Anatomy and Cell Biology 3309 Lecture Notes - Lecture 5: Muscular Layer, Muscularis Mucosae, Stratified Squamous Epithelium
15 May 2018
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Lecture 5 – Esophagus & Stomach
Layers and functions of the GI tract
- GI tract is an epithelial lined tube is organized in several layers and the organization reflects
the function
- Mucosa:
o Inner lining of tubular GI tract and it consists of an epithelium and loose CT
o The epithelium is where the interact with the food that comes in
o Located on a lamina properia (loose CT)
- Supportive submucosa:
o DICT that carries nerves and blood vessels into the mucosa
o E.g. absorption in the small intestine: submucosa will gather all of the nutrients and
carry them out of the GI tract
- Muscularis externa:
o Tube is surrounded by a double layer of smooth muscle (2 layers)
o 2 layers are running in directions at right angles to one another
o Innervated
o Allows the gut to move the food along so it does not get stuck
- Adventita or serosa:
o Depending on the location in the body, either have an adventita or a serosa
o Dense CT covering (adventitia)
o In certain parts of the GI tract, there are things suspended or hanging in the body
cavity. In the body cavity, instead of having an adventitia, there is a layer of
mesothelium
o Mesothelium is a lining of the body cavity (simple epithelium)
- Specific functions are organized in concentric layers
- Why is it organized like that?
o Creates a barrier to the outside world
▪ Immune system: GALT (gut associated lymphoid tissue) → located in the
mucosa and submucosa
o Absorption and digestion
o To facilitate that, there are glands in the submucosa that provide lubrication to
move things and liquefy food content
o Secretion: endo/exo
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General organization of the GI tract ***
- Tracts that the food passes through to nourish us:
o Esophagus/stomach
o Small and large intestine
- Along the entire GI tract, the submucosa and muscularis externa look very similar and there
are not many changes (organization is pretty much the same)
- Mucosa: business end of the G) tract
o Many changes occur along the GI tract in the mucosa
o Can use the changes in the mucosa to distinguish the different subparts of the GI
tract → this reflects its function
- Similarity to blood vessels:
o Lumen is always lined by an epithelium
o Both have smooth muscle
o But mucosa, submucosa and muscularis are specific adaptations to the GI tract
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Esophagus
- Epithelial lined tube designed to deliver food into the stomach
- The type of muscle in the muscle layer of the muscularis externa changes
- Type of muscle found depends on location
o Upper third has muscularis externa composed mainly of striated muscle (voluntary)
▪ When we have taken food in, we can reactively regurgitate stuff don’t do
that unless we throw up)
▪ Some species depends on this – bird feed their children by actively
regurgitating their food
o Lower end towards the stomach is predominantly smooth muscle
o Both types of muscle start mixing in the middle
- If see a section of esophagus, can look at the nature of muscularis externa and tell where the
section was taken from (upper third, low third or the middle)
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Document Summary
Gi tract is an epithelial lined tube is organized in several layers and the organization reflects the function. Inner lining of tubular gi tract and it consists of an epithelium and loose ct: the epithelium is where the interact with the food that comes in, located on a lamina properia (loose ct) Supportive submucosa: dict that carries nerves and blood vessels into the mucosa, e. g. absorption in the small intestine: submucosa will gather all of the nutrients and carry them out of the gi tract. Muscularis externa: tube is surrounded by a double layer of smooth muscle (2 layers, 2 layers are running in directions at right angles to one another. Innervated: allows the gut to move the food along so it does not get stuck. Adventita or serosa: depending on the location in the body, either have an adventita or a serosa, dense ct covering (adventitia)
