BI 356L - Respiratory Contribution to Acid-Base Regulation

If the pH decreases, then hydrogen ion concentration _______________

increases

If the pH increases, then hydrogen ion concentration _______________

decreases

What is acidosis?

- decreased pH

- increased hydrogen ion concentration

What is alkalosis?

- increased pH

- decreased hydrogen ion concentration

What indicates a respiratory origin of a hydrogen ion concentration shift?

a shift due to CO2 buildup or removal

What indicates a metabolic origin of a hydrogen ion concentration shift?

a shift due to direct hydrogen ion buildup or removal

Henderson-Hasselbach bicarbonate buffering system

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

The henderson-hasselbach bicarbonate buffering system is a reversible and very sensitive system which is easily shifted in either direction due to the unstable nature of the _____________________, and the reversible action of ___________________

carbonic acid; carbonic anhydrase

When does respiratory acidosis develop?

when carbon dioxide is not eliminated across the respiratory membrane at the rate at which it is produced. thus, the carbon dioxide buildup increases hydrogen ions and bicarbonate stores (shifts the equation to the right)

What are some causes of respiratory acidosis?

- any limitation of gas exchange across the respiratory membrane

--- emphysema

--- COPD

--- atelectasis

--- acute asthma

- shallow breaths (often due to pain) that dont exceed the functional dead space

- brainstem injury

- chemical depression of respiratino

- Cheyne-Stokes respiration

What happens to bicarbonate stores in respiratory acidosis?

increase

What are some symptoms of respiratory acidosis - if respiratory control is intact and if it is not? What visible sign would be seen?

if respiratory control is intact:

- deep, rapid and dyspneic breathing

if respiratory control is not intact:

- aberrant and shallow breathing

patient shows the typical vasodilatory red flush of hypercapnea

When does respiratory alkalosis develop?

when carbon dioxide is eliminated across the respiratory membrane at a faster rate than that at which it builds up. thus, the carbon dioxide loss decreases hydrogen ions and bicarbonate stores (shifts the equation to the left)

What are some causes of respiratory alkalosis?

hyperventilation

- emotional factors

- some states of asthmatic attack

- some states of pneumonia

- as an attempt to deal with decreased oxygen available at higher altitudes

- anxiety-driven hyperventilation syndrome

What happens to bicarbonate stores in respiratory alkalosis?

decrease

What are some symptoms of respiratory alkalosis?

- rapid deep breathing

- dyspnea

When respiratory alkalosis is driven by anxiety what is the goal of fixing it?

- control breathing depth and rate

- drive the PCO2 back up

What is the solution to respiratory alkalosis?

breathing into a paper bag

What is the effect of hyperventilation on CO2 pressure?

decreased CO2 pressure because CO2 is being exhaled faster than it is being produced

When does metabolic acidosis develop?

when hydrogen ions are introduced into the body tissues and blood at a faster rate than it is removed by the kidney and other buffering mechanisms. this depletes bicarbonate stores and increases the load of carbon dioxide that must be eliminated across the respiratory membrane

If metabolic acidosis is caused by the metabolic loss of bicarbonate stores leaving an excess amount of hydrogen ions, how is compensation accomplished?

by the kidney

- cannot be accomplished in the respiratory system

What are some causes of metabolic acidosis?

- renal disease which limits the kidney's ability to excrete hydrogen ions

- diabetes which results in excessive utilization of fat stores and ketoacidosis

- starvation which results in excessive utilization of fat stores and ketoacidosis

- excess alcohol ingestion

- severe diarrhea which removes bicarbonate-rich pancreatic secretions at an excessive rate

What happens to bicarbonate stores in metabolic acidosis?

decrease

What are some symptoms of metabolic acidosis?

variable depending on cause and acute/chronic nature

acute:

- dyspnea and its observable effects (deep, rapid breathing)

chronic:

- dyspnea may be absent

When does metabolic alkalosis develop?

when hydrogen ions are removed from the body tissues and blood at a faster rate than it is produced. this increases bicarbonate stores (shift equation to the right)

What are some causes of metabolic alkalosis?

- severe vomiting which removed gastric acid from the body leaving behind large stores of bicarbonate

- some kidney conditions of drug interactions which cause the kidney to excessively excrete hydrogen ions

- excessive intake of bicarbonate as an antacid (geriatric medicine mainly)

- severe prolonged constipation which retains the bicarbonate of pancreatic secretions

What happens to bicarbonate stores in metabolic alkalosis?

increase

What are some symptoms of metabolic alkalosis?

