The sugar glucose is necessary for human survival. Living requires energy and glucose is the principal fuel your body uses to produce energy. Your body has numerous mechanisms to control your blood glucose level, ensuring that a relatively constant supply is available to your tissues at all times. As circumstances change throughout the day, your metabolism shifts to maintain your blood glucose at a steady concentration, that is, to achieve glucose homeostasis.
Time to Eat
It's late afternoon and the notion hits you, "I'm hungry." The thought is simple but the processes that underlie it are highly complex. A small gland on the underside of your brain, the hypothalamus, controls whether you feel hungry or satisfied. Nerves that detect stretch tell your hypothalamus if your stomach is empty or full. Falling blood glucose and insulin levels also stimulate your hypothalamus to send the message, "It's time to eat." Although annoying at times, hunger is an important sugar control mechanism because it helps ensure that you eat regularly.
Distribution
You've had a good dinner and the presence of food in your digestive system causes the release of gut hormones called incretins. Stimulating your pancreas to produce and secrete insulin is an important function of these hormones. As sugar floods your bloodstream, insulin enables uptake of the sugar by your muscles, liver and other tissues. This distribution function of insulin is the key to keeping your blood sugar level from rising beyond normal levels. Diabetes mellitus, which is characterized by high blood sugar levels, occurs when you lack sufficient insulin or your tissues develop resistance to the hormone.
Storage
Your body uses glucose around the clock. But since you only eat periodically, your body has short- and long-term storage mechanisms to save glucose absorbed from a meal for later use. Glucose storage processes are stimulated by insulin. Your muscles and liver store glucose as glycogen, a short-term storage chemical. When you have enough glycogen stored, your liver converts any remaining excess sugar into triglycerides. which travel through the blood to your fat cells for long-term energy storage.
Bridging the Gaps
It's 3 a.m. and you are sound asleep. Your glucose homeostasis mechanisms, however, are in high gear. To prevent your blood sugar level from plummeting as you fast throughout the night, your pancreas releases the hormone glucagon, which has the opposite effect of insulin. Glucagon triggers breakdown of liver glycogen, releasing glucose into your bloodstream. If your glycogen stores are depleted during periods of prolonged fasting or heavy glucose use, your liver has the capacity to manufacture glucose to keep your brain and other organs supplied with fuel.
When you wake up in the morning and eat breakfast, the glucose homeostasis processes repeat, seamlessly balancing distribution, storage, release and production as needed.
References
- Endotext: Insulin Biosynthesis, Secretion, Structure, and Structure-Activity Relationships; Isaiah Pittman IV, D.M.Sc., et al.; October 2009
- "Pharmacological Reviews;" The Role of Incretins in Glucose Homeostasis and Diabetes Treatment; Wook Kim, Ph.D., Josephine M. Egan, M.D.; December 2008
- Elmhurst College Virtual Chembook: Glycogenesis, Glycogenolysis, and Gluconeogenesis; Charles E. Ophardt, Ph.D.; 2003
- The Medical Biochemistry Page: Glycogen Metabolism; Michael W. King, Ph.D.; February 2011
- The Medical Biochemistry Page: Glycolysis: Regulating Blood Glucose; Michael W. King, Ph.D.; February 2011
- The Medical Biochemistry Page: Gluconeogenesis; Michael W. King, Ph.D., February 2011
