imported>Chunbum Park |
imported>John Stephenson |
| (220 intermediate revisions by 8 users not shown) |
| Line 1: |
Line 1: |
| '''[[Gut-brain signalling]]''' describes the interaction between the gastrointestinal tract and the brain, and how secretion of varying hormones from different areas of the body causes appetite-enhancing and satiety signals to be sent to the brain. The hormones that have been most intensely studied are: ghrelin, obestatin, cholecystokinin (CCK), GLP-1, peptide YY (PYY) and insulin which all play major roles in appetite regulation. The vagus nerve is also a key mediator of regulation, and all of these inputs are processed by areas in the brain such as the hypothalamus and the nucleus tractus solitarii (NTS).
| | {{:{{FeaturedArticleTitle}}}} |
| | | <small> |
| ==Anorexic Signals== | | ==Footnotes== |
| {{Image|diagram 3.jpg|right|400px|''Gut-Brain signaling Pathways'' Proteins and hormones activate brain pathways in different ways, either by eventual vagal activation or through peripheral circulation. The nucleus tractus solitarii and the arcuate nucleus are then activated. }} | | {{reflist|2}} |
| '''Cholecystokinin''' (CCK) is a peptide hormone synthesised by L-cells in the mucosal epithelium of the duodenum, and secreted in response to the presence of partly digested lipids and protein]]s. CCK inhibits gastric emptying and stimulates the release of digestive enzymes from the pancreas and bile from the gall bladder by acting at CCK-A receptors (mainly found in the periphery but also found in some areas of the CNS). Because gastric emptying is inhibited, the partly digested lipids and proteins are exposed to the digestive enzymes and bile so are further broken down. As the lipids and proteins are broken down, CCK secretion declines.
| | </small> |
| | |
| CCK acts as a ‘gatekeeper’ for the response of other gut-brain signalling hormones on the afferent vagal neurons. At low levels (after fasting), CCK stimulates the expression of receptors associated with the stimulation of food intake, including receptors for melanin concentrating hormone (MCH)-1 and cannabinoid CB1 receptors. At high levels (after food consumption), MCH-1 and CB1 receptors are down- regulated. Therefore CCK, at a high or low concentration, can affect how afferent vagal neurons respond to other neurohormones.
| |
| | |
| In rats, CCK inhibits food intake in younger individuals more effectively than in older individuals. It also has a greater effect in males than in females.
| |
| | |
| '''Glucagon-like peptide-1''' (GLP-1) is a hormone secreted from L-cells in the mucosal epithelium of the duodenum and small intestine. It is derived from the ''pro-glucagon'' gene, and is secreted into the circulation in response to the presence of nutrients. It acts at the pancreas, where it stimulates insulin secretion and suppresses glucagon secretion. It also increases insulin sensitivity. GLP-1 also activates anorexigenic neurons in the arcuate nucleus via the caudal brainstem. Activation of these neurons induces satiety and decreases food intake/hunger. It also decreases gastric emptying, so adds to the feeling of being ‘full’. At higher concentrations, GLP-1 causes nausea, and can induce conditioned taste aversion, where the brain associates the taste of a certain food with being toxic (usually after an individual consumes a food that had made them sick).
| |
| | |
| [[Gut-brain signalling|.....]]
| |
Latest revision as of 09:19, 11 September 2020
After decades of failure to slow the rising global consumption of coal, oil and gas,[1] many countries have proceeded as of 2024 to reconsider nuclear power in order to lower the demand for fossil fuels.[2] Wind and solar power alone, without large-scale storage for these intermittent sources, are unlikely to meet the world's needs for reliable energy.[3][4][5] See Figures 1 and 2 on the magnitude of the world energy challenge.
Nuclear power plants that use nuclear reactors to create electricity could provide the abundant, zero-carbon, dispatchable[6] energy needed for a low-carbon future, but not by simply building more of what we already have. New innovative designs for nuclear reactors are needed to avoid the problems of the past.
(CC) Image: Geoff Russell Fig.1 Electricity consumption may soon double, mostly from coal-fired power plants in the developing world.
[7] Issues Confronting the Nuclear Industry
New reactor designers have sought to address issues that have prevented the acceptance of nuclear power, including safety, waste management, weapons proliferation, and cost. This article will summarize the questions that have been raised and the criteria that have been established for evaluating these designs. Answers to these questions will be provided by the designers of these reactors in the articles on their designs. Further debate will be provided in the Discussion and the Debate Guide pages of those articles.
- ↑ Global Energy Growth by Our World In Data
- ↑ Countries, organizations, and public figures that have reconsidered their stance on nuclear power are listed on the External Links tab of this article.
- ↑ Pumped storage is currently the most economical way to store electricity, but it requires a large reservoir on a nearby hill or in an abandoned mine. Li-ion battery systems at $500 per KWh are not practical for utility-scale storage. See Energy Storage for a summary of other alternatives.
- ↑ Utilities that include wind and solar power in their grid must have non-intermittent generating capacity (typically fossil fuels) to handle maximum demand for several days. They can save on fuel, but the cost of the plant is the same with or without intermittent sources.
- ↑ Mark Jacobson believes that long-distance transmission lines can provide an alternative to costly storage. See the bibliography for more on this proposal and the critique by Christopher Clack.
- ↑ "Load following" is the term used by utilities, and is important when there is a lot of wind and solar on the grid. Some reactors are not able to do this.
- ↑ Fig.1.3 in Devanney "Why Nuclear Power has been a Flop"
