Respiratory System Gas Transport

Gas Transport Oxygen and carbon dioxide are carried between the lungs and body cells by the blood These gases can be: Dissolved into blood plasma Or, chemically combined with other atoms or molecules present in the blood

Oxygen Transport Oxygen can be carried in the blood by: Loosely binding to the iron present in the protein hemoglobin in the red blood cells (creating a new compound called oxyhemoglobin). Or, dissolving in the plasma.

Oxygen Transport Transport via hemoglobin: Accounts for over 98% of oxygen transport The amount of oxygen that hemoglobin binds is determined by the partial pressure of the oxygen

Oxygen Transport Transport via hemoglobin: Greater partial pressure leads to an increase in the number of oxygen molecules bound to hemoglobin Oxygen atoms continue to be bound to hemoglobin until the hemoglobin is saturated Each molecule of hemoglobin can bind up to four oxygen molecules

Oxygen Transport Transport via hemoglobin: Oxygen is released from the oxyhemoglobin molecule as the partial pressure of oxygen decreases The number of oxygen molecules released increases when: Oxygen is used for respiration in nearby tissues Partial pressure of carbon dioxide in the blood increases Acidity increases Temperature increases

Carbon Dioxide Transport Carbon dioxide is transported: Dissolved in plasma (about 7%) Bound to hemoglobin (15% to 25%) As part of a bicarbonate ion (about 70%)

Carbon Dioxide Transport Transport via plasma: Amount of carbon dioxide dissolved in plasma is determined by the partial pressure of carbon dioxide The higher the partial pressure of carbon dioxide in nearby tissues the higher the amount dissolved into solution

Carbon Dioxide Transport Transport via hemoglobin: Carbon dioxide loosely binds to the amino groups (-NH2) of hemoglobin to form the compound carbaminohemoglobin (very slow process) Carbon dioxide is released from carbaminohemoglobin when the partial pressure of carbon dioxide is low

Carbon Dioxide Transport Transport via bicarbonate ions: Carbon dioxide enters the red blood cells and combines with water to form carbonic acid This process is normally very slow but is very quick in the red blood cells where the enzyme carbonic anhydrase is present

Carbon Dioxide Transport Transport via bicarbonate ions: After carbonic acid forms in the red blood cells it immediately dissociates releasing hydrogen ions and bicarbonate ions The hydrogen ions bind to deoxyhemoglobin in the red blood cells The bicarbonate ions diffuse back into the blood plasma and are replaced in the red blood cells by chloride ions from the plasma (called the chloride shift)

Carbon Dioxide Transport Transport via bicarbonate ions: As blood passes into the capillaries of the lungs, dissolved CO2 diffuses into the alveoli, dropping the partial pressure of carbon dioxide in the plasma As this happens, hydrogen ions and bicarbonate ions in the red blood cells recombine to form carbonic acid, which then quickly forms carbon dioxide and water