CHAPTER 15: DIGESTIVE TRACT
DIGESTIVE TRACT GENERAL STRUCTURE OF THE DIGESTIVE TRACT:
• The digestive system consists of the: Figure 15–12. Major layers and organization of the digestive tract.
o DIGESTIVE TRACT
▪ Oral Cavity
▪ Esophagus
▪ Stomach
▪ Small and Large Intestines
▪ Anus
o ASSOCIATED GLANDS
▪ Salivary Glands
▪ Liver
▪ Pancreas
• Also called the gastrointestinal (GI) tract or alimentary
canal.
• Its function is to obtain molecules from the ingested food
that are necessary for the maintenance, growth, and
energy needs of the body.
• The inner layer of the entire digestive tract forms an
important protective barrier.
FUNCTIONS OF THE STRUCTURES WITHIN THE
DIGESTIVE TRACT
• The GI tract is a hollow tube with a lumen of variable
• INGESTION diameter and a wall made up of four main layers:
o Introduction of food and liquid into the oral cavity. o MUCOSA
▪ Also called as mucous membrane.
• MASTICATION ▪ Consists of an epithelial lining.
o Chewing, which divides solid food into digestible ▪ An underlying lamina propria and a thin layer
pieces. of smooth muscle called the muscularis
mucosae that separate mucosa from
• MOTILITY submucosa.
o Muscular movements of materials through the tract. o SUBMUCOSA
▪ Contains denser connective tissue and
• SECRETION submucosal (meissner) plexus of autonomic
o Secretion of lubricating and protective mucus, nerve.
digestive enzymes, acidic and alkaline fluids, and bile. o MUSCULARIS
▪ Also called as muscularis externa.
• HORMONE RELEASE ▪ Composed of smooth muscle cells organized as
o For local control of motility and secretion. two or more sublayers.
o SEROSA
• CHEMICAL DIGESTION ▪ A thin sheet of loose connective tissue.
o Enzymatic degradation of large macromolecules in ▪ Covered with simple squamous epithelium or
food to smaller molecules and their subunits. mesothelium.
▪ Outermost layer of the digestive tract located
• ABSORPTION within the abdominal cavity.
o Absorption of the small molecules and water into the
blood and lymph; and
• ELIMINATION
o Elimination of indigestible, unabsorbed components of
food.
MONTAÑO, ONTONG, PADILLA, SANGARIOS | MLS 2F
1
, TRANS: CHAPTER 15 DIGESTIVE TRACT
ORAL CAVITY • Provides continuous flow of fluid over
the taste buds, washing the food
• Lined with stratified squamous epithelium (keratinized,
particles to receive and process new
partially keratinized or nonkeratinized depending on the
location).
gustatory stimuli.
• Contain lipase that prevents
• KERATINIZED LAYERS hydrophobic film.
o Resist damage from abrasion, best developed in the
masticatory mucosa (gingiva and hard palate). TASTE BUDS
• NONKERATINIZED • Stratified epithelium on the tongue’s surface.
o Predominates in the lining mucosa (soft palate, • Sample the general chemical composition of ingested
cheeks, floor of the mouth, pharynx, and posterior material.
region leading to the esophagus). • 250 taste buds are present.
• 50-100 cells, about half of which are elongated gustatory
• The epithelium contains transient antigen-presenting cells (taste) cells with 7-10 days life span.
(APC) and rich sensory innervation.
• Other cell present:
o Supportive cells
o Immature cells
o Stem cells
• Taste bud detect at least five broad categories of tastants:
o Salty
o Sour
o Sweet
o Bitter
o Savory
TEETH
• Normally 32 permanent teeth in adult.
• Each quadrant has 8 teeth:
o (2) Incisors
o (1) Canine
TONGUE o (2) Premolars
o (3) Permanent Molars
• A mass of striated muscle covered by mucosa. • 20 of permanent teeth are preceded by primary teeth
(milk teeth).
• Manipulates ingested material during mastication and
swallowing. • Each tooth has a crown covered by enamel and the roots
by a bone-like tissue called cementum.
• SULCUS TERMINALIS
o A V-shaped groove that separates papillary and DENTIN
tonsillar areas. • Calcified tissue harder than bone.
