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Regulation Of Blood Glucose Level In Biochemistry

Chapter 20. Gluconeogenesis & The Control Of Blood Glucose

Chapter 20. Gluconeogenesis & The Control Of Blood Glucose

After studying this chapter, you should be able to: Explain the importance of gluconeogenesis in glucose homeostasis. Describe the pathway of gluconeogenesis, how irreversible enzymes of glycolysis are bypassed, and how glycolysis and gluconeogenesis are regulated reciprocally. Explain how plasma glucose concentration is maintained within narrow limits in the fed and fasting states. Gluconeogenesis is the process of synthesizing glucose or glycogen from noncarbohydrate precursors. The major substrates are the glucogenic amino acids (Chapter 29), lactate, glycerol, and propionate. Liver and kidney are the major gluconeogenic tissues; the kidney may contribute up to 40% of total glucose synthesis in the fasting state and more in starvation. The key gluconeogenic enzymes are expressed in the small intestine, but it is unclear whether or not there is significant glucose production by the intestine in the fasting state. A supply of glucose is necessary especially for the nervous system and erythrocytes. After an overnight fast, glycogenolysis (Chapter 19) and gluconeogenesis make approximately equal contributions to blood glucose; as glycogen reserves are depleted, so gluconeogenesis becomes progressively more important. Failure of gluconeogenesis is usually fatal. Hypoglycemia causes brain dysfunction, which can lead to coma and death. Glucose is also important in maintaining the level of intermediates of the citric acid cycle even when fatty acids are the main source of acetyl-CoA in the tissues. In addition, gluconeogenesis clears lactate produced by muscle and erythrocytes, and glycerol produced by adipose tissue. In ruminants, propionate is a product of rumen metabolism of carbohydrates, and is a major substrate for gluconeogenesis. Excessive gluconeogenesis occurs in c Continue reading >>

A Whole-body Model For Glycogen Regulation Reveals A Critical Role For Substrate Cycling In Maintaining Blood Glucose Homeostasis

A Whole-body Model For Glycogen Regulation Reveals A Critical Role For Substrate Cycling In Maintaining Blood Glucose Homeostasis

Abstract Timely, and sometimes rapid, metabolic adaptation to changes in food supply is critical for survival as an organism moves from the fasted to the fed state, and vice versa. These transitions necessitate major metabolic changes to maintain energy homeostasis as the source of blood glucose moves away from ingested carbohydrates, through hepatic glycogen stores, towards gluconeogenesis. The integration of hepatic glycogen regulation with extra-hepatic energetics is a key aspect of these adaptive mechanisms. Here we use computational modeling to explore hepatic glycogen regulation under fed and fasting conditions in the context of a whole-body model. The model was validated against previous experimental results concerning glycogen phosphorylase a (active) and glycogen synthase a dynamics. The model qualitatively reproduced physiological changes that occur during transition from the fed to the fasted state. Analysis of the model reveals a critical role for the inhibition of glycogen synthase phosphatase by glycogen phosphorylase a. This negative regulation leads to high levels of glycogen synthase activity during fasting conditions, which in turn increases substrate (futile) cycling, priming the system for a rapid response once an external source of glucose is restored. This work demonstrates that a mechanistic understanding of the design principles used by metabolic control circuits to maintain homeostasis can benefit from the incorporation of mathematical descriptions of these networks into “whole-body” contextual models that mimic in vivo conditions. Author Summary Homeostasis of blood glucose concentrations during circadian shifts in survival-related activities, sleep and food availability is crucial for the survival of mammals. This process depends upon gluc Continue reading >>

Describe The Regulation Of Blood Glucose Level.

Describe The Regulation Of Blood Glucose Level.

The glucose level is regulated in pancreas by negative feedback loop, which means that when there is too much glucose, it is removed from the blood, and when there's too little, it is released into the blood. When there is too much glucose, beta cells in the islets in the pancreas are activated and produce hormone insulin. What insilin does is that it minds to receptors on muscles and liver and stimulate the uptake of glucose from blood. The uptaken glucose is then either used in cell respiration (muscles) or stored in a long-term form as a glycogen (liver). Thus the level of glucose decreases to the desired level. On the other hand, when the glucose level is too low, glucose needs to be replenished in the bloodstream. Low level glucose activates the alpha cells, which produce glucagon and release it into the blood. What glucagon does is that it stimulates breakdown of glycogen stored in the liver and converts it to glucose (reverse of what insulin does in liver). Glucose is released and the glucose level in the blood increases up to the required amount. Continue reading >>

