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What Do Insulin And Glucagon Regulate

Physiology Of The Pancreatic Α-cell And Glucagon Secretion: Role In Glucose Homeostasis And Diabetes

Physiology Of The Pancreatic Α-cell And Glucagon Secretion: Role In Glucose Homeostasis And Diabetes

Abstract The secretion of glucagon by pancreatic α-cells plays a critical role in the regulation of glycaemia. This hormone counteracts hypoglycaemia and opposes insulin actions by stimulating hepatic glucose synthesis and mobilization, thereby increasing blood glucose concentrations. During the last decade, knowledge of α-cell physiology has greatly improved, especially concerning molecular and cellular mechanisms. In this review, we have addressed recent findings on α-cell physiology and the regulation of ion channels, electrical activity, calcium signals and glucagon release. Our focus in this review has been the multiple control levels that modulate glucagon secretion from glucose and nutrients to paracrine and neural inputs. Additionally, we have described the glucagon actions on glycaemia and energy metabolism, and discussed their involvement in the pathophysiology of diabetes. Finally, some of the present approaches for diabetes therapy related to α-cell function are also discussed in this review. A better understanding of the α-cell physiology is necessary for an integral comprehension of the regulation of glucose homeostasis and the development of diabetes. Introduction The principal level of control on glycaemia by the islet of Langerhans depends largely on the coordinated secretion of glucagon and insulin by α- and β-cells respectively. Both cell types respond oppositely to changes in blood glucose concentration: while hypoglycaemic conditions induce α-cell secretion, β-cells release insulin when glucose levels increase (Nadal et al. 1999, Quesada et al. 2006a). Insulin and glucagon have opposite effects on glycaemia as well as on the metabolism of nutrients. Insulin acts mainly on muscle, liver and adipose tissue with an anabolic effect, inducing th Continue reading >>

Islets Of Langerhans

Islets Of Langerhans

Islets of Langerhans, also called islands of Langerhans, irregularly shaped patches of endocrine tissue located within the pancreas of most vertebrates. They are named for the German physician Paul Langerhans, who first described them in 1869. The normal human pancreas contains about 1,000,000 islets. The islets consist of four distinct cell types, of which three (alpha, beta, and delta cells) produce important hormones; the fourth component (C cells) has no known function. The most common islet cell, the beta cell, produces insulin, the major hormone in the regulation of carbohydrate, fat, and protein metabolism. Insulin is crucial in several metabolic processes: it promotes the uptake and metabolism of glucose by the body’s cells; it prevents release of glucose by the liver; it causes muscle cells to take up amino acids, the basic components of protein; and it inhibits the breakdown and release of fats. The release of insulin from the beta cells can be triggered by growth hormone (somatotropin) or by glucagon, but the most important stimulator of insulin release is glucose; when the blood glucose level increases—as it does after a meal—insulin is released to counter it. The inability of the islet cells to make insulin or the failure to produce amounts sufficient to control blood glucose level are the causes of diabetes mellitus. The alpha cells of the islets of Langerhans produce an opposing hormone, glucagon, which releases glucose from the liver and fatty acids from fat tissue. In turn, glucose and free fatty acids favour insulin release and inhibit glucagon release. The delta cells produce somatostatin, a strong inhibitor of somatotropin, insulin, and glucagon; its role in metabolic regulation is not yet clear. Somatostatin is also produced by the hypothalamu Continue reading >>

Insulin Vs Glucagon

Insulin Vs Glucagon

Insulin and glucagon have both similarities and differences. Both are hormones secreted by the pancreas but they are made from different types of cells in the pancreas. Both help manage the blood glucose levels in the body but they have opposite effects. Both respond to blood glucose levels but they have opposite effects. Each of us has insulin and glucagon in our systems because it is a strict requirement that the blood sugar level in the body is kept in a narrow therapeutic range. You need both insulin and glucagon to respond to various levels of glucose in the bloodstream. While insulin responds and is secreted by the pancreas upon having high glucose levels in the bloodstream, glucagon responds and is secreted by the pancreas upon having low glucose levels in the bloodstream. This maintains homeostasis in the body and keeps the blood sugar stable at all times. Function of Insulin Insulin is a protein-based hormone that is secreted by the beta cells inside the pancreas whenever the pancreas senses that the blood sugar is too high. Low levels of insulin are constantly being secreted into the bloodstream by the pancreas, even when blood glucose levels are normal. After you eat a meal, the glucose from the food you eat is taken up by the gastrointestinal tract, increasing the level of glucose in the blood. When this happens, the beta cells get activated and more insulin is secreted to help decrease the glucose levels, primarily by helping the glucose enter the cells to be used as cellular fuel. When the glucose level in the blood decreases, insulin levels by the islet (beta) cells of the pancreas return to a baseline status. In response to the elevated insulin level, the various cells of the body bind to insulin and the insulin facilitates the transfer of glucose from t Continue reading >>

