Carbon Dioxide Transport

The body is continuously producing acid through normal metabolism. What must happen to prevent pH from progressively changing?

Acid must be excreted at a rate equivalent to its production to maintain pH homeostasis

A form of acid can be converted into a gas and eliminated through the lungs. Would it be considered fixed or volatile?

Volatile, because it can change into a gaseous form for excretion

An acid cannot be converted into a gas. Based on your notes, how must it leave the body?

In a fixed liquid form through the urine

If the amount of one substance in a reversible chemical reaction changes, why can the whole reaction change direction?

Because the law of mass action says equilibrium changes in response to a change in one of the reaction constituents

Carbon dioxide is continuously being produced by tissues. Why does this matter for CO₂ transport?

CO₂ is continually being added to the blood and must continually be transported away

Blood flow through a tissue suddenly stops. What would happen to CO₂ around that capillary bed?

CO₂ would rise because the tissues continue producing it but the blood is no longer carrying it away

If you wanted to identify the main way CO₂ is transported in blood, which mechanism would you choose?

Plasma bicarbonate formation because it accounts for about 80% of CO₂ transport

A patient is transporting 100 arbitrary units of CO₂. Roughly how many would be transported as bicarbonate?

About 80 units

Of those same 100 units, approximately how many would remain as dissolved CO₂?

About 8 units

Of those 100 units, approximately how many would be transported as carbamino compounds?

About 12 units

If bicarbonate formation became impaired, which major CO₂ transport pathway would be most affected?

The pathway responsible for about 80% of CO₂ transport

Why is dissolved CO₂ still important even though it represents only about 8% of transport?

It contributes to PCO₂ and acts as the driving force for CO₂ movement

PaCO₂ is 40 mmHg. Using the CO₂ solubility coefficient of 0.072 vol%/mmHg, what dissolved CO₂ value would you expect?

2.88 vol%

PaCO₂ is 40 mmHg. Using 0.03 mEq/L/mmHg, approximately how much dissolved CO₂ is present?

About 1.2 mEq/L

PaCO₂ rises. What would you expect to happen to the amount of dissolved CO₂?

It would increase because dissolved CO₂ depends on PCO₂ and its solubility coefficient

Why can CO₂ move readily from tissues into blood?

CO₂ is very soluble and is continuously being produced by the tissues

Once CO₂ dissolves and interacts with water, what reaction begins?

H₂O + CO₂ ⇌ H₂CO₃ ⇌ HCO₃− + H+

More CO₂ enters the blood. According to the reaction in your notes, what products can increase?

Carbonic acid, bicarbonate, and H+

Why can increasing CO₂ make the body more acidic?

CO₂ combines with water and ultimately produces H+, so increasing H+ increases acidity

The dissolved CO₂:H₂CO₃ ratio is approximately 340:1. Which side is heavily favoured?

The dissolved CO₂ side, so the reaction is described as left shifted

At the tissues, cells are producing CO₂. Which general direction does CO₂ move?

From the tissues into the blood

Once tissue CO₂ enters the blood, what happens to some of it through the hydrolysis reaction?

It forms carbonic acid, which can dissociate into bicarbonate and H+

At the lungs, CO₂ diffuses from blood into the alveoli. What happens to the bicarbonate/H+ reaction?

H+ and bicarbonate combine toward carbonic acid and then CO₂ so CO₂ can move into the alveoli

Why must the bicarbonate reaction essentially reverse at the lungs?

CO₂ needs to be recreated so it can diffuse into the alveoli and be breathed out

If CO₂ is continuously being removed into the alveoli, how would the law of mass action affect the reaction?

Removing CO₂ promotes the reactions that recreate CO₂ from bicarbonate and H+

CO₂ can react with water in plasma, so why is the RBC especially important for bicarbonate formation?

The reaction is very slow in plasma but occurs in the RBC in the presence of carbonic anhydrase

What enzyme makes CO₂ conversion much faster inside the RBC?

Carbonic anhydrase

How much faster does your material say carbonic anhydrase makes the reaction?

About 13,000 times faster

Why would slow bicarbonate formation be a problem without carbonic anhydrase?

The hydrolysis reaction would take too long for efficient CO₂ transport

More CO₂ enters an RBC. What would you expect to happen to bicarbonate production?

Bicarbonate formation would increase because more CO₂ is available for the hydrolysis reaction

If products such as HCO₃− and H+ simply accumulated inside the RBC, what would normally happen to the reaction?

Product buildup would eventually halt the reaction as equilibrium is approached

Yet the bicarbonate reaction continues inside the RBC. What process shown in your material helps prevent product buildup?

