Gas diffusion is described by Fick's law of diffusion, which basically says that gases diffuse due to five factors, but really there are 3 important ones that we're going to look at, and those are surface area, surface area that diffusion will occur over, distance across which the diffusion will occur, and the partial pressures of the gas diffusing. Now increasing surface area for gas exchange will increase the rate of diffusion. More surface area, more diffusion. Hopefully that's not a surprise, that's a concept that comes up again and again in biology. Now decreasing the distance that the gas has to travel will actually increase the rate of diffusion. So think about this like the thickness of a membrane. The gas has to get across the membrane. The thinner the membrane, the, the, you know, higher the rate of diffusion, you know, less distance to travel. And lastly, partial pressure. We said that partial pressure will drive the diffusion of gases. So surface area and distance are great, but if you don't have a difference in partial pressures, you're not going to have diffusion of gases. And by increasing the difference in partial pressure between the two environments, you will increase the rate of diffusion. So, the greater the difference in the partial pressures of the gas in those two environments, the higher the rate of diffusion you'll have. Now partial pressure is, of course, what's going to drive oxygen and carbon dioxide diffusion in the lungs, the blood, and the tissues. Now, the partial pressure of oxygen in the lungs is going to be higher than the partial pressure of oxygen in the blood. That's going to drive oxygen from the lungs into the blood. And, of course, it would make sense then that the partial pressure of oxygen in the blood is higher than that in the tissues. And that's what's going to allow oxygen to unload from the blood to tissues. Now with carbon dioxide, we kind of have the reverse scenario. The partial pressure of carbon dioxide in the lungs is lower than the partial pressure of carbon dioxide in the blood, and that's what drives CO2 into the lungs to be exhaled. And likewise, the partial pressure of CO2 in the blood is going to be lower than the partial pressure of CO2 in the tissues. So that's what's going to drive CO2 from the tissues into the blood. So, you know, basically partial pressure is what drives the diffusion of gases, and these gases that we're focusing on, which we breathe in and out, are no exception. Now it's worth noting that muscles tend to have particularly low partial pressure of oxygen, especially during exercise when their energy demands increase, and this is why, you know, the muscles are going to be super greedy with oxygen. It's, that they have they tend to have, you know, a lower partial pressure of oxygen, so they're going to suck up a lot of the oxygen out of the blood, which is good because they need it. Now in mammals, as I said before, each breath of fresh air is going to mix with some oxygen depleted air. Right? That air that was that stale air that was sitting in the dead space is going to mix with the fresh air and that's what's going to, go into your alveoli and, you know, what what's going to be performing gas exchange. So point is that the partial pressure of oxygen in alveoli is going to be less than the partial pressure of oxygen that's in the atmosphere. And, you know, it's not ideal but clearly the system still works. So, you know, I'm here, I'm alive, you guys are here alive, so, clearly it's good enough. Now, hemoglobin is going to be that magic little protein that will bind oxygen and transport it in the blood and also unload oxygen at the tissues. Hemoglobin is a protein with quaternary structure. It has 4 subunits, and it actually has this really cool property we call cooperative binding, which is basically a property of a binding system, it's not exclusive to hemoglobin, where the binding of one thing alters the binding of subsequent things. That's kind of a very vague general way to describe cooperative binding. In the case of hemoglobin, what's actually happening is that when hemoglobin binds one oxygen, it actually undergoes a conformational change, so it's, it physically changes shape, and this shape change actually makes it easier to bind another oxygen. So binding oxygen makes it easier to bind more oxygen. And, you know, that's super cool because it leads to, you know, this this interesting pattern of loading and unloading oxygen when hemoglobin doesn't have oxygen, right, when it gets to the lungs, for example, and it picks up oxygen, and it picks up that one oxygen, it's gonna make it way easier for it to bind the remaining 3 oxygen that it can carry. Right? Conversely, when it gets to the tissues and it offloads an oxygen, because, you know, the tissues are demanding that oxygen, by offloading that one oxygen it will actually undergo a conformational change that makes it easier to offload the rest of its oxygens. So, this cooperative binding just makes hemoglobin more efficient at doing its job basically. And you can see, the, you know, conformational change between the deoxy and the oxy form, you know, here we have the deoxy form, here's the oxy form. You know, I don't expect you to look at this and say, oh, of course, I see how this shape change would drive oxygen binding. I just want you to notice that it's a different shape. That's all. Now, the cooperative binding that hemoglobin experiences is going to lead to a graph of oxygen saturation that looks like this. It's going to have a shape like that which we call sigmoidal, it's a sigmoidal graph. And the significance of this is going to come into play on the next page, so why don't we go ahead and flip the page.
