Once the blastocyst is formed, it has to implant in the uterus. This is called implantation. Getting really creative with the names here. Now, hCG is a chemical secreted by the implanted blastocyst, and it lets the body know that pregnancy is underway. In fact, most early pregnancy tests actually test for the presence of hCG. hCG is not the end-all-be-all hormone involved in this, and eventually, it will be replaced by the secretion of estrogen and progesterone, but all of this is a little beyond the scope of what you need to know for Bio 1. So, what you should know is that those trophoblast cells will develop into the placenta, and they will take over the production of estrogen and progesterone and will continue to produce it throughout pregnancy. These hormones are very important to pregnancy and to supporting the developing organism. Now, once we have our blastocyst implanted, it can start to undergo what's called gastrulation, which is the formation of three germ layers, forming a gastrula. As you can see here, we have our blastocyst, right? It has cells around the outside, blastocele, that fluid-filled cavity inside, and what happens is it starts to kind of poke inward like we see happening right here. This is gastrulation, and the result is what we see here, the gastrula. What I'm highlighting in red is the mass of cells. There's a space inside, however, a hollow cavity. Now, let's go over a little terminology real quick. We have our blastopore, that's the opening to this space. We also have our three germ layers. The three germ layers are the ectoderm, which are the cells that give rise to nerves, the adrenal medulla which is a gland in the body, skin, brain, eyes, inner ear, or your vestibular system, if you will. You also have the mesoderm. And the mesoderm, you can see there's actually one little patch right here. This is also mesoderm over here. I'm going to take myself out of the shot so it's easier to see all of this. The mesoderm consists of internal cells that will give rise to organs, the adrenal cortex which is also part of the adrenal gland, a different part though, the blood, bone, gonads, and soft tissues. And then lastly, we have the endoderm. The endoderm is the layer of those innermost cells that you can see in this mustard color. I'm going to circle it in blue right now. This is our endoderm. Those innermost cells form the epithelial linings of the digestive tract, the liver, pancreas, and lungs. In a large part, they form the inner cells of what's called the alimentary canal or, basically, the cavity that runs through our bodies.
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. Phylogeny40m
- 26. Prokaryotes4h 59m
- 27. Protists1h 6m
- 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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