Basic structure of GI Flashcards
Role of the GI tract
Bring nutrients/water into internal
environment to be used by the body
Roles of the GI tract
- Motility
- Secretion
- Digestion
- Absorption
Motility
Transport food into & through the body, mixing luminal contents, and transport waste out
Secretion
Synthesise and release enzymes,
mucus & serous fluid into the lumen
Digestion
Break nutrients into smaller pieces
(mechanically and chemically)
Absorption
Bring nutrients/water from the lumen to
internal environment
Why does the GI tract have different areas and how are they seperated?
They have different functions and they are seperated by Sphincters
Components of the main tube
Oral cavity –> pharynx –> eso –> stomach –> SI –> LI –> Anus
What are the outgrowths of the main tube called
The accessory structures
Where are the different sphincters
*Mouth
*Base of eso to control flow into stomach + prevent backflow
* Stomach and SI to control flow
*Between SI and LI
* 2 in the anus to control defecation
Type of epithelia in the Moth/oral cavity, pharynx and eso + their function
Stratified squamous epithelia
- protection from abrasion
Type of epithelia in the Stomach, SI and LI + their function
Simple columnar epithelia
- Secretion and absorption
Type of epithelia in the Anus + their function
Stratified squamous
- Protection from abrasion
Why does the middle of the tract have different type of epithelia?
- The contents are more watery so dont have to worry about abrasion
Unicellular glands
- Columnar/Goblet shape
- Secretes mucus onto the apical surface
- Basal nucleus
- Function is to lubricate the lumen and provide a barrier
Multicellular glands
Epithelium can invaginate to form glands:
* Simple
* Compound
Simple multicellular glands
Gland with single duct (e.g. stomach and small intestine)
Compound multicellular glands
Gland with 2 or more ducts (e.g. salivary glands)
4 layers of the gut tube
- Mucosa
- Submucosa
- Muscularis (externa/proper)
- Adventitia
Components of the mucosa
- Epithelium connected to
- Basement membrane attatched to
- Lamina propria (made of FCT)
- Muscularis mucosae
What can be found in the Lamina Propria
Blood vessels lymphatics and sometimes glands
What does the Muscularis mucosae do
Band of smooth muscle that moves the mucosa
Components of the submucosa
- Predom FCT
- Glands
- Blood vessels
*Submucosal nerve plexus
What does the Submucosal nerve plexus do?
Network of nerves that are part of the enteric system, controls the secretion of the glands
The muscularis
(externa/proper) components + functions
*Made of smooth muscle
*Has two layers: inner circular arrangement and outer longitdinal arrangement
*Myenteric plexus (Part of ENS)
- Located between muscle layers and regulates motility
The Adventitia
*Outermost layer
*Mostly FCT
*Supports and sometimes anchors to other organs
What happens in the oral cavity + mouth
Digestion begins
* Mechanical through the teeth
* Chemical– requires
enzymes
* Lubrication needed
* Passes through fauces, into
oropharynx &
laryngopharynx then into
esophagus
How is the oral cavity lubricated
Through salivary glands –> secretes watery serous fluid and mucus
Chemical that digests carbs
Amylase
Features of the salivary glands
3 pairs:
- Parotid glands
- Sublingual glands
-Submandibular glands
Parotid
Parotid glands are beside the ear and secrete watery serous fluid
Sublingual
secrete mucus, found underneath the tongue
Submandibular
found on the side of jaw, secretes both, opening at the bottom of the tongue, helps move food around when chewing
Salivary glands have…
Multiple ductsW
What is an acinus
cluster of cells connected to ducts that can secrete
* Serous fluid & enzymes
(amylase)
* mucus
What do the ducts do
- transport the fluids secreted by acinus to the surface
- Also the cells secretes bicarbonate to act as a pH buffer as it is very basic
Features of the eso
- Long tube (~25cm) that carries food from mouth to stomach
- Located posterior
to the trachea, extends from
pharynx to stomach - Epiglottis ensures
that food enters the
esophagus, and
not the trachea
How is the epiglottis activated?
The tongue pushes back and puts pressure on the epi
How is the eso modified
- First 1/3: skeletal muscle to have concious control
- Middle 1/3: a mixture
- Last 1/3: smooth muscle
Highly folded submucosa and
mucosa that flattens and unflods to allow food to pass
Mucus around the eso
- Stratified squamous
epithelium - Need mucus for
lubrication and
protection - No goblet cells,
instead have glands
with ducts to
surface - In submucosa
- Plus in mucosa
close to stomach
