• The second line of defense against acid–base disturbances is the lungs.
• The lungs regulate the CO₂ concentration in the extracellular fluid.
• Increased ventilation removes more CO₂ from the extracellular fluid.
• Removal of CO₂ decreases H⁺ concentration by mass action.
• Decreased H⁺ concentration increases pH.
• Decreased ventilation causes CO₂ to accumulate.
• Increased CO₂ increases H⁺ concentration.
• Increased H⁺ concentration decreases pH.

Easy Concept

↑ Ventilation

↓

↓ CO₂

↓

↓ H₂CO₃

↓

↓ H⁺

↓

↑ pH (Alkalosis)

↓ Ventilation

↓

↑ CO₂

↓

↑ H₂CO₃

↓

↑ H⁺

↓

↓ pH (Acidosis)

Pulmonary Expiration of CO₂ Balances Metabolic Formation of CO₂

• CO₂ is continuously produced inside body cells.
• CO₂ is formed during intracellular metabolism.
• CO₂ diffuses from cells into the interstitial fluid.
• CO₂ then diffuses into the blood.
• Blood transports CO₂ to the lungs.
• CO₂ diffuses from blood into the alveoli.
• Pulmonary ventilation removes CO₂ into the atmosphere.
• Normally, the extracellular fluid contains about 1.2 mmol/L of dissolved CO₂.
• This corresponds to a PCO₂ of 40 mm Hg.

Mathematical Relationship

$$\boxed{ 1.2\ \text{mmol/L dissolved CO₂} \Longleftrightarrow PCO_2 = 40\ \text{mm Hg} }$$1.2 mmol/L dissolved CO₂⟺PCO2​=40 mm Hg​

Easy Concept

Cells

↓

Produce CO₂

↓

Blood carries CO₂

↓

Lungs remove CO₂

↓

Body maintains normal PCO₂ = 40 mm Hg

• If metabolic CO₂ production increases, extracellular PCO₂ increases.
• If metabolic CO₂ production decreases, extracellular PCO₂ decreases.
• Increasing pulmonary ventilation removes more CO₂ from the lungs.
• Increased ventilation decreases extracellular PCO₂.
• Therefore, extracellular PCO₂ depends on:
  • Pulmonary ventilation.
  • Tissue CO₂ production.

Easy Concept

More Tissue Metabolism

↓

More CO₂

↓

Higher PCO₂

More Ventilation

↓

More CO₂ Removed

↓

Lower PCO₂

Increasing Alveolar Ventilation Decreases Extracellular Fluid H⁺ Concentration and Raises pH

Figure Mentioned: Fig. 31.2

• If metabolic CO₂ production remains constant, alveolar ventilation is the only factor that changes extracellular PCO₂.
• Higher alveolar ventilation produces a lower PCO₂.
• Increased CO₂ increases H₂CO₃ concentration.
• Increased H₂CO₃ increases H⁺ concentration.
• Increased H⁺ lowers extracellular fluid pH.

Easy Concept

↑ CO₂

↓

↑ H₂CO₃

↓

↑ H⁺

↓

↓ pH

• Fig. 31.2 shows the changes in blood pH produced by changing alveolar ventilation.
• Increasing alveolar ventilation to 2 times normal raises extracellular fluid pH by about 0.23.

Mathematical Solution

Normal pH$$7.40$$7.40

Increase in pH$$+0.23$$+0.23

Final pH$$7.40+0.23=7.63$$7.40+0.23=7.63

Final Answer

$$\boxed{pH=7.63}$$pH=7.63​

• Therefore, if normal pH is 7.40, doubling alveolar ventilation raises the pH to about 7.63.

Easy Concept

Ventilation ×2

↓

CO₂ decreases

↓

H⁺ decreases

↓

pH increases

↓

7.40 → 7.63

• Decreasing alveolar ventilation to one-fourth normal lowers pH by about 0.45.