• Consists of 70% hydroxyapatite.
• 4 TYPES OF LINGUAL PAPILLAE
o FILIFORM PAPILLAE • ODONTOBLASTS
▪ Numerous, elongated conical shape, and o Tall, polarized cells derived from the cranial neural
heavily keratinized. crest that line the tooth’s pulp cavity.
▪ Gray or whitish appearance. ▪ Secretes the mineralization of predentin matrix.
▪ Provide a rough surface that facilitates ▪ Important for the maintenance of dentin matrix.
movement of food during chewing. ▪ Develop from neural crest cell and mesoderm.
o FUNGIFORM PAPILLAE
▪ Less numerous, lightly keratinized, and
interspersed among the filiform papillae.
▪ Mushroom-shaped with well-vascularized
and innervated cores of lamina propria.
o FOLIATE PAPILLAE
▪ Consist of several parallel ridges on each
side of the tongue.
▪ Anterior to the sulcus terminalis, but
rudimentary in humans (older individuals).
o VALLATE (CIRCUMVALLATE) PAPILLAE
▪ Largest papillae (1-3 mm)
▪ Salivary (von Ebner) glands
• Moat-like groove surrounding each
vallate papilla.
MONTAÑO, ONTONG, PADILLA, SANGARIOS | MLS 2F
2
, TRANS: CHAPTER 15 DIGESTIVE TRACT
ENAMEL ESOPHAGUS
• Hardest component of the human body.
Figure 15–12. Esophagus.
• Consists of 96% calcium hydroxyapatite and 2-3% organic
materials.
• Consists of uniform, interlocking columns called enamel
rods (prism).
• AMELOBLASTS (TOMES)
o Tall, polarized cells that secretes the matrix for the
enamel rods in a developing tooth bud.
▪ Part of specialized epithelium called enamel
organ.
▪ Derived from ectodermal lining of the embryonic
oral cavity.
o AMELOGENIN
▪ Main structural protein of developing enamel.
o These tissues produce:
▪ (52) Tooth Buds • A muscular tube, about 25-cm long in adults, which
▪ (20) Primary teeth transports swallowed material from the pharynx to the
stomach.
▪ (32) Secondary or permanent teeth.
o Permanent teeth erupt about 6 months after birth. • The esophageal mucosa has nonkeratinized stratified
squamous epithelium, and the submucosa contains
small mucus-secreting glands, the esophageal glands,
which lubricate and protect the mucosa.
• Near the stomach the mucosa also contains groups of
glands, the esophageal cardiac glands, which secrete
additional mucus.
• SWALLOWING
o Begins with voluntary muscle action but finishes with
involuntary peristalsis.
o In approximately the upper one-third of the esophagus,
the muscularis is exclusively skeletal muscle like
that of the tongue.
o The middle portion of the esophagus has a
combination of skeletal and smooth muscle fibers,
PERIODONTIUM and in the lower third the muscularis is exclusively
smooth muscle.
• Responsible for maintaining the teeth in the maxillary and o Only the distal 1-2 cm of the esophagus, in the
mandibular bones. peritoneal cavity, is covered by serosa; the rest is
enclosed by the loose connective tissue of the
o CEMENTUM adventitia, which blends into the surrounding tissue.
▪ Covers dentin of the root and resembles bone,
but it is avascular.
Figure 15–13. Esophagus.
o PERIODONTAL LIGAMENTS
▪ Fibrous connective tissue with bundled collagen
fibers binding the cementum and the alveolar
bone.
o ALVEOLAR BONE
▪ Lacks the typical lamellar pattern of adult bone
but has osteoblasts and osteocytes engaging in
continuous remodeling of bone matrix.
o GINGIVA
▪ The keratinized oral mucosa firmly bound to the
periosteum of the maxillary and mandibular
bones.
o JUNCTIONAL EPITHELIUM
▪ Specialized part of this epithelium, bound to the
tooth enamel by means of a cuticle, which
resembles a thick basal lamina to which the
epithelial cells are attached by numerous
hemidesmosomes.