The chloride shift, along with hemoglobin handling H+, helps remove reaction products from their available form

At the tissues, CO₂ enters an RBC and is converted into HCO₃− and H+. What happens to the bicarbonate?

Bicarbonate moves out of the RBC into the plasma

If negatively charged HCO₃− leaves the RBC, what moves in to help maintain electrical balance?

Chloride moves into the RBC

Why does chloride move in when bicarbonate moves out?

The exchange helps keep the membrane’s electrical charge balanced

At the tissue level, hemoglobin has already released O₂. How does this affect its ability to deal with H+?

Its affinity for H+ is greater when O₂ is no longer attached

Why is hemoglobin buffering H+ useful for continued CO₂ transport?

It takes H+ out of its freely available concentration, helping the hydrolysis reaction continue

Tissue metabolism keeps producing CO₂. How does conversion of CO₂ inside the RBC help more CO₂ enter?

Converting CO₂ reduces the available CO₂ concentration in the RBC, maintaining a driving pressure for additional CO₂ to enter

When blood reaches the lungs, does the chloride shift continue in the same direction?

No. It reverses

At the lungs, what happens to bicarbonate that was carried in the plasma?

It moves back into the RBC

As bicarbonate moves into the RBC at the lungs, what happens to chloride?

Chloride moves out

Why does bringing HCO₃− back into the RBC at the lungs help eliminate CO₂?

HCO₃− can recombine with H+ to form carbonic acid and then CO₂ for exhalation

CO₂ is continuously being exhaled from the lungs. What does this do to the CO₂ concentration gradient?

It creates a gradient that favours continued CO₂ movement toward the alveoli

CO₂ binds directly to a protein in plasma. What transport form has been created?

A plasma carbamino compound

CO₂ binds to an amino group on hemoglobin. What has formed?

Carbaminohemoglobin

According to your notes, about what percentage of total CO₂ transport comes from plasma carbamino compounds?

About 2%

About what percentage comes from carbaminohemoglobin?

About 10%

Together, what percentage of CO₂ transport do the carbamino pathways account for?

About 12%

Hemoglobin arrives at the tissues and unloads O₂. What happens to its ability to carry CO₂?

Its affinity for CO₂ increases

What effect explains why deoxygenated hemoglobin carries CO₂ more readily?

The Haldane effect

Why is the Haldane effect useful specifically at the tissues?

Hemoglobin has less O₂ there, so its capacity to take up CO₂ is increased

Blood becomes less oxygenated. According to the Haldane effect, what happens to its capacity for CO₂?

Its capacity for CO₂ increases

At the lungs, hemoglobin gains O₂. Based on the Haldane relationship, what should happen to CO₂ binding?

Hemoglobin’s affinity for CO₂ decreases, favouring CO₂ release

Hemoglobin is exposed to increased CO₂ at the tissues. What happens to its affinity for O₂?

Its affinity for O₂ decreases

Which effect explains the reduced O₂ affinity when hemoglobin is associated with CO₂?

The Bohr effect

Why is the Bohr effect useful at metabolically active tissues?

CO₂ and H+ encourage hemoglobin to release O₂ where the tissues are using it

Tissue CO₂ rises. Would the Bohr effect favour hemoglobin holding onto or releasing O₂?

Releasing O₂

A tissue is generating more CO₂. How does this help its own oxygen supply according to the material?

Increased CO₂ promotes the Bohr effect, decreasing hemoglobin’s affinity for O₂ and facilitating O₂ release

At the tissues, O₂ leaves hemoglobin while CO₂ enters the blood. Why do the Haldane and Bohr effects work well together?

O₂ release increases hemoglobin’s capacity for CO₂, while CO₂ and H+ further promote O₂ release

Why are the Haldane and Bohr effects described as mutually enhancing?

Each process helps strengthen the other during O₂ unloading and CO₂ loading

Tissue cells consume O₂. What happens to hemoglobin’s ability to buffer H+ as O₂ is released?

H+ buffering by hemoglobin is enhanced

Why does buffering H+ help CO₂ transport at the tissues?

It handles one of the products of CO₂ hydrolysis and helps continued CO₂ conversion and transport

At the lungs, O₂ binds to hemoglobin. Based on the complementary interaction, what should happen to the blood’s CO₂-carrying capacity?

It decreases, supporting CO₂ unloading

At the tissues, oxygenation decreases. What two things are simultaneously favoured?

O₂ unloading and increased blood capacity for CO₂

A red blood cell arrives at metabolically active tissue. What major gas enters the blood?

CO₂

Once that CO₂ enters the RBC, what enzyme rapidly facilitates its conversion?