Mathematical Solution

Normal pH$$7.40$$7.40

Decrease in pH$$-0.45$$−0.45

Final pH$$7.40-0.45=6.95$$7.40−0.45=6.95

Final Answer

$$\boxed{pH=6.95}$$pH=6.95​

• Therefore, reducing alveolar ventilation to one-fourth normal decreases the pH from 7.40 to 6.95.

Easy Concept

Ventilation = ¼ Normal

↓

CO₂ increases

↓

H⁺ increases

↓

pH decreases

↓

7.40 → 6.95

• Alveolar ventilation can change over a very wide range.
• It may decrease to 0.
• It may increase up to 15 times normal.
• Therefore, the respiratory system can produce large changes in body fluid pH.

Easy Concept

Ventilation Range$$0 \longrightarrow 15 \times \text{Normal}$$0⟶15×Normal

↓

Large changes in CO₂

↓

Large changes in H⁺

↓

Large changes in pH

KEY CONCEPT

• Respiratory system is the second line of defense against acid–base disorders.
• ↑ Ventilation → ↓ CO₂ → ↓ H₂CO₃ → ↓ H⁺ → ↑ pH (Respiratory Alkalosis).
• ↓ Ventilation → ↑ CO₂ → ↑ H₂CO₃ → ↑ H⁺ → ↓ pH (Respiratory Acidosis).
• Normal dissolved CO₂ = 1.2 mmol/L.
• Normal PCO₂ = 40 mm Hg.
• Doubling ventilation: pH = 7.40 → 7.63.
• Reducing ventilation to one-fourth: pH = 7.40 → 6.95.
• Alveolar ventilation can vary from 0 to 15 times normal, allowing large changes in body fluid pH.

Mathematical/Biochemical Equations Solved

1. ↑ Ventilation → ↓ CO₂ → ↓ H₂CO₃ → ↓ H⁺ → ↑ pH
2. ↓ Ventilation → ↑ CO₂ → ↑ H₂CO₃ → ↑ H⁺ → ↓ pH
3. Normal dissolved CO₂

$$\boxed{1.2\ \text{mmol/L}\Longleftrightarrow PCO_2=40\ \text{mmHg}}$$1.2 mmol/L⟺PCO2​=40 mmHg​

4. Doubling ventilation

$$7.40+0.23=7.63$$7.40+0.23=7.63

5. Reducing ventilation to one-fourth

$$7.40-0.45=6.95$$7.40−0.45=6.95

6. Ventilation range

$$0\rightarrow15\times\text{Normal}$$0→15×Normal

Figure 31.2: Effect of Alveolar Ventilation on Extracellular Fluid pH

• (Figure 31.2) shows how changes in alveolar ventilation affect the pH of body fluids (extracellular fluid).

Understanding the Axes

X-Axis (Horizontal)

Rate of Alveolar Ventilation (Normal = 1)

This shows how fast a person is breathing compared with normal.

Value	Meaning
0.5	Breathing at half the normal rate (Hypoventilation)
1.0	Normal breathing
1.5	Breathing 1.5 times faster than normal
2.0	Breathing 2 times faster than normal
2.5	Breathing 2.5 times faster than normal (Hyperventilation)

• Moving to the right = Breathing faster
• Moving to the left = Breathing slower

Y-Axis (Vertical)

pH Change in Body Fluids

This axis shows how much the extracellular fluid pH changes from the normal value.

Upper Half (Positive Values)

• +0.1
• +0.2
• +0.3

These indicate that pH increases.

• Blood becomes more alkaline (basic).

Middle Point (0)

This is the Normal pH.

• Normal ventilation
• Normal CO₂
• Normal blood pH

This point is marked “Normal” on the graph.

Lower Half (Negative Values)

The graph labels them as 0.1, 0.2, 0.3, 0.4, 0.5 below zero.

These represent a decrease in pH.

• Blood becomes more acidic.

