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How Insulin And Glucose Are Involved In Cell Communication

Minireview Insulin Feedback Action On Pancreatic Β-cell Function

Minireview Insulin Feedback Action On Pancreatic Β-cell Function

1. Introduction In adult mammals, β-cells of the pancreatic islets of Langerhans are the only source for the peptide hormone insulin and therefore these cells are of vital importance in maintaining blood glucose homeostasis. β-cells not only produce insulin but secrete the hormone in amounts appropriate to the blood glucose concentration in order to keep blood glucose levels within narrow limits. Dysfunction of pancreatic β-cells is a major cause of the development of so-called non-insulin-dependent diabetes or type 2 diabetes mellitus, the most common metabolic disorder in man. Multiple signals of different origin guarantee appropriate β-cell function under both basal and glucose-stimulated conditions. These signals include humoral factors (hormones, vitamins, nutrients, ions, etc.), nerve stimulation, as well as factors of intraislet cell–cell communication. Whereas the paracrine effects on β-cells of glucagon, secreted from pancreatic α-cells and stimulating insulin release, and of somatostatin, secreted from δ-cells and inhibiting insulin release, are well accepted (for review see [1]), the autocrine effect of secreted insulin on β-cell function was and still is a matter of debate. Although the idea of an autocrine feedback by insulin is not new and dates back to the 1940s [2], both conceptual disagreement and different results in the respective experiments contribute to this still ongoing controversy. With regard to the conceptual disagreement, the major argument is that β-cells are exposed to so much insulin that the respective signal transduction pathways must be desensitized. Experimentally, with regard to the effect of insulin upon insulin secretion for example, all possible outcomes like negative feedback [3–8], positive feedback [9–11], and no Continue reading >>

Insulin Signal Transduction Pathway

Insulin Signal Transduction Pathway

The insulin transduction pathway is a biochemical pathway by which insulin increases the uptake of glucose into fat and muscle cells and reduces the synthesis of glucose in the liver and hence is involved in maintaining glucose homeostasis. This pathway is also influenced by fed versus fasting states, stress levels, and a variety of other hormones. When carbohydrates are consumed, digested, and absorbed the pancreas senses the subsequent rise in blood glucose concentration and releases insulin to promote an uptake of glucose from the blood stream. When insulin binds to the insulin receptor, it leads to a cascade of cellular processes that promote the usage or, in some cases, the storage of glucose in the cell. The effects of insulin vary depending on the tissue involved, e.g., insulin is most important in the uptake of glucose by muscle and adipose tissue. This insulin signal transduction pathway is composed of trigger mechanisms (e.g., autophosphorylation mechanisms) that serve as signals throughout the cell. There is also a counter mechanism in the body to stop the secretion of insulin beyond a certain limit. Namely, those counter-regulatory mechanisms are glucagon and epinephrine. The process of the regulation of blood glucose (also known as glucose homeostasis) also exhibits oscillatory behavior. On a pathological basis, this topic is crucial to understanding certain disorders in the body such as diabetes, hyperglycemia and hypoglycemia. Transduction pathway[edit] The functioning of a signal transduction pathway is based on extra-cellular signaling that in turn creates a response which causes other subsequent responses, hence creating a chain reaction, or cascade. During the course of signaling, the cell uses each response for accomplishing some kind of a purpose al Continue reading >>

Cell Signalling

Cell Signalling

4 Glucose metabolism: an example of integration of signalling pathways 4.1 Glucose metabolism We are now in a position to draw together the major concepts and components of signalling, and show how they operate in one well-understood system, namely the regulation of the storage or release of glucose in the human body. From this, you will be able to recognize archetypal pathways represented in specific examples, you will be able to appreciate how the same basic pathways can be stimulated by different hormones in different tissues, and you will see how opposing hormones activate separate pathways that affect the same targets but in opposite ways. Following a meal, insulin is released into the bloodstream by pancreatic β cells. The overall systemic effects of insulin are to increase uptake of blood glucose into cells, and to promote its storage as glycogen in muscle and liver cells. (Note that glycogen is a polysaccharide consisting of repeated units of glucose used for shortterm energy storage by animal cells.) A rise in the concentration of blood glucose, such as that following the consumption of food, stimulates insulin production, which signals through the insulin RTK. The insulin RTK phosphorylates various substrate proteins, which link to several key signalling pathways such as the Ras–MAP kinase pathway. There are, however, two major pathways that control glycogen synthesis and breakdown in animal cells (Figure 47). Figure 47 The control of glycogen synthesis by insulin. Several proteins bind, and are phosphorylated by, the activated insulin receptor. Cbl activates a pathway that is implicated in the translocation of the glucose transporter GLUT4 to the membrane, allowing glucose transport into the cell. Meanwhile, IRS-1 serves as a docking protein for PI 3-kinas Continue reading >>

How Involved Are Starch And Glucose Tests?

