Respiration: Part 3 How does gas exchange happen? Substances diffuse from high concentrations to low concentrations Example: Scent molecules move across a room

Gas exchange: Diffusion of gases Gases move by diffusion from high to low concentration capillaries are thin-walled tubes of circulatory system alveoli are thin-walled sacs of respiratory system capillaries in lungs capillaries in muscle O2 O2 O2 O2 CO2 CO2 CO2 CO2 blood lungs blood body

External Respiration (Lungs) Exchange between gases in the air and the blood Through Alveoli and capillary walls (only one cell thick!)

How do you diffuse the most O2 into the blood? Alveolus Lung Capillary O2 O2 Hemoglobin O2 O2 O2 O2 O2 O2 O2 O2 O2 O2 O2 = O2 O2 O2 O2 O2 O2 O2 HIGH Concentration LOW Concentration

Result: We get MORE oxygen diffusing into the blood! What just happened? Breathe in and there is more O2 in the alveoli than in the blood O2 moves from HIGH to LOW concentration Alveoli and blood are at the same concentration Hemoglobin took up four more O2 Alveoli had more O2 than the blood again Result: We get MORE oxygen diffusing into the blood!

Helpful Hemoglobin! (Hb) Contains iron 250 million Hb / red blood cell 4 O2 molecules can attach to each Hb molecule Increases carrying capacity of O2 by 60 times O2 O2 O2 O2

Internal Respiration (Body) Exchange between gases in the blood and the tissues Through capillary walls into cells

How does the O2 get from the blood to the cells? Body Cell Body Capillary Hemoglobin O2 O2 O2 O2 O2 O2 O2 O2 = O2 O2 O2 O2 O2 O2 O2 LOW Concentration HIGH Concentration

What happened this time? Blood arrives with a HIGH concentration of O2 Cells have a LOW concentration of O2 O2 diffuses out of the blood into the cells (HIGH  LOW) Hb gives up its four O2 There is more O2 in the blood again More O2 diffuses out of the blood into the cells Result: We get MORE oxygen diffusing into the cells!

Consider this reaction: Hb + O2  HbO2 (hemoglobin + O2) (oxyhemoglobin) Why will this help you to diffuse more oxygen into the blood? When there is lots of O2 the reaction shifts this way: Hb + O2  HbO2 When there is lots of HbO2 the reaction shifts this way: Hb + O2  HbO2 Happens in LUNGS Happens in TISSUES

How do we maximize the transfer of O2 using Hb? Effect of temperature: Hb gives up O2 better at higher temperatures Hb attaches to O2 better at lower temperatures Effect of pH: At higher or neutral pH, Hb attaches to O2 better At lower pH, Hb gives up O2 better

What are the best conditions? For TAKING UP O2? pH = Temperature = This occurs in the _________________. For GIVING AWAY O2? High pH (Basic) Low Temperature (Cool) Lungs Low pH (Acid) High Temperature (Hot) Tissues

What happens with CO2? CO2 also diffuses from HIGH to LOW concentration In the lungs: Blood is HIGH in CO2  Alveolus is LOW in CO2 In the tissues: Cells are HIGH in CO2  Blood is LOW in CO2 Some CO2 changes into carbonic acid (H2CO3) in the blood This lets more CO2 diffuse in from the cells

CO2 produced INTERSTITIAL FLUID CO2 BLOOD PLASMA WITHIN CAPILLARY Capillary wall H2O H2CO3 RED BLOOD CELL HCO3– + H+ Hemoglobin picks up CO2 and H+ ALVEOLAR SPACE IN LUNG Hemoglobin releases CO2 and H+

Why is carbon monoxide poisonous? CO + Hb   HbCO Carbon monoxide + hemoglobin carboxyhemoglobin Hb has an affinity for carbon monoxide 230 times greater than its affinity for O2  Hemoglobin can’t carry oxygen because it is taken up with carbon monoxide