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Regulation of Blood Glucose -- Glucose Homeostasis -- Biochemistry Glucosw people eat a food containing procexses, the digestive system breaks down Glucose regulation processes digestible regulatiob into sugar, which enters the blood. These reulation are Antioxidant and digestive health Energy boosting tips for swimmers sugars Energy boosting tips for swimmers as fructose and glucose regu,ation have simple chemical structures composed of only one sugar monosaccharides or eegulation sugars disaccharides. Simple carbohydrates are easily and quickly utilized for energy by the body because of their simple chemical structure, often leading to a faster rise in blood sugar and insulin secretion from the pancreas — which can have negative health effects. These carbohydrates have more complex chemical structures, with three or more sugars linked together known as oligosaccharides and polysaccharides. Many complex carbohydrate foods contain fiber, vitamins and minerals, and they take longer to digest — which means they have less of an immediate impact on blood sugar, causing it to rise more slowly.Glucose regulation processes -
This section will give us a look at the importance of maintaining blood glucose levels in the body and how this is regulated. You will learn about the processes and hormones involved in changing glucose concentrations in the blood. You will gain an understanding of the difference between insulin and glucagon and how and when they work to modify blood glucose levels to maintain homeostasis.
Furthermore, you will learn how glucose is synthesized by various enzymes through gluconeogenesis and how glucose is broken down through the process of glycolysis.
We will also explore the role of the pancreas in generating and secreting hormones necessary for glucose regulation. Several real-world examples will be given to further your understanding. Glucose is a simple sugar that is required for energy ATP production throughout the body.
Due to the central importance of glucose as a source of energy in the body, blood glucose concentrations are constantly monitored and regulated through physiological mechanisms. These symptoms occur because glucose is the primary fuel source used by the brain. In desperate circumstances the brain can use ketone bodies that are derived from fat, however this is not ideal.
In states of hypoglycemia the brain limits its glucose use, shutting off all functions not required for survival which causes impaired cognitive functioning.
In extreme and prolonged states of hypoglycemia the brain starves, leading to cerebral damage and possibly death. When blood glucose concentrations are high, excess glucose is removed from the body at the level of the kidney. The kidney is very good at removing excess glucose from the blood, however water follows the glucose by osmotic draw and is also excreted from the body.
This leads to osmotic diuresis, or increased urine production, and can lead to severe dehydration. Once glucose is absorbed into skeletal muscle cells or adipocytes it is trapped and must be used by that cell.
Only the liver is capable of releasing glucose back into circulation. Skeletal muscle and adipose tissue can indirectly liberate glucose by releasing molecules such as amino acids and lipid byproducts into the blood.
These molecules can then be taken up and used by the liver to make new glucose molecules that can be released in circulation. During digestion carbohydrates are broken down into simple soluble sugars like glucose that can be transported across the intestinal wall into the circulatory system. Once in circulation, absorbed glucose is transported into tissues and the process of cellular respiration begins.
Glucose enters cells around the body through glucose transporters by facilitated diffusion. Thus, in order for glucose to get into the cells a concentration gradient must be established with glucose levels being higher outside of the cell.
There are 15 different glucose transporters found throughout the body; however, for the purpose of this chapter we will focus on 2 main types: 1 GLUT2 which is found in the liver and 2 GLUT4 which is found in skeletal muscle and adipose tissue. The GLUT4 transporter is special because it is insulin sensitive — whenever skeletal muscle or adipocytes interact with the hormone insulin, GLUT4 transporters are recruited to the cell surface.
When insulin levels are low GLUT4 transporters are recycled slowly between the cell membrane and cell interior. When glucose enters a cell, the enzyme hexokinase in muscle and adipose or glucokinase in the liver rapidly adds a phosphate to convert it into glucosephosphate G6P.
This conversion step essentially traps the glucose in the cell, preventing it from passing back through the plasma membrane, thus allowing glycolysis to proceed.
