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In medicine, blood sugar is a term used to refer to levels of glucose in the blood. Blood sugar concentration, or serum glucose level, is tightly regulated in the human body. Glucose, transported via the bloodstream, is the primary source of energy for the body's cells.
Normally, blood glucose levels stay within narrow limits throughout the day: 4 to 8mmol/l. Levels rise after meals and are usually lowest in the morning, before the first meal of the day.
Diabetes mellitus is the most prominent disease related to failure of blood sugar regulation.
Direct Health Effects of Blood Sugar Problems
If blood sugar levels drop too low, a potentially fatal condition called hypoglycemia develops. Symptoms may include lethargy, impaired mental functioning, irritability, and loss of consciousness.
If levels remain too high, appetite is suppressed over the short term. Long-term hyperglycemia causes many of the long-term health problems associated with diabetes, including eye, kidney, and nerve damage.
Mechanisms of Blood Sugar Regulation
Blood sugar levels are regulated by negative feedback in order to keep the body in homeostasis. The levels of glucose in the blood are monitored by the pancreas. When the concentration of glucose falls, as it is consumed to meet the body's energy demands, the pancreas releases glucagon, a hormone which targets cells in the liver. These cells then convert glycogen into glucose (this process is called glycogenolysis). The glucose is released into the bloodstream, increasing blood sugar levels.
When levels of blood sugar rise, whether as a result of glycogen conversion, or from digestion of a meal, a different hormone is released from islet cells found in the pancreas. This hormone, insulin, causes the liver to convert more glucose into glycogen (this process is called glyogenosis), decreasing blood sugar levels.
Diabetes mellitus type 1 is caused by insufficient or non-existent production of insulin, while type 2 is due to inadequate response to released insulin ( "insulin resistance"). Both types of diabetes result in too much glucose remaining in the blood.
Low Blood Sugar
Some people report drowsiness or impaired cognitive function several hours after meals, which they believe is related to a drop in blood sugar, or "low blood sugar". For more information, see:
idiopathic postprandial syndrome hypoglycemia
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