In humans and other mammals, digestion isn't sequestered to one single organ. It actually occurs in multiple organs as the food moves through the body. And as we'll see, certain organs are specialized for certain types of digestion. Now, the first place where digestion begins is actually in the mouth itself. The food there is going to be mechanically digested and subdivided, and this serves the benefit of actually increasing the surface area of food particles, which is going to be really useful later on when we get to chemical digestion because this increased surface area is going to help increase the efficiency of the chemical breakdown. Now, there actually is some chemical digestion going on here. You see, salivary glands release a substance, of course, saliva. And saliva is a mixture of water, mucus, and enzymes. It actually contains something called salivary amylase, and amylase breaks down carbohydrates. And this salivary amylase is going to break down carbohydrates into maltose and what are called dextrins. Now maltose is basically 2 glucose subunits. You can see a maltose right here, behind my head. A single one of these is glucose. Now, behind me, let me jump out of the way here, this is what you could think of as a dextrin. Now it wouldn't be quite as long, this is basically saying, you know, that you just are repeating this unit some number of times. Now, you know, it's not going to be the, you know, 100 long it's it shows in this figure. A dextrin is, you know, going to be like a couple units of glucose linked together. So the idea is that salivary amylase breaks down carbohydrates into small units, but not into glucose itself. That's the point to take away. Now, mucus, speaking of glucose and all that good stuff, mucus is actually made from glycoproteins that form a slimy substance when they mix with water. And of course, there's water in saliva, so you get that nice slimy mucus, and this is going to be good because it lubricates the food bolus. And the bolus is basically what, you know, that ball of chewed up food that you swallow is referred to in a technical sense. Now salivary amylase isn't the only enzyme there. Actually, also going to have lingual lipase, which is basically an enzyme that's going to break down fats. Right? Lipase, lip-like lipid, ace. So this is going to break down fats, and it's released along with the saliva, but it's actually coming from glands in the tongue, as opposed to these salivary glands that you see here. So these are salivary glands, and the lingual lipase is going to be coming from a gland in the tongue. You don't need to worry about the details of that. Here you can see a nice overview of the mouth, and once that food is chewed up, or you know that bolus as we should probably call it, be technical about it, once that bolus is ready to be swallowed, it's going to move through the pharynx to the esophagus. The pharynx is back here, it's kind of like the throat region, or you know, the back of the mouth region, and it's going to connect to the esophagus, which is an organ that connects the mouth to the stomach. As you can see here that's going to lead to the stomach, And you should note that there's actually another opening in here, the, opening, the larynx, which will, it's commonly, you know, called like the windpipe, that's going to lead to the lungs, that's where air goes. So these guys actually share an area together, which is, you know, why if you've ever eaten or drank anything for long enough as a human, I'm sure you've had some water or food very unpleasantly go down your windpipe. That's why, because they are right there next to each other. Now once the bolus is in the esophagus it needs to be moved to the stomach. In part, gravity is going to help with this, but the esophagus is lined with smooth muscle that's going to go through these rhythmic motions known as peristalsis. This is basically a wave-like contraction in the smooth muscle that has the effect of pushing the food bolus down through the esophagus. So, it's it's, you know, a little hard to visualize in a static image, but essentially, this right here, these are these, smooth muscle contractions that are in a wave-like motion going to travel down the esophagus and cause that food bolus to move towards the stomach. Now, birds actually, or some birds I should say, have an interesting modification to the esophagus known as a crop. And this is, you can see this right here, it's this kinda like big chunky ball that's, attached to the esophagus, which is this tube here leading from the mouth. In case you're curious, this other tube you're seeing from the mouth is actually the windpipe right there. So anyways, their esophagus has this big chunky area on it, and it is known as a crop and it is modified for food storage. This is, you know, how all those birds will go eat a bunch of food, and then they regurgitate it to their young, you know, they're actually storing it in their crop. And, that is again, just part of the esophagus that's been modified by evolution. With that, let's turn 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
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- 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
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- Autosomal Inheritance21m
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- X-Inactivation9m
- 14. DNA Synthesis2h 27m
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- 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
39. Digestive System
Digestion
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