Digestive System
Digestive system consists of the digestive (GI) tract or alimentary canal, oral cavity, esophagus, stomach, small and
large intestines, and anus—and its associated glands—salivary glands, liver, and pancreas
Its function is to obtain from ingested food the molecules necessary for the maintenance, growth, and energy needs
of the body.
1. Structures within the digestive tract allow the following (functions)
2. Ingestion, or introduction of food and liquid into the oral cavity.
3. Mastication, or chewing, which divides solid food into digestible pieces.
4. Motility, muscular movements of materials through the tract.
5. Secretion of lubricating and protective mucus, digestive enzymes, acidic and alkaline fluids, and bile.
6. Hormone release for local control of motility and secretion.
7. Chemical digestion or enzymatic degradation of large macromolecules to smaller ones and their subunits.
8. Absorption of the small molecules and water into the blood and lymph.
9. Elimination of indigestible, unabsorbed components of food.
General structure of GI tract (4 main layers):
o Mucosa (mucous membrane):
Epithelial lining
Lamina propria of loose connective tissue rich in blood vessels, lymphatics, lymphocytes, smooth muscle cells, and
often small glands.
Muscularis mucosae which is smooth muscle separating mucosa from submucosa.
o Submucosa:
Has denser connective tissue with larger blood and lymph vessels
Has submucosal (Meissner) plexus of autonomic nerves.
Might contain glands and lymphoid tissue.
o Muscularis Externa:
2 or more layers of smooth muscle
A. Internal one is usually circular
B. External one is usually longitudinal
Connective tissue between muscle layers has blood and lymph vessels, and myenteric (Auerbach) nerve plexus of
many autonomic neurons.
A. This plexus with the submucosal plexus form the enteric nervous system of the digestive tract.
o This system contracts the smooth muscles to propel luminal contents forward.
, o Serosa:
Thin layer of loose connective tissue rich in blood vessels, lymphatics, and adipose tissue with mesothelium.
In abdominal cavity, it is continuous with mesenteries (both sides of intestines)
A. Mesenteries are continuous with the peritoneum, a serous membrane that lines that cavity
NOTE: In places where the digestive tract is not suspended in a cavity but bound to adjacent structures (esophagus),
serosa is replaced by a thick adventitia (a connective tissue that merges with the surrounding tissues and lacks
mesothelium)
Digestive system consists of the digestive (GI) tract or alimentary canal, oral cavity, esophagus, stomach, small and
large intestines, and anus—and its associated glands—salivary glands, liver, and pancreas
Its function is to obtain from ingested food the molecules necessary for the maintenance, growth, and energy needs
of the body.
1. Structures within the digestive tract allow the following (functions)
2. Ingestion, or introduction of food and liquid into the oral cavity.
3. Mastication, or chewing, which divides solid food into digestible pieces.
4. Motility, muscular movements of materials through the tract.
5. Secretion of lubricating and protective mucus, digestive enzymes, acidic and alkaline fluids, and bile.
6. Hormone release for local control of motility and secretion.
7. Chemical digestion or enzymatic degradation of large macromolecules to smaller ones and their subunits.
8. Absorption of the small molecules and water into the blood and lymph.
9. Elimination of indigestible, unabsorbed components of food.
General structure of GI tract (4 main layers):
o Mucosa (mucous membrane):
Epithelial lining
Lamina propria of loose connective tissue rich in blood vessels, lymphatics, lymphocytes, smooth muscle cells, and
often small glands.
Muscularis mucosae which is smooth muscle separating mucosa from submucosa.
o Submucosa:
Has denser connective tissue with larger blood and lymph vessels
Has submucosal (Meissner) plexus of autonomic nerves.
Might contain glands and lymphoid tissue.
o Muscularis Externa:
2 or more layers of smooth muscle
A. Internal one is usually circular
B. External one is usually longitudinal
Connective tissue between muscle layers has blood and lymph vessels, and myenteric (Auerbach) nerve plexus of
many autonomic neurons.
A. This plexus with the submucosal plexus form the enteric nervous system of the digestive tract.
o This system contracts the smooth muscles to propel luminal contents forward.
, o Serosa:
Thin layer of loose connective tissue rich in blood vessels, lymphatics, and adipose tissue with mesothelium.
In abdominal cavity, it is continuous with mesenteries (both sides of intestines)
A. Mesenteries are continuous with the peritoneum, a serous membrane that lines that cavity
NOTE: In places where the digestive tract is not suspended in a cavity but bound to adjacent structures (esophagus),
serosa is replaced by a thick adventitia (a connective tissue that merges with the surrounding tissues and lacks
mesothelium)
