Systems Biology
Carbon dioxide transport in the body begins with its production via aerobic metabolism in active tissues. There are three physiologically important forms of carbon dioxide: dissolved CO2, carbaminohemoglobin, and bicarbonate. Dissolved CO2 makes up about 5% of transported CO2 and helps create the partial pressure of CO2 in arterial blood. Carbaminohemoglobin, accounting for about 20% of carbon dioxide, forms when CO2 binds to the polypeptide chain of hemoglobin rather than the heme group. This plays a key role in the physiological interplay between CO2, oxygen, and hemoglobin, leading to the Bohr effect and Haldane effect.
Bicarbonate, which comprises the majority of transported CO2, is key for various physiological functions. Its formation involves a five-step process: CO2 production, catalyzed hydration with the help of the enzyme carbonic anhydrase, spontaneous dissociation of carbonic acid into hydrogen ions and bicarbonate, acid buffering by deoxyhemoglobin, and chloride shift to maintain electrochemical neutrality. In the lungs, bicarbonate is converted back to carbon dioxide and water, which are then exhaled to remove CO2 from the body.
Lesson Outline
<ul> <li>Carbon dioxide transport in the body <ul> <li>Production via aerobic metabolism in active tissues</li> </ul> </li> <li>Three physiologically important forms of carbon dioxide <ul> <li>Dissolved CO<sub>2</sub> <ul> <li>Makes up about 5% of transported CO<sub>2</sub></li> <li>Helps create partial pressure of CO<sub>2</sub> in arterial blood</li> </ul> </li> <li>Carbaminohemoglobin <ul> <li>Accounts for about 20% of carbon dioxide</li> <li>Forms when CO<sub>2</sub> binds to the polypeptide chain of hemoglobin</li> <li>Key role in physiological interplay between CO<sub>2</sub>, oxygen, and hemoglobin</li> <li>Contributes to the Bohr effect and Haldane effect</li><ul> <li>Bohr effect: the phenomenon where increased levels of carbon dioxide and decreased pH (acidic conditions) result in a decreased affinity of hemoglobin for oxygen <li>Haldane effect: the binding of oxygen to hemoglobin influences the ability of blood to carry carbon dioxide</li> </ul> </li> <li>Bicarbonate <ul> <li>Comprises the majority of transported CO<sub>2</sub></li> <li>Key for various physiological functions</li> </ul> </li> </ul> </li> <li>Bicarbonate formation <ul> <li>Five-step process <ul> <li>CO<sub>2</sub> production</li> <li>Catalyzed hydration</li> <li>Spontaneous dissociation of carbonic acid into hydrogen ions and bicarbonate</li> <li>Acid buffering by deoxyhemoglobin</li> <li>Chloride shift to maintain electrochemical neutrality</li> </ul> </li> <li>In the lungs <ul> <li>Bicarbonate is converted back to carbon dioxide and water</li> <li>Exhaled to remove CO<sub>2</sub> from the body</li> </ul> </li> </ul> </li> </ul>
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FAQs
There are three primary mechanisms through which carbon dioxide is transported in blood: 1) as dissolved CO2, which makes up about 5 of total CO2 transport; 2) as carbaminohemoglobin, which accounts for about 20% of total CO2 transport, and 3) as bicarbonate ions, which represent around 70% of total CO2 transport in the blood.
Henry's Law states that the amount of dissolved gas in a liquid is directly proportional to the partial pressure of the gas in contact with the liquid. In respiratory physiology, this means that the concentration of dissolved CO2 in blood plasma is directly related to the partial pressure of CO2 in the blood. A higher partial pressure of CO2 leads to more CO2 dissolved in the blood plasma, whereas a lower partial pressure results in less dissolved CO2.
Carbonic anhydrase is an enzyme that catalyzes the reversible conversion of CO2 and water (H2O) into carbonic acid (H2CO3), which subsequently dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+). This enzyme is found in high concentrations in red blood cells and plays a crucial role in the formation of bicarbonate ions, which serve as one of the primary ways CO2 is transported in the blood. The rapid conversion of CO2 into bicarbonate ions allows for efficient CO2 transport and removal from the tissues.
The Bohr effect is a phenomenon in respiratory physiology where an increase in the partial pressure of CO2, a decrease in pH (increase in hydrogen ion concentration) or an increase in temperature causes a decrease in the affinity of hemoglobin for oxygen. This effect facilitates oxygen delivery to metabolically active tissues that produce higher amounts of CO2 and have lower pH due to an increased rate of cellular respiration. In these conditions, hemoglobin releases oxygen more readily to supply the tissues with the necessary oxygen for metabolic processes.
The Haldane effect is the phenomenon where lower oxygen saturation of hemoglobin increases its affinity for CO2, promoting the binding of CO2 to hemoglobin as carbaminohemoglobin (HbCO2). As the bicarbonate ions (HCO3-) are formed within the red blood cells, an electrochemical gradient is created. To maintain electroneutrality, the negatively charged bicarbonate ions are exchanged for negatively charged chloride ions (Cl-) in a process known as the chloride shift. This helps maintain the proper balance of charges within red blood cells and blood plasma during CO2 transport and facilitates the efficient removal of CO2 from the tissues.
