Lecture 20: The Basic Structure of the GI System Flashcards
What is the primary function of the GI system?
Bring nutrients into the internal environment so that they can be used
What functions is the GI system specialised for?
4
- Motility
- Secretion
- Digestion
- Absorption
What are the 2 types of digestion?
- Mechanical
- Chemical
What are the major organs of the digestive tract?
6
- Oral cavity (mouth)
- Pharynx
- Oesophagus
- Stomach
- Small intestine
- Large intestine
What causes the ends of the GI tract to be closed off?
Sphincters
How is the GI system described?
Long tube with outgrowths
What are the accessory organs of the digestive system?
5
- Teeth/tongue
- Salivary glands
- Liver
- Gallbladder
- Pancreas
What type of epithelium is the mouth/oral cavity and oesophagus lined with?
Stratified squamous
What type of epithelium is the Stomach, Small intestine and large intestine lined with?
Simple columnar
What type of epithelium is the Anal canal lined with?
Stratified squamous
Why is the epithelium of the mouth/oral and oesophagus stratified squamous?
For protection from abrasion
Why is the epithelium of the Stomach, Small intestine and large intestine simple columnar?
For secretion and absorption
Why is the epithelium of the anal canal stratified squamous?
For protection from abrasion
What is the only type of unicellular gland?
Goblet cells
What type of epithelium are goblet cells?
Columnar
What is the shape of unicellular glands/goblet cells?
Goblet shape
What is contained within goblet cells?
2
- Apical mucous granules
- Basal nucleus
What do multicellular glands do?
Their epithelium invaginate into the underlying tissue
What are the 2 types of multicellular glands?
- Simple
- Compound
What are simple glands?
Glands with a single duct
What are compound glands?
Glands with 2 or more ducts
What are 2 examples of a simple gland?
- Stomach
- Small intestine
What is an example of a compound gland?
Salivary gland
What are the 4 layers of the gut tube?
- Mucosa
- Submucosa
- Muscularis (externa/proper)
- Adventitia
What does the mucosa consist of?
4
- Epithelium
- Lamina propria (FCT)
- Muscularis Mucosae
- Sometimes glands
What can be found within the lamina propria of the mucosa?
2
- Lymphatics
- Blood vessels
What does the submucosa consist of?
2
- Glands
- Blood vessels
What is secretion from glands in the submucosa regulated by?
Submucosal nerve plexus
What is the submucosal nerve plexus apart of?
The enteric nervous system (ENS)
What does the muscularis (externa/proper) consist of?
Smooth muscle
What are the 2 main layers of smooth muscle in the muscularis?
- Inner circular
- Outer longitudinal
Where is the Myenteric plexus found?
In between the inner circular/outer longitudinal layers of smooth muscle in the muscularis
What is the myenteric plexus apart of?
The enteric nervous system
What does the myenteric plexus regulate?
Motility
What is the outer most layer of the gut tube?
The adventitia
When organs are in the peritoneal cavity what happens?
They have an additional outer covering, the serosa
What is the peritoneum?
A serous membrane
What 2 layer make up the peritoneum?
- Parietal layer, lining the body wall
- Visceral layer, lining the organs
What is found between the 2 layers of the peritoneum?
Fluid
What does retroperitoneal mean?
Posterior to the peritoneum
What is mesentery?
A double layer of visceral peritoneum that connects organs to the body wall
What is omenta?
A double layer of visceral peritoneum that connects an organ to another organ
Once food is ingested through the mouth/oral cavity where does it go?
Through the fauces, into the oropharynx, then into the oesophagus
Once digestion begins what is required?
Enzymes to be applied and lubrication of food
What are the 3 pairs of salivary glands connected to the oral cavity via ducts?
- Paratoid
- Submandibular
- Sublingual
What does the paratoid gland secret?
Serous fluid with amylase
What does the sublingual gland secret?
Mucous
What does the submandibular gland secret?
A mix of mucous and serous fluid with amylase
What is the total volume of salivary secretions in a day?
1 litre
What does acinus mean?
Cells in clusters (these can be found in salivary glands)
What type of cells can be found in salivary glands?
2
- Acinar cells
- Duct cells
What do acinar cells secret?
Enzymes (amylase)
What do duct cells secret?
bicarbonate (buffer)
Where is the oesophagus located?
Posterior to the trachea
Where does the oesophagus extend from and to?
From the pharynx to the stomach
What does the epiglottis do?
Ensures that food enters the oesophagus not the trachea
What does the highly folded submucosa and mucosa of the oesophagus allow for?
The capacity to expand
How is the mucosa of the oesophagus lined?
With stratified squamous epithelium
What is the function of the muscularis externa?
Move food bolus
What is the first 1/3 of the muscularis externa in the oesophagus composed of?
Skeletal muscle
What is the second 1/3 of the muscularis externa in the oesophagus composed of?
A mixture of smooth and skeletal muscle
What is the third 1/3 of the muscularis externa in the oesophagus composed of?
Smooth muscle
What does the oesophagus need mucous for?
Lubrication and protection
Instead of goblet cells what does the oesophagus have?
Glands with ducts to the surface