Understanding the Red Curve

The red curve shows the relationship between:

Breathing Rate → CO₂ Level → Blood pH

Normal Point (Ventilation = 1)

At ventilation = 1

The graph passes through the Normal point.

Meaning:

• Normal breathing
• Normal CO₂ removal
• Normal extracellular fluid pH

No pH change occurs.

Left Side of the Curve (Ventilation Less Than Normal)

Move left from the normal point.

Example:

Ventilation decreases from 1 → 0.5

This means:

• Breathing becomes slower.
• Less CO₂ is removed by the lungs.
• CO₂ accumulates in the blood.
• More carbonic acid (H₂CO₃) forms.
• H⁺ concentration increases.
• Blood pH decreases.

Result:

Blood becomes more acidic.

The graph moves downward.

Right Side of the Curve (Ventilation Greater Than Normal)

Move right from the normal point.

Example:

Ventilation increases from 1 → 2

This means:

• Breathing becomes faster.
• More CO₂ is removed by the lungs.
• Blood CO₂ decreases.
• Carbonic acid (H₂CO₃) decreases.
• H⁺ concentration decreases.
• Blood pH increases.

Result:

Blood becomes more alkaline (basic).

The graph moves upward.

Why is the Curve Curved Instead of a Straight Line?

Notice:

Near the normal point, the curve is steeper.

At very high ventilation, the curve becomes flatter.

This means:

• Around normal breathing, small changes in ventilation produce noticeable changes in pH.
• At very high ventilation rates, further increases in breathing cause only smaller additional increases in pH.

Understanding the Entire Curve

Far Left (Very Slow Breathing)

• Very low ventilation
• CO₂ retained
• H₂CO₃ increases
• H⁺ increases
• pH falls markedly

Result: Severe acidosis.

Middle (Normal)

• Normal ventilation
• Normal CO₂
• Normal H⁺
• Normal pH

Far Right (Very Fast Breathing)

• Very high ventilation
• Excess CO₂ removed
• H₂CO₃ decreases
• H⁺ decreases
• pH rises

Result: Alkalosis.

Easy Concept

Think of the lungs as a CO₂ remover.

If you breathe slowly

➡ CO₂ stays in the blood.

➡ More acid forms.

➡ pH falls.

If you breathe faster

➡ CO₂ leaves the blood.

➡ Less acid remains.

➡ pH rises.

One-Line Memory Trick

Slow breathing → ↑ CO₂ → ↑ H⁺ → ↓ pH → Acidosis

Fast breathing → ↓ CO₂ → ↓ H⁺ → ↑ pH → Alkalosis

KEY CONCEPT

• Figure 31.2 shows how alveolar ventilation changes extracellular fluid pH.
• Normal ventilation (1× normal) maintains normal blood pH.
• Decreased ventilation (hypoventilation) causes CO₂ retention, H⁺ increases, and pH decreases (acidosis).
• Increased ventilation (hyperventilation) causes more CO₂ removal, H⁺ decreases, and pH increases (alkalosis).
• The lungs regulate blood pH by controlling the amount of CO₂ removed from the body.

Increased H⁺ Concentration Stimulates Alveolar Ventilation

Figure Mentioned: Fig. 31.3

• Alveolar ventilation not only changes H⁺ concentration.
• H⁺ concentration also controls the rate of alveolar ventilation.
• Fig. 31.3 shows the relationship between blood pH and alveolar ventilation.
• As pH decreases from the normal value of 7.4 to 7.0, alveolar ventilation increases 4 to 5 times normal.

Mathematical Values

Normal pH$$\boxed{7.4}$$7.4​

↓

Acidic pH$$\boxed{7.0}$$7.0​

↓

Alveolar ventilation$$\boxed{4\text{–}5\times \text{Normal}}$$4–5×Normal​

Easy Concept

↓ pH (↑ H⁺)

↓

Respiratory center stimulated

↓

Alveolar ventilation increases

↓

4–5 × Normal

• When plasma pH rises above 7.4, alveolar ventilation decreases.

