excitability → muscle weakness, weak reflexes
Excess H+ ions bind to negative charges causing fewer sites available for Ca2+
How is neuromuscular function affected by alkalosis?
↑ NM excitability → fewer H+ compete with Ca2+ for PB sites → less Ca2+ blocks sodium channels
What are the NM function of alkalosis?
- Trousseasu
- Hyperactive reflexes
- Paresthesias
- Convulsion
- Larynospasm
- Tetany
How is the CNS altered by acidosis?
Increased cerebral BF → decreased sodium entry → vasodilation of cerebral blood vessels → HA, increased intracranial pressure
How is the CNS altered by alkalosis?
Vasoconstriction of cerebral BV → ↓ cerebral BF and O2 delivery → DZ, AX, SZ, Confusion, coma