675
C h a p t e r
28
Structure and
Function of the
Gastrointestinal
System
Organization and Function of the Gastrointestinal
Tract
Upper Gastrointestinal Tract
Small Intestine
Lower Gastrointestinal Tract
Gastrointestinal Wall Structure
Mucosa
Submucosa
Muscularis Externa
Serosa and Adventitia
Gastrointestinal Innervation and Motility
Neural Control of Gastrointestinal Motility
Enteric Nervous System Innervation
Autonomic Innervation
Swallowing and Esophageal Motility
Gastric Motility
Small Intestinal Motility
Colonic Motility and Defecation
Secretory Functions of the Gastrointestinal Tract
Gastrointestinal Secretions
Salivary Secretions
Gastric Secretions
Intestinal Secretions
Gastrointestinal Hormones
Digestion and Absorption in the Gastrointestinal
Tract
Small Intestinal Digestion and Absorption
Carbohydrate Digestion and Absorption
Protein Digestion and Absorption
Fat Digestion and Absorption
Colonic Absorption and Intestinal Flora
Anorexia, Nausea, and Vomiting
Anorexia
Nausea and Vomiting
he gastrointestinal (GI) tract is an amazing struc-
ture in which food is dismantled and its nutrients
absorbed, wastes are collected and eliminated, and vita-
mins synthesized. The GI tract is also becoming increas-
ingly recognized as an endocrine organ that produces
and augments hormones that contribute to the regula-
tion of appetite and food intake and function in the use
and storage of nutrients.
As a matter of semantics, the GI tract also is referred
to as the
digestive tract
, the
alimentary canal
, and, at
times, the
gut.
The intestinal portion also may be called
the
bowel.
For the purposes of this text, the liver and
pancreas (discussed in Chapter 30), which produce
secretions that aid in digestion, are considered
accessory
organs.
Organization and Function of
the Gastrointestinal Tract
The major physiologic function of the GI tract is to
provide the body with a continual supply of water and
other nutrients. It carries out this function through
processes involving motility, secretion, digestion, and
absorption. In the digestive tract, as food moves slowly
along its length it is systematically broken down into
ions and molecules that can be absorbed into the blood
T
U N I T
Gastrointestinal
and Hepatobiliary
Function
8
