Glucose is a simple sugar, also known as a monosaccharide, and it is a fundamental source of energy for living organisms, including humans. Glucose is an important source of energy in the body and the sole source of energy for the brain. Free glucose is not found in many foods (grapes are an exception); however, glucose is one of the constituents of both sucrose and starch, both of which yield glucose after digestion. Glucose is stored in the body in the form of glycogen. The concentration of glucose in the blood is maintained at around 5 mmol/L by a variety of hormones, principally insulin and glucagon. If the blood-glucose concentration falls below this level neurological and other symptoms may result (see HYPOGLYCAEMIA). Conversely, if the blood-glucose level is raised above its normal level, to 10 mmol/L, the condition of hyperglycaemia develops. This is a symptom of diabetes mellitus.

Unit 2,

Reference: Oxford Concise Colour Medical Dictionary (7th Edition, Kindle Edition) Oxford University Press 2020 ISBN-13: 978-0198836629, p1552