Carbonic anhydrase

What two products then form from carbonic acid?

HCO₃− and H+

Where does much of the newly formed HCO₃− go?

Out of the RBC into the plasma

What ion enters the RBC as HCO₃− leaves?

Cl−

What happens to much of the H+ produced inside the RBC?

Hemoglobin buffers it

Why is hemoglobin especially suited to buffer H+ at the tissues?

O₂ has been released, which enhances hemoglobin’s ability to buffer H+

What happens to some CO₂ independently of bicarbonate formation?

It remains dissolved or binds to proteins/hemoglobin as carbamino compounds

Blood reaches the lungs carrying bicarbonate in plasma. What must happen before that carbon can be exhaled as CO₂?

Bicarbonate must re-enter the RBC and recombine through the reverse reaction to form CO₂

During this lung process, which ion leaves the RBC as bicarbonate comes back in?

Chloride

Once CO₂ is regenerated inside the RBC, where does it move?

Into the alveoli

Why does continuous exhalation help keep CO₂ moving out of blood?

Removing alveolar CO₂ maintains the concentration gradient favouring CO₂ movement toward the alveoli

A patient’s metabolic activity increases significantly. What could happen to CO₂ production?

CO₂ can increase because increased metabolism is listed as a cause of increased CO₂

Why can exercise become a problem for someone with end-stage COPD according to your notes?

Increased metabolic CO₂ production may exceed their ability to increase breathing enough, and they can become acidotic

A patient produces a normal amount of CO₂ but alveolar ventilation decreases. What happens to CO₂?

CO₂ increases because decreased ventilation reduces its elimination

If the problem causing high CO₂ is inadequate alveolar ventilation, what ventilatory variables are identified in your notes as ways of increasing minute ventilation?

Tidal volume and respiratory rate

A patient develops more deadspace because blood flow is reduced. What can happen to CO₂?

CO₂ can increase

Why is increased deadspace associated with increased CO₂ in your notes?

Deadspace can increase because of a lack of blood flow, reducing effective CO₂ exchange

According to the conditions listed in your notes, what happens to CO₂ when H+ concentration increases?

Increased H+ is listed as a condition associated with increased CO₂

A patient with very high CO₂ becomes increasingly confused. Could the CO₂ itself contribute?

Yes. Elevated CO₂ can alter neuron function and decrease neurologic function

As CO₂ becomes very high, what happens to respiratory drive according to your notes?

Respiratory drive can become blunted

Why can severe CO₂ elevation become dangerous neurologically?

High CO₂ can act as a narcotic agent, decrease neurologic function, and progress to coma

A hypercapnic patient becomes less responsive rather than more tachypneic. Does that rule out worsening CO₂?

No. Very high CO₂ can blunt respiratory drive and reduce neurologic function

Why could worsening CO₂ potentially create a vicious cycle in a severely affected patient?

High CO₂ can blunt respiratory drive, while decreased ventilation is itself listed as a cause of further CO₂ elevation

A patient’s lungs are eliminating CO₂ normally, but another major acid-regulating system fails. Why could pH homeostasis still be disrupted?

Acid homeostasis depends on ventilation, the kidneys, and buffering systems working together

A dissolved CO₂ value is given in vol%. What conversion from your notes can be used to express it in mEq/L?

Divide vol% by 2.23

What normal dissolved CO₂ range in mEq/L is listed in your notes?

About 1.2–1.3 mEq/L

CO₂ is constantly being produced by tissues and removed by blood flow. Why does the CO₂/H₂CO₃/HCO₃⁻ reaction not reach a true equilibrium?

CO₂ is continuously being added and moved away, so the reaction is constantly changing rather than settling at true equilibrium

Why is the RBC important for both oxygen and carbon dioxide transport?

It carries O₂ to the tissues through hemoglobin and also facilitates CO₂ transport

CO₂ moves through plasma and into RBCs. What helps drive this movement according to your notes?

Pressure gradients help facilitate the movement and reactions involved in CO₂ transport

Why is chloride well suited to exchange with bicarbonate during the chloride shift?

Chloride is present in large quantities as an extracellular anion and can exchange with bicarbonate to maintain electrical balance

A patient develops very high CO₂ levels. Besides directly affecting neurologic function, what oxygen/CO₂ transport relationships may also be altered?

Excess CO₂ can alter the Bohr and Haldane effects

What additional acid-base change is listed among the conditions associated with increased CO₂?

Decreased HCO₃

A patient has increased anaerobic metabolism. What supportive action is specifically mentioned in your notes?

Oxygenate anaerobic patients