The Role of Insulin

The carbs we consume are broken down into glucose in the blood stream; with insulin, glucose can be absorbed by the body. Diabetes diseases prevent a proper absorption of glucose, either because insulin is no longer produced (Type 1 diabetes) or because the body resists it (Type 2 diabetes). But what is insulin and how does it work?

Insulin

Insulin is a substance (hormone) produced by the pancreas (specifically, the beta cells in the pancreas). The pancreas is a gland organ behind the stomach that produces different hormones. One of the roles of the pancreas is to regulate the amount of glucose in the blood stream by making sure that there’s enough but not too much of it, at any moment of the day.

During a Meal

As mentioned, when we consume food, carbs are digested and elevate the amount of glucose in the blood stream. Simple carbs are digested faster are result in a “spikes” (a lot of glucose in minutes); complex carbs are digested slower (over hours) and release glucose slowly, which is preferable. Regardless of the types of carbs, the pancreas releases insulin based on the amount of glucose (although glucose spikes can lead to Type 2 diabetes over time among other reasons). The insulin allows the glucose to be absorbed by the body (brain, muscles, etc) as a primary source of energy. The extra glucose (what’s not needed by the body) is stored in the liver and muscles as glycogen for future use (more on this in a moment). If there’s still some glucose left, it is stored in fat cells.

Between Meals

The body continually needs glucose to work, every second of the day. Some time after eating, as the glucose levels become lower (between meals), the pancreas significantly reduces insulin, and starts releasing glucagon (from the pancreas’ alpha cells). Glucagon works the opposite way of insulin: it instructs the liver to release glucose in the blood stream. The liver does that by breaking down the glycogen it built up after eating.

The pancreas, by constantly monitoring the glucose level in the blood, releases either insulin (to lower blood glucose) or glucagon (to increase blood glucose).

Also while fasting (when glucose is low), fat cells release glycerol and fatty acids in the blood stream:

  • Glycerol is converted into glucose by the liver and released in the blood stream, where it can be used for energy by the body.
  • Some fatty acids are directly absorbed by muscles (for energy), and some fatty acids are converted into ketones by the liver. Ketones are a by-product i.e. a waste that the body wants to get rid of.

When glucose is not absorbed, either because there’s not enough in the blood stream (while on a low-carb diet for instance) or because of diabetes (which prevents the proper absorption of glucose by the body), fatty acids are released and the level of ketones increases. The body can adjust after a few days and start using ketones for energy, especially the brain when it cannot absorb enough glucose.

Effects of Diabetes

When people start to suffer from diabetes (lack of insulin or resistance to it), a series of conditions occur:

  • Glucose is not properly absorbed and its volume increases in the blood after each meal. This leads to a condition called hyperglycemia, which is life-threatening.
  • The liver continues to breakdown stored glycogen into more glucose (the liver normally stops doing so when there’s insulin around), further increasing the amount of glucose in the blood stream.
  • The body responds to the increase of glucose by making people thirsty, as drinking more fluids helps reducing the amount of glucose (which is expelled by the kidneys in the urine), but that is eventually not sufficient. Worse, as glucose is expelled, so is water, leading to dehydration.
  • Because glucose is not absorbed, fat cells and the liver work together to produce more ketones as an alternate source of energy. The level of ketones becomes so high that it becomes toxic, a condition called ketoacidosis, another life-threatening condition. The liver fights this condition by releasing more glucose, exasperating the prevailing hyperglycemia condition.
  • When people are finally diagnosed with diabetes, the first symptoms are sure enough very high levels of glucose (hyperglycemia) and ketones (ketoacidosis).

For people diagnosed with Type 1 diabetes, their immune system (which attacks foreign bodies) starts to attack their pancreas’ beta cells (which produce insulin) at a very young age. They are diagnosed when the level of insulin falls below a certain threshold, which initiates the problems mentioned above. Insulin injections help regulate the glucose, but the immune system will eventually destroy all remaining beta cells, a process that cannot be stopped today.

For people diagnosed with Type 2 diabetes, a series of factors (improper diet, lack of exercise, genetic predisposition) have rendered their body insensitive to insulin. Despite the presence of insulin,  the body does not properly responds to it. Through a combination of a proper diet, exercise regiment and medication, they can restore their natural body sensitivity to insulin, and be diabetes-free.

Source
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001363/
http://www.medbio.info/Horn/Time%203-4/homeostasis_2.htm
http://en.wikipedia.org/wiki/Hyperglycemia 

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