How Involved Are Starch And Glucose Tests?

I am not sure what you are asking. Starch testing is a big 0 in my understanding or recollection. Starch easily turns to glucose in the body, even in your mouth from saliva. Glucose testing has many possibilities. As a medical practitioner we have a few different glucose testing strategies to determine if someone is not controlling their blood glucose levels. Normal blood glucose in most conditions should be between 65-99 mg/dl. Strangely enough it used to be up to 120. When I was checked it was down to 110. Mine was 111 and both the doctor and I were not impressed. Six months later I was a full blown diabetic. Today random elevated blood glucose above 100 is technically suspect. The truth be known if you eat something and take the test which can be done today as a finger stick in five seconds. Anything below 140 can be seen as simply the body trying to accommodate the glucose load of a meal. Random blood glucose levels between 140-160 mg/dl are in the level of what may be pre-diabetes. Whereas anything with a random blood glucose greater than 160 is considered diagnostic for full diabetes. Now the advent of the hemoglobin A1c are much more accurate. This requires a blood draw from the arm, and results are available in 2 days. There are personal units at about $10 each that can be bought on the Relion brand from Wal-Mart and other pharmacies. They require a deep finger stick, and requires a 5 minute wait for results. They are accurate enough for Medicare to accept the results. So what are the results? This test determines what percentage of glucose has the red blood cells been floating in for the last 3 months. Normal is 4.8% to 5.6%. Pre-diabetes is 5.7% to 6.4%. Diabetes is 6.5% or greater. Controlled diabetes is under 8%. Uncontrolled diabetes is >8%. Severely uncont Continue reading >>

Glucose Insulin And Diabetes

Glucose Insulin And Diabetes

Every cell in the human body needs energy to survive and do its different functions. If we're talking about a brain cell, it needs energy to keep stimulating other brain cells and sending on signals and messages. If it's a muscle cell, it needs energy to contract. They need energy just to do the basic functions of a cell. And the place that they get that energy from, or the primary source of that energy, is from glucose. Glucose is a simple sugar. If you were to actually taste glucose, it would taste sweet. And glucose gets delivered to cells through the bloodstream. So this right here, I'm drawing some blood that's passing by a cell. Maybe the blood is going in that direction over there. And inside the blood, let me draw some small glucose molecules passing by. And so in an ideal situation, when a cell needs energy, glucose will enter the cell. Unfortunately, it's not that simple for the great majority of cells in the human body. The glucose won't enter by itself. It needs the assistance of a hormone or a molecule called insulin. So let me label all of these. This right here is the glucose, and it needs insulin. So let me draw insulin as these magenta molecules right over here. That over there, that is insulin. And the surface of the cells, they have insulin receptors on them. And I'm just drawing very simplified versions of them, kind of a place where these magenta circles can attach, can bind. And what happens is, in order for the glucose to be taken up by the cell, insulin has to attach to these receptors, which unlocks the channels for glucose. In order for the glucose to go in, insulin has to bind to the insulin receptors. And then, once that happens, then the glucose can be taken up by the cell. Now, unfortunately, things don't always work as planned. So let me d Continue reading >>

Hormones

Hormones

Hormones are chemicals messengers that travel in the blood. Hormonal communication is much slower than neural impulses. Response times of target organs can range from minutes to hours. However, hormones can have more widespread effects than neural impulses: Hormone is produced by an endocrine gland (hormone-secreting organ) Gland secretes hormone into the blood Hormone travels to the target organ(s) Target organs produce a response Hormones are removed from the blood and broken down by the liver. Glands and hormones are effectors. Glands respond to stimuli by altering the release of hormones. Before a meal, the gut secretes a hormone (ghrelin) which increases appetite! Hormones are the chemical messengers of the endocrine system. The endocrine system coordinates the release of hormones across all the glands in the body. Cell signalling describes the ways in which cells communicate. Extracellular chemical messages released from one cell can result in changes within another cell. There are several stages within cell signalling: Binding of the signal to the receptor (ligand-receptor interaction) Transduction of the signal - when a signalling molecule activates a receptor Cellular response Tyrosine kinase receptors and G-protein coupled receptors are common types of receptors. There are several common features of cell signalling pathways. One is the amplification of the signal and the other is the phosphorylation of intermediate reactants. Amplification is important as it allows for low concentrations of a hormone to have large effects within the cell. Insulin is a hormone. It lowers glucose levels in the blood. Insulin is released from cells in the islets of Langerhans of the pancreas. Insulin lowers glucose levels in the blood by: Increasing the permeability of cells to g Continue reading >>

