Junqueira’s Basic Histology Text and Atlas, 16th Edition
Mescher, A.L., 2021
Jay Ryan Erbito
Bachelor of Science in Biology
University of the Philippines Mindanao
Chapter 15 Digestive Tract ▪ Covered with a simple squamous epithelium.
• Consists of the digestive tract and its associated glands. ▪ Outermost layer of the digestive tract.
• Function: ▪ Serosa of the small and large intestines is continuous with the
o To obtain molecules from ingested food necessary for the maintenance, mesentery, a CT that suspends the intestines and is continuous
growth, and energy needs of the body. with the peritoneum, the serosa of the abdominal cavity.
▪ During digestion, complex molecules are broken down into their ▪ The esophagus is not suspended in a cavity and therefore lacks
small molecule subunits that are easily absorbed by the small serosa and having instead a thick adventitia, a layer of CT
intestine. continuous with the surrounding tissues.
▪ Most of the water and electrolytes are absorbed in the large • Mucosa-associated lymphoid tissue (MALT) provides an essential backup to the
intestines. thin physical barrier of the epithelial lining. The lamina propria is rich with
o Inner layer of the digestive tract forms an important barrier between the macrophages and lymphocytes for the production of IgA antibodies. These IgA
contents of the lumen and the underlying connective tissue and antibodies undergo transcytosis to form complex with proteins produced by the
vasculature. epithelial cells which can resist proteolysis by the digestive enzymes.
• Processes in the digestive system: Oral Cavity
o Ingestion – introduction of food and liquids • Lined with stratified squamous epithelium, which may be keratinized, partially
o Mastication – chewing, mechanical breakdown keratinized, or nonkeratinized depending on the location.
o Motility – muscular movements • The epithelium also undergoes continuous desquamation.
o Secretion – mucus, digestive enzymes, acidic and alkaline fluids, and bile o Keratinized epithelium
o Hormone release – local control of motility and secretion ▪ Resist damage from abrasion.
o Chemical digestion – enzymatic degradation ▪ Best developed in the masticatory mucosa on the gingiva and
o Absorption – small molecules and water enter the blood and lymph hard palate.
o Elimination – indigestible, unabsorbed components ▪ The lamina propria rests directly on the periosteum of the
General Structure of the Digestive Tract underlying bone in these regions.
• GI tract is a hollow tube with a lumen of variable diameter o Nonkeratinized epithelium
• Wall is made up of four layers: ▪ Predominates in the lining mucosa over the soft palate, cheeks,
o Mucosa or mucous membrane floor of the mouth, the pharynx, and the posterior region of the
▪ Consists of epithelial lining and an underlying lamina propria of oral cavity.
LCT ▪ Lining mucosa overlies a thick submucosa containing many
▪ Thin layer of smooth muscle (muscularis mucosae)—enables minor salivary glands to keep the mucosal surface wet.
local movements of the mucosa and separates the mucosa from • The well-developed core of striated muscle in the labia makes the structures of the
the submucosa. oral cavity highly mobile for ingestion, speech, and other forms of communication.
o Submucosa • Labial surfaces:
▪ Contains denser connective tissue and the submucosal (Meissner) o Internal mucous surface
plexus of the ENS (enteric nervous system) ▪ Has lining mucosa with thick, nonkeratinized epithelium and
o Muscularis or muscularis externa minor labial salivary glands
▪ Smooth muscle layer organized as two or more sublayers, the ▪ Red vermilion zone covered by very thin keratinized stratified
internal circular sublayer and the external longitudinal sublayer. squamous epithelium and is transitional between the oral mucosa
▪ Contains myenteric (Auerbach) nerve plexus of the ENS and the skin (mucocutaneous junction). The underlying CT is
▪ Auerbach plexus – generates and coordinates the contractions of very rich in sensory innervation and capillaries.
the muscularis which mixes and propels luminal contents ▪ Outer surface has thin skin, consisting of epidermal and dermal
forward. layers, sweat glands, and pilosebaceous units.
o Serosa Tongue
▪ Thin sheet of LCT. • Mass of striated muscle covered by mucosa.
