Let's Journey Through the Digestive System
LEARNING OBJECTIVES
1.
List
the organs of the gastrointestinal tract and
their functions.
2.
Identify
the accessory organs of the digestive
system and the function of their secretions.
3.
Describe
the tissue layers that form the walls of
the digestive tract.
4.
Explain
the processes associated with digestion.
5.
Compare
the absorption of water-soluble nutri-
ents and the absorption of fat-soluble nutrients.
he cells in your body require many small
molecules to function properly, such as car-
bohydrates,
lipids,
and amino acids
(see
Chapter 2). However, food is most commonly
available in much larger forms, such as your waffle, sau-
sage, and egg breakfast. Your cells cannot use the food in
such a meal directly, so the body must break down food
into smaller, usable components. This is the job of the
digestive system.
The digestive system basically consists of a long,
continuous
tube
called
the
gastrointestinal
(GI)
InSight
T h e d i g e s t i v e s y s t e m
F ig u r e 1 4 .1
Mouth
(oral cavity) forms the
chamber where food is
chewed.
Teeth
mechanically digest
food by chewing.
• Muscular
tongue
manipulates food and holds
taste sensors.
Salivary glands
(outside
mouth) secrete
saliva
, which
lubricates food and begins
chemical digestion with the
enzyme
salivary amylase
.
Stomach
is a muscular mixing chamber
and storage container for food.
• Contractions of stomach muscle
mechanically mix the food.
• Secretions of hydrochloric acid, pepsin,
and lipase chemically break down food.
• Intrinsic factor secretion assists
absorption of vitamin B12.
• Some absorption of water, ions,
short-chain fatty acids, and drugs
(alcohol, aspirin, ibuprofen) occurs in the
stomach.
• Stomach controls rate of food expulsion
into the small intestine (gastric emptying).
P harynx
and
esophagus
are muscular
conduits that propel
swallowed food from the
mouth to the stomach.
400 CHAPTER 14
The Digestive System, Nutrition, and Metabolism
previous page 435 Craig Freudenrich, Gerard J  Tortora   Visualizing Anatomy and Physiology   2011 read online next page 437 Craig Freudenrich, Gerard J  Tortora   Visualizing Anatomy and Physiology   2011 read online Home Toggle text on/off