This process also functions to maintain a concentration gradient with higher glucose levels in the blood than in the tissues. By establishing this concentration gradient, the glucose in the blood will be able to flow from an area of high concentration the blood into an area of low concentration the tissues to be either used or stored.
G6P can then enter one of two pathways: 1 glycolysis for energy release or 2 glycogenesis for storage. Glycolysis is a series of metabolic steps that breaks down one glucose molecule into two pyruvate molecules, and creates two net ATP molecules and two NADH molecules.
Thus, glycolysis generates energy for the cell and creates pyruvate molecules that can be processed further through the citric acid cycle aerobic respiration or converted into lactic acid anaerobic respiration. During the citric acid cycle, high-energy molecules, including ATP, NADH, and FADH 2 , are created.
NADH and FADH 2 then pass electrons through the electron transport chain in the mitochondria to generate ATP.
When glucose levels are plentiful, any excess acetyl CoA generated by glycolysis can be converted into fatty acids and triglycerides.
This process, called lipogenesis , creates lipid droplets for storage of energy and takes place in adipocytes fat cells and hepatocytes liver cells. Additionally, when there is sufficient energy in the cell G6P will be used for glycogen synthesis glycogenesis rather than entering glycolysis.
Glycogenesis, is the formation of glycogen a storage molecules from glucose by the enzyme glycogen synthase. This process occurs in the liver and muscle cells when glucose and ATP are present in relatively high amounts.
When blood glucose levels fall, as during fasting, the opposite reactions occur within the cell. Glycolysis is reduced and fuel stores, including glycogen and lipid droplets, are broken down to release energy.
Glycogenolysis occurs mainly in the liver and skeletal muscle and is the process of breaking down glycogen stores back into glucose to provide immediate energy and maintain blood glucose levels.
During each round of glycogenolysis the enzyme glycogen phosphorylase removes one molecule of G6P, leaving the remaining chain of glycogen with one less molecule of glucose.
In the muscle, the liberated glucose must be used inside the cell for energy. The liver, however, can release the glucose back into the blood stream. To obtain energy from fat, triglycerides in the liver or adipose tissue are broken down by hydrolysis into their two principle components; free fatty acids and glycerol.
This process is called lipolysis. Glycerol from fat, along with pyruvate, lactate and glucogenic amino acids can also be used by the liver to create new molecules of glucose. This process is termed gluconeogenesis. All of these cellular mechanisms fall under the control of two main hormones: insulin and glucagon.
These hormones are generated and secreted by the pancreas and work together to maintain optimal blood glucose concentrations. The following diagram demonstrates an overview of aerobic respiration. You do not need to know the whole process in detail, but it is expected that you have a base understanding of this process from your previous courses, focussing on the big picture.
The pancreas is a glandular organ located in the abdomen. It plays a critical role in converting the food we eat into fuel for our bodies. In terms of functionality, the pancreas can be broken down into two main parts the exocrine pancreas which aids in digestion and the endocrine pancreas which regulates blood sugar.
The bulk of the pancreas is composed of exocrine cells which produce enzymes that aid in digestion. When food enters the stomach, the exocrine cells release their digestive enzymes into a series of small ducts that eventually join together into the main pancreatic duct.
The pancreatic duct runs the length of the pancreas and releases the digestive enzymes along with other secretions, collectively called pancreatic juice, into the small intestine. The second functional component of the pancreas is the endocrine pancreas. The endocrine pancreas is composed of small islands of cells called the islets of Langerhans.
There are at least 4 cell types found within the islets which produce hormones that are released into the blood stream and help regulate blood glucose levels. This information is summarized in table 1. The functional distribution of the four cell types within the islets of Langerhans is shown in figure 2.
Beta cells, which make up the majority of the islets, are located centrally and surrounded by the alpha, delta and F cells. This learning object is above the course level and for your information only.
This learning object is beyond what you are expected to know; however, think about where the cell type subsets are situated and the functional role location might have. Glucagon and insulin are antagonistic hormones and somatostatin inhibits them both!