Blood Glucose: Regulation And Renal Threshold

Blood Glucose: Regulation And Renal Threshold

ADVERTISEMENTS: In this article we will discuss about the Regulation and Renal Threshold for Blood Glucose. Regulation of the Blood Glucose: The stable blood glucose level is maintained by the role of liver, skeletal muscle, kidney, muscular exercise and hormones. Role of Liver: 1. Liver is the pivot of carbohydrate metabolism of the whole body. The presence of glucose-6-phosphatase in the liver converts glucose-6-phosphate to glucose which diffuses into the blood stream to form the constant and the only source of glucose of blood unless and until glucose is available from the intestine from carbohydrate diet. 2. Muscle glycogen cannot be converted to glucose due to the lack of the enzyme glucose-6-phosphatase. Therefore, glycogen is converted to lactic acid which by “Cori Cycle” or “Lactic Acid Cycle” is converted to glucose in the liver and the glucose is diffused to the blood stream. 3. The liver cells, like other cells, require the oxidation of organic substances to maintain their own vital functioning. In the absence of fuel glucose, glycogen is diminished and the oxidation of fat occurs forming keto acids. Some of the keto acids are utilized for cellular energy. But if the concentration of keto acids is increased, the keto acids diffuse into the blood stream and accumulate producing ketosis. 4. When the glycogen reservoir diminishes, the amino acids of the body proteins are utilized by the liver for gluconeogenesis. Role of Skeletal Muscle: 1. Extra-hepatic tissues are relatively impermeable to glucose and, therefore, insulin is required for the uptake of glucose to these cells. 2. Increased blood glucose promotes glycogenesis and oxidation of glucose in muscles. Muscle glycogen does not serve directly as a source of glucose during hypoglycemia. But glucos Continue reading >>

Regulation Of Blood Glucose Level

Regulation Of Blood Glucose Level

Transport of the monosaccharide glucose to all cells is a key function of the blood circulation. In humans, the normal level of blood glucose is about 90 mg of glucose/100 cm3 of blood, but this can vary. For example, during an extended period without food, or after prolonged and heavy physical activity, the blood glucose level may drop to as low as 70 mg. After a meal rich in carbohydrate has been digested, the blood glucose level may rise to 150 mg. Respiration is a continuous process in all living cells. To maintain their metabolism, cells need a regular supply of glucose, which can be quickly absorbed across the cell membrane. Glucose is the principal fuel used for respiration Most cells hold additional glucose reserves in the form of glycogen, which is quickly converted to glucose during prolonged physical activity; however, glycogen reserves may be used up quickly. In the brain, glucose is the only fuel the cells can use and there are no glycogen reserves held there at all. If our blood glucose falls below 60 mg/100cm3 a condition called hypoglycaemia develops. If this is not quickly reversed, the person may faint. If the body and brain continue to be deprived of adequate glucose levels, then convulsions and hypoglycaemic coma follow, which can be fatal. An abnormally high concentration of blood glucose, known as hyperglycaemia, is also a problem. Since high concentrations of any soluble metabolite lower the water potential of the blood plasma, water is drawn out of the cells and tissue fluid by osmosis, back into the blood. As the volume of blood increases, water is excreted by the kidney in an attempt to maintain the correct concentration of blood. As a result the body tends to become dehydrated, and the circulatory system is deprived of fluid. Ultimately, the c Continue reading >>

Interactive Resources For Schools

Interactive Resources For Schools

Page 1 - What is diabetes? Two hormones are involved in the regulation of glucose in the blood: insulin and glucagon. Both are produced by specialised cells in the islets of Langerhans in the pancreas. There are a number of interactive features in this e-source: A glossary of terms: any word with a glossary entry is highlighted like this. Moving the mouse over the highlighted word will show a definition of that word. Quick questions: at the end of most pages or sections there is a question or set of quick questions to test your understanding. Animations: most of the animations can be expanded to full screen size, ideal for showing on an interactive whiteboard. The animations will play all the way through or can be viewed one section at a time. Downloads: Teachers can download individual diagrams, animations and other content from the Download Library area of the website. Terms and Conditions apply. Type 1 diabetes is an autoimmune disease and accounts for up to 10% of diabetes cases in the UK. It typically develops before the age of 40 and occurs when the pancreas can no longer produce insulin. There are two types of cells in the pancreas. Exocrine cells are responsible for the production and secretion of digestive enzymes. These pass along the pancreatic duct into the duodenum. These cells are not usually affected in diabetes. The pancreas also contains groups of cells called the islets of Langerhans. These cells release their products directly into the blood and so are a form of endocrine gland. Two hormones are produced in these islets. Insulin is made in beta cells and glucagon in alpha cells. Type 1 diabetes develops when the person's own immune system destroys the beta cells. As a result insulin is no longer produced and blood sugar levels rise. This leads to the Continue reading >>