Insulin Receptor

Insulin Receptor

The cellular receptor for insulin helps control the utilization of glucose by cells Cells throughout the body are fueled largely by glucose that is delivered through the bloodstream. A complex signaling system is used to control the process, ensuring that glucose is delivered when needed and stored when there is a surplus. Two hormones, insulin and glucagon, are at the center of this signaling system. When blood glucose levels drop, alpha cells in the pancreas release glucagon, which then stimulates liver cells to release glucose into the circulation. When blood glucose levels rise, on the other hand, beta cells in the pancreas release insulin, which promotes uptake of glucose for metabolism and storage. Both hormones are small proteins that are recognized by receptors on the surface of cells. Signal Transduction The receptor for insulin is a large protein that binds to insulin and passes its message into the cell. It has several functional parts. Two copies of the protein chains come together on the outside of the cell to form the receptor site that binds to insulin. This is connected through the membrane to two tyrosine kinases, shown here at the bottom. When insulin is not present, they are held in a constrained position, but when insulin binds, these constraints are released. They first phosphorylate and activate each other, and then phosphorylate other proteins in the signaling network inside the cell. Since the whole receptor is so flexible, researchers have determined its structure in several pieces: the insulin-binding portion is shown here from PDB entry 3loh , the transmembrane segment from 2mfr , and the tyrosine kinase from 1irk . When Things Go Wrong Problems with insulin signaling can impair the proper management of glucose levels in the blood, leading to Continue reading >>

Get Unlimited Access On Medscape.

Get Unlimited Access On Medscape.

You’ve become the New York Times and the Wall Street Journal of medicine. A must-read every morning. ” Continue reading >>

Diabetes: What’s Insulin Resistance Got To Do With It?

Diabetes: What’s Insulin Resistance Got To Do With It?

Invisible changes in the body begin long before a person is diagnosed with type 2 diabetes. That’s both bad news (no symptoms mean you won’t know you have it) and good news (you can prevent or delay it if you’re at risk). One of the most important unseen changes? Insulin resistance. Insulin in a Nutshell Insulin is a key player in developing type 2 diabetes. This vital hormone—you can’t survive without it—regulates blood sugar (glucose) in the body, a very complicated process. Here are the high points: The food you eat is broken down into glucose. Glucose enters your bloodstream, which signals the pancreas to release insulin. Insulin helps glucose enter the body’s cells so it can be used for energy. Insulin also signals the liver to store glucose for later use. Glucose enters cells, and glucose levels in the bloodstream decrease, signaling insulin to decrease too. Lower insulin levels alert the liver to release stored glucose so energy is always available, even if you haven’t eaten for a while. That’s when everything works smoothly. But this finely tuned system can quickly get out of whack, as follows: A lot of glucose enters the bloodstream. The pancreas pumps out more insulin to get glucose into cells. Over time, cells stop responding to all that insulin—they’ve become insulin resistant. The pancreas keeps making more insulin to try to make cells respond. Eventually, the pancreas can’t keep up, and glucose keeps rising. Now What? Lots of glucose in the bloodstream is very damaging to the body and needs to be moved into cells as soon as possible. There’s lots of insulin, too, telling the liver and muscles to store glucose. When they’re full, the liver sends the excess glucose to fat cells to be stored as body fat. Yep, weight gain. And what Continue reading >>