It makes sense that they are all found close together. Before pancreatic hormones make it into circulation and act on tissues around the body, they first play a role in paracrine regulation of the pancreas itself.
This paracrine feedback system is demonstrated in figure 3. Take note of the signalling contrast between glucagon and insulin and somatostatin.
Glucagon will always stimulate the release of the other two hormones, while insulin and somatostatin both have an inhibitory effect on the other hormones in this relationship. Insulin and glucagon have opposing actions on one another, so if you learn one, you know the other! And remember that somatostatin will always inhibit both insulin and glucagon release.
Secretion of insulin, from beta cells within the islet of Langerhans, inhibits the surrounding alpha cells from releasing glucagon and the delta cells from releasing somatostatin. Secretion of glucagon, which is antagonistic to insulin, stimulates the delta cells to release somatostatin.
Interestingly, glucagon also activates the beta cells and stimulates insulin release. Considering insulin and glucagon have opposing actions throughout the body this may seem counterintuitive. To better understand why this occurs imagine a runner nearing the end of a marathon — after running almost 42 kilometers, glucose within the body will be severely depleted.
In order to correct this state of hypoglycaemia, alpha cells in the pancreas will release glucagon, resulting in the production and liberation of glucose from the liver and adipocytes.
Insulin is then needed to help cells around the body especially the skeletal muscle cells absorb the liberated glucose and use it for energy.
This interplay between glucagon and insulin allows the runner to keep moving and finish the race! It is also important to understand that not all regulatory signals are equal; the stimulatory effects that glucagon has on beta cells is much smaller than the stimulatory effects of increased blood sugar after eating a meal.
Lastly, secretion of somatostatin within the islets inhibits the activity of both the beta and alpha cells. Regulation of pancreatic hormones is a complex process, involving much more than just the paracrine feedback system within the islet of Langerhans.
Secretion of insulin and glucagon is controlled by the integration and interaction of multiple inputs including nutrients, hormones, neurotransmitters and drugs. For both insulin and glucagon, changes in blood glucose concentrations are the primary stimuli that activates, or inhibits, their release.
Blood glucose is the regulated variable within this system, meaning it is constantly monitored by sensors i. receptors in the body and kept within a limited range through physiological mechanisms. When the body is in a state of hyperglycemia , and blood glucose levels are elevated, sensors in the pancreas detect this and stimulate the beta cells to increase their release of insulin.
When blood glucose levels drop, putting the body is in a state of hypoglycemia , the alpha cells are stimulated and glucagon is released. The integration of blood glucose levels, and other regulatory stimuli, on alpha and beta cells is discussed in further detail below.
The following figure depicts how insulin release is regulated by different inputs throughout the body. Keep the big picture in mind. Which one of the following exhibits paracrine control? The following figure demonstrates how the release of glucagon from alpha cells is regulated by different inputs throughout the body.
Remember that both insulin and somatostatin will both inhibit the secretion of glucagon from alpha cells in the pancreas.
The endocrine pancreas is always secreting some level of insulin and glucagon. Figure 6 below shows how plasma concentrations of glucose, glucagon and insulin change over a hour period. Pay close attention to how these levels change before and after a meal and the relationships between the different plasma concentrations.
Think about the relationship between insulin, glucagon and glucose and what causes fluctuations to each. This diagram presents information that you have already learned in a new way! As one hormone increases its activity the other one decreases but is never completely shut off.
All inputs that regulate the activity of alpha and beta cells combine in the pancreas. The overall summation of these inputs determines if the system favours insulin or glucagon release.
After eating a meal glucose levels rise. In response to this the body increases the concentration of insulin in the blood and decreases the concentration of glucagon. The opposite effect is seen in between meals when blood glucose concentration decreases — now blood glucagon concentrations rise and insulin concentrations fall.