MONTAÑO, ONTONG, PADILLA, SANGARIOS | MLS 2F
3
DIGESTIVE TRACT GENERAL STRUCTURE OF THE DIGESTIVE TRACT:
• The digestive system consists of the: Figure 15–12. Major layers and organization of the digestive tract.
o DIGESTIVE TRACT
▪ Oral Cavity
▪ Esophagus
▪ Stomach
▪ Small and Large Intestines
▪ Anus
o ASSOCIATED GLANDS
▪ Salivary Glands
▪ Liver
▪ Pancreas
• Also called the gastrointestinal (GI) tract or alimentary
canal.
• Its function is to obtain molecules from the ingested food
that are necessary for the maintenance, growth, and
energy needs of the body.
• The inner layer of the entire digestive tract forms an
important protective barrier.
FUNCTIONS OF THE STRUCTURES WITHIN THE
DIGESTIVE TRACT
• The GI tract is a hollow tube with a lumen of variable
• INGESTION diameter and a wall made up of four main layers:
o Introduction of food and liquid into the oral cavity. o MUCOSA
▪ Also called as mucous membrane.
• MASTICATION ▪ Consists of an epithelial lining.
o Chewing, which divides solid food into digestible ▪ An underlying lamina propria and a thin layer
pieces. of smooth muscle called the muscularis
mucosae that separate mucosa from
• MOTILITY submucosa.
o Muscular movements of materials through the tract. o SUBMUCOSA
▪ Contains denser connective tissue and
• SECRETION submucosal (meissner) plexus of autonomic
o Secretion of lubricating and protective mucus, nerve.
digestive enzymes, acidic and alkaline fluids, and bile. o MUSCULARIS
▪ Also called as muscularis externa.
• HORMONE RELEASE ▪ Composed of smooth muscle cells organized as
o For local control of motility and secretion. two or more sublayers.
o SEROSA
• CHEMICAL DIGESTION ▪ A thin sheet of loose connective tissue.
o Enzymatic degradation of large macromolecules in ▪ Covered with simple squamous epithelium or
food to smaller molecules and their subunits. mesothelium.
▪ Outermost layer of the digestive tract located
• ABSORPTION within the abdominal cavity.
o Absorption of the small molecules and water into the
blood and lymph; and
• ELIMINATION
o Elimination of indigestible, unabsorbed components of
food.
MONTAÑO, ONTONG, PADILLA, SANGARIOS | MLS 2F
1
, TRANS: CHAPTER 15 DIGESTIVE TRACT
ORAL CAVITY • Provides continuous flow of fluid over
the taste buds, washing the food
• Lined with stratified squamous epithelium (keratinized,
particles to receive and process new
partially keratinized or nonkeratinized depending on the
location).
gustatory stimuli.
• Contain lipase that prevents
• KERATINIZED LAYERS hydrophobic film.
o Resist damage from abrasion, best developed in the
masticatory mucosa (gingiva and hard palate). TASTE BUDS
• NONKERATINIZED • Stratified epithelium on the tongue’s surface.
o Predominates in the lining mucosa (soft palate, • Sample the general chemical composition of ingested
cheeks, floor of the mouth, pharynx, and posterior material.
region leading to the esophagus). • 250 taste buds are present.
• 50-100 cells, about half of which are elongated gustatory
• The epithelium contains transient antigen-presenting cells (taste) cells with 7-10 days life span.
(APC) and rich sensory innervation.
• Other cell present:
o Supportive cells
o Immature cells
o Stem cells
• Taste bud detect at least five broad categories of tastants:
o Salty
o Sour
o Sweet
o Bitter
o Savory
TEETH
• Normally 32 permanent teeth in adult.
• Each quadrant has 8 teeth:
o (2) Incisors
o (1) Canine
TONGUE o (2) Premolars
o (3) Permanent Molars
• A mass of striated muscle covered by mucosa. • 20 of permanent teeth are preceded by primary teeth
(milk teeth).
• Manipulates ingested material during mastication and
swallowing. • Each tooth has a crown covered by enamel and the roots
by a bone-like tissue called cementum.
• SULCUS TERMINALIS
o A V-shaped groove that separates papillary and DENTIN
tonsillar areas. • Calcified tissue harder than bone.