General Paper Blood Glucose Regulation In An Intertidal Crab, Chasmagnathus Granulata (dana, 1851)

General Paper Blood Glucose Regulation In An Intertidal Crab, Chasmagnathus Granulata (dana, 1851)

Abstract 1. 1. Blood glucose regulation was investigated in an intertidal crab from south Brazil, Chasmagnathus granulata. 2. 2. There is no significant difference (P > 0.05) between blood glucose levels of males and females, ♂ ♀. 3. 3. There is no significant difference (P > 0.05) between blood glucose levels of normal and eyestalkless males until 96 hr after eyestalk ablation. 4. 4. There is a transitory but large increase in blood glucose levels of animals exposed to atmospheric air, the highest values being reached 1 hr after this exposure; 17.04 mg/100 ml. 5. 5. Handling and alien environment produce only a small increase in blood glucose levels of normal animals. 6. 6. There is a significant increase (P < 0.05) of crustacean hyperglycemie hormone (CHH) content in the eyestalks of animals exposed to atmospheric air for 1 hr, suggesting a higher rate of its synthesis during this period. 7. 7. Since the CHH seems to increase blood glucose by decreasing its utilization by the tissues and since there is a decrease in oxygen consumption in C. granulata exposed to atmospheric air, it is quite possible that this hormone is involved in the lack of the Pasteur effect, usually observed in facultative anaerobes. Continue reading >>

Digestion Of Dietary Carbohydrates

Digestion Of Dietary Carbohydrates

The main polymeric-carbohydrate digesting enzyme of the small intestine is α-amylase. This enzyme is secreted by the pancreas and has the same activity as salivary amylase, producing disaccharides and trisaccharides. The latter are converted to monosaccharides by intestinal saccharidases, including maltase that hydrolyzes di- and trisaccharides composed of glucose, and the more specific disaccharidases, sucrase-isomaltase, lactase (β-galactosidase), and trehalase. The net result is the almost complete conversion of digestible carbohydrate to its constituent monosaccharides. The resultant glucose, fructose, and galactose are transported into the intestinal enterocytes via the actions of various carbohydrate transporters. Glucose is transported into enterocytes via the action of two transporters. One of these transporters is the Na+-dependent glucose transporter 1 (SGLT1) while the other is the Na+-independent glucose transporter 2 (GLUT2). SGLT1 is the major transporter of glucose from the lumen of the small intestine. Although GLUT2 does indeed transport glucose into intestinal enterocytes, this only occurs in response glucose-mediated translocation of intracellular vesicle-associated GLUT2, thus even in the absence of GLUT2 (such as is the case in individuals with Fanconi-Bickel disease), intestinal uptake of dietary glucose is unimpaired. Galactose is also absorbed from the gut via the action of SGLT1. Fructose is absorbed from the intestine via GLUT5 uptake. Indeed, GLUT5 has a much higher affinity for fructose than for glucose. These monosaccharides are then transported into the circulation via the action of enterocyte GLUT2 present in the basolateral membrane. Following entry into the duodenal superior mesenteric vein the dietary sugars travel to the hepatic port Continue reading >>

Regulation Of Blood Glucose Level

Regulation Of Blood Glucose Level

Presentation on theme: "Regulation of Blood Glucose Level"— Presentation transcript: 2 INTRODUCTION Blood sugar concentration, or glucose level, refers to the amount of glucose present in the blood of a human. Normally, in mammals the blood glucose level is maintained at a reference range between about 3.6 and 5.8 mM (mmol/l). It is tightly regulated as a part of metabolic homeostasis. 3 INTRODUCTION….. 4 INTRODUCTION….. 6 Glucagon…. Glucagon binding to its' receptors on the surface of liver cells triggers an increase in cAMP production leading to an increased rate of glycogenolysis by activating glycogen phosphorylase via the PKA-mediated cascade. 7 The glucose enters extrahepatic cells where it is re-phosphorylated by hexokinase. 9 INSULIN 10 When blood glucose levels are low, the liver does not compete with other tissues for glucose since the extrahepatic uptake of glucose is stimulated in response to insulin. 11 Under conditions of high blood glucose, liver glucose levels will be high and the activity of glucokinase will be elevated. 12 Regulation of Glucose Metabolism During Exercise 13 Regulation of Glucose Metabolism During Exercise 15 1) Enhances gluconeogenesis; 2) Antagonizes Insulin. 1) Enhances entry of glucose into cells; 2) Enhances storage of glucose as glycogen, or conversion to fatty acids; 3) Enhances synthesis of fatty acids and proteins; 4) Suppresses breakdown of proteins into amino acids, of adipose tissue into free fatty acids. 16 Insulin Synthesis and Secretion 17 Biosynthesis of Insulin The insulin mRNA is translated as a single chain precursor called preproinsulin, and removal of its signal peptide during insertion into the endoplasmic reticulum generates proinsulin. 18 Proinsulin consists of three domains: an amino-terminal B chain, a Continue reading >>