Easy Concept

↑ pH (↓ H⁺)

↓

Respiratory center depressed

↓

Ventilation decreases

• The change in ventilation for each unit change in pH is much greater when pH is low.
• The response is stronger when H⁺ concentration is high.
• The response is weaker when pH is high.

Easy Concept

Low pH

↓

Strong respiratory response

High pH

↓

Weak respiratory response

• Increased pH decreases alveolar ventilation.
• Decreased ventilation lowers the amount of oxygen entering the blood.
• Blood PO₂ decreases.
• Low PO₂ stimulates ventilation.
• Therefore, respiratory compensation for increased pH is limited.
• Respiratory compensation is much more effective during marked decreases in pH.

Easy Concept

↑ pH

↓

↓ Ventilation

↓

↓ Oxygen (PO₂)

↓

Oxygen receptors stimulated

↓

Ventilation increases again

↓

Compensation for alkalosis is limited

Feedback Control of H⁺ Concentration By the Respiratory System

• Increased H⁺ concentration stimulates respiration.
• Increased alveolar ventilation decreases H⁺ concentration.
• Therefore, the respiratory system works as a negative feedback controller of H⁺ concentration.

Easy Concept

↑ H⁺

↓

↑ Respiration

↓

↑ CO₂ Removal

↓

↓ CO₂

↓

↓ H₂CO₃

↓

↓ H⁺

↓

Back to Normal

• When H⁺ concentration rises above normal, the respiratory system is stimulated.
• Alveolar ventilation increases.
• Increased ventilation decreases extracellular PCO₂.
• Lower PCO₂ decreases H⁺ concentration.
• H⁺ concentration returns toward normal.

Easy Concept

↑ H⁺

↓

↑ Ventilation

↓

↓ PCO₂

↓

↓ H⁺

↓

Normal pH restored

• When H⁺ concentration falls below normal, the respiratory center is depressed.
• Alveolar ventilation decreases.
• Decreased ventilation increases PCO₂.
• Increased PCO₂ increases H⁺ concentration.
• H⁺ concentration returns toward normal.

Easy Concept

↓ H⁺

↓

↓ Ventilation

↓

↑ PCO₂

↓

↑ H⁺

↓

Normal pH restored

• Alkalosis depresses the respiratory centers.
• The respiratory response during alkalosis is weaker.
• The respiratory response during alkalosis is less predictable.
• Reduced alveolar ventilation causes hypoxemia.
• Hypoxemia activates oxygen-sensitive chemoreceptors.
• Oxygen-sensitive chemoreceptors stimulate ventilation.
• This limits respiratory compensation during metabolic alkalosis.

Easy Concept

Metabolic Alkalosis

↓

↓ Ventilation

↓

Hypoxemia

↓

Oxygen-sensitive chemoreceptors activated

↓

Ventilation increases

↓

Respiratory compensation is limited

KEY CONCEPT

• Figure Mentioned: Fig. 31.3
• Fig. 31.3 shows that decreasing pH increases alveolar ventilation.
• pH 7.4 → 7.0 increases ventilation to about 4–5 times normal.
• ↑ H⁺ → ↑ Ventilation → ↓ PCO₂ → ↓ H₂CO₃ → ↓ H⁺.
• ↓ H⁺ → ↓ Ventilation → ↑ PCO₂ → ↑ H₂CO₃ → ↑ H⁺.
• The respiratory system acts as a negative feedback mechanism to maintain normal H⁺ concentration.
• Respiratory compensation is stronger during acidosis than during alkalosis.
• During alkalosis, hypoxemia stimulates oxygen-sensitive chemoreceptors, limiting the decrease in ventilation.

