Fundamentals of Anatomy and Physiology

374

Key Terms (continued)

Periodontal ligament......... 382
Peristalsis................... 374
Pharynx....................
382
Plicae...................... 390
Premolars................... 382
Prothrombin................. 389
Pulp cavity.................. 382
Pyloric sphincter.............
39 0
Pylorus/antrum.............. 385
Rectum..................... 391
Right colic (hepatic)
flexure...................
391

Root.......................

382

Root canals..................

382

Rugae...................... 385

Sigmoid colon...............

391

The Small Intestine.

Soft palate.................. 379

Sublingual gland............. 380

Submandibular/

submaxillary gland.........

380

Submucosa.................. 390

Thrombin................... 389

Tongue..................... 379

Transverse colon............. 391

Tricuspids................... 382

Tunica mucosa............... 376

Tunica muscularis............ 377

Tunica serosa................ 375

Tunica submucosa............ 377

Uvula...................... 379

Vermiform appendix.......... 391

Villi........................ 390

Visceral peritoneum..........

377

Zymogenic/chief cells......... 385

Introduction

The function of the digestive system is to break down food
(complex carbohydrates, proteins, and fats) via hy-drolysis
into simpler substances or molecules, called nu-trients, that
can be used by the body’s cells (Table 16-1). This process
is called digestion. Digestion allows the body’s cells to
convert food energy into the high-energy adenosine
triphosphate (ATP) molecules that run the cell’s machinery.
The major organs and accessory struc-tures that perform
this function are collectively referred to as the digestive
system. The digestive system prepares food for use by cells
through five basic activities:

1.^ Ingestion or the taking of food into the body^
2. Peristalsis or the physical movement or pushing

of^ food along the digestive tract^

3. Digestion or the breakdown of food by both me-

chanical and chemical mechanisms^

4. Absorption or the passage of digested food from the
   digestive tract into the cardiovascular and lymphatic
   systems for distribution to the body’s cells
   5. Defecation or the elimination from the body of those
   substances that are indigestible and cannot be
   absorbed.
   See Concept Maps 16-1 and 16-2: The Digestive System-.

General Organization

The organs of digestion are part of two main groups. The

first is the gastrointestinal tract, or alimentary ca-

nal, which is a long continuous tube that runs through the

ventral cavity of the body and extends from the mouth to

the anus (Figure 16-1). The length of this tube is

approximately 30 feet, or 9 meters. Its organs include the

mouth or oral cavity, oropharynx, esophagus, stomach, and

the small and large intestine. Muscular contractions in the

tube break down food physically by churning it; enzymes

from cells in the tube’s wall break down food chemically.

The second group of or-gans consists of accessory

structures. They include the teeth, tongue, salivary glands,

liver and gallbladder, and pancreas.

Table 16 - 1 Digestion: An Example of Hydrolysis
Digestion is an example of a hydrolytic chemical reaction that uses water and enzymes to cause the breakdown of
-ingested food into smaller, simpler compounds.

Food Categories 1 Enzyme 1 Water Simpler Compounds (^)

1. Complex carbohydrates 1 Amylase 1 Water S Simple sugars (from the complex carbohydrates: starch, glycogen) (^)


2. Proteins 1 Proteases 1 Water S Amino acids (^)


3. Fats 1 Lipases 1 Water S Fatty acids and glycerol (^)