Now after those germ layers have formed, we can begin organogenesis or the process of organ and tissue development. And you might remember that the mesoderm was made up of those 2 pockets. Well, we call those somites, those are pairs of mesodermal tissues. And the cell's position in this, in the somite, determines what it will turn into. So let's imagine that, here is our somite, and it's made up of a bunch of little individual cells. Again, this is just for the purpose of example. So depending on where the cell is located in the somite, it'll turn into different things. It'll actually break away in groups and migrate and form different things. So, this cell might form, let's say, cardiac muscle, like we see here. And maybe these cells, the cell breaks away and forms skeletal muscle. So it's the actual physical position of the cell in the somite that determines what it will develop into. And I'm sure you have some pretty good guesses as to how and why that can happen based on what we've already learned about development, concentration gradients, and chemical signals. Now the mesoderm layer develops into many different things as we can see here, including cardiac muscle, skeletal muscle, tubule cells of the kidney, red blood cells, and smooth muscle cells like those around the intestine. Now in addition to organogenesis, there is another really important process that occurs in animal development, and this is neurulation, which is the actual formation of nervous tissue from primary germ layers. So a couple of points of terminology here. We have the notochord, which you can see here in the picture, this structure. And if I scroll down a little so you can see the other images, The notochord is also present here and here, and it is labeled in this last image here. So, what is the notochord? The notochord is kind of like a primitive backbone that develops in chordates, which is a, a big class of types of animals. And in some animals, it actually develops into the vertebrae of the spine. But in many animals, it is actually just a transient structure. It forms during development, and then it goes away at some point. And that's a totally normal part of the process. And it's because of that link to evolution, that close link that development has to evolution. Now, in addition to the notochord, you should be aware of the neural tube, which is a hollow structure that will eventually form the brain and spinal cord. The neural tube forms in kind of an interesting way. We have this neural plate as it is called, and it basically, as you can see here, it folds in on itself and seals the ectoderm. There is ectoderm on this side. This is also ectoderm. It seals the ectoderm together. So let me get rid of some of these arrows just so this becomes a little more clear, so you can see the ectoderm, or the neural plate folds in on itself and then, eventually, boom, we have the ectoderm fuse. And, again, this neural tube structure that you see here will form the brain and spinal cord. In fact, it swells in certain places to form the embryonic brain. So it'll swell and form little bulges that actually become embryonic brain structures. So the mesoderm cells, that form the notochord are actually the same cells that induce, remember, induction, induce the ectoderm cells to furrow or form this fold and then fuse together to form the, neural tube. The Neural Folds that surround the Neural Group actually give rise to the, central nervous system. Now, the last thing we need to talk about is cell determination, which is that irreversible commitment of a cell to a particular developmental path, which results in a specific cell type. We've talked about this. It happens through the process of differentiation. But what we haven't talked about is how differentiation is actually a gradual process. Cell a can give rise to cell b or cell c. Cell b is capable of giving rise to cell d and cell e, and cell c can give rise to cell e or f. So differentiation occurs in stages. To get from cell a to, let's say, cell f, the cell has to go through that intermediary phase of being cell c. And at that point, its fate as becoming cell f is still not sealed. It could also become cell e. It has options. So differentiation is a gradual process. However, once the cell is committed to a particular path, its fate is sealed. Its destiny is sown in the stars, and it is going to become differentiated to that particular type of cell. Alright. That's all I have for this lesson. See you guys next time.
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
20. Development
Animal Development
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