1 | Digestive Tract
Mescher, A.L., 2021
Jay Ryan Erbito
Bachelor of Science in Biology
University of the Philippines Mindanao
Chapter 15 Digestive Tract ▪ Covered with a simple squamous epithelium.
• Consists of the digestive tract and its associated glands. ▪ Outermost layer of the digestive tract.
• Function: ▪ Serosa of the small and large intestines is continuous with the
o To obtain molecules from ingested food necessary for the maintenance, mesentery, a CT that suspends the intestines and is continuous
growth, and energy needs of the body. with the peritoneum, the serosa of the abdominal cavity.
▪ During digestion, complex molecules are broken down into their ▪ The esophagus is not suspended in a cavity and therefore lacks
small molecule subunits that are easily absorbed by the small serosa and having instead a thick adventitia, a layer of CT
intestine. continuous with the surrounding tissues.
▪ Most of the water and electrolytes are absorbed in the large • Mucosa-associated lymphoid tissue (MALT) provides an essential backup to the
intestines. thin physical barrier of the epithelial lining. The lamina propria is rich with
o Inner layer of the digestive tract forms an important barrier between the macrophages and lymphocytes for the production of IgA antibodies. These IgA
contents of the lumen and the underlying connective tissue and antibodies undergo transcytosis to form complex with proteins produced by the
vasculature. epithelial cells which can resist proteolysis by the digestive enzymes.
• Processes in the digestive system: Oral Cavity
o Ingestion – introduction of food and liquids • Lined with stratified squamous epithelium, which may be keratinized, partially
o Mastication – chewing, mechanical breakdown keratinized, or nonkeratinized depending on the location.
o Motility – muscular movements • The epithelium also undergoes continuous desquamation.
o Secretion – mucus, digestive enzymes, acidic and alkaline fluids, and bile o Keratinized epithelium
o Hormone release – local control of motility and secretion ▪ Resist damage from abrasion.
o Chemical digestion – enzymatic degradation ▪ Best developed in the masticatory mucosa on the gingiva and
o Absorption – small molecules and water enter the blood and lymph hard palate.
o Elimination – indigestible, unabsorbed components ▪ The lamina propria rests directly on the periosteum of the
General Structure of the Digestive Tract underlying bone in these regions.
• GI tract is a hollow tube with a lumen of variable diameter o Nonkeratinized epithelium
• Wall is made up of four layers: ▪ Predominates in the lining mucosa over the soft palate, cheeks,
o Mucosa or mucous membrane floor of the mouth, the pharynx, and the posterior region of the
▪ Consists of epithelial lining and an underlying lamina propria of oral cavity.
LCT ▪ Lining mucosa overlies a thick submucosa containing many
▪ Thin layer of smooth muscle (muscularis mucosae)—enables minor salivary glands to keep the mucosal surface wet.
local movements of the mucosa and separates the mucosa from • The well-developed core of striated muscle in the labia makes the structures of the
the submucosa. oral cavity highly mobile for ingestion, speech, and other forms of communication.
o Submucosa • Labial surfaces:
▪ Contains denser connective tissue and the submucosal (Meissner) o Internal mucous surface
plexus of the ENS (enteric nervous system) ▪ Has lining mucosa with thick, nonkeratinized epithelium and
o Muscularis or muscularis externa minor labial salivary glands
▪ Smooth muscle layer organized as two or more sublayers, the ▪ Red vermilion zone covered by very thin keratinized stratified
internal circular sublayer and the external longitudinal sublayer. squamous epithelium and is transitional between the oral mucosa
▪ Contains myenteric (Auerbach) nerve plexus of the ENS and the skin (mucocutaneous junction). The underlying CT is
▪ Auerbach plexus – generates and coordinates the contractions of very rich in sensory innervation and capillaries.
the muscularis which mixes and propels luminal contents ▪ Outer surface has thin skin, consisting of epidermal and dermal
forward. layers, sweat glands, and pilosebaceous units.
o Serosa Tongue
▪ Thin sheet of LCT. • Mass of striated muscle covered by mucosa.
1 | Digestive Tract