Normal Regulation Of Blood Glucose

Normal Regulation Of Blood Glucose

The human body wants blood glucose (blood sugar) maintained in a very narrow range. Insulin and glucagon are the hormones which make this happen. Both insulin and glucagon are secreted from the pancreas, and thus are referred to as pancreatic endocrine hormones. The picture on the left shows the intimate relationship both insulin and glucagon have to each other. Note that the pancreas serves as the central player in this scheme. It is the production of insulin and glucagon by the pancreas which ultimately determines if a patient has diabetes, hypoglycemia, or some other sugar problem. In this Article Insulin Basics: How Insulin Helps Control Blood Glucose Levels Insulin and glucagon are hormones secreted by islet cells within the pancreas. They are both secreted in response to blood sugar levels, but in opposite fashion! Insulin is normally secreted by the beta cells (a type of islet cell) of the pancreas. The stimulus for insulin secretion is a HIGH blood glucose...it's as simple as that! Although there is always a low level of insulin secreted by the pancreas, the amount secreted into the blood increases as the blood glucose rises. Similarly, as blood glucose falls, the amount of insulin secreted by the pancreatic islets goes down. As can be seen in the picture, insulin has an effect on a number of cells, including muscle, red blood cells, and fat cells. In response to insulin, these cells absorb glucose out of the blood, having the net effect of lowering the high blood glucose levels into the normal range. Glucagon is secreted by the alpha cells of the pancreatic islets in much the same manner as insulin...except in the opposite direction. If blood glucose is high, then no glucagon is secreted. When blood glucose goes LOW, however, (such as between meals, and during Continue reading >>

Facts About Diabetes And Insulin

Facts About Diabetes And Insulin

Diabetes is a very common disease, which, if not treated, can be very dangerous. There are two types of diabetes. They were once called juvenile-onset diabetes and adult diabetes. However, today we know that all ages can get both types so they are simply called type 1 and type 2 diabetes. Type 1, which occurs in approximately 10 percent of all cases, is an autoimmune disease in which the immune system, by mistake, attacks its own insulin-producing cells so that insufficient amounts of insulin are produced - or no insulin at all. Type 1 affects predominantly young people and usually makes its debut before the age of 30, and most frequently between the ages of 10 and 14. Type 2, which makes up the remaining 90 percent of diabetes cases, commonly affects patients during the second half of their lives. The cells of the body no longer react to insulin as they should. This is called insulin resistance. In the early 1920s, Frederick Banting, John Macleod, George Best and Bertram Collip isolated the hormone insulin and purified it so that it could be administered to humans. This was a major breakthrough in the treatment of diabetes type 1. Insulin Insulin is a hormone. Hormones are chemical substances that regulate the cells of the body and are produced by special glands. The hormone insulin is a main regulator of the glucose (sugar) levels in the blood. Insulin is produced in the pancreas. To be more specific, it's produced by the beta cells in the islets of Langerhans in the pancreas. When we eat, glucose levels rise, and insulin is released into the bloodstream. The insulin acts like a key, opening up cells so they can take in the sugar and use it as an energy source. Sugar is one of the top energy sources for the body. The body gets it in many forms, but mainly as carbohydr Continue reading >>

Cell Signalling

Cell Signalling

Cells need to interact with their environment and other cells around them. This is called Cell Signalling. Single cellular organisms need to detect nutrients in their environment, and cells in multicellular organisms are involved in a complex system of communication with each other. Cells detect signals with Cell Receptors on their plasma membrane, which are usually Glycoproteins or Glycolipids. The signalling molecule binds to the Repeptor because its shape is complementary. This then instigates a chain of reaction withing the cell, leading to a response. Cell Signalling Pathways can be categorised based the distance over which the signalling occurs. Endocrine Signalling involves signalling over large distances, often where the signalling molecule is transported in the circulatory system Paracrine Signalling occurs between cells which are close together, sometime directly, sometimes via extracellular fluid Autocrine Signalling is where the cell stimulates a response within itself by releasing signals for its own Receptors Hormones are often used as cell signalling molecules in multicellular organisms. Hormones are produced in a cell, sometimes in response to environmental changes. The Hormones are are released and bind to Receptor Sites on a Target Cell, which starts a response. An example of a hormone mediated cell signalling pathway is in the use of Insulin to lower blood glucose levels. In response to high glucose levels, Beta-Cells in the pancreas release the hormone Insulin in to the blood, which binds to cells such as muscle and liver cells. This causes them to take up more glucose. Some Medicinal Drugs work because they are complementary to certain Cell Receptor Sites. Some drugs block these Receptors so that they natural signalling molecules cannot instigate a Continue reading >>

