Insulin: Difference between revisions

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Insulin is constantly released into the blood stream at a basal level. When blood glucose levels rise after a meal containing carbohydrates (sugars and starches), increased intracellular glucose in the beta cells triggers a series of processes that change the intracellular calcium concentration. First, the calcium concentration rises and stays elevated for 5-10 minutes, and then it spikes in intervals of roughly 3 minutes. Whenever calcium concentrations are high, insulin-containing vesicles merge with the plasma membrane, releasing insulin into the blood stream in the same temporal pattern as the calcium spikes<ref>DOI: 10.1007/s00125-009-1314-y</ref>. The insulin is released into the bloodstream, where it first reaches the liver via the portal vein<ref>"https://www.diabetesselfmanagement.com/diabetes-resources/definitions/portal-vein/"</ref>, and then the other organs after insulin-containing blood returns from the heart.

[[Image:Insulin receptor cartoon.gif|frame|Artist's conception of insulin receptor (purple) binding to insulin outside of the cell and being phosphorylated inside of the cell]]Liver cells and other cells contain [[insulin receptor|receptors]] with insulin binding sites on the cell surface. These intermembrane receptors<ref>https://pdb101.rcsb.org/motm/182</ref> change conformation upon insulin binding, activating intracellular tyrosine kinase domains<ref name="gutmann">DOI: 10.1083/jcb.201711047</ref>. This starts a signalling cascade within the cell that changes glucose uptake as well as carbohydrate and lipid metabolism. The liver stores available glucose in the form of glycogen and, when there is additional glucose, converts it into fatty acids and carbon dioxide. Cells in other organs (e.g. adipose tissue, muscles) also alter their metabolism depending on insulin levels.

[[Image:Insulin receptor cartoon.gif|frame|Artist's conception of insulin receptor (purple) binding to insulin outside of the cell and being phosphorylated inside of the cell]]Liver cells and other cells contain [[insulin receptor|receptors]] with insulin binding sites on the cell surface. These intermembrane receptors<ref>https://pdb101.rcsb.org/motm/182</ref> change conformation upon insulin binding, activating intracellular tyrosine kinase domains<ref name="gutmann">DOI: 10.1083/jcb.201711047</ref>. This starts a signalling cascade within the cell that changes glucose uptake as well as carbohydrate and lipid metabolism<ref>http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/pancreas/insulin_phys.html</ref>. The liver stores available glucose in the form of glycogen and, when there is additional glucose, converts it into fatty acids and carbon dioxide. Cells in other organs (e.g. adipose tissue, muscles) also alter their metabolism depending on insulin levels.

Once insulin binds to its receptor, the receptor is removed from the plasma membrane, insulin is degraded and the receptor is recycled<ref>PMID:28974775</ref>. The majority of insulin is removed from the bloodstream this way on its first pass through the liver. The half-life of insulin in the blood plasma is about about 4-6 minutes<ref>DOI:10.1210/edrv.19.5.0349</ref>.

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 Insulin is constantly released into the blood stream at a basal level. When blood glucose levels rise after a meal containing carbohydrates (sugars and starches), increased intracellular glucose in the beta cells triggers a series of processes that change  the intracellular calcium concentration. First, the calcium concentration rises and stays elevated for 5-10 minutes, and then it spikes in intervals of roughly 3 minutes. Whenever calcium concentrations are high, insulin-containing vesicles merge with the plasma membrane, releasing insulin into the blood stream in the same temporal pattern as the calcium spikes<ref>DOI: 10.1007/s00125-009-1314-y</ref>. The insulin is released into the bloodstream, where it first reaches the liver via the portal vein<ref>"https://www.diabetesselfmanagement.com/diabetes-resources/definitions/portal-vein/"</ref>, and then the other organs after insulin-containing blood returns from the heart.
-[[Image:Insulin receptor cartoon.gif|frame|Artist's conception of insulin receptor (purple) binding to insulin outside of the cell and being phosphorylated inside of the cell]]Liver cells and other cells contain [[insulin receptor|receptors]] with insulin binding sites on the cell surface. These intermembrane receptors<ref>https://pdb101.rcsb.org/motm/182</ref> change conformation upon insulin binding, activating intracellular tyrosine kinase domains<ref name="gutmann">DOI: 10.1083/jcb.201711047</ref>. This starts a signalling cascade within the cell that changes glucose uptake as well as carbohydrate and lipid metabolism. The liver stores  available glucose in the form of glycogen and, when there is additional glucose, converts it into fatty acids and carbon dioxide. Cells in other organs (e.g. adipose tissue, muscles) also alter their metabolism depending on insulin levels.
+[[Image:Insulin receptor cartoon.gif|frame|Artist's conception of insulin receptor (purple) binding to insulin outside of the cell and being phosphorylated inside of the cell]]Liver cells and other cells contain [[insulin receptor|receptors]] with insulin binding sites on the cell surface. These intermembrane receptors<ref>https://pdb101.rcsb.org/motm/182</ref> change conformation upon insulin binding, activating intracellular tyrosine kinase domains<ref name="gutmann">DOI: 10.1083/jcb.201711047</ref>. This starts a signalling cascade within the cell that changes glucose uptake as well as carbohydrate and lipid metabolism<ref>http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/pancreas/insulin_phys.html</ref>. The liver stores  available glucose in the form of glycogen and, when there is additional glucose, converts it into fatty acids and carbon dioxide. Cells in other organs (e.g. adipose tissue, muscles) also alter their metabolism depending on insulin levels.
 Once insulin binds to its receptor, the receptor is removed from the plasma membrane, insulin is degraded and the receptor is recycled<ref>PMID:28974775</ref>. The majority of insulin is removed from the bloodstream this way on its first pass through the liver. The half-life of insulin in the blood plasma is about about 4-6 minutes<ref>DOI:10.1210/edrv.19.5.0349</ref>.