Regulation Of Blood Glucose: Importance & Nutrient Conversion

Regulation Of Blood Glucose: Importance & Nutrient Conversion

Blood glucose levels are closely regulated and maintained within a narrow range. Learn how the pancreatic hormones, insulin and glucagon, maintain normal blood sugar levels and how other nutrients can be converted to blood glucose in this lesson. If you drink a 12-ounce can of soda, did you know that you are consuming almost ten teaspoons of sugar? So, what does your body do with all of that sugar? Well, refined sugar is handled like any other simple or complex carbohydrate that you consume, which means it gets converted to glucose. Glucose is a simple sugar that is used as energy by your body and brain. Now, just because every cell in your body uses glucose doesn't mean you should start eating more sugar. Your body only allows a certain amount of glucose to be present in your bloodstream at one time. If there's too much, the extra is sent to storage, and as we will discover, one of your body's favorite storage places is your fat cells. In this lesson, we will take a look at how the amount of glucose found in your blood, referred to as blood glucose or blood sugar, is regulated and how nutrients other than carbs can be converted into glucose. When you stop by a fast food restaurant and enjoy a double cheeseburger, fries, and a soda, the carbohydrates in your meal get broken down into glucose within your digestive tract. These molecules are small enough to pass into your bloodstream causing your blood glucose level to rise. Your pancreas is not happy about this rising blood sugar. In fact, your pancreas acts somewhat like a bouncer at a nightclub; there is too much sugar crowding your bloodstream, so your pancreas tells some of it to leave. To do this your pancreas secretes insulin, which is a hormone that moves glucose out of the blood and into the cells. In other words Continue reading >>

Glucose Regulation Of Insulin Gene Expression In Pancreatic Β-cells

Glucose Regulation Of Insulin Gene Expression In Pancreatic Β-cells

Production and secretion of insulin from the β-cells of the pancreas is very crucial in maintaining normoglycaemia. This is achieved by tight regulation of insulin synthesis and exocytosis from the β-cells in response to changes in blood glucose levels. The synthesis of insulin is regulated by blood glucose levels at the transcriptional and post-transcriptional levels. Although many transcription factors have been implicated in the regulation of insulin gene transcription, three β-cell-specific transcriptional regulators, Pdx-1 (pancreatic and duodenal homeobox-1), NeuroD1 (neurogenic differentiation 1) and MafA (V-maf musculoaponeurotic fibrosarcoma oncogene homologue A), have been demonstrated to play a crucial role in glucose induction of insulin gene transcription and pancreatic β-cell function. These three transcription factors activate insulin gene expression in a co-ordinated and synergistic manner in response to increasing glucose levels. It has been shown that changes in glucose concentrations modulate the function of these β-cell transcription factors at multiple levels. These include changes in expression levels, subcellular localization, DNA-binding activity, transactivation capability and interaction with other proteins. Furthermore, all three transcription factors are able to induce insulin gene expression when expressed in non-β-cells, including liver and intestinal cells. The present review summarizes the recent findings on how glucose modulates the function of the β-cell transcription factors Pdx-1, NeuroD1 and MafA, and thereby tightly regulates insulin synthesis in accordance with blood glucose levels. Abbreviations: bHLH, basic helix–loop–helix; CAMKII, Ca2+/calmodulin-dependent protein kinase II; CBP, CREB (cAMP-response-element-binding p Continue reading >>

Regulation Of Blood Glucose Level In Diabetes Mellitus Using Palatable Diet Composition

Regulation Of Blood Glucose Level In Diabetes Mellitus Using Palatable Diet Composition