Glucose Represses Connexin36 In Insulin-secreting Cells

Glucose Represses Connexin36 In Insulin-secreting Cells

The gap-junction protein connexin36 (Cx36) contributes to control the functions of insulin-producing cells. In this study, we investigated whether the expression of Cx36 is regulated by glucose in insulin-producing cells. Glucose caused a significant reduction of Cx36 in insulin-secreting cell lines and freshly isolated pancreatic rat islets. This decrease appeared at the mRNA and the protein levels in a dose- and time-dependent manner. 2-Deoxyglucose partially reproduced the effect of glucose, whereas glucosamine, 3-O-methyl-D-glucose and leucine were ineffective. Moreover, KCl-induced depolarization of β-cells had no effect on Cx36 expression, indicating that glucose metabolism and ATP production are not mandatory for glucose-induced Cx36 downregulation. Forskolin mimicked the repression of Cx36 by glucose. Glucose or forskolin effects on Cx36 expression were not suppressed by the L-type Ca2+-channel blocker nifedipine but were fully blunted by the cAMP-dependent protein kinase (PKA) inhibitor H89. A 4 kb fragment of the human Cx36 promoter was identified and sequenced. Reporter-gene activity driven by various Cx36 promoter fragments indicated that Cx36 repression requires the presence of a highly conserved cAMP responsive element (CRE). Electrophoretic-mobility-shift assays revealed that, in the presence of a high glucose concentration, the binding activity of the repressor CRE-modulator 1 (CREM-1) is enhanced. Taken together, these data provide evidence that glucose represses the expression of Cx36 through the cAMP-PKA pathway, which activates a member of the CRE binding protein family. The homeostasis of multicellular organisms depends on many systems allowing the cells to review the functional state of their neighbors (Spray, 1998). Channels located at gap juncti Continue reading >>

Role Of Insulin And Other Hormones In Diabetes

Role Of Insulin And Other Hormones In Diabetes

SHARE RATE★★★★★ Insulin and glucose Our bodies require energy to function properly and we get that energy from three food groups: protein, fat, and carbohydrates (sugars, starches, and fibers). When the body digests carbohydrates, they are transformed through digestion into a very important source of instant energy, a form of sugar called glucose.1,2 Three forms of simple sugars (also called monosaccharides) are able to enter the bloodstream directly after digestion. These are often broken down from more complex sugars (polysaccharides and disaccharides). These simple sugars include glucose (found in most carbohydrates, including grains and starches), fructose (found in fruits and vegetables), and galactose (found in dairy products and in certain vegetables). The word glucose comes from the Greek word for sweet, and it is the key source of energy for cells in the body. Upon digestion, glucose can be used for instant energy or stored in the form of glycogen when the body’s energy needs are being met.1,2 Hormones and glucose control Our bodies depend on the action of a number of different hormones, working together in conjunction, to control how we use glucose. We depend on insulin, a hormone produced in the beta cells of the pancreas (an organ located behind the stomach) to use glucose. Insulin serves as sort of a “gate keeper,” allowing glucose to enter cells where it can be transformed into energy and used to support vital cell functions. Insulin also has other important functions related to the way our body uses glucose.3,4 In addition to insulin, another hormone produced by beta cells called amylin controls how quickly glucose is released into the blood stream after a meal. It does this by slowing emptying of the stomach and increasing the feeling tha Continue reading >>

Insulin Secretion And Sensitivity

Insulin Secretion And Sensitivity

Introduction In the 1930s Sir Harold Himsworth devised a primitive test of glucose disposal in response to insulin injection, and made the key observation that lean young people with or without diabetes respond similarly, whereas older overweight people with diabetes require much more insulin to achieve the same effect. From this he inferred that there were two types of diabetes: an insulin-sensitive form due to simple insulin deficiency, and an insulin-insensitive form in which the tissues were resistant to the actions of insulin.[1] In recent decades, observations in high-risk relatives have shown that clinical onset of type 1 diabetes is preceded by progressive glucose intolerance, loss of the FPIR, and loss of pulsatile insulin secretion. Progression to diabetes is more rapid in those who are less sensitive to insulin. Insulin secretion There are sub-populations of beta cells within healthy islets, and these have varying levels of responsiveness to glucose. Those with a low threshold for response are more active at normal glucose levels; others cut in at higher glucose levels.[2] Fully functional beta cells are metabolically very active, shedding and replacing 30–50% of their surface membrane daily in the course of insulin secretion. A lean healthy individual might secrete about 35 units of insulin per day, yet will have about 10 times this amount stored within his pancreas. By contrast, an obese insulin-resistant person might need to produce >100 units daily to maintain normal blood glucose levels. Type 1 diabetes results from progressive beta cell loss by apoptosis, thus increasing the work-load of the residue. A further consequence is loss of beta to beta cell communication and an altered cell-to-cell (paracrine) interaction between beta cells and glucagon-prod Continue reading >>

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