Acid Base Balance

Why is water neutral in pH?

There is no change in the ion/electron balance

Equal numbers of H+ and OH-

What is the electron difference between acids and bases?

• Acids - higher H+ or lower OH-

• Bases - higher OH- or lower H+

What is the pH scale based on?

The relative concentration of H+ ions

• Acids - low pH

  • High H+

• Base - high pH

  • Low H+

What are buffer systems used for?

Used to maintain body fluid homeostasis - if H+ is bound to a buffer, it doesn’t affect pH

• Changes in pH affect enzymes and cell function in the body

• Examples of buffer systems in the body - can bind H+ ions

  • Proteins - hemoglobin

  • Phosphates

  • Carbonic acid

Buffers are the fastest way for our bodies to maintain their homeostatic pH level

How do buffer systems operate?

Help regulate our pH by converting strong acids or bases into weak acids or bases

H⁺ + HCO₃^- ←→ H₂CO₃

Hydrogen + Bicarbonate ←→ Carbonic acid

• If H⁺ ↓ or HCO₃^- ↑ - Alkalosis → body is too basic

  • Buffers will release H⁺ to lower pH

• If H⁺ ↑ or HCO₃^- ↓ - Acidosis → body is too acidic

  • Buffer will bind H⁺ to remove H⁺ effect; remove from pH equation to raise pH

How does the carbonic acid equation function during acidosis?

H⁺ + HCO₃^- ←→ H₂CO_{3 ←→} H₂O + CO₂

If the body is too acidic - reaction pushes to the right - produces more CO₂ - respiration blows CO₂ off to raise pH

How does the carbonic acid equation function during alkalosis?

H⁺ + HCO₃^- ←→ H₂CO_{3 ←→} H₂O + CO₂

If the body is too alkalotic - reaction pushes to the left - more carbon dioxide combines with water (less CO₂ to blow off) - carbonic acid releases H⁺ to lower pH

What does normal body pH look like?

pH of 7.38-7.42

H⁺ concentration is closely regulated by the buffer system

What are some things that abnormal pH does to the body?

• Can alter the tertiary structure of proteins (denatures proteins)

  • Affects metabolism + anything metabolism does

• Affects the nervous system

If the pH becomes abnormal, the entire body becomes affected

What is the difference between short-term and long-term pH correction?

• Short-term - buffer binding

• Long-term - ventilation or kidney

What are some sources of hydrogen ions (H⁺)?

• Cell metabolism - CO₂ production

  • Higher CO₂ levels → higher H⁺ levels

• Metabolic intermediate by-products

  • Lactic acid

  • Pyruvic acid

  • Acetoacetic acid

  • Fatty acids

• Food products - break-down releases H⁺

  • Grains and nuts

  • Yogurt/dairy

  • Citric acid in fruit

  • Legumes

  • Meats

• Medications - can stimulate HCl production by parietal cells of the stomach

• Some disease processes

  • e.g. diabetes - improper fat metabolism, generation of ketoacids

What are some sources of bicarbonate ions (HCO₃^-)?

• Fruits and veggies

  • The breakdown of some can produce bases - can help equalize acid production

• Antacids

  • e.g. Tums

What are the 2 ways the body might increase it’s concentration of H⁺ ions?

• An accumulation of acids

• A loss of bases

What are the 2 types of pH disturbances and their effects?

• Acidosis

  • Neurons become less excitable

  • CNS depression

• Alkalosis

  • Hyperexcitability of the CNS

  • Tingling, twitches in the muscles + heart

How does pH affect potassium balance?

A change in pH levels will affect K⁺ balance

• Affects nerve and muscle function

• Affects enzyme activity

Potassium levels in plasma - maintained in a narrow range by aldosterone

What are the effects of abnormal potassium levels?

• Hypokalemia - low blood potassium

  • Muscle weakness

  • Failure of respiratory muscles and heart

• Hyperkalemia - high blood potassium

  • Cardiac arrhythmias

Why does pH affect potassium?

The kidney has a H⁺/K⁺ exchanger - excretes H⁺ and retains K⁺

• With acidosis

  • [H⁺] is high → more H⁺ secreted → less K⁺ excretion

• K⁺ retention affects cardiac function + other systems

How does pH affect enzyme activity?

pH changes (up or down) can alter the shape of the enzyme (denature)

• Enzyme can become non-functional

• Affects metabolic activity

How does acidosis/alkalosis occur?