How Insulin And Glucagon Work

How Insulin And Glucagon Work

Insulin and glucagon are hormones that help regulate the levels of blood glucose, or sugar, in your body. Glucose, which comes from the food you eat, moves through your bloodstream to help fuel your body. Insulin and glucagon work together to balance your blood sugar levels, keeping them in the narrow range that your body requires. These hormones are like the yin and yang of blood glucose maintenance. Read on to learn more about how they function and what can happen when they don’t work well. Insulin and glucagon work in what’s called a negative feedback loop. During this process, one event triggers another, which triggers another, and so on, to keep your blood sugar levels balanced. How insulin works During digestion, foods that contain carbohydrates are converted into glucose. Most of this glucose is sent into your bloodstream, causing a rise in blood glucose levels. This increase in blood glucose signals your pancreas to produce insulin. The insulin tells cells throughout your body to take in glucose from your bloodstream. As the glucose moves into your cells, your blood glucose levels go down. Some cells use the glucose as energy. Other cells, such as in your liver and muscles, store any excess glucose as a substance called glycogen. Your body uses glycogen for fuel between meals. Read more: Simple vs. complex carbs » How glucagon works Glucagon works to counterbalance the actions of insulin. About four to six hours after you eat, the glucose levels in your blood decrease, triggering your pancreas to produce glucagon. This hormone signals your liver and muscle cells to change the stored glycogen back into glucose. These cells then release the glucose into your bloodstream so your other cells can use it for energy. This whole feedback loop with insulin and gluca Continue reading >>

How Insulin And Glucagon Work To Regulate Blood Sugar Levels

How Insulin And Glucagon Work To Regulate Blood Sugar Levels

The pancreas secretes insulin and glucagon, both of which play a vital role in regulating blood sugar levels. The two hormones work in balance. If the level of one hormone is outside the ideal range, blood sugar levels may spike or drop. Together, insulin and glucagon help keep conditions inside the body steady. When blood sugar is too high, the pancreas secretes more insulin. When blood sugar levels drop, the pancreas releases glucagon to bring them back up. Blood sugar and health The body converts carbohydrates from food into sugar (glucose), which serves as a vital source of energy. Blood sugar levels vary throughout the day but, in most instances, insulin and glucagon keep these levels normal. Health factors including insulin resistance, diabetes, and problems with diet can cause a person's blood sugar levels to soar or plummet. Blood sugar levels are measured in milligrams per decilitre (mg/dl). Ideal blood sugar ranges are as follows: Before breakfast - levels should be less than 100 mg/dl for a person without diabetes and 70-130 mg/dl for a person with diabetes. Two hours after meals - levels should be less than 140 mg/dl for a person without diabetes and less than 180 mg/dl for a person with diabetes. Blood sugar regulation Blood sugar levels are a measure of how effectively an individual's body uses glucose. When the body does not convert enough glucose for use, blood sugar levels remain high. Insulin helps the body's cells absorb glucose, lowering blood sugar and providing the cells with the glucose they need for energy. When blood sugar levels are too low, the pancreas releases glucagon. Glucagon forces the liver to release stored glucose, which causes the blood sugar to rise. Insulin and glucagon are both released by islet cells in the pancreas. These cells Continue reading >>

Regulation Of Insulin And Glucagon Secretion

Regulation Of Insulin And Glucagon Secretion

Insulin and glucagon secretion is largely regulated by the plasma concentrations of glucose and, to a lesser degree, of amino acids. The alpha and beta cells, therefore, act as both the sensors and effectors in this control system. Since the plasma concentration of glucose and amino acids rises during the absorption of a meal and falls during fasting, the secretion of insulin and glucagon likewise fluctuates between the absorptive and postabsorptive states. These changes in insulin and gluca-gon secretion, in turn, cause changes in plasma glucose and amino acid concentrations and thus help to maintain homeosta-sis via negative feedback loops (fig. 19.6). As described in chapter 6, insulin stimulates the insertion of GLUT4 channels into the plasma membrane (due to the fusion of intracellular vesicles with the plasma membrane—see fig. 6.15) of its target cells, primarily in the skeletal and cardiac muscles, adipose tissue, and liver. This permits the entry of glucose into its target cells by facilitated diffusion. As a result, in- ■ Figure 19.6 The regulation of insulin and glucagon secretion. The secretion from the P (beta) cells and a (alpha) cells of the pancreatic islets is regulated largely by the blood glucose concentration. (a) A high blood glucose concentration stimulates insulin and inhibits glucagon secretion. (b) A low blood glucose concentration stimulates glucagon and inhibits insulin secretion. sulin promotes the production of the energy-storage molecules of glycogen and fat. Both actions decrease the plasma glucose concentration. Insulin also inhibits the breakdown of fat, induces the production of fat-forming enzymes, and inhibits the breakdown of muscle proteins. Thus, insulin promotes an-abolism as it regulates the blood glucose concentration. The me Continue reading >>

