Lecture 20 Flashcards
What is the role of the GI system?
To bring nutrients and water into the internal environment to be used by the body