Structures of the Gastrointestinal System
MOUTH cystic duct
hard palate hepatic duct
soft palate PANCREAS
cheeks pancreatic duct
SALIVARY GLANDS accessory pancreatic duct
TEETH SMALL INTESTINE
tongue DUODENUM
lips ampulla of Vater
epiglottis ILEUM
ESOPHAGUS JEJUNUM
lower esophageal sphincter COLON
stomach APPENDIX
fundus CECUM
rugae ascending colon
gastric glands transverse colon
pylorus descending colon
pyloric sphincter sigmoid colon
LIVER RECTUM
GALLBLADDER ANUS
common bile duct
Functions of the Gastrointestinal System
TRADITIONAL CHINESE MEDICINE(TCM), a centuries-
old philosophy of health centered on balance
among the body’s systems and functions, views
the torso as the “triple burner” or “triple heater.”
Here the upper, middle, and lower segments of
the body converge, becoming the core that distrib-
utes energy throughout the body much like a
burner or heater. Western medicine shares a simi-
lar understanding, translated into the tangibility
of physical structures and their functions.
The gastrointestinal system, also called the
digestive or alimentary system, functions as the
body’s furnace. Fuel—food—enters the gastroin-
testinal tract in raw form at the MOUTH. Some 20
hours or so later, the compressed residue—feces,
also called stool—exits at the other end of the
gastrointestinal tract, from the ANUS. Along its pas-
sage, the food undergoes numerous transforma-
tions as the gastrointestinal organs and structures
break it down, mechanically and chemically, into
particles and eventually into molecules of energy
(NUTRIENTS) that the bloodstream can transport to
cells throughout the body. That the typical adult
eats three to five times (or more) in 24 hours, yet
the body often passes a single BOWEL MOVEMENTin
the same period is testament to the gastrointesti-
nal system’s efficiency in extracting every mole-
cule, literally, of useful matter from all that food.
The LIVER and PANCREAS produce numerous
chemical substances to aid in breaking down the
core nutrients of food—carbohydrate, protein,
and fat—into molecules that can pass through the
membrane of the small intestine to enter the
bloodstream. The liver synthesizes BILE, a complex
fluid containing water, electrolytes, cholesterol,
biliary acids, and BILIRUBIN(400 to 800 milliliters
per day). A network of channels, the BILE DUCTS,
collect bile from the liver and transport it to the
GALLBLADDER. The gallbladder extracts water from
the bile to form a concentrated solution, which it
stores until DIGESTIVE HORMONESsignal the need to
release bile for digestion. The bile flows through
another duct, the common bile duct, mixes withTHE GASTROINTESTINAL SYSTEM
The gastrointestinal system converts ingested foods to nutrients the body can absorb and use. Physician specialists who
treat gastrointestinal conditions are gastroenterologists. This section, “The Gastrointestinal System,” presents a discus-
sion of gastrointestinal structures and their functions, an overview of gastrointestinal health and disorders, and entries
about the health conditions that can affect the gastrointestinal system.
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