Insulin And Glucagon Postabsorptive State

Insulin And Glucagon Postabsorptive State

The plasma glucose concentration is maintained surprisingly constant during the fasting, or postabsorptive, state because of the secretion of glucose from the liver. This glucose is derived from the processes of glycogenolysis and gluconeogenesis, which are promoted by a high secretion of glucagon coupled with a low secretion of insulin. Glucagon stimulates and insulin suppresses the hydrolysis of liver glycogen, or glycogenolysis. Thus during times of fasting, when glucagon secretion is high and insulin secretion is low, liver glycogen is used as a source of additional blood glucose. This results in the liberation of free glucose from glucose 6-phosphate by the action of an enzyme called glucose 6-phosphatase (chapter 5; see fig. 5.4). Only the liver has this enzyme, and therefore only the liver can use its stored glycogen as a source of additional blood glucose. Since muscles lack glucose 6-phosphatase, the glucose 6-phosphate produced from muscle glycogen can be used for glycolysis only by the muscle cells themselves. Since there are only about 100 grams of stored glycogen in the liver, adequate blood glucose levels could not be maintained 614 Chapter Nineteen Fasting (i insulin, T glucagon) ■ Figure 19.9 Catabolism during fasting. Increased glucagon secretion and decreased insulin secretion during fasting favors catabolism. These hormonal changes promote the release of glucose, fatty acids, ketone bodies, and amino acids into the blood. Notice that the liver secretes glucose that is derived both from the breakdown of liver glycogen and from the conversion of amino acids in gluconeogenesis. for very long during fasting using this source alone. The low levels of insulin secretion during fasting, together with elevated glu-cagon secretion, however, promote gluconeoge Continue reading >>

What Is Glucagon?

What Is Glucagon?

Tweet The effects of glucagon are the opposite of the effects induced by insulin. The two hormones need to work in partnership with each other to keep blood glucose levels balanced. Glucagon is a hormone that is produced by alpha cells in a part of the pancreas known as the islets of Langerhans. The role of glucagon in the body Glucagon plays an active role in allowing the body to regulate the utilisation of glucose and fats. Glucagon is released in response to low blood glucose levels and to events whereby the body needs additional glucose, such as in response to vigorous exercise. When glucagon is released it can perform the following tasks: Stimulating the liver to break down glycogen to be released into the blood as glucose Activating gluconeogenesis, the conversion of amino acids into glucose Breaking down stored fat (triglycerides) into fatty acids for use as fuel by cells Glucagon and blood glucose levels Glucagon serves to keep blood glucose levels high enough for the body to function well. When blood glucose levels are low, glucagon is released and signals the liver to release glucose into the blood. Glucagon secretion in response to meals varies depending on what we eat: In response to a carbohydrate based meal, glucagon levels in the blood fall to prevent blood glucose rising too high. In response to a high protein meal, glucagon levels in the blood rise. Glucagon in diabetes In people with diabetes, glucagon’s presence can raise blood glucose levels too high. The reason for this is either because not enough insulin is present or, as is the case in type 2 diabetes, the body is less able to respond to insulin. In type 1 diabetes, high levels of circulating insulin can inhibit the release of glucagon in response to hypoglycemia. Medications which affect gluca Continue reading >>

