The body's cells need (require) sufficient quantities of raw materials for their energy and
synthetic processes.Several exocrine organs outside the gastrointestinal tract play key roles in digestion by
secreting essential digestive fluids (juices):
- Salivary glands (three pairs) produce saliva, primarily to lubricate the upper GI tract
and aid food movement.Along the way, it is transformed into a semi-fluid mixture as digestive secretions
enter at various points to dissolve and break down nutrients.The overall function of the digestive
system is to transfer nutrients contained in food from the external environment to the internal
environment, where they can be distributed to the body's cells through the bloodstream.