The Digestive System and Body Metabolism

The Digestive System Functions

Ingestion—taking in foodDigestion—breaking food down both

physically and chemicallyAbsorption—movement of nutrients into

the bloodstreamDefecation—rids the body of indigestible

waste

Organs of the Digestive SystemTwo main groups

Alimentary canal (gastrointestinal or GI tract)—continuous coiled hollow tube

Accessory digestive organs

Organs of the Digestive System

Figure 14.1

Organs of the Alimentary CanalMouthPharynxEsophagusStomachSmall intestineLarge intestineAnus

Mouth (Oral Cavity) AnatomyLips (labia)—protect the anterior openingCheeks—form the lateral wallsHard palate—forms the anterior roofSoft palate—forms the posterior roofUvula—fleshy projection of the soft palate

Mouth (Oral Cavity) AnatomyVestibule—space between lips externally

and teeth and gums internallyOral cavity proper—area contained by the

teethTongue—attached at hyoid bone and

styloid processes of the skull, and by the lingual frenulum to the floor of the mouth

TonsilsPalatineLingual

Mouth (Oral Cavity) Anatomy

Figure 14.2a

Mouth PhysiologyMastication (chewing) of foodMixing masticated food with salivaInitiation of swallowing by the tongueAllows for the sense of taste

Pharynx AnatomyNasopharynx—not part of the digestive

systemOropharynx—posterior to oral cavityLaryngopharynx—below the oropharynx

and connected to the esophagus

Pharynx Anatomy

Figure 14.2a

Pharynx PhysiologyServes as a passageway for air and foodFood is propelled to the esophagus by two

muscle layersLongitudinal inner layerCircular outer layer

Food movement is by alternating contractions of the muscle layers (peristalsis)

Esophagus Anatomy and PhysiologyAnatomy

About 10 inches longRuns from pharynx to stomach through the

diaphragmPhysiology

Conducts food by peristalsis (slow rhythmic squeezing)

Passageway for food only (respiratory system branches off after the pharynx)

Layers of Alimentary Canal OrgansFour layers

MucosaSubmucosaMuscularis externaSerosa

Layers of Alimentary Canal OrgansMucosa

Innermost, moist membrane consisting ofSurface epitheliumSmall amount of connective tissue

(lamina propria)Small smooth muscle layer

Layers of Alimentary Canal OrgansSubmucosa

Just beneath the mucosaSoft connective tissue with blood vessels,

nerve endings, and lymphatics

Layers of Alimentary Canal OrgansMuscularis externa—smooth muscle

Inner circular layerOuter longitudinal layer

Serosa—outermost layer of the wall contains fluid-producing cellsVisceral peritoneum—outermost layer that is

continuous with the innermost layerParietal peritoneum—innermost layer that

lines the abdominopelvic cavity

Alimentary Canal Nerve PlexusesTwo important nerve plexuses serve the

alimentary canalBoth are part of the autonomic nervous

systemSubmucosal nerve plexusMyenteric nerve plexus

Function is to regulate mobility and secretory activity of the GI tract organs