Regulation is super important to all metabolic and physiological processes. One of the best strategies for regulating is known as negative feedback, and this is a type of regulation where the output of a system will actually reduce the system's output. Now that's kind of a confusing general way to put it, so let me give you an example that kind of makes this a lot more clear. Here, we are looking at glycolysis, which is the first step of cellular respiration, and a super important process no matter what type of biology you're doing. Now, you don't need to worry about memorizing any of these names or technicalities, you'll have plenty of time for that, if and when you take biochemistry. I just want you to get a sense of how negative feedback works. So glycolysis begins with glucose and you wind up with pyruvate. In the process, you produce some ATP. Right? Now glycolysis is the first step of cellular respiration, which ultimately results in the production of a lot of ATP through oxidative phosphorylation. So ATP is not only a direct product of glycolysis, it's also the major downstream, like endgame product that this whole process is gunning for. So glycolysis is under negative feedback control. The way this works is one of the enzymes that catalyzes a reaction very early in the process, it's a very important step of the reaction, for reasons that you don't need to worry about. This enzyme is called phosphofructokinase, and it is negatively regulated by ATP. So ATP will feed back and shut off phosphofructokinase, shutting down this chemical pathway. So essentially, if there's too much ATP being produced, either directly from glycolysis, but more likely, through the downstream cellular respiration, oxidative sorry, the downstream oxidative phosphorylation process. If there's too much ATP being produced, it's going to negatively feedback and shut off the very beginning of this whole process to conserve resources, not waste energy, and just maintain the balance of generating just as much ATP as is needed. So you can see how powerful and eloquent a system negative feedback is, where a system's output will actually reduce this output of the system in order to control the levels in a nice passive way. Now, positive feedback is very much so a different beast. And it's also a lot rarer to see. And the reason for that is because with positive feedback, the output of a system actually increases the system's output. Right? So the most common example of positive feedback is in birth, where the infant's head pushes and sets off some receptors that send a signal, which induce greater labor contractions, which in turn are going to cause the infant's head to push harder against those receptors, which of course means more labor contractions. And so these two things just up the ante and feed back positively on each other, creating a bigger and a bigger effect. So you can see why something like that you wouldn't want to use in a lot of systems. It could very easily get out of control, which is why negative feedback is everywhere and positive feedback is a lot less common. Now, to look at an example of negative feedback that involves actual systems in the body, want to take a look at something known as the HPA axis. Now, this is going to involve the nervous system and the endocrine system. The nervous system is going to be a system responsible for transmitting information throughout the body, as well as receiving information from the body and the environment. It's going to transmit these signals via nerves, through those electric signals called action potentials. If you want to know more about this check out, the nervous system videos. The endocrine system is also a signaling system, but it functions differently than the nervous system. The endocrine system is a hormone signaling system. So it's going to involve glands that secrete hormones into the bloodstream, and those hormones are going to target and set off reactions at various organs that have their appropriate receptors. So both of these are signaling systems and they're actually connected by this really cool brain structure called the hypothalamus, which basically just means underneath the thalamus, which is where it's located. So very creative naming here. This structure coordinates the autonomic nervous system, which is going to be the part of the nervous system that we don't have direct control over. Right? Things like breathing, heart rate, that sort of stuff. We don't have direct conscious control over what I mean. You know, obviously our hypothalamus is controlling that. So we have control, we don't have conscious control. It's not like the part of the nervous system where I can say, alright, finger wants you to poke, and move, or whatever. So, the hypothalamus links the nervous and endocrine system by coordinating the autonomic nervous system, and also by coordinating the pituitary gland, which is a very important gland in the endocrine system, and in it has a variety of functions. I don't want to get ahead of myself because I could go off on tangents on all of this forever. So here's the important thing to note. You have the hypothalamus, that is a brain structure. Right? And in the HPA axis, which stands for hypothalamic pituitary adrenal axis. Right? HPA. Essentially, what you have is a stress hormone, you know, signaling system. So the hypothalamus can release something called corticotropin-releasing hormone. Don't worry about these names just now. This will stimulate the pituitary, the "P" in the HPA, to release ACTH or adrenocorticotropic hormone, again, like, don't worry about these names. These are just stress hormones, that's all you need to know, that will eventually lead the adrenal cortex to secrete, and let me jump out of the way here, cortisol, which is that main stress hormone. Now, the thing about cortisol is it actually feeds back negatively to the pituitary and the hypothalamus, as you can see here. This is standing for Cortisol, will actually have a negative feedback effect on the hypothalamus and the pituitary, to cause them to stop releasing corticotropin-releasing hormone, and adrenocorticotropic releasing hormone. Or as it's much easier to say, CRH and ACTH. Essentially, the downstream output of that system, cortisol, will go back to earlier points in the system and cause them to shut down that pathway. Again, this is known as the HPA axis and is a really nice example of negative feedback regulation. That's all I have for this video. I'll 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. 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
38. Animal Form and Function
Metabolism and Homeostasis
Video duration:
8mPlay a video:
Related Videos
Related Practice
Metabolism and Homeostasis practice set
- Problem sets built by lead tutorsExpert video explanations