• Consists of 70% hydroxyapatite.
• 4 TYPES OF LINGUAL PAPILLAE
o FILIFORM PAPILLAE • ODONTOBLASTS
▪ Numerous, elongated conical shape, and o Tall, polarized cells derived from the cranial neural
heavily keratinized. crest that line the tooth’s pulp cavity.
▪ Gray or whitish appearance. ▪ Secretes the mineralization of predentin matrix.
▪ Provide a rough surface that facilitates ▪ Important for the maintenance of dentin matrix.
movement of food during chewing. ▪ Develop from neural crest cell and mesoderm.
o FUNGIFORM PAPILLAE
▪ Less numerous, lightly keratinized, and
interspersed among the filiform papillae.
▪ Mushroom-shaped with well-vascularized
and innervated cores of lamina propria.
o FOLIATE PAPILLAE
▪ Consist of several parallel ridges on each
side of the tongue.
▪ Anterior to the sulcus terminalis, but
rudimentary in humans (older individuals).
o VALLATE (CIRCUMVALLATE) PAPILLAE
▪ Largest papillae (1-3 mm)
▪ Salivary (von Ebner) glands
• Moat-like groove surrounding each
vallate papilla.
MONTAÑO, ONTONG, PADILLA, SANGARIOS | MLS 2F
2
, TRANS: CHAPTER 15 DIGESTIVE TRACT
ENAMEL ESOPHAGUS
• Hardest component of the human body.
Figure 15–12. Esophagus.
• Consists of 96% calcium hydroxyapatite and 2-3% organic
materials.
• Consists of uniform, interlocking columns called enamel
rods (prism).
• AMELOBLASTS (TOMES)
o Tall, polarized cells that secretes the matrix for the
enamel rods in a developing tooth bud.
▪ Part of specialized epithelium called enamel
organ.
▪ Derived from ectodermal lining of the embryonic
oral cavity.
o AMELOGENIN
▪ Main structural protein of developing enamel.
o These tissues produce:
▪ (52) Tooth Buds • A muscular tube, about 25-cm long in adults, which
▪ (20) Primary teeth transports swallowed material from the pharynx to the
stomach.
▪ (32) Secondary or permanent teeth.
o Permanent teeth erupt about 6 months after birth. • The esophageal mucosa has nonkeratinized stratified
squamous epithelium, and the submucosa contains
small mucus-secreting glands, the esophageal glands,
which lubricate and protect the mucosa.
• Near the stomach the mucosa also contains groups of
glands, the esophageal cardiac glands, which secrete
additional mucus.
• SWALLOWING
o Begins with voluntary muscle action but finishes with
involuntary peristalsis.
o In approximately the upper one-third of the esophagus,
the muscularis is exclusively skeletal muscle like
that of the tongue.
o The middle portion of the esophagus has a
combination of skeletal and smooth muscle fibers,
PERIODONTIUM and in the lower third the muscularis is exclusively
smooth muscle.
• Responsible for maintaining the teeth in the maxillary and o Only the distal 1-2 cm of the esophagus, in the
mandibular bones. peritoneal cavity, is covered by serosa; the rest is
enclosed by the loose connective tissue of the
o CEMENTUM adventitia, which blends into the surrounding tissue.
▪ Covers dentin of the root and resembles bone,
but it is avascular.
Figure 15–13. Esophagus.
o PERIODONTAL LIGAMENTS
▪ Fibrous connective tissue with bundled collagen
fibers binding the cementum and the alveolar
bone.
o ALVEOLAR BONE
▪ Lacks the typical lamellar pattern of adult bone
but has osteoblasts and osteocytes engaging in
continuous remodeling of bone matrix.
o GINGIVA
▪ The keratinized oral mucosa firmly bound to the
periosteum of the maxillary and mandibular
bones.
o JUNCTIONAL EPITHELIUM
▪ Specialized part of this epithelium, bound to the
tooth enamel by means of a cuticle, which
resembles a thick basal lamina to which the
epithelial cells are attached by numerous
hemidesmosomes.
MONTAÑO, ONTONG, PADILLA, SANGARIOS | MLS 2F
3
