What are the primary functions of the digestive system?
•
... [Show More] Ingestion, Secretion, Mixing and Propulsion (motility), Digestion, Absorption, Defecation.
2. What is the alimentary canal?
• It is a continuous tube that extends from mouth to anus through the thoracic and abdominopelvic
cavities.
3. What are the accessory organs of the digestive system?
• Teeth, tongue, salivary glands, liver, gallbladder, and pancreas.
4. Describe, in detail, all the layers of the gastrointestinal system. You should be as specific as possible with
respect to tissue types found, functions, etc. This is a very likely exam question, although I may ask you to refer
more specifically to how this paradigm is modified in some subregions of the GI tract.
Four layers of GI tract:
Mucosa: It is the innermost layer of the GI tract, and is a mucous membrane.
Subregions of Mucosa:
1. Layer of Epithelium: The epithelium in the mouth, pharynx, esophagus, and anal canal is
nonkeratinized stratified squamous epithelium which serves as a protection.
The epithelium that lines the stomach and small intestine is simple columnar epithelium which
functions in secretion and absorption.
2. Lamina Propria: is areolar connective tissue, and containing many blood vessels and lymphatic
vessels. Nutrients reach other tissues via these blood vessels. This layer supports the epithelium and
binds it to muscularis mucosae. The lamina propria also contains Mucosa Associated Lymphatic
Tissue (MALT). These specialized lymphatic tissues contain immune system cells that protect against
disease.
3. Muscularis Mucosae: Thin layer of smooth muscle fibers throws the mucous membrane of the
stomach and small intestine into many small folds, which increase the surface area for digestion and
absorption.
• Submucosa: It consists of areolar connective tissue that binds the mucosa to the muscularis. It contains
many blood vessels that receive absorbed food particles. Submucosa is an extensive network of neurons
known as the submucosal plexus.
• Muscularis: Muscularis of mouth, pharynx, and superior part of the esophagus means upper respiratory
system contains skeletal muscles that produce voluntary swallowing.
o Throughout the rest of the tract, muscularis consists of smooth muscles that are generally
found in two layers: circular fibers and longitudinal fibers. Involuntary contraction of the
smooth muscles helps break down the food, and mix it with digestive secretion.
o Between the two layers of muscularis is a second plexus of neurons called Myenteric Plexus.
• Serosa: It is serous membrane composed of areolar connective tissues and simple squamous epithelium.
The serosa is also called the visceral peritoneum because it forms a portion of the peritoneum. The
esophagus has adventitia as its outer layer instead of serosa.
5. What is the brain guy axis?
• The continuous feedback loop between sensory neurons in the gastrointestinal tract and motor
response generated in the central nervous system. Hypersensitivity in the brain-gut axis contributes to
functional GI disorders, including irritable bowel syndrome.
6. Describe the short reflex and long reflex pathways of the enteric nervous system.
• Short reflex: reflexes from the gut to prevertebral sympathetic ganglia and then back to GI tract. These
reflexes transmit signals long distance to other areas of the GI tract.
• Long Reflexes: reflexes from the gut to spinal cord or brain stem and then back to GI tract.
7. Describe, in detail, the peritoneal cavity. This should include a detailed analysis of the 5 ‘folds’ of the cavity and
their respective functions.
• The slim space containing lubricating serous fluid that is between the parietal and visceral portions of
the peritoneum is called the peritoneal cavity. [Show Less]