How Diabetes Works

How Diabetes Works

Since diabetes is a disease that affects your body's ability to use glucose, let's start by looking at what glucose is and how your body controls it. Glucose is a simple sugar that provides energy to all of the cells in your body. The cells take in glucose from the blood and break it down for energy (some cells, like brain cells and red blood cells, rely solely on glucose for fuel). The glucose in the blood comes from the food that you eat. When you eat food, glucose gets absorbed from your intestines and distributed by the bloodstream to all of the cells in your body. Your body tries to keep a constant supply of glucose for your cells by maintaining a constant glucose concentration in your blood -- otherwise, your cells would have more than enough glucose right after a meal and starve in between meals and overnight. So, when you have an oversupply of glucose, your body stores the excess in the liver and muscles by making glycogen, long chains of glucose. When glucose is in short supply, your body mobilizes glucose from stored glycogen and/or stimulates you to eat food. The key is to maintain a constant blood-glucose level. To maintain a constant blood-glucose level, your body relies on two hormones produced in the pancreas that have opposite actions: insulin and glucagon. Insulin is made and secreted by the beta cells of the pancreatic islets, small islands of endocrine cells in the pancreas. Insulin is a protein hormone that contains 51 amino acids. Insulin is required by almost all of the body's cells, but its major targets are liver cells, fat cells and muscle cells. For these cells, insulin does the following: As such, insulin stores nutrients right after a meal by reducing the concentrations of glucose, fatty acids and amino acids in the bloodstream. See the next 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 >>

Regulation Of Body Processes

Regulation Of Body Processes

Hormonal Regulation of the Excretory System The contrasting actions of antidiruetic hormone and aldosterone work to regulate the level of water in the body. Learning Objectives Explain how the actions of different hormones regulate the excretory system Key Takeaways The hypothalamus monitors the amount of water in the body by sensing the concentration of electrolytes in the blood; a high concentration of electrolytes means that the level of water in the body is low. Antidiuretic hormone (ADH), produced by the hypothalamus and released by the posterior pituitary, causes more water to be retained by the kidneys when water levels in the body are low. ADH effects water retention by creating special channels for water, called aquaporins, inside the kidneys so that more water can be reabsorbed before it is excreted. Aldosterone, produced by the adrenal cortex, causes the retention of water in the body by increasing the levels of sodium and potassium ions in the blood, which causes the body to reabsorb more water. When blood pressure is low, the enzyme renin is released, which cleaves the protein angiotensinogen into angiotensin I, which is further converted into angiotensin II. Angiotensin II signals the adrenal cortex to release aldosterone, which then increases the retention of sodium ions, enhancing the secretion of postassium ions, resulting in water retention and an increase in blood pressure. renin: a circulating enzyme released by mammalian kidneys that converts angiotensinogen to angiotensin-I that plays a role in maintaining blood pressure mineralocorticoid: any of a group of steroid hormones, characterised by their similarity to aldosterone and their influence on salt and water metabolism electrolyte: any of the various ions (such as sodium or chloride) that regulat Continue reading >>

Insulin And Glucagon: How To Manipulate Them And Lose Fat

Insulin And Glucagon: How To Manipulate Them And Lose Fat

I know many of you lean, mean, workout machine Breaking Muscle readers could care less about body fat reduction. You're already there. Your focus goes to your lift resistance amounts, improving training times, shoring up your exercise techniques, strategic planning to defeat your opponents, future competition preparation, and feeling good about your training. That's how it should be. What About Fat Loss? But guess what? There is a large segment of the population who are only concerned about shedding their "love handles.” Yes, most of these people will admit they're over-fat due to lack of physical activity and eating like it's Thanksgiving day multiple times per week. If taken to task, most people don't want to resemble an unshapely blob of protoplasm. They would rather look better, but they just don't know where to start to achieve that goal. On top of this, we all exist in a society where a plethora of high-calorie and/or low nutritional value food exists. Wise decisions must be made by all, regardless of your goals. Is it possible to eat your favorite foods, be happy, and attain your fitness goals simultaneously? Maybe. There are hundreds of diets and workout programs purportedly geared toward expunging body fat while enjoying your favorite foods. Many of them work, provided you actually adhere to their guidelines and remain disciplined with sensible calorie intake and exercise. But here’s my advice if you are attempting to maximally lose body fat: maintain your blood sugar level between 70 mg/dl and 110 mg/dl. Do this, and all other factors being equal, you will burn more fat. Biologically, it comes down to your body's innate ability to regulate two hormones - insulin and glucagon - relative to dietary intake. How Insulin and Glucagon Affect Fat Storage Insulin Continue reading >>

