Question

Most carbon dioxide is transported in what part of the blood, and in what form? Explain the function of hemoglobin with respect to carbon dioxide transport. (p. 359)

Short answer

Explain the role of hemoglobin in this process. Answer: Most carbon dioxide is transported in the blood plasma as bicarbonate ions (HCO3-). Hemoglobin plays a crucial role by binding to hydrogen ions and a small amount of carbon dioxide directly, maintaining the blood's pH levels and aiding in the transportation of carbon dioxide.

Step-by-step solution

Part of the blood where most carbon dioxide is transported

Most of the carbon dioxide is transported in the blood plasma, which is the liquid portion of the blood.

Form of carbon dioxide transportation

Carbon dioxide is not transported in its gaseous state in the blood. Instead, it is converted to a molecule called bicarbonate (HCO3-) through a series of chemical reactions.

Carbon dioxide transport process

When carbon dioxide diffuses into the blood from tissues, it reacts with water to form carbonic acid (H2CO3), a weak acid. This reaction is catalyzed by an enzyme called carbonic anhydrase. Carbonic acid then dissociates into a hydrogen ion (H+) and a bicarbonate ion (HCO3-). Most of the bicarbonate ions are transported in the plasma, while hydrogen ions combine with hemoglobin.

Function of hemoglobin with respect to carbon dioxide transport

Hemoglobin not only plays a role in oxygen transportation but also has an essential role in carbon dioxide transport. As mentioned earlier, hydrogen ions resulting from the dissociation of carbonic acid combine with hemoglobin, forming a compound called carbaminohemoglobin. This process reduces the acidity of the blood and is known as the "Haldane effect." Hemoglobin acts as a buffer, preventing significant changes in blood pH levels. Additionally, a small percentage of carbon dioxide can bind directly to hemoglobin, further aiding in its transport. In summary, most carbon dioxide is transported in the blood plasma as bicarbonate ions, and hemoglobin plays a crucial role in maintaining the blood's pH levels by binding to hydrogen ions and a small amount of carbon dioxide directly.

Key concepts

Blood Plasma: The Medium for Carbon Dioxide Transport

Blood plasma serves as the primary medium for carbon dioxide transport. Plasma makes up about 55% of our total blood volume and is a yellowish liquid that carries cells and proteins throughout the body. Most of the carbon dioxide produced by our tissues dissolves in the blood plasma.
This transport in plasma allows for efficient circulation throughout the body, carrying substances like hormones, nutrients, and waste products including carbon dioxide.

• Carbon dioxide is largely transported within the plasma as bicarbonate ions.
• It is soluble in plasma and does not travel as a gas within the liquid medium.

Bicarbonate Ions: The Form of Carbon Dioxide in Blood

Once carbon dioxide enters the bloodstream from body tissues, it is quickly converted into bicarbonate ions. This conversion is crucial for maintaining the efficiency of carbon dioxide transport.
Here's how it works:

• When CO2 enters the blood, it combines with water to form carbonic acid (H2CO3).
• This reaction is catalyzed by the enzyme carbonic anhydrase, which speeds up the process significantly.
• The formed carbonic acid then dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+).

The bicarbonate ions travel through the plasma to the lungs, where the process is reversed, allowing CO2 to be expelled during exhalation.

Hemoglobin Function: Key to Carbon Dioxide Transport

Hemoglobin is well-known for its role in oxygen transport, but it also assists with carbon dioxide transport.
Here's how hemoglobin contributes:

• Hemoglobin helps mop up the hydrogen ions produced during the conversion of carbon dioxide to bicarbonate, preventing the blood from becoming too acidic.
• These hydrogen ions bind to hemoglobin to form carbaminohemoglobin.

This buffering action helps maintain the pH balance in the blood, promoting homeostasis. Moreover, a minor portion of carbon dioxide binds directly to hemoglobin, further facilitating its journey to the lungs.
Thus, hemoglobin serves doubly both as a carrier of oxygen and a proponent of carbon dioxide elimination.

Haldane Effect: Improving Carbon Dioxide Transport

The Haldane effect is a physiological phenomenon that enhances carbon dioxide transport by hemoglobin. This effect is crucial for optimizing the way our bodies handle carbon dioxide.

• According to the Haldane effect, deoxygenated hemoglobin has a higher affinity for binding carbon dioxide and hydrogen ions.
• This means that in the tissues, where oxygen has been delivered and hemoglobin is more deoxygenated, it can efficiently pick up CO2 and H+.
• Conversely, in the lungs, where hemoglobin binds oxygen, it releases CO2 for exhalation.

This efficient unloading and loading mechanism highlights the sophisticated adaptation of hemoglobin to facilitate both oxygen and carbon dioxide transport, keeping our bodily functions in balance.