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Insulin is produced by the pancreas in a region called islets of Langerhans. In the islets of Langerhans, there are beta-cells, which are responsible for production and storage of insulin. Insulin is secreted as a response mechanism for counteracting the increasing excess amounts of glucose in the blood.
Increased insulin levels cause the uptake of glucose into the cells. GLUT4 is stored in the cell in transport vesicles, and is quickly incorporated into the plasma membrane of the cell when insulin binds to membrane receptors. [24] Under conditions of low insulin, most GLUT4 is sequestered in intracellular vesicles in muscle and fat cells.
This hormone, insulin, causes the liver to convert more glucose into glycogen (this process is called glycogenesis), and to force about 2/3 of body cells (primarily muscle and fat tissue cells) to take up glucose from the blood through the GLUT4 transporter, thus decreasing blood sugar.
GLUT4 transporters are insulin sensitive, and are found in muscle and adipose tissue. As muscle is a principal storage site for glucose and adipose tissue for triglyceride (into which glucose can be converted for storage), GLUT4 is important in post-prandial uptake of excess glucose from the bloodstream. Moreover, several recent papers show ...
Levels in cell membranes are increased by reduced glucose levels and decreased by increased glucose levels. GLUT1 expression is upregulated in many tumors. GLUT2: Is a bidirectional transporter, allowing glucose to flow in 2 directions. Is expressed by renal tubular cells, liver cells and pancreatic beta cells.
This is possible because Insulin causes the insertion of the GLUT4 transporter in the cell membranes of muscle and fat tissues which allows glucose to enter the cell. [66] Increased fat synthesis – insulin forces fat cells to take in blood glucose, which is converted into triglycerides; decrease of insulin causes the reverse. [71]
The net effect is an increase of free cortisol. This contributes to insulin resistance of pregnancy and possibly striae. [5] Despite the increase in cortisol, the pregnant mom does not exhibit Cushing syndrome or symptoms of high cortisol. One theory is that high progesterone levels act as an antagonist to the cortisol.
When insulin is secreted, glucose uptake of cells increase, since insulin stimulates GLUT4 to move from the intracellular surface to the outer surface. In a similar fashion, TUG retains GLUT4 within unstimulated cells, but when insulin is secreted it causes GLUT4 to dissociate and so GLUT4 moves to the cell surface. TUG binds directly and ...