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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.

The body's cells need (require) sufficient quantities of raw materials for their energy and
synthetic processes. These raw materials are obtained from the external environment through
the ingestion of food (solid, semi-solid and liquid). 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.
Digestive system
The gastrointestinal tract includes the mouth, oesophagus, stomach, small intestine, and
large intestine (Figure 1). Food enters through the mouth and is moved to the pharynx by
skeletal muscle activity, then propelled through the rest of the tract by smooth muscle
contractions. Along the way, it is transformed into a semi-fluid mixture as digestive secretions
enter at various points to dissolve and break down nutrients. Muscle contractions also help mix
these secretions with the food, aiding digestion.
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.


• Exocrine pancreas releases pancreatic juice rich in enzymes that break down food into
  absorbable molecules.


• Liver (exocrine function) produces bile, which is crucial for fat digestion (fats) and also
  helps eliminate waste metabolites and drugs.