Either metabolic or respiratory function

• Metabolic - imbalance in the production and excretion of acids or bases

  • Caused by change in metabolism or kidney function

• Respiratory - due to lung or breathing disorders (or environmental changes)

How might metabolic acidosis occur?

• Metabolic organic acid production

  • Lactic acid (exercise)

  • Ketoacids - diabetes

• Diarrhea

• Organic acid intake in diet

How might respiratory acidosis occur?

Production of CO₂ with decreased removal from lungs → accumulation of CO₂ in the blood → acid production

e.g. caused by poor ventilation

How might metabolic alkalosis occur?

• Vomitting → loss of acid

• Dietary sources of bases - e.g. Tums

• Pyloric stenosis

How might respiratory alkalosis occur?

Hyperventilation

e.g. caused by high altitudes

What do the terms acidemia and alkalemia mean?

Indicates a change in pH of the blood - can be acute or chronic

• Acidemia - lower than normal blood pH

• Alkalemia - higher than normal blood pH

Normal blood pH

• 7.35 - venous (deoxygenated)

• 7.45 - arterial (oxygenated)

Why does venous blood have a lower pH than arterial blood?

Venous blood removes CO₂ from tissues, which can convert to H⁺ if it interacts with water

What 3 mechanisms are responsible for maintaining pH homeostasis in the body?

• Buffers - combines or releases H⁺

  • Quickest corrrection

• Ventilation - increase or decrease breathing rate

  • Also responsible for 75% of acid/base imbalances

• Renal regulation - directly excreting/reabsorbing H⁺

  • Slowest of the 3 mechanisms

Describe buffers as a pH fixing mechanism

• Fastest response to pH disturbances - within seconds

• Combines with H⁺/releases H⁺ so pH isn’t affected

  • Phosphate

  • Protein - hemoglobin carriers

  • Bicarbonate equation

Describe respiratory compensations as a pH fixing mechanism

pH is adjusted by changing the rate and depth of breathing - response occurs within minutes

H⁺ + HCO₃^- ←→ H₂CO₃ ←→ H₂O + CO₂

• Acidosis lowers pH → breathing increases → decreases blood CO₂ and H⁺ → increases pH

• Alkalosis raises pH → breathing decreases → increases blood CO₂ and H⁺ → decreases pH

Describe renal compensation as a pH fixing mechanism

Kidneys can retain or eliminate H⁺ or HCO₃^- - response occurs within hours (slowest)

• Apical Na⁺/H⁺ exchanger (NHE)

  • Reabsorbs Na⁺ while it removes H⁺

• Na⁺/HCO₃^- symport

  • Reabsorbs HCO₃^- while it reabsorbs Na⁺

• H⁺/ATPase

  • Removes or reabsorbs H⁺

• H⁺/K⁺/ATPase

  • Reabsorbs K⁺ while it removes H⁺ (acidosis)

  • Reabsorbs H⁺ while it removes K⁺ (alkalosis)

• Na⁺/NH₄⁺ antiport

What are the body’s corrections for acidosis?

To raise body pH

• Buffers bind to H⁺

• Breathing increases

  • Decreases CO₂ and H⁺ via carbonic acid

• Kidneys excrete H⁺ and reabsorb HCO₃^-

What is the function of intercalated type A cells?

Type A intercalated cells function to correct for acidosis

• Secrete H⁺ into the urine

• Reabsorb HCO₃^-

What are the body’s corrections for alkalosis?

To lower body pH

• Buffers release H⁺

• Breathing slows

  • Retains CO₂ and H⁺

• Kidneys retain H⁺ and excrete HCO₃^-

What is the function of intercalated type B cells?

Type B intercalated cells function to correct for alkalosis

• Secrete HCO₃^- into the urine

• Reabsorb H⁺

What are the compensations for metabolic pH disturbances?

If the kidneys are causing the pH disturbance, the respiratory system can compensate

• Kidneys excreting too much H⁺ in the urine (metabolic alkalosis) → breathing slows to reduce CO₂ loss → less H⁺ is lost

• Kidneys reabsorbing too much H⁺ (metabolic acidosis) → breathing increases to increase CO₂ loss → more H⁺ is lost

What are the compensations for respiratory pH disturbances?

If the respiratory system is the problem, the kidneys can compensate

• Breathing is too rapid → excessive loss of CO₂ (respiratory alkalosis) → kidneys reabsorb more H⁺

• Breathing is too shallow → keeping too much CO₂ (respiratory acidosis) → kidneys secrete more H⁺ in the urine