Glucose

Glucose is the end product of carbohydrate metabolism and is the chief source of energy for living organisms. The human body converts most dietary carbohydrates into a substance called blood sugar or glucose. In respiration, through a series of enzyme-catalysed reactions, glucose is oxidized to eventually form carbon dioxide and water, yielding energy, mostly in the form of ATP. Glucose is one of the main products of photosynthesis and starts respiration. Blood glucose concentrations are kept within a relatively narrow range by such factors as hepatic and renal uptake and release, glucose removal by peripheral tissues, hormone influences on uptake and release, and intestinal absorption. The normal concentration of glucose in the blood is about 0.1%, but it becomes much higher in persons suffering from diabetes. Insulin is the main hormone that affects glucose blood levels. When glucose levels fall to hypoglycemic levels, cells cannot function normally, and symptoms develop such as nervousness, cool skin, headache, confusion, convulsions or coma.

Glucose is found in the sap of plants, and is found in the human bloodstream where it is referred to as "blood sugar". The only endogenous sources of glucose are the liver and kidneys which convert glucose-6-phosphate to glucose. Glucose is usually manufactured by hydrolysis of cornstarch with steam and dilute acid. Liquid glucose is known as corn syrup in the USA. The corn syrup thus obtained contains also some dextrins and maltose. When glucose is mixed with maple syrup, it is called pancake syrup. Industrially glucose is used in the manufacture of candy, chewing gum, jams, jellies, table syrups, and other foods, and for many other purposes. Glucose is most commonly used in confectionery to give elasticity to caramel or sugar piece and to help prevent crystallization. It can also be added to chocolate to produce a modeling paste.

Glucose's role in metabolism

Carbohydrates are the human body's key source of energy. Glucose is absorbed into the bloodstream through the intestinal wall. Only the monosaccharides glucose, fructose and galactose are absorbed in humans. Breakdown of carbohydrates yields mono- and disaccharides, most of which is glucose. Oxidation of glucose is known as glycolysis. Glucose is oxidized to either lactate or pyruvate. Two different pathways are involved in the metabolism of glucose: one anaerobic and one aerobic. The anaerobic process occurs in the cytoplasm and is only moderately efficient. The aerobic cycle takes place in the mitochondria and is results in the greatest release of energy. Under aerobic conditions, the dominant product in most tissues is pyruvate and the pathway is known as aerobic glycolysis. Through glycolysis, glucose is directly involved in the production of ATP, the cell's energy carrier. The NADH generated during glycolysis is used to fuel mitochondrial ATP synthesis via oxidative phosphorylation, producing either two or three equivalents of ATP depending upon whether the glycerol phosphate shuttle or the malate-aspartate shuttle is used to transport the electrons from cytoplasmic NADH into the mitochondria.

Glucose is a major source of energy for most cells of the body. Some of glucose goes directly to fuel brain cells, while the rest makes its way to the liver and muscles, where it is stored as glycogen, and to fat cells, where it is stored as fat. Glycogen is the body's auxiliary energy source, tapped and converted back into glucose when it needs more energy. Although stored fat can also serve as a backup source of energy, it is never directly converted into glucose. The fructose and galactose are taken up by the liver, where they are converted into glucose. Glucose in the bloodstream diffuses into the cytoplasm and is locked there by phosphorylation. A glucose molecule is then rearranged slightly to fructose and phosphorylated again to fructose diphosphate. Glucose is vital to brain function. The brain requires that glucose concentrations in the blood remain within a certain range in order to function normally. Glucose metabolism is disturbed in depression, manic-depression, anorexia, and bulimia. In addition, Alzheimer’s patients, for instance, register much lower glucose levels than those with other forms of brain malfunction that resulted from stroke or other vascular disease.

Glucose and diabetes (high blood sugar)

Insulin is a hormone produced by the beta cells of the pancreas. It helps to regulate the amount of glucose in the blood. Insulin works antagonistically with glucagon to control blood sugar levels. Insulin accelerates the uptake of glucose into peripheral tissue, thereby lowering blood glucose concentrations. Insulin helps glucose move out of the blood and into the cells in the body, where the glucose can be used as energy and nourishment. Insulin is the principal signal in converting many of the bidirectional processes of metabolism from a catabolic to an anabolic direction. Diabetes mellitus is the inadequate secretion of insulin, which results in the inability of the cells to take in glucose or store glycogen. If the pancreas is unable to produce insulin, a person develops Type 1 diabetes. If the pancreas does not produce enough insulin, or the body cannot metabolize the insulin that is produced, a person develops Type 2 diabetes. Currently, type 1 is treated with insulin injections, lifestyle adjustments, and careful monitoring of blood glucose levels using blood test kits. Type 2 is initially treated by changes in diet and through weight loss, Followed with oral antidiabetic drugs: the sulphonylureas, metformin, or (if these are insufficient) thiazolidinediones, if necessary.

Blood glucose level test

A glucose test measures the amount of sugar (glucose) in the blood. A way of testing how much glucose (sugar) is in the blood. Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. A single drop of blood is placed on a strip in a portable instrument called a glucometer. The test strips are coated with chemicals (glucose oxidase, dehydrogenase, or hexokinase) that combine with glucose in blood. The glucometer quickly determines the blood sugar and shows the results on a small screen in usually a few seconds. Most glucose meters are able to read glucose levels over a broad range of values from as low as 0 to as high as 600 mg/dL. Since the range is different among meters, interpret very high or low values carefully. Levels up to 100 mg/dL are considered normal. Levels between 100 and 126 mg/dl are referred to as impaired fasting glucose or pre-diabetes. These levels are considered to be risk factors for type 2 diabetes and its complications. Diabetes is typically diagnosed when fasting blood glucose levels are 126 mg/dl or higher. In the diabetic patient, more specifically type 2 patients, it is important to maintain good glucose control, with a before meal level of <6.1 mmol/L (<110 mg/dL) and a level two hours after the start of a meal of <7.8 mmol/L (<140 mg/dL). Levels greater than 13-15 mmol/L (230-270 mg/dL) should be monitored closely and the patient is advised to seek urgent medical attention as soon as possible if this continues to rise after 2-3 tests. Glucose levels in plasma (one of the components of blood) are generally 10-15% higher than glucose measurements in whole blood (and even more after eating). A Glucose tolerance test in medical practice is the administration of glucose to determine how quickly it is cleared from the blood. The test is usually used to test for diabetes, insulin resistance, and sometimes reactive hypoglycemia. The glucose is most often given orally so the common test is technically an oral glucose tolerance test (OGTT). Diabetes must be diagnosed as early as possible. If left untreated, it can damage or cause failure of the eyes, kidneys, nerves, heart, blood vessels, and other body organs. Hypoglycemia, or low blood sugar, may also be discovered through blood sugar testing. Hypoglycemia is caused by various hormone disorders and liver disease, as well as by too much insulin.