Biology » The Respiratory System » Transport of Gases in Human Bodily Fluids

Summarizing Transport of Gases in Human Bodily Fluids


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.

Carbon dioxide can be transported through the blood via three methods. It is dissolved directly in the blood, bound to plasma proteins or hemoglobin, or converted into bicarbonate. The majority of carbon dioxide is transported as part of the bicarbonate system. Carbon dioxide diffuses into red blood cells. Inside, carbonic anhydrase converts carbon dioxide into carbonic acid (H2CO3), which is subsequently hydrolyzed into bicarbonate \({\text{(HCO}}_{\text{3}}^{-}\text{)}\) and H+. The H+ ion binds to hemoglobin in red blood cells, and bicarbonate is transported out of the red blood cells in exchange for a chloride ion. This is called the chloride shift. Bicarbonate leaves the red blood cells and enters the blood plasma. In the lungs, bicarbonate is transported back into the red blood cells in exchange for chloride. The H+ dissociates from hemoglobin and combines with bicarbonate to form carbonic acid with the help of carbonic anhydrase, which further catalyzes the reaction to convert carbonic acid back into carbon dioxide and water. The carbon dioxide is then expelled from the lungs.


bicarbonate buffer system

system in the blood that absorbs carbon dioxide and regulates pH levels

bicarbonate \({\text{(HCO}}_{\text{3}}^{-}\text{)}\) ion

ion created when carbonic acid dissociates into H+ and \({\text{(HCO}}_{\text{3}}^{-}\text{)}\)


molecule that forms when carbon dioxide binds to hemoglobin

carbonic anhydrase (CA)

enzyme that catalyzes carbon dioxide and water into carbonic acid

chloride shift

chloride shift exchange of chloride for bicarbonate into or out of the red blood cell

heme group

centralized iron-containing group that is surrounded by the alpha and beta subunits of hemoglobin


molecule in red blood cells that can bind oxygen, carbon dioxide, and carbon monoxide

oxygen-carrying capacity

amount of oxygen that can be transported in the blood

oxygen dissociation curve

curve depicting the affinity of oxygen for hemoglobin

sickle cell anemia

genetic disorder that affects the shape of red blood cells, and their ability to transport oxygen and move through capillaries


rare genetic disorder that results in mutation of the alpha or beta subunits of hemoglobin, creating smaller red blood cells with less hemoglobin

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