Take note that the concentration of both insulin and glucagon in the blood never reaches 0, there is always some level of hormone being secreted from the pancreas. We know that regardless of blood glucose levels, the concentrations of insulin and glucagon never reach zero. Why do you think that is?
Hint: Think about what would happen if you needed to produce a hormone quickly and it was not readily available. So far we have covered where insulin and glucagon come from, and how they are regulated.
Now we will dive into the effects these hormones have on the body. The absorptive state , or the fed state, occurs after a meal when your body is digesting the food and absorbing the nutrients.. Digestion begins the moment you put food into your mouth, as the food is broken down into its constituent parts to be absorbed through the intestine.
The digestion of carbohydrates begins in the mouth, whereas the digestion of proteins and fats begins in the stomach and small intestine.
The constituent parts of these carbohydrates, fats, and proteins are transported across the intestinal wall and enter the bloodstream sugars and amino acids or the lymphatic system fats. The ingestion of food and the rise of glucose concentrations in the bloodstream stimulate pancreatic beta cells to release insulin.
For the purpose of this course we will focus on the effects of insulin in adipose tissue, skeletal muscle and the liver. Figure 7 below provides a visual representation of how the adipose tissue, skeletal muscle and liver respond to an increase in insulin, caused by high blood glucose levels.
Note the negative feedback that allows this response to be highly regulated. In adipose tissue, when insulin concentrations are low, glucose transport proteins are recycled slowly between the cell membrane and cell interior. Vesicles then fuse with the cell membrane and expose the GLUT4 transporters to the extracellular fluid.
Insulin also increases the activity of pyruvate dehydrogenase and acetylCoA carboxylase within adipocytes, facilitating the conversion of absorbed glucose into triglycerides for lipid storage.
In a similar fashion to adipose tissues, insulin causes the recruitment of GLUT4 transporters to the surface of skeletal muscle cells. Following a ketogenic diet means eating a high fat diet with very little carbohydrate and moderate protein.
This means eating lots of meat, fish, eggs, cheese, butter, oils, and low carbohydrate vegetables, and eliminating grain products, beans, and even fruit. Being in ketosis also seems to reduce appetite, and it causes you to lose a lot of water weight initially.
There are also concerns that the high levels of saturated fat in most ketogenic diets could increase risk of heart disease in the long term.
There are three main types of diabetes: type 1, type 2, and gestational diabetes. This is an autoimmune disease in which the beta-cells of the pancreas are destroyed by your own immune system.
Excess glucose from the blood is also excreted in the urine, increasing urination and thirst. Once diagnosed, type 1 diabetics have to take insulin in order to regulate their blood glucose.
Traditionally, this has required insulin injections timed with meals. New devices like continuous glucose monitors and automatic insulin pumps can track glucose levels and provide the right amount of insulin, making managing type 1 diabetes a little easier. Figuring out the right amount of insulin is important, because chronically elevated blood glucose levels can cause damage to tissues around the body.
However, too much insulin will cause hypoglycemia , which can be very dangerous. Type 1 diabetes is most commonly diagnosed in childhood, but it has been known to develop at any age. Development of type 2 diabetes begins with a condition called insulin resistance. The result is the same: high blood glucose.
At this point, you may be diagnosed with a condition called prediabetes. The pancreas tries to compensate by making more insulin, but over time, it becomes exhausted and eventually produces less insulin, leading to full-blown type 2 diabetes.
According to the CDC, million Americans are living with diabetes Although people of all shapes and sizes can get Type 2 diabetes, it is strongly associated with abdominal obesity.
In the past, it was mainly diagnosed in older adults, but it is becoming more and more common in children and adolescents as well, as obesity has increased in all age groups.
In the maps below, you can see that as obesity has increased in states around the country, so has diabetes. The complications of type 2 diabetes result from long-term exposure to high blood glucose, or hyperglycemia.
