The endocrine system consists of hormone-producing tissues located throughout the body. The circulating hormones control the rates of body processes and maintain homeostasis. Within an endocrine gland endocrine cells secrete hormones which diffuse into nearby capillaries. The cardiovascular system transports these hormones throughout the body, affecting target cells in various tissues. Target cells for a specific hormone have receptors that bind the unique three-dimensional shape of that hormone. Cells that lack a specific hormone receptor are unresponsive to that hormone, even if a high concentration of the hormone is present around the cells. Although cells express a variety of receptors, we'll focus on one particular class: receptors that bind water-soluble hormones and exert their effects through the intracellular second messenger cyclic AMP. These receptors are embedded in the cell's plasma membrane, because water-soluble hormones cannot enter the target cell directly. A hormone molecule, acting as the first messenger, binds to its receptor, causing the receptor to change shape. The receptor can now activate specific intracellular G proteins. The activation process begins with the release of a GDP molecule from the G protein in exchange for a GTP molecule. This causes the G protein to change shape and become active. The hormone-bound receptor activates many individual G proteins, which greatly amplifies the signal from a single hormone molecule. An activated G protein diffuses along the plasma membrane until it binds to, and activates, the enzyme adenylate cyclase. Once active, adenylate cyclase converts ATP to the second messenger cyclic AMP. These many molecules of cyclic AMP, from each activated cyclase enzyme, represent a further amplification of the initial hormone signal. The increased concentration of cyclic AMP activates enzymes known as protein kinases. These activated protein kinases phosphorylate a variety of proteins within the cell. This changes the activity of those proteins and generates the cell's hormone response. The cell's response is characterized by the specific proteins present in the cytoplasm, only some of which can be phosphorylated by protein kinase. The cellular response diminishes rapidly once the hormone is no longer bound to its receptor. G proteins hydrolyze their bound GTP to GDP, returning to their inactive state, and dissociate from adenylate cyclase. This ends cyclic AMP production. Existing cyclic AMP is degraded by the enzyme phosphodiesterase, which is already present in the cyctoplasm. As the cyclic AMP concentration returns to resting levels, protein kinase inactivates, preventing further protein phosphorylation. The target cell has now returned to its pre-stimulus condition, ready to respond to future hormone signals. The signal, of a water-soluble hormone binding to a receptor on the plasma membrane, is amplified through the activation of many G proteins and the generation of even more cyclic AMP. This cyclic AMP activates many protein kinases, which affect many thousands of introcellular proteins, all shaping the target cell's response. The response of many target cells produces the homeostatic and regulatory effects controlled by the endocrine system.
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
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- Punnett Square Probability26m
- Incomplete Dominance vs. Codominance20m
- Epistasis7m
- Non-Mendelian Genetics12m
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- Autosomal Inheritance21m
- Sex-Linked Inheritance43m
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- 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
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- 21. Evolution3h 1m
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- 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
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- 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
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- Community Interactions: Mutualism (+/+) & Commensalism (+/0)9m
- Community Structure35m
- Community Dynamics26m
- Geographic Impact on Communities21m
- 52. Ecosystems2h 36m
- 53. Conservation Biology24m
37. Plant Sensation and Response
Tropisms and Hormones
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