How is carbon dioxide transported

First, carbon dioxide is more soluble in blood than oxygen. About 5 to 7 percent of all carbon dioxide is dissolved in the plasma. Second, carbon dioxide can bind to plasma proteins or can enter red blood cells and bind to hemoglobin.

This form transports about 10 percent of the carbon dioxide. When carbon dioxide binds to hemoglobin, a molecule called carbaminohemoglobin is formed. Binding of carbon dioxide to hemoglobin is reversible. Therefore, when it reaches the lungs, the carbon dioxide can freely dissociate from the hemoglobin and be expelled from the body.

Third, the majority of carbon dioxide molecules 85 percent are carried as part of the bicarbonate buffer system. In this system, carbon dioxide diffuses into the red blood cells. Carbonic anhydrase CA within the red blood cells quickly converts the carbon dioxide into carbonic acid H 2 CO 3.

Since carbon dioxide is quickly converted into bicarbonate ions, this reaction allows for the continued uptake of carbon dioxide into the blood down its concentration gradient.

The newly synthesized bicarbonate ion is transported out of the red blood cell into the liquid component of the blood in exchange for a chloride ion Cl — ; this is called the.

When the blood reaches the lungs, the bicarbonate ion is transported back into the red blood cell in exchange for the chloride ion. This produces the carbonic acid intermediate, which is converted back into carbon dioxide through the enzymatic action of CA. The carbon dioxide produced is expelled through the lungs during exhalation. This is important because it takes only a small change in the overall pH of the body for severe injury or death to result.

The presence of this bicarbonate buffer system also allows for people to travel and live at high altitudes: When the partial pressure of oxygen and carbon dioxide change at high altitudes, the bicarbonate buffer system adjusts to regulate carbon dioxide while maintaining the correct pH in the body.

While carbon dioxide can readily associate and dissociate from hemoglobin, other molecules such as carbon monoxide CO cannot. Carbon monoxide has a greater affinity for hemoglobin than oxygen. Therefore, when carbon monoxide is present, it binds to hemoglobin preferentially over oxygen. As a result, oxygen cannot bind to hemoglobin, so very little oxygen is transported through the body Figure Carbon monoxide is a colorless, odorless gas and is therefore difficult to detect.

It is produced by gas-powered vehicles and tools. Carbon monoxide can cause headaches, confusion, and nausea; long-term exposure can cause brain damage or death. Administering percent pure oxygen is the usual treatment for carbon monoxide poisoning. Administration of pure oxygen speeds up the separation of carbon monoxide from hemoglobin. Hemoglobin is a protein found in red blood cells that is comprised of two alpha and two beta subunits that surround an iron-containing heme group. Oxygen readily binds this heme group.

The ability of oxygen to bind increases as more oxygen molecules are bound to heme. Disease states and altered conditions in the body can affect the binding ability of oxygen, and increase or decrease its ability to dissociate from hemoglobin.

The imidazole group of the amino acid histidine gives haemoglobin a very significant buffering capacity, not present in other amino acids. This buffering capacity is made possible by the fact that each tetramer of haemoglobin contains 38 histidine residues and the dissociation constant of the imidazole groups of the four histidine residues, to which the haem groups are attached, is affected by the state of oxygenation of the haem.

In the acidic state, the oxygen bond is weakened, while reduction of haemoglobin causes the imidazole group to become more basic. In the tissues, the acidic form of the imidazole group weakens the strength of the oxygen bond at the same time as hydrogen ions are being buffered by the more basic haemoglobin.

Total carbon dioxide in venous blood is 52 ml per ml and in arterial blood 48 ml per ml. Consequently, the curve is more linear than the O 2 Hb dissociation curve.

Figure 4 illustrates the difference between the content in blood of oxygen and carbon dioxide with change in partial pressure. It emphasizes that the carbon dioxide content rises throughout the increase in partial pressure.

Oxygen content rises more steeply until a point at which the haemoglobin is fully saturated. After that, the increase is small because of the small increased amount in solution.

The plasma concentration of chloride ion is lower but bicarbonate ion concentration is greater. The total reduction of all haemoglobin would result in a rise in blood pH by 0. The net effect is a fall in pH of 0. In pulmonary capillary blood, the red blood cell releases carbon dioxide and the haemoglobin affinity for oxygen is increased.

The outward shift of water gives a smaller MCV and reduced haematocrit. The oxygen dissociation curve will shift to the left Bohr effect. The plasma concentration of chloride ion is higher in arterial compared with venous blood; bicarbonate concentration is lower.

Every minute, ml of carbon dioxide is exhaled; this is the equivalent to 12—13 mol of hydrogen ions in 24 h. Therefore, the passage of 3 litres of urine accounts for a relatively small amount of hydrogen ion elimination in 24 h; however, this includes the phosphate and sulphate ions that cannot be converted to carbon dioxide. The total body content of carbon dioxide including bicarbonate ion is litres or times that of oxygen. Therefore, the patient becomes rapidly hypoxaemic.

See multiple choice questions — Ganong WF. Review of Medical Physiology , 21st Edn. Lange Medical Books, Nunn JF. Respiratory Physiology , 5th Edn. Butterworth Heinemann, West JB. Respiratory Physiology , 7th Edn. Oxford University Press is a department of the University of Oxford.

It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide. Sign In or Create an Account. Sign In. Advanced Search. Search Menu. Therefore, when carbon monoxide is present, it binds to hemoglobin preferentially over oxygen. As a result, oxygen cannot bind to hemoglobin, so very little oxygen is transported throughout the body. Carbon monoxide is a colorless, odorless gas which is difficult to detect. It is produced by gas-powered vehicles and tools.

Carbon monoxide can cause headaches, confusion, and nausea; long-term exposure can cause brain damage or death. Administering percent pure oxygen is the usual treatment for carbon monoxide poisoning as it speeds up the separation of carbon monoxide from hemoglobin.

Learning Objectives Explain how carbon dioxide is transported from body tissues to the lungs. Key Points Carbon dioxide is more soluble in blood than is oxygen; about 5 to 7 percent of all carbon dioxide is dissolved in the plasma.

Carbon dioxide has the ability to attach to hemoglobin molecules; it will be removed from the body once they become dissociated from one another. In the bicarbonate buffer system, the most common form of carbon dioxide transportation in the blood, carbon dioxide is finally expelled from the body through the lungs during exhalation. Importantly, the bicarbonate buffer system allows little change to the pH of the body system; it allows for people to travel and live at high altitudes because the system can adjust itself to regulate carbon dioxide while maintaining the correct pH in the body.

Key Terms carbaminohemoglobin : a compound made up of hemoglobin and carbon dioxide; one of the forms in which carbon dioxide exists in the blood carbonic anhydrase : a family of enzymes that catalyze the rapid interconversion of carbon dioxide and water to bicarbonate and protons carbon monoxide : a colorless, odourless, flammable, highly toxic gas.

Transport of Carbon Dioxide in the Blood Carbon dioxide molecules are transported in the blood from body tissues to the lungs by one of three methods: Dissolution directly into the blood Binding to hemoglobin Carried as a bicarbonate ion Several properties of carbon dioxide in the blood affect its transport.

Carbon Monoxide Poisoning While carbon dioxide can readily associate and dissociate from hemoglobin, other molecules, such as carbon monoxide CO , cannot. Therefore, CO exposure leads to death due to a decreased transportation of oxygen in the body.