The Digestive System Functions
! Ingestion—taking in food
! Digestion—breaking food into nutrient molecules
! Absorption—movement of nutrients into the bloodstream
! Defecation—elimination of indigestible waste
Organs of the Digestive System
! Two main groups of organs
o Alimentary canal (gastrointestinal or GI tract)—continuous, coiled, hollow tube
! These organs ingest, digest, absorb, defecate
o Accessory digestive organs
! Includes teeth, tongue, and other large digestive organs
Organs of the Alimentary Canal
! The alimentary canal is a continuous, coiled, hollow tube that runs through the ventral
cavity from stomach to anus:
o Mouth
o Pharynx
o Esophagus
o Stomach
o Small intestine
o Large intestine
o Anus
Mouth (Oral Cavity)
! Anatomy of the mouth
o The mouth (oral cavity)—mucous membrane–lined cavity
o Lips (labia)—protect the anterior opening
o Cheeks—form the lateral walls
o Hard palate—forms the anterior roof
o Soft palate—forms the posterior roof
o Uvula—fleshy projection of the soft palate
Mouth (Oral Cavity)
! Anatomy of the mouth (continued)
o Vestibule—space between lips externally and teeth and gums internally
o Oral cavity proper—area contained by the teeth
o Tongue—attached at hyoid bone and styloid processes of the skull, and by the
lingual frenulum to the floor of the mouth
© 2015 Pearson Education, Inc.
,Mouth (Oral Cavity)
! Anatomy of the mouth (continued)
o Tonsils
! Palatine—located at posterior end of oral cavity
! Lingual—located at the base of the tongue
Mouth
! Functions of the mouth
o Mastication (chewing) of food
o Tongue mixes masticated food with saliva
o Tongue initiates swallowing
o Taste buds on the tongue allow for taste
Pharynx
! Food passes from the mouth posteriorly into the:
o Oropharynx—posterior to oral cavity
o Laryngopharynx—below the oropharynx and continuous with the esophagus
Pharynx
! The pharynx serves as a passageway for food, fluids, and air
! Food is propelled to the esophagus by two skeletal muscle layers in the pharynx
o Longitudinal inner layer
o Circular outer layer
! Alternating contractions of the muscle layers (peristalsis) propel the food
Esophagus (Gullet)
! Anatomy
o About 10 inches long
o Runs from pharynx to stomach through the diaphragm
! Physiology
o Conducts food by peristalsis (slow rhythmic squeezing) to the stomach
o Passageway for food only (respiratory system branches off after the pharynx)
Layers of Tissue in the Alimentary Canal Organs
! Summary of the four layers from innermost to outermost (detailed next):
1. Mucosa
2. Submucosa
3. Muscularis externa
4. Serosa
Layers of Tissue in the Alimentary Canal Organs
© 2015 Pearson Education, Inc.
, 1. Mucosa
o Innermost, moist membrane consisting of:
! Surface epithelium that is mostly simple columnar tissue (except for
esophagus)
! Small amount of connective tissue
(lamina propria)
! Small smooth muscle layer
o Lines the cavity (known as the lumen)
Layers of Tissue in the Alimentary Canal Organs
2. Submucosa
o Just beneath the mucosa
o Soft connective tissue with blood vessels, nerve endings, mucosa-associated
lymphoid tissue, and lymphatics
Layers of Tissue in the Alimentary Canal Organs
3. Muscularis externa—smooth muscle
o Inner circular layer
o Outer longitudinal layer
4. Serosa—outermost layer of the wall contains
fluid-producing cells
o Visceral peritoneum—innermost layer that is continuous with the outermost
layer
o Parietal peritoneum—outermost layer that lines the abdominopelvic cavity by
way of the mesentery
Alimentary Canal Nerve Plexuses
! Two important nerve plexuses serve the alimentary canal
! Both are part of the autonomic nervous system
o Submucosal nerve plexus
o Myenteric nerve plexus
! Function is to regulate mobility and secretory activity of the GI tract organs
Stomach
! The stomach is a C-shaped organ located on the left side of the abdominal cavity
! Food enters at the cardioesophageal sphincter from the esophagus
! Food empties into the small intestine at the pyloric sphincter (valve)
Stomach
! Regions of the stomach
o Cardial part (cardia)—near the heart
o Fundus—expanded portion lateral to the cardiac region
© 2015 Pearson Education, Inc.