Table of contents
- 1. Introduction to Biology2h 40m
- 2. Chemistry3h 40m
- 3. Water1h 26m
- 4. Biomolecules2h 23m
- 5. Cell Components2h 26m
- 6. The Membrane2h 31m
- 7. Energy and Metabolism2h 0m
- 8. Respiration2h 40m
- 9. Photosynthesis2h 49m
- 10. Cell Signaling59m
- 11. Cell Division2h 47m
- 12. Meiosis2h 0m
- 13. Mendelian Genetics4h 41m
- Introduction to Mendel's Experiments7m
- Genotype vs. Phenotype17m
- Punnett Squares13m
- Mendel's Experiments26m
- Mendel's Laws18m
- Monohybrid Crosses16m
- Test Crosses14m
- Dihybrid Crosses20m
- Punnett Square Probability26m
- Incomplete Dominance vs. Codominance20m
- Epistasis7m
- Non-Mendelian Genetics12m
- Pedigrees6m
- Autosomal Inheritance21m
- Sex-Linked Inheritance43m
- X-Inactivation9m
- 14. DNA Synthesis2h 27m
- 15. Gene Expression3h 20m
- 16. Regulation of Expression3h 31m
- Introduction to Regulation of Gene Expression13m
- Prokaryotic Gene Regulation via Operons27m
- The Lac Operon21m
- Glucose's Impact on Lac Operon25m
- The Trp Operon20m
- Review of the Lac Operon & Trp Operon11m
- Introduction to Eukaryotic Gene Regulation9m
- Eukaryotic Chromatin Modifications16m
- Eukaryotic Transcriptional Control22m
- Eukaryotic Post-Transcriptional Regulation28m
- Eukaryotic Post-Translational Regulation13m
- 17. Viruses37m
- 18. Biotechnology2h 58m
- 19. Genomics17m
- 20. Development1h 5m
- 21. Evolution3h 1m
- 22. Evolution of Populations3h 52m
- 23. Speciation1h 37m
- 24. History of Life on Earth2h 6m
- 25. Phylogeny2h 31m
- 26. Prokaryotes4h 59m
- 27. Protists1h 12m
- 28. Plants1h 22m
- 29. Fungi36m
- 30. Overview of Animals34m
- 31. Invertebrates1h 2m
- 32. Vertebrates50m
- 33. Plant Anatomy1h 3m
- 34. Vascular Plant Transport2m
- 35. Soil37m
- 36. Plant Reproduction47m
- 37. Plant Sensation and Response1h 9m
- 38. Animal Form and Function1h 19m
- 39. Digestive System10m
- 40. Circulatory System1h 57m
- 41. Immune System1h 12m
- 42. Osmoregulation and Excretion50m
- 43. Endocrine System4m
- 44. Animal Reproduction2m
- 45. Nervous System55m
- 46. Sensory Systems46m
- 47. Muscle Systems23m
- 48. Ecology3h 11m
- Introduction to Ecology20m
- Biogeography14m
- Earth's Climate Patterns50m
- Introduction to Terrestrial Biomes10m
- Terrestrial Biomes: Near Equator13m
- Terrestrial Biomes: Temperate Regions10m
- Terrestrial Biomes: Northern Regions15m
- Introduction to Aquatic Biomes27m
- Freshwater Aquatic Biomes14m
- Marine Aquatic Biomes13m
- 49. Animal Behavior28m
- 50. Population Ecology3h 41m
- Introduction to Population Ecology28m
- Population Sampling Methods23m
- Life History12m
- Population Demography17m
- Factors Limiting Population Growth14m
- Introduction to Population Growth Models22m
- Linear Population Growth6m
- Exponential Population Growth29m
- Logistic Population Growth32m
- r/K Selection10m
- The Human Population22m
- 51. Community Ecology2h 46m
- Introduction to Community Ecology2m
- Introduction to Community Interactions9m
- Community Interactions: Competition (-/-)38m
- Community Interactions: Exploitation (+/-)23m
- Community Interactions: Mutualism (+/+) & Commensalism (+/0)9m
- Community Structure35m
- Community Dynamics26m
- Geographic Impact on Communities21m
- 52. Ecosystems2h 36m
- 53. Conservation Biology24m
40. Circulatory System
Gas Exchange
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