Mathematical/Biochemical Equations Solved

1. Normal pH → Acidic pH

$$\boxed{7.4 \rightarrow 7.0}$$7.4→7.0​

2. Ventilation Response

$$\boxed{\text{Alveolar Ventilation}=4\text{–}5\times\text{Normal}}$$Alveolar Ventilation=4–5×Normal​

3. Acidosis Feedback

$$\boxed{ \uparrow H^+ \rightarrow \uparrow Ventilation \rightarrow \downarrow PCO_2 \rightarrow \downarrow H_2CO_3 \rightarrow \downarrow H^+ }$$↑H+→↑Ventilation→↓PCO2​→↓H2​CO3​→↓H+​

4. Alkalosis Feedback

$$\boxed{ \downarrow H^+ \rightarrow \downarrow Ventilation \rightarrow \uparrow PCO_2 \rightarrow \uparrow H_2CO_3 \rightarrow \uparrow H^+ }$$↓H+→↓Ventilation→↑PCO2​→↑H2​CO3​→↑H+​

5. Respiratory Compensation During Alkalosis

$$\boxed{ \downarrow Ventilation \rightarrow \downarrow PO_2 \rightarrow Hypoxemia \rightarrow Chemoreceptor\ Stimulation \rightarrow \uparrow Ventilation }$$↓Ventilation→↓PO2​→Hypoxemia→Chemoreceptor Stimulation→↑Ventilation​

Figure 31.3: Effect of Blood pH on the Alveolar Ventilation Rate

• (Figure 31.3) shows how changes in arterial blood pH affect the rate of alveolar ventilation (breathing).

Understanding the Axes

X-Axis (Horizontal)

pH of Arterial Blood

This shows how acidic or alkaline the blood is.

pH	Meaning
7.0	Very acidic
7.1	Acidic
7.2	Mildly acidic
7.3	Slightly acidic
7.4	Normal blood pH
7.5	Alkaline
7.6	More alkaline

• Moving left = Blood becomes more acidic (↑ H⁺).
• Moving right = Blood becomes more alkaline (↓ H⁺).

Y-Axis (Vertical)

Alveolar Ventilation (Normal = 1)

This shows the breathing rate compared with normal.

Value	Meaning
1	Normal breathing
2	2 times normal breathing
3	3 times normal breathing
4	4 times normal breathing

• Moving up = Faster breathing.
• Moving down = Slower breathing.

Understanding the Red Curve

The red curve shows the relationship between:

Blood pH → Breathing Rate

Left Side of the Curve (Low pH)

Look at the left end of the graph.

Blood pH is about 7.0.

This means:

• Blood is very acidic.
• H⁺ concentration is high.

The body responds by:

• Increasing alveolar ventilation to about 4 times normal.

Why?

• Faster breathing removes more CO₂.
• Less CO₂ means less carbonic acid (H₂CO₃).
• Less H₂CO₃ means fewer H⁺ ions.
• Blood pH increases toward normal.

Result: Severe acidosis causes a marked increase in breathing.

Middle of the Curve

As blood pH increases from 7.1 → 7.3:

• Blood becomes less acidic.
• H⁺ concentration decreases.
• The need for rapid breathing decreases.

Therefore:

• Alveolar ventilation gradually decreases.

Normal Point (pH ≈ 7.4)

At about pH 7.4:

• Blood pH is normal.
• H⁺ concentration is normal.
• Alveolar ventilation is approximately 1× normal.

This is the normal operating point.

Right Side of the Curve (High pH)

Move toward pH 7.5–7.6.

Now:

• Blood becomes alkaline.
• H⁺ concentration decreases.

The respiratory center receives less stimulation.

Therefore:

• Breathing becomes slower than normal.

Less CO₂ is removed.

CO₂ begins to accumulate.

More H₂CO₃ forms.

More H⁺ is produced.

Blood pH moves back toward normal.

Why is the Curve Curved?

Notice:

The curve is very steep at low pH.

This means:

A small fall in pH causes a large increase in breathing.

As pH becomes normal or alkaline,

the curve becomes flatter.