This causes damage to the heart, blood vessels, kidneys, eyes, and nerves, increasing the risk of heart disease and stroke, kidney failure, blindness, and nerve dysfunction. People with uncontrolled Type 2 diabetes can also end up with foot infections and ulcers because of impaired nerve function and wound healing.
If left untreated, this results in amputation. This video reviews the causes, complications, and treatments for type 2 diabetes. Gestational diabetes is diabetes that develops during pregnancy in women that did not previously have diabetes.
It affects approximately 6 percent of pregnancies in the U. It can cause pregnancy complications, mostly associated with excess fetal growth because of high blood glucose. Although it usually goes away once the baby is born, women who have gestational diabetes are more likely to develop type 2 diabetes later in life, so it is a warning sign for them.
This video does a nice job of explaining the causes of the different types of diabetes. All of the following have been shown to help manage diabetes and reduce complications. Nutrition Science and Everyday Application Callahan, Leonard, and Powell. Search site Search Search. Go back to previous article.
Sign in. Hormones Involved in Blood Glucose Regulation Central to maintaining blood glucose homeostasis are two hormones, insulin and glucagon , both produced by the pancreas and released into the bloodstream in response to changes in blood glucose.
Insulin is made by the beta-cells of the pancreas and released when blood glucose is high. It causes cells around the body to take up glucose from the blood, resulting in lowering blood glucose concentrations.
Glucagon is made by the alpha-cells of the pancreas and released when blood glucose is low. It causes glycogen in the liver to break down, releasing glucose into the blood, resulting in raising blood glucose concentrations.
Remember that glycogen is the storage form of glucose in animals. In this image, cell nuclei are stained blue, insulin is stained red, and blood vessels are stained green. You can see that this islet is packed with insulin and sits right next to a blood vessel, so that it can secrete the two hormones, insulin and glucagon, into the blood.
This allows glucose to enter the cell, where it can be used in several ways. If the cell needs energy right away, it can metabolize glucose through cellular respiration, producing ATP step 5. Alternatively, it can be converted to fat and stored in that form step 6.
You receive messages from your brain and nervous system that you should eat. Glucagon is released from the pancreas into the bloodstream. In liver cells, it stimulates the breakdown of glycogen , releasing glucose into the blood.
In addition, glucagon stimulates a process called gluconeogenesis , in which new glucose is made from amino acids building blocks of protein in the liver and kidneys, also contributing to raising blood glucose. Glucose can be used to generate ATP for energy, or it can be stored in the form of glycogen or converted to fat for storage in adipose tissue.
Glucose, a 6-carbon molecule, is broken down to two 3-carbon molecules called pyruvate through a process called glycolysis. Pyruvate enters a mitochondrion of the cell, where it is converted to a molecule called acetyl CoA. Acetyl CoA goes through a series of reactions called the Krebs cycle. This cycle requires oxygen and produces carbon dioxide.
It also produces several important high energy electron carriers called NADH 2 and FADH 2. These high energy electron carriers go through the electron transport chain to produce ATP—energy for the cell!
Note that the figure also shows that glucose can be used to synthesize glycogen or fat, if the cell already has enough energy.
Therefore, they start breaking down body proteins, which will cause muscle wasting. It can go through the Krebs cycle to produce ATP, but if carbohydrate is limited, the Krebs cycle gets overwhelmed.
In this case, acetyl CoA is converted to compounds called ketones or ketone bodies. These can then be exported to other cells in the body, especially brain and muscle cells.
The brain can adapt to using ketones as an energy source in order to conserve protein and prevent muscle wasting.
Insulin Omega- for overall well-being glucagon help Glucose regulation processes blood sugar levels. Glucagon regulaiton prevent blood sugar from dropping, while tegulation stops it from rising too high. Glucagon Energy boosting tips for swimmers down glycogen to glucose in the liver. Insulin enables blood glucose to enter cells, where they use it to produce energy. Together, insulin and glucagon help maintain homeostasis, where conditions inside the body hold steady. When their blood sugar levels drop, their pancreas releases glucagon to raise them.
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