Below picture. Islets of Langerhans contain beta cells and are located within the pancreas. Beta cells produce insulin which
is needed to metabolize glucose within the body.
As seen in site: http://news.bbc.co.uk/1/hi/health/3584090.stm

The sugar level in diabetes is too high due to the body's inability to use it properely. Normally, the body breaks sugar down
by the hormone insulin, which is made in the pancreas by beta cells. Type 1 diabetics get the disease because their beta cells
are destroyed. This causes them the need to use insulin injections in order to help control their sugar level.
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