Gas Exchange

How does the air in our mouth differ from the air in our alveoli?

Gas exchange on many levels

1. External respiration is the exchange of gas between alveoli and the blood in the capillaries of the pulmonary circulation

2. Internal respiration is the exchange of gas between the blood of the systemic circulation and the cells of the body.

3. Cellular respiration is the process by which mitochondria convert and store the chemical energy of glucose as ATP. O2 is used and CO2 is produced in this process.

External Respiration

• Gas concentration is measured as partial pressure.

• Gasses will diffuse from an area of high partial pressure to low partial pressure.

• The air we breathe contains nitrogen, oxygen, carbon

dioxide, and other trace factors

• The partial pressure of each gas depends on the location in the respiratory system (see handout) and the circulatory system

N2

Blood entering lungs from body:

O2 = 40 mmHgCO2 = 45 mmHg

Air in alveoli:

O2 = 110mmHgCO2 = 40mmHg

In which direction will each gas diffuse?

N2

Internal Respiration

• The partial pressures of oxygen and carbon dioxide in our blood change depending on location:

• Blood entering lungs from body:

• O2 = 40 mmHg

• CO2 = 45 mmHg

• Blood entering body from lungs:

• O2 = 95 mmHg

• CO2 = 40 mmHg

Why is there such a difference in gas composition coming to our lungs and from our lungs?

Remember during cellular respiration, our cells use 02 during ETC and create CO2 when glucose is broken down.

Internal respiration occurs when cells get rid of CO2 into the blood and take in more O2 from the blood.

Pause for Thought

• In grade nine, Mrs. Baker left her hometown in Newfoundland (0m elevation) for Mexico City (2km elevation).

• Atmospheric (gas) pressure lowers as elevation increases.

• What difference in gas pressure would you expect to see in the air and in Mrs. Baker’s blood at that elevation?

• What would happen to Mrs. Baker’s body over time if she remained in Mexico City?

Getting the gas from here to there:

Transporting gas from lungs to body cells.

1. Transport of Oxygen in Blood• ~1% of oxygen is dissolved in blood plasma

• ~99% of oxygen is carried through blood by hemoglobin. (When hemoglobin is carrying oxygen it is called oxyhemoglobin)

THIS IS WHY WE NEED IRON!!!!!!!

• Oxygen is weakly bound to hemoglobin. This is a good thing!

• Bond between oxygen and hemoglobin becomes less stable as temperature increases, environment becomes more acidic, and as oxygen concentration in the surroundings decreases

(WHERE IN THE BODY DO YOU FIND THESE CONDITIONS? What happens to the oxygen bound to hemoglobin in these conditions?)

Hemoglobin changes shape when oxygen is bound to it

• REVIEW:

• Conditions that promote the release of oxygen by hemoglobin are:

• 1

• 2

• 3

2. Transport of Carbon Dioxide in Blood

• 7% of CO2 is dissolved in plasma

• 23% of CO2 travels attached to hemoglobin

• 70% of CO2 travels as bicarbonate ion (HCO3- ) in

plasma

Converting CO2 to HCO3-

• Step ONE:

• In the red blood cell, the enzyme carbonic anhydrase converts carbon dioxide and water into carbonic acid

CO2 + H20 H2CO3

carbonic anhydrase

Converting CO2 to HCO3-

• Step TWO:

• Carbonic acid dissociates to form bicarbonate and hydrogen ions

H2CO3 HCO3- + H+

Converting CO2 to HCO3-

• H+ ions in the blood would greatly decrease the pH (this is BAD for the body)

• To prevent the blood from becoming too acidic, hydrogen ions bind to hemoglobin.

• When hydrogen ions bind to hemoglobin, oxygen is more easily released (this is why hemoglobin releases more oxygen when the blood is more acidic)

Recap: Gas Exchange

1. How does gas go from air we breathe to blood?

2. How does oxygen travel from blood in lungs to a leg muscle cell?

3. How does carbon dioxide travel from blood in lung to a leg muscle cell?

4. How does gas go from blood into muscle cell?

Carbon Monoxide Poisoning (Good to know)

• Carbon monoxide binds to hemoglobin more easily than oxygen (so if both carbon monoxide and oxygen are present, hemoglobin will bind to carbon monoxide first)

• Once carbon monoxide is bound to hemoglobin, it is very difficult to remove it

• In carbon monoxide poisoning, oxygen does not get delivered to the tissues in the body

Group Task 1

• Spend fifteen minutes going through following problems:

(We will correct answers when everyone is done!)

Individual Task

• Create a concept map that includes all terms and LINKING WORDS.

Use terms below:

Oxygen Carbon dioxide Blood

Hemoglobin Bicarbonate H+ ion

Partial pressure Carbonic acid carbonic anhydrase

Oxyhemoglobin Gas trasport Acidic

Red Blood CellMuscle Cell Lung

Plasma

(HINT: Use paper squares to rearrange terms)