14.3 ~ GAS EXCHANGE AND TRANSPORT

Respiration

exchange of gas in lungs and tissues

• Critical to homeostasis

Diffusion

molecules move from higher concentrations to lower concentrations

• Principles of diffusion govern whether oxygen or carbon dioxide enter or leave blood in lungs and tissues

External Respiration

• Air exchanged between alveolar air and pulmonary capillary blood

  • Due to low O2 blood entering capillaries is dark maroon

After inspiration what happens to the alveoli?

• alveoli have higher concentration of O2 than blood entering lungs

  • CO2 diffuses out of pulmonary blood into alveoli 

    • This CO2 exits body during expiration

What is the amount of pressure each gas exerts in the alveoli?

partial pressure

• Symbolized as Po2 and Pco2

Alveolar air has a much higher Po2 than blood, what does this cause?

oxygen to rush into blood

Blood in pulmonary capillaries has higher Pco2 than air in alveoli, what does this allow CO2 to do?

CO2 escape the pulmonary blood and enter alveoli

Internal respiration

Exchange of gases in tissues

• Specifically exchanged between blood in systemic capillaries and tissue fluid

What color is the blood entering systemic capillaries and wh?

bright red because rich in O2

Why does tissue fluid have low O2 concentration?

cells continuously consume O2 during cellular respiration as they metabolize food

• Producing CO2 and ATP energy

What does CO2 diffuse into from tissue?

CO2 diffuses into blood

Why does oxygen flow out of blood into tissues?

Po2 in tissue fluid is lower than that out of blood

WHy does CO2 rush into blood from tissues?

Pco2 in tissue fluid is higher than that of blood

Gas transport

O2 and CO2 are transported differently in blood, although red blood cells are involved in transporting both gases 

Where is blood combined with the iron part of hemoglobin? How does it get there?

• red blood cells

• O2 enters blood in pulmonary capillaries of lungs and flows into red blood cells

What is a small amount of O2 transported as?

dissolved gas in watery blood plasma

How much of body’s oxygen is made up of dissolved O2 at any given time? Why?

only about 2-3%

• oxygen is not very soluble in water

Why is hemoglobin well-suited to transport O2?

Hemoglobin can easily combine with or easily release O2

When concentration of O2 in alveoli is high, what is the internal temperature?

slightly cooler than body temperature

Pulmonary capillary blood has high O2 concentration. What is the temperature and pH?

lower temperature, its pH is slightly high

Oxyhemoglobin

During these conditions hemoglobin takes up oxygen

Systemic capillary blood has lower concentration of O2. What is the temperature and pH? What is this due to?

slightly warmer temperature and slightly lower pH

• Due to tissue metabolism

How many different ways can CO2 diffused into blood at tissues be transported?

in one of three ways

What is the first way CO2 diffused into tissues can be transported?

10% transported as dissolved gas in blood plasma and in cytoplasm of red blood cells

• CO2 more soluble in H2O than O2 - 3 to 5 times as much CO2 can be transported in blood plasma as dissolved gas

What is the second way CO2 diffused into tissues can be transported?

30% CO2 molecules taken up by protein portion of hemoglobin (globin)

• Forms compound carbaminohemoglobin 

What is the third way CO2 diffused into tissues can be transported?

60% CO2 combines with water to form carbonic acid (H2CO3) 

• carbonic acid dissociates to hydrogen (H+) and bicarbonate ions (HCO-3)

  • This reaction is catalyzed enzyme, carbonic anhydrase - present in all body cells especially red blood cells

  • Hydrogen ions released from carbonic acid diffuse into plasma and increase concentration of free hydrogen ion in blood plasma

    • This is why blood in systemic capillaries has lower pH than blood in pulmonary capillaries 

When there is a small pH number, how is the number of free hydrogen ions affected?

there is a greater number

What is the difference in pH during CO2 transport?

slight due to many excess hydrogen ions being buffered by hemoglobin

What happens when free hydrogen ions combine with globin, instead of being in a free solution?

reduced hemoglobin is created

Why are bicarbonate ions carried in plasma?

They diffuse out of red blood cells and go into plasma

• Most CO2 in blood is carried as bicarbonate ions (HCO-3)

Chloride shift

 As bicarbonate ions diffuse out of red blood cells, chloride ions (CL-) diffusion into cells in an exchange of negatively charged ions - exchange is one for one

• Maintains electrical balance between plasma and red blood cells

Where does the reverse reaction occur?

pulmonary capillaries

Why must CO2 constantly be released form carbonic acid?

CO2 is eliminated from our bodies when we exhale

Step 1 of forming CO2

Bicarbonate ions recombine with hydrogen ions to form carbonic acid

Step 2 of forming CO2

 Carbonic acid splits into CO2 and H2O

• CO2 diffuses out of blood into alveoli

• CO2  +  H2O tissues/lungs H2CO3 tissues/lungs H+  +  HCO-3

What kind of relationship is breathing rate? What does it help regulate?

a chemical relationship that helps regulate arterial blood pH

• pH of arterial blood 7.35-7.45

What do tissue cells constantly produce as a waste product of metabolism?

CO2

What does CO2 do when it accumulates?

it combines with available water to form carbonic acid

What happens as carbonic acid dissociates?

free H+ are released

What causes blood pH to decrease?

enough H+ released

If breathing rate quickens, what happens to the carbon dioxide in the blood?

decreases as more is exhaled

What causes the release of CO2? What does this do tho pH and H+ in plasma?

• carbonic acid reforming from hydrogen ions and bicarbonate

• increases pH levels and decreases H+ in plasma

What part of the brainstem helps maintain homeostasis?

Brainstem respiratory centers

What do many respiratory diseases interfere with? What does this cause?

normal excretion of CO2

• Causes excess carbonic acid to be formed 

• Excess free hydrogen ions accumulate

What develops when blood pH levels fall below normal range?

acidosis

Other conditions may cause hyperventilation. What problem does this cause?

too much CO2 elimination raises blood pH above normal level, causing alkalosis

• Stress, anxiety, and disorders involving respiratory control center can cause hyperventilation

What do acidosis and alkalosis interfere with?

cell enzyme functions

• can be fatal