Encyclopedia of Health and Medicine

THE 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 discussion
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.
MOUTH
Structures of the Gastrointestinal System
hard palate
soft palate
cheeks
SALIVARY GLANDS
TEETH
tongue
lips
epiglottis
ESOPHAGUS
lower esophageal sphincter
stomach
fundus
rugae
gastric glands
pylorus
pyloric sphincter
LIVER
GALLBLADDER
common bile duct
cystic duct
hepatic duct
PANCREAS
pancreatic duct
accessory pancreatic duct
SMALL INTESTINE
DUODENUM
ampulla of Vater
ILEUM
JEJUNUM
COLON
APPENDIX
CECUM
ascending colon
transverse colon
descending colon
sigmoid colon
RECTUM
ANUS
Functions of the Gastrointestinal System
TRADITIONAL CHINESE MEDICINE (TCM), a centuriesold
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 distributes
energy throughout the body much like a
burner or heater. Western medicine shares a similar
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 gastrointestinal
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 passage,
the food undergoes numerous transformations
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 MOVEMENT in
the same period is testament to the gastrointestinal
system’s efficiency in extracting every molecule,
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 HORMONES signal the need to
release bile for digestion. The bile flows through
another duct, the common bile duct, mixes with
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