! Ingestion—taking in food
! Digestion—breaking food into nutrient molecules
! Absorption—movement of nutrients into the bloodstream
! Defecation—elimination of indigestible waste
Organs of the Digestive System
! Two main groups of organs
o Alimentary canal (gastrointestinal or GI tract)—continuous, coiled, hollow tube
! These organs ingest, digest, absorb, defecate
o Accessory digestive organs
! Includes teeth, tongue, and other large digestive organs
Organs of the Alimentary Canal
! The alimentary canal is a continuous, coiled, hollow tube that runs through the ventral
cavity from stomach to anus:
o Mouth
o Pharynx
o Esophagus
o Stomach
o Small intestine
o Large intestine
o Anus
Mouth (Oral Cavity)
! Anatomy of the mouth
o The mouth (oral cavity)—mucous membrane–lined cavity
o Lips (labia)—protect the anterior opening
o Cheeks—form the lateral walls
o Hard palate—forms the anterior roof
o Soft palate—forms the posterior roof
o Uvula—fleshy projection of the soft palate
Mouth (Oral Cavity)
! Anatomy of the mouth (continued)
o Vestibule—space between lips externally and teeth and gums internally
o Oral cavity proper—area contained by the teeth
o Tongue—attached at hyoid bone and styloid processes of the skull, and by the
lingual frenulum to the floor of the mouth
© 2015 Pearson Education, Inc.
,Mouth (Oral Cavity)
! Anatomy of the mouth (continued)
o Tonsils
! Palatine—located at posterior end of oral cavity
! Lingual—located at the base of the tongue
Mouth
! Functions of the mouth
o Mastication (chewing) of food
o Tongue mixes masticated food with saliva
o Tongue initiates swallowing
o Taste buds on the tongue allow for taste
Pharynx
! Food passes from the mouth posteriorly into the:
o Oropharynx—posterior to oral cavity
o Laryngopharynx—below the oropharynx and continuous with the esophagus
Pharynx
! The pharynx serves as a passageway for food, fluids, and air
! Food is propelled to the esophagus by two skeletal muscle layers in the pharynx
o Longitudinal inner layer
o Circular outer layer
! Alternating contractions of the muscle layers (peristalsis) propel the food
Esophagus (Gullet)
! Anatomy
o About 10 inches long
o Runs from pharynx to stomach through the diaphragm
! Physiology
o Conducts food by peristalsis (slow rhythmic squeezing) to the stomach
o Passageway for food only (respiratory system branches off after the pharynx)
Layers of Tissue in the Alimentary Canal Organs
! Summary of the four layers from innermost to outermost (detailed next):
1. Mucosa
2. Submucosa
3. Muscularis externa
4. Serosa
Layers of Tissue in the Alimentary Canal Organs
© 2015 Pearson Education, Inc.
, 1. Mucosa
o Innermost, moist membrane consisting of:
! Surface epithelium that is mostly simple columnar tissue (except for
esophagus)
! Small amount of connective tissue
(lamina propria)
! Small smooth muscle layer
o Lines the cavity (known as the lumen)
Layers of Tissue in the Alimentary Canal Organs
2. Submucosa
o Just beneath the mucosa
o Soft connective tissue with blood vessels, nerve endings, mucosa-associated
lymphoid tissue, and lymphatics
Layers of Tissue in the Alimentary Canal Organs
3. Muscularis externa—smooth muscle
o Inner circular layer
o Outer longitudinal layer
4. Serosa—outermost layer of the wall contains
fluid-producing cells
o Visceral peritoneum—innermost layer that is continuous with the outermost
layer
o Parietal peritoneum—outermost layer that lines the abdominopelvic cavity by
way of the mesentery
Alimentary Canal Nerve Plexuses
! Two important nerve plexuses serve the alimentary canal
! Both are part of the autonomic nervous system
o Submucosal nerve plexus
o Myenteric nerve plexus
! Function is to regulate mobility and secretory activity of the GI tract organs
Stomach
! The stomach is a C-shaped organ located on the left side of the abdominal cavity
! Food enters at the cardioesophageal sphincter from the esophagus
! Food empties into the small intestine at the pyloric sphincter (valve)
Stomach
! Regions of the stomach
o Cardial part (cardia)—near the heart
o Fundus—expanded portion lateral to the cardiac region
© 2015 Pearson Education, Inc.