Abstract Diabetes mellitus results from the failure of the endocrine system to control the blood glucose levels within the normal limits. Normal people have fasting sugar level that generally run between 70–110 mg/dl, while a person is said to suffer from diabetes if the blood glucose level in the interval of 2 hours equals to or exceeds 180 mg/dl. It can be understood as a disorder of carbohydrate metabolism and characterized primarily by hyperglycemia and glycosuria with second anomalies of the metabolism of protein and fat. It is not only the leading cause of blindness, renal failure and non-traumatic amputations in adults but also a major cardiovascular risk factor in developing countries. So, it is of great interest to propose a palatable composition of quantitative diet for the human beings suffering from Diabetes Mellitus to regulate the blood glucose and insulin level. In the present study, the palatable composition is calculated by two mathematical models and given in the form of calories for protein (P), fat (F) and carbohydrate (C). For the calculations, the mixed population has been distinguished into three categories namely men, women and juvenile having various body frames i.e. small, medium and large. With the substitution of this composition in the solutions, the near- normal level of blood glucose and insulin is achieved. Hence, a plausible palatable composition of protein, fat and carbohydrate has been proposed which can be incorporated in diet for the significant regulation of blood glucose and insulin level in diabetic patients. 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 >>

Hormonal Regulation Of Fuel Metabolism

Hormonal Regulation Of Fuel Metabolism

Our discussions of metabolic regulation and hormone action now come together as we return to the hormonal regulation of blood glucose level. The minute-by-minute adjustments that keep the blood glucose level near 4.5 mM involve the combined actions of insulin, glucagon, and epinephrine on metabolic processes in many body tissues, but especially in liver, muscle, and adipose tissue. Insulin signals these tissues that the blood glucose concentration is higher than necessary; as a result, the excess glucose is taken up from the blood into cells and converted to storage compounds, glycogen and triacylglycerols. Glucagon carries the message that blood glucose is too low, and the tissues respond by producing glucose through glycogen breakdown and gluconeogenesis and by oxidizing fats to reduce the use of glucose. Epinephrine is released into the blood to prepare the muscles, lungs, and heart for a burst of activity. Insulin, glucagon, and epinephrine are the primary determinants of the metabolic activities of muscle, liver, and adipose tissue. Epinephrine Signals Impending Activity When an animal is confronted with a stressful situation that requires increased activity-fighting or fleeing, in the extreme case-neuronal signals from the brain trigger the release of epinephrine and norepinephrine from the adrenal medulla. Both hormones increase the rate and strength of the heartbeat and raise the blood pressure, thereby increasing the flow of 02 and fuels to the tissues, and dilate the respiratory passages, facilitating the uptake of O2 (Table 22-3). In its effects on metabolism, epinephrine acts primarily on muscle, adipose tissue, and liver. It activates glycogen phosphorylase and inactivates glycogen synthase (by cAMP-dependent phosphorylation of the enzymes; see Fig. 14-18 a Continue reading >>

Effects Of Serotonin And Fluoxetine On Blood Glucose Regulation In Two Decapod Species

Effects Of Serotonin And Fluoxetine On Blood Glucose Regulation In Two Decapod Species

E.A. Santos1, R. Keller2, E. Rodriguez3 and L. Lopez3 1Laboratório de Zoofisiologia, Departamento de Ciências Fisiológicas, Fundação Universidade do Rio Grande, Rio Grande, RS, Brasil 2Institut für Zoophysiologie, Rheinische Friedrich-Wilhelms-Universität, Bonn, Germany 3Laboratório de Fisiologia Animal, Universidad de Buenos Aires, Buenos Aires, Argentina One of the best known crustacean hormones is the crustacean hyperglycemic hormone (CHH). However, the mechanisms involved in hormone release in these animals are poorly understood, and thus constitute the central objective of the present study. Different groups of crustaceans belonging to diverse taxa (Chasmagnathus granulata, a grapsid crab and Orconectes limosus, an astacid) were injected with serotonin, fluoxetine, or a mixture of both, and glycemic values (C. granulata and O. limosus) and CHH levels (O. limosus) were determined after 2 h in either submerged animals or animals exposed to atmospheric air. Both serotonin and fluoxetine caused significant hyperglycemia (P<0.05) after injection into the blood sinus of the two species, an effect enhanced after exposure to atmospheric air. In C. granulata blood glucose increased from 6.1 to 43.3 and 11.4 mg/100 ml in submerged animals and from 5.7 to 55.2 and 22.5 mg/100 ml in air-exposed animals after treatment with serotonin and fluoxetine, respectively. In O. limosus the increases were from 1.2 to 59.7 and 135.2 mg/100 ml in submerged animals and from 2.5 to 200.3 and 193.6 mg/100 ml in air-exposed animals after treatment with serotonin and fluoxetine, respectively. Serotonin and fluoxetine also caused a significant increase in the circulating levels of CHH in O. limosus, from 11.9 to 43 and 45.7 fmol/ml in submerged animals and from 13.2 to 32.6 and 45.7 fmol Continue reading >>

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