1. Cardiovascular System and Diffusion Katerina Lin Kiran Pandher Rachel Gibbs Group 5

2. Goals  Explain how gas exchange takes place at the cellular level.  What prevents gas from being exchanged in non-optimal places?

3. An Overview: The Respiratory System  Respiratory system: takes oxygen from the air into the body and releases CO 2, the waste product.  Gas exchange occurs because of partial pressure gradients (oxygen and CO 2 ). Higher pressure = more diffusion. Lungs: Gases pass through capillaries and alveoli down partial pressure gradients. Capillaries and alveoli share a membrane (Starr). Body: Gases diffuse through capillaries.

4. Oxygen…  Simple diffusion  Lungs: oxygen flows from the alveoli (high) to the bloodstream (low) (“Respiration”). More pressure/higher temp/lower pH = more oxygen diffuses (Starr).  Most (98.5%) of the oxygen flowing into the bloodstream binds onto the hemoglobin in RBCs (Starr).  Oxygen does not dissolve well in blood so needs help from hemoglobin (Starr).

5. Carbon Dioxide…  Simple diffusion  Body: diffuses from interstitial fluid (high) into capillaries and carried in blood (low): 10%: dissolves in blood 30%: binds to hemoglobin (carbamino hemoglobin) 60%: becomes bicarbonate (HCO 3 - ) when CO 2 dissociates in water or with enzyme (carbonic anhydrase)  Lung: from the bloodstream (high) to alveoli (low) (“Respiration”). CO 2 is released from the CO 2 bound to hemoglobin and HCO 3 - dissolved in the blood (Freudenrich).

6. Diffusion of Carbon Dioxide

7. What prevents gas from being exchanged in non-optimal places?  Surface areas and rates of flow influence gas exchange The more surface area and larger the partial pressure gradient, the faster diffusion will occur (Fick’s law) (Starr).  Alveoli sacs provide a lot of surface area for optimum diffusion. Gas exchange is most efficient when the rate of air coming into the body equals blood flow (Starr).

8. What prevents gas from being exchanged in non-optimal places?  Different parts of body have characteristics that help create optimal gas exchange.  Capillaries Very small and only one cell thick (“Capillaries”). Network throughout body Blood flow slows down  Alveoli respiratory surface: thin layer of epithelium/other tissue that is moist at all times  gas molecules can diffuse only when dissolved in a liquid (Starr). Quick diffusion because very thin and a lot of surface area (Starr). Electron Micrograph of a Capillary

9. Gas Exchange Simulation!

10. References  “Capillaries: Connecting Arteries and Veins.” 1996-2009. The Franklin Institute. 10 Nov. 2009..  Freudenrich, Craig. “How Your Lungs Work.” 30 Oct. 2008. How Stuff Works. 8 Nov. 2009.. .  “Human Physiology: Respiration.” 7 Nov. 2009..  Starr, Cecie, and Ralph Taggart. Biology: The Unity and Diversity of Life. 9th ed. United States: Brooks/Cole, 2001. Note: pictures are also cited throughout this powerpoint in the “Notes” section at the bottom of the screen.