- decreased respiratory depth and rate

- lowered blood PCO2

What can breathing into a bag cause or worsen?

respiratory acidosis

Solutions about pH 7.4 (the typical pH of plasma) give a ___________________ color

light green/blue

Solutions about pH 5.0 (far more acidic than blood ever gets) give a _____________________ color

yellow/orange

Solutions about pH 9.0 (far more alkaline than blood) give a ________________________ color

dark ink-blue

Even a serious acidosis never drops the pH lower than about ____________

7.2

Even a serious alkalosis never raises the pH higher than about ___________

7.6

What is the order of strength, from weakest to strongest, of the buffers used during this lab (completely unbuffered water, 2% bicarbonate solution in water, 1% albumin solution in water)?

1. completely unbuffered water

2. 1% albumin solution in water

3. 2% bicarbonate solution in water

What is the weakest buffer used in this lab?

completely unbuffered water

What is the strongest buffer used in this lab?

2% bicarbonate solution in water

What is the job of a buffer?

resist change in pH

What is a simple treatment for respiratory acidosis?

- treat underlying cause

- mechanical ventilation if severe

- oxygen therapy

- clear airway

What is a simple treatment for respiratory alkalosis?

- breath into a paper bag

What is a simple treatment for metabolic acidosis?

- treat the cause

- IV bicarbonate in severe cases

What is a simple treatment for metabolic alkalosis?

- treat the cause

Understand how the 4 conditions could relate to the urinary and respiratory systems

Respiratory System’s Role - The lungs regulate CO₂, which affects pH through the bicarbonate buffer system: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻

Respiratory Acidosis

Cause: Hypoventilation → CO₂ retention → ↑ H⁺ (↓ pH)

Compensation: The kidneys excrete H⁺ and retain/reabsorb HCO₃⁻

Respiratory Alkalosis

Cause: Hyperventilation → CO₂ loss → ↓ H⁺ (↑ pH)

Compensation: The kidneys excrete HCO₃⁻ and retain H⁺

Urinary (Renal) System’s Role - The kidneys regulate H⁺ excretion and HCO₃⁻ reabsorption to maintain pH.

Metabolic Acidosis

Cause: ↑ H⁺ or ↓ HCO₃⁻ (e.g., renal failure, DKA, diarrhea)

Compensation: The lungs increase ventilation to blow off CO₂ → ↓ H⁺ (via respiratory compensation)

Metabolic Alkalosis

Cause: ↓ H⁺ or ↑ HCO₃⁻ (e.g., vomiting, diuretics)

Compensation: The lungs reduce ventilation to retain CO₂ → ↑ H⁺ (mild respiratory compensation)

What is the general effect of a buffer on the amount of acid/base that is required to produce a given pH change?

a buffer increases the amount of acid or base required to produce a given pH change

In the carbon dioxide dissolution experiment, after CO₂ was introduced and the flask was capped and swirled, the solution became more acidic. How does this observation fit with the Henderson-Hasselbalch equilibrium?

Experiment:

1. Rinse and dry the flask as before. With 40 ml of DI water and indicator in the flask, using a soda straw, gently blow two complete breaths (remember to exhale completely through the straw; CO2 concentrations are very low in the first half-liter or so of exhaled air) into the air space ABOVE the liquid (DON'T BUBBLE the liquid). This will make the CO2 concentration in the gas space about 5%.

2. Cap the flask with parafilm and swirl it for about a minute to equilibrate the dissolved gas with the liquid. Note any change in color

Adding CO₂ increases its concentration in the liquid, shifting the equilibrium

This increases H⁺, lowering the pH.

A rise in CO₂ shifts the ratio, decreasing pH — matching the acidic color change observed.

This models respiratory acidosis, where CO₂ buildup causes blood pH to drop.

In the carbon dioxide dissolution experiment, after CO₂ was absorbed and the solution became acidic, you added NaOH dropwise until the original color (neutral pH) returned. According to the Henderson-Hasselbalch equilibrium, what does adding NaOH do to the system?

Experiment:

1. Rinse and dry the flask as before. With 40 ml of DI water and indicator in the flask, using a soda straw, gently blow two complete breaths into the air space ABOVE the liquid (DON'T BUBBLE the liquid). This will make the CO2 concentration in the gas space about 5%.

2. Cap the flask with parafilm and swirl it for about a minute to equilibrate the dissolved gas with the liquid. Note any change in color

3. Now remove the parafilm and add 0.1 M base (NaOH) dropwise until the solution returns to its original color. This gives you an indication of how much CO2 was absorbed from the gas.

NaOH removes free H⁺ ions by neutralizing them

This decreases [H⁺], causing the equilibrium to shift leftward:

This shift reduces acidity and raises pH. The amount of NaOH required reflects how much CO₂ was dissolved.

It models the buffering and compensatory mechanisms used in the body, especially in respiratory acidosis recovery.

In the carbon dioxide dissolution in the presence of bicarbonate, blowing CO₂ into a 2% bicarbonate solution caused a much smaller pH color change than in plain water. Does this mean less CO₂ was absorbed? Why or why not?