This means:

Further increases in pH produce only small decreases in breathing.

Understanding the Diagram Above the Graph

The small diagram summarizes the body’s negative feedback response.

Step 1

↑ H⁺

Means:

Hydrogen ion concentration increases.

Blood becomes acidic.

↓

Step 2

↑ Alveolar Ventilation

The respiratory center stimulates faster breathing.

↓

Step 3

↓ PCO₂

More CO₂ is exhaled.

Blood CO₂ falls.

↓

Step 4

Less CO₂ produces less carbonic acid (H₂CO₃).

↓

Step 5

H⁺ concentration decreases.

Blood pH returns toward normal.

Meaning of the Dotted Arrow and (⊖)

The dotted arrow points from ↓ PCO₂ back toward ↑ H⁺.

The ⊖ (negative sign) represents negative feedback.

Meaning:

• An increase in H⁺ starts the response.
• The lungs increase ventilation.
• CO₂ decreases.
• H⁺ decreases.

Therefore, the original increase in H⁺ is opposed (reduced).

This is a negative feedback mechanism that stabilizes blood pH.

Easy Concept

Imagine the lungs as an automatic CO₂ exhaust fan.

When blood becomes acidic

• H⁺ increases.
• The fan works faster.
• More CO₂ is blown out.
• Acid decreases.
• Blood pH returns toward normal.

When blood becomes alkaline

• H⁺ decreases.
• The fan slows down.
• Less CO₂ is removed.
• CO₂ builds up.
• More H⁺ forms.
• Blood pH falls back toward normal.

One-Line Memory Trick

↓ pH (↑ H⁺) → ↑ Breathing → ↓ CO₂ → ↓ H⁺ → pH returns toward normal

↑ pH (↓ H⁺) → ↓ Breathing → ↑ CO₂ → ↑ H⁺ → pH returns toward normal

KEY CONCEPT

• Figure 31.3 shows the effect of arterial blood pH on alveolar ventilation.
• Low blood pH (high H⁺) strongly stimulates alveolar ventilation.
• High blood pH (low H⁺) reduces alveolar ventilation.
• Increased breathing removes CO₂, reducing H₂CO₃ and H⁺, which raises blood pH.
• Decreased breathing retains CO₂, increasing H₂CO₃ and H⁺, which lowers blood pH.
• This is a negative feedback mechanism that helps maintain normal blood pH.

Efficiency of Respiratory Control of H⁺ Concentration

• The respiratory system cannot completely restore H⁺ concentration to normal when the disturbance is caused outside the respiratory system.
• Respiratory control is usually 50% to 75% effective.
• This corresponds to a feedback gain of 1 to 3 during metabolic acidosis.

Mathematical Values

Respiratory effectiveness:$$\boxed{50\%\ \text{to}\ 75\%}$$50% to 75%​

Feedback gain:$$\boxed{1\ \text{to}\ 3}$$1 to 3​

Easy Concept

Respiratory compensation

↓

Does not correct 100%

↓

Corrects about

50–75%

• If acid is suddenly added to the extracellular fluid, pH decreases.
• The pH may fall from 7.4 to 7.0.

Mathematical Solution

Initial pH$$\boxed{7.4}$$7.4​

↓

After acid is added$$\boxed{7.0}$$7.0​

• The respiratory system increases ventilation.
• This response raises the pH to about 7.2–7.3.

Mathematical Solution

After respiratory compensation$$\boxed{7.2\ \text{to}\ 7.3}$$7.2 to 7.3​

Easy Concept

Normal pH$$7.4$$7.4

↓

Acid Added

↓$$7.0$$7.0

↓

Respiratory Compensation

↓$$7.2\text{–}7.3$$7.2–7.3

Not completely back to 7.4

• Respiratory compensation occurs within 3 to 12 minutes.

