Understanding how the body controls and uses glucose in a normally healthy person will help you to understand what happens when diabetes develops. First we will briefly introduce the main cells, tissues and hormones involved in glucose regulation.

Hormones in Glucose Regulation

The main role of glucose in the body is like fuel in a car: glucose is a source of energy in human beings. When you are in good health the body controls the level of blood glucose and doesn't allow this to become very high or very low. The normal range is 80-110 mg (milligrammes) of glucose for every 10 ml of blood. Glucose control is due to the action of hormones.

These hormones are signalling substances produced by collections of cells, called endocrine glands, which release their hormones into the blood. Cells are the tiny building blocks of the body, which can only be seen through a microscope. In the human body, there are many different types of cells doing many different tasks. Hormones are carried around the body in the blood and on that journey they interact with whichever "target tissue" is receptive to their signals.

There are many different hormones acting throughout the body. Insulin and glucagon are the two most important hormones involved in the control of blood glucose levels.

The Pancreas

The pancreas is a "leaf-shaped" organ found deep inside the abdomen. The abdomen is the part of the body between the chest and pelvis. The abdomen contains such organs as the stomach, liver, spleen, pancreas, intestines and other structures (see Figure 4.2).

The pancreas has a short connecting tube (the pancreatic duct, see Figure 4.3), which opens into the small intestine so that pancreatic juices can help with the process of digestion. Specialised cells in a part of the pancreas called the islets of Langerhans produce the hormones insulin and glucagon.

The beta cells produce insulin and the alpha cells produce glucagon. When the body is healthy these two hormones help to keep the amount of glucose in the blood at the normal level. If the pancreas is severely damaged or removed by operation, the production of insulin and glucagon will stop and diabetes will result.

Figure 4.2 The digestive tract

The digestive tract (or gastrointestinal system) is the tube-like passage from the mouth, through the stomach and intestines to the anus, together with the organs that connect with it (e.g. the liver and pancreas).

Figure 4.3: The islets of Langerhans in the pancreas (Source: L 4 HES training module)

Insulin and its role in glucose regulation

Insulin has many functions, but its main role is to help glucose enter into the body's cells, so they can use it as a fuel for all the processes that need energy. The pancreas releases insulin into the blood when we eat a meal.

  • Can you suggest why this timing is important?
  • As we digest our food, the level of glucose in the blood rises as it is absorbed from the intestines. It makes sense for insulin levels also to rise in response to the increase in blood glucose. Insulin not only enables glucose to be transported into the cells that need it as a source of fuel, and it also prevents the glucose level in the blood from rising too high when we eat a sugary meal. It acts on the liver, muscles and body fat, stimulating them to take up excess glucose and store it, and it stops stored glucose from being released from these tissues when the level in the blood is already too high.
  • Between meals and overnight the insulin level in the blood falls. If this did not happen, what would be the effect on the blood glucose level, and why?
  • It would become too low, because insulin would go on stimulating the body's cells to take up glucose from the blood and to store it in the liver, muscles and body fat. So, adjustments in the amount of insulin released by the pancreas regulate the blood glucose level to stay within the tight range that the body needs to function normally. In a person with diabetes mellitus, problems in insulin production result in poor regulation of blood glucose, with serious effects, as you will see later in this study session.

Glucagon

The action of the hormone glucagon works in the opposite direction to insulin. Glucagon causes the blood glucose level to rise if it has fallen too low. It does this by stimulating the liver, muscles and body fat to release their stored glucose back into the blood. The brain does not function properly if glucose levels in the blood drop even a small amount below normal, and if they drop further still the person becomes confused and eventually becomes unconscious. Brain damage and eventually death results if the brain is starved of glucose for a long period.

The liver in glucose regulation

The liver is a large and important organ, with many functions, which lies across the top and towards the right of the abdomen. As you already know, it is important in helping to control glucose levels, by storing excess glucose and releasing it back into the blood when the level falls too low. Insulin stimulates the liver to take up glucose and change it into glycogen, a substance made of chains of glucose units stuck together. You can think of glycogen as a storage form of glucose. If there is plenty of glucose in the blood, the body makes glycogen to use later, at times when glucose is scarce. For example, to keep the blood glucose level constant in the body overnight (when one is not eating), the liver slowly releases glucose from its glycogen stores. After a meal when there is plenty of glucose in the blood, the liver stores glucose as glycogen again. Similarly, when you exercise and need additional fuel, the liver can slowly release glucose to provide energy.

The muscles in glucose regulation

There are different types of muscles in the body and they have different functions. Skeletal muscles are the ones used for movement, for example in your arms and legs. The involuntary muscles are the ones over which we have no conscious control, for example, the muscles in the walls of the stomach and intestines that move food through the digestive tract.

Like the liver, skeletal muscles store glucose as glycogen and are able to use glucose as a fuel. Insulin stimulates muscles to take up glucose. When the muscles are active (for example, while exercising), the absorbed glucose is used to fuel muscular activity.

Fats and diabetes

Fats in the body have an important role in diabetes. Being overweight or obese increases the health risk for people who are already diabetic, and it is a significant risk for developing diabetes in later life. The breakdown of fats in the body as an alternative source of fuel to glucose is more likely to occur in people with diabetes, because their cells cannot take up glucose easily when insulin levels are low.

When fats are broken down to be used as fuel, one of the side-effects is the production of small molecules called ketones. They can build up to dangerously high levels in a person with diabetes, making the blood too acid (the condition is called ketoacidosis), and the person's breath has a distinctive "fruity" smell.

Last modified: Tuesday, 28 February 2017, 7:02 PM