No — the smaller color change does not mean less CO₂ was absorbed.

The difference is due to the buffering capacity of bicarbonate, not a difference in gas absorption.

When CO₂ dissolves, it forms H⁺. The extra bicarbonate already present in solution absorbs the H⁺, minimizing the pH shift:

This buffering effect masks the pH change, even though CO₂ absorption still occurs.

It models how the bicarbonate buffer system in blood stabilizes pH during CO₂ fluctuations — a key interaction between the respiratory and urinary systems.

In the model for the metabolic "blowing off" of carbon dioxide experiment, after adding acid to a bicarbonate solution, you observed a shift in the indicator drop. Based on the Henderson-Hasselbalch equilibrium, what happened, and how does this model metabolic acidosis during intense exercise or disease?

The added acid increased H⁺, shifting the equilibrium leftward as bicarbonate buffered the H⁺, forming CO₂:

The CO₂ exited into the gas space, mimicking respiratory compensation.

This models how the body reacts to metabolic acidosis (e.g. during heavy anaerobic exercise or diabetes):

- Excess acid is neutralized by bicarbonate.

- The resulting CO₂ is exhaled by increased breathing (like Kussmaul respiration), linking the urinary (H⁺ excretion) and respiratory systems (CO₂ elimination).

Water: Indicator Behavior in an Unbuffered Medium

What you saw:

Only a few drops of HCl or NaOH changed the color drastically.

What this taught:

DI water has no buffering capacity — pH changes rapidly with small acid/base additions.

Relation to systems:

Shows how important buffers (like those in blood) are. Without buffers, the body would be dangerously sensitive to minor pH changes.

Urinary system plays a huge role in buffering by excreting H⁺ and reabsorbing HCO₃⁻.

Effect of Bicarbonate Buffer

What you saw:

Many more drops (maybe >30) were needed to change the color.

What this taught:

Bicarbonate is a strong buffer. It resists pH changes by neutralizing added acid or base.

Relation to systems:

Bicarbonate is the main buffer in blood plasma, regulated by:

Respiratory system: adjusts CO₂ (which affects H⁺)

Urinary system: adjusts H⁺ excretion and HCO₃⁻ reabsorption

Protein as a Buffer (1% albumin)

What you saw:

More drops needed than pure water, but fewer than with bicarbonate.

What this taught:

Proteins can buffer pH by binding or releasing H⁺ via their amino acid side chains.

Relation to systems:

Plasma proteins (like albumin) help maintain blood pH.

The kidneys filter and reabsorb these proteins as part of acid-base regulation.

CO2 Dissolution in Water

What you saw:

After swirling the flask, the solution became more acidic (color change).

What this taught:

CO₂ dissolves in water and forms carbonic acid (H₂CO₃), which dissociates into H⁺ and HCO₃⁻ — lowering pH.

Relation to systems:

Demonstrates respiratory acidosis: CO₂ retention → ↑H⁺

Respiratory system expels CO₂ to regulate blood pH.

CO2 Dissolution in Bicarbonate

What you saw:

Less or no visible color change despite same CO₂ input.

What this taught:

Bicarbonate buffer neutralized the additional H⁺ from CO₂, so pH didn’t drop as much.

Relation to systems:

Mimics blood plasma — shows how bicarbonate buffering prevents large pH swings when CO₂ rises.

Kidneys maintain bicarbonate levels long-term.

Evidence for CO2 Dissolution: Water

What you saw:

The indicator drop moved (volume decreased), showing gas absorption.

What this taught:

CO₂ actually dissolves into the water, reducing the airspace pressure and volume.

Relation to systems:

Confirms that gas exchange happens — just like in lungs, where CO₂ moves from blood to alveoli (or vice versa depending on concentration gradient).

Evidence for CO2 Dissolution: Bicarbonate

What you saw:

Less movement of the indicator drop than in water.

What this taught:

Bicarbonate is absorbing CO₂ and buffering its effects, maintaining more constant pressure.

Relation to systems:

Again mimics blood buffering: CO₂ dissolved into plasma gets buffered by HCO₃⁻.

Respiratory compensation maintains this balance by adjusting ventilation.

Model for Metabolic "Blowing Off" of CO2

What you saw:

Adding HCl increased acid, which shifted equilibrium → CO₂ production → increase in gas pressure (drop in pipette moved).

What this taught:

The acid drives the Henderson-Hasselbalch equation to produce more CO₂, which is then “blown off” through respiration in real physiology.

Relation to systems:

Models metabolic acidosis (like in exercise, DKA, or lactic acidosis), where the body compensates by hyperventilating to blow off CO₂ (↓H⁺).

Long-term compensation is by the kidneys, which excrete H⁺ and regenerate bicarbonate.