Mathematical Values

$$\boxed{3\text{–}12\ \text{minutes}}$$3–12 minutes​

• Respiratory responses to metabolic alkalosis are rapid.
• Respiratory compensation during metabolic alkalosis is limited.
• This limitation is caused by hypoxemia due to reduced alveolar ventilation.

Easy Concept

Metabolic Alkalosis

↓

↓ Ventilation

↓

Hypoxemia

↓

Compensation Limited

Buffering Power of the Respiratory System

• Respiratory regulation acts as a physiological buffer system.
• It responds rapidly.
• It prevents large changes in H⁺ concentration.
• It provides protection until the kidneys respond.
• The kidneys respond more slowly.
• The kidneys remove the acid–base imbalance.
• The buffering power of the respiratory system is 1 to 2 times greater than all extracellular chemical buffers combined.

Mathematical Values

$$\boxed{1\text{–}2\times}$$1–2×​

Easy Concept

Respiratory Buffer

↓

1–2 times stronger

↓

Than all chemical buffers combined

• The respiratory system buffers 1–2 times more acid or base than chemical buffers.

Impairment of Lung Function Can Cause Respiratory Acidosis

• Normal respiration helps buffer changes in H⁺ concentration.
• Abnormal respiration can also change H⁺ concentration.
• Severe emphysema is an example of impaired lung function.
• Impaired lungs cannot remove CO₂ effectively.
• CO₂ accumulates in the extracellular fluid.
• Increased CO₂ causes respiratory acidosis.

Easy Concept

Lung Disease

↓

↓ CO₂ Removal

↓

↑ CO₂

↓

↑ H₂CO₃

↓

↑ H⁺

↓

Respiratory Acidosis

• Lung disease also reduces the body’s ability to compensate for metabolic acidosis.
• Normally, metabolic acidosis increases ventilation.
• Increased ventilation lowers PCO₂.
• In lung disease, this compensatory decrease in PCO₂ is reduced.

Easy Concept

Metabolic Acidosis

↓

Should increase ventilation

↓

Lung disease prevents adequate ventilation

↓

PCO₂ remains high

↓

Poor compensation

• After initial chemical buffering, the kidneys become the only remaining physiological mechanism.
• The kidneys gradually return the pH toward normal.

Easy Concept

Chemical Buffers

↓

Respiratory Compensation Fails

↓

Kidneys become the only long-term regulator

↓

pH gradually returns toward normal

KEY CONCEPT

• Respiratory compensation is 50–75% effective.
• Feedback gain = 1–3 during metabolic acidosis.
• Acid can lower pH from 7.4 → 7.0.
• Respiratory compensation raises pH to about 7.2–7.3 within 3–12 minutes.
• Respiratory compensation is limited during metabolic alkalosis because of hypoxemia.
• The respiratory system has 1–2 times greater buffering power than all extracellular chemical buffers combined.
• Lung diseases (e.g., emphysema) reduce CO₂ elimination.
• CO₂ retention → ↑ H₂CO₃ → ↑ H⁺ → Respiratory acidosis.
• When respiratory compensation is impaired, the kidneys become the main mechanism for restoring normal pH.

Mathematical/Biochemical Equations Solved

1. Respiratory effectiveness

$$\boxed{50\%-75\%}$$50%−75%​

2. Feedback gain

$$\boxed{1-3}$$1−3​

3. Respiratory compensation

$$7.4 \rightarrow 7.0 \rightarrow 7.2-7.3$$7.4→7.0→7.2−7.3

4. Time required

$$\boxed{3-12\ \text{minutes}}$$3−12 minutes​

5. Buffering power

$$\boxed{1-2\times}$$1−2×​

6. Respiratory acidosis pathway

$$\boxed{ \downarrow Lung\ Function \rightarrow \uparrow CO_2 \rightarrow \uparrow H_2CO_3 \rightarrow \uparrow H^+ \rightarrow Respiratory\ Acidosis }$$↓Lung Function→↑CO2​→↑H2​CO3​→↑H+→Respiratory Acidosis