The endocrine portion of the pancreas comprises
approximately one million small clusters of cells, called
islets of Langerhans. These islets are richly vascularised,
allowing their secreted hormones ready access to the
circulation and, although they comprise only 1-2 per
cent of the mass of the pancreas, they receive about
10-15 per cent of the pancreatic blood flow.
Additionally, they are innervated by parasympathetic
and sympathetic neurons, which modulate secretion
of insulin and glucagon.