Insulin And Glucagon

Insulin And Glucagon

Snapshot A 15-year-old high school student presents with sudden weight loss, increased urination and increased thirst. He is an otherwise healthy individual who plays soccer on his schools team. On physical exam you see a lean young man with dry mucous membranes. Fingerstick glucose reveals a blood glucose of 469 mg/dL. Insulin Overview Synthesis/Release synthesized as proinsulin in β cells of pancreas proinsulin = insulin + C-peptide detection in serum is a mechanism to determine origin of hyperinsulinemia present with endogenous insulin, but absent with exogenous administration hyperglycemia, GH, and cortisol ↑ insulin while hypoglycemia and somatostatin ↓ insulin secretion Function ↓ glucagon release by α cells of pancreas ↑ Na+ retention (kidneys) ↑ glycogen synthesis and storage ↑ triglyceride synthesis and storage recall babies of diabetic mothers are macrosomic ↑ protein synthesis (muscles) recall babies of diabetic mothers are macrosomic ↑ cellular uptake of K+ recall used with glucose to treat hyperkalemia Pathology a patient with an insulinoma will secrete abnormally high levels of insulin as well as C-peptide and will not produce anti-insulin antibodies these patients will have severe hypoglycemia Glucagon Overview Production secreted by the pancreas (alpha cells) major stimulus for secretion is hypoglycemia major inhibition of secretion in hyperglycemia also inhibited by insulin and somatostatin Function increase blood glucose glycogenolysis gluconeogenesis inhibition of insulin release increase blood levels of other energy forms lipolysis ketone body production Pathology a glucogonoma is a tumor that secretes excess glucagon leading to hyperglycemia as well as the characteristic rash of necrolytic migratory erythema Recent Videos Continue reading >>

Endocrine Pancreas

Endocrine Pancreas

This page outlines information on the pancreas. Several hormones participate in the regulation of carbohydrate metabolism. Four of them are secreted by the cells of the islets of Langerhans in the pancreas: two, insulin and glucagon, with major actions on glucose metabolism and two, somatostatin and pancreatic polypeptide, with modulating actions on insulin and glucagon secretion. Other hormones affecting carbohydrate metabolism include: epinephrine, thyroid hormones, glucocorticoids, and growth hormone. Structure and Function of the Pancreas The pancreas lies inferior to the stomach, in a bend of the duodenum. It is both an endocrine and an exocrine gland. The exocrine functions are concerned with digestion. The endocrine function consists primarily of the secretion of the two major hormones, insulin and glucagon. Four cell types have been identified in the islets, each producing a different hormone with specific actions: * A cells produce glucagon; * B cells produce insulin; * D cells produce somatostatin; and * F or D1 cells produce pancreatic polypeptide. These hormones are all polypeptides. Insulin is secreted only by the B cells whereas the other hormones are also secreted by the gastrointestinal mucosa and somatostatin is also found in the brain. Both insulin and glucagon are important in the regulation of carbohydrate, protein and lipid metabolism: Insulin is an anabolic hormone, that is, it increases the storage of glucose, fatty acids and amino acids in cells and tissues. Glucagon is a catabolic hormone, that is, it mobilizes glucose, fatty acids and amino acids from stores into the blood. Somatostatin may regulate, locally, the secretion of the other pancreatic hormones; in brain (hypothalamus) and spinal cord it may act as a neurohormone and neurotransmitter Continue reading >>

How Glucose Levels Are Regulated In The Blood Stream

How Glucose Levels Are Regulated In The Blood Stream

Insulin and glucagon are like our yin and yang in regards to blood sugar levels. Both are produced by the pancreatic islets, the endocrine portion of the pancreas. Insulin is made by the beta cells in the pancreatic islets. Glucagon is made by the alpha cells in the pancreatic islets. Mnemonic: I remember this by remembering a vowel goes with a consonant, so Insulin starts with a vowel (i) and is matched up with Beta cells, which starts with a consonant (b). Glucagon starts with a consonant (g) and matches up with Alpha, which starts with a vowel (a). Insulin and glucagon are both protein hormones which means if you had to give either one to a patient it would have to be done through an injection, as opposed to steroid hormones which are lipids and can be taken orally. Insulin causes sugars in the blood stream to be transported into the cells, decreasing the blood sugar level. This sugar is usually used for creating ATP. In the liver, however, the glucose molecules join together to form a polysaccharide called glycogen. This process is called glycogenesis which literally means “to produce glycogen.” Glucagon causes the breakdown of glycogen from the liver to release glucose into the blood stream, thus raising blood sugar levels. Interestingly enough, muscle glycogen can only be used by the muscle while liver glycogen can be re-released into the blood stream to be used by the muscles as well. This process is called glycogenolysis which literally means the breakdown (-lysis) of glycogen. Fundamentally, insulin and glucagon are very important for keeping this balance. If you eat a bunch of sugar, insulin is going to be released to get rid of all the sugar in the blood stream. If you haven’t eaten anything for several hours, your body prevents your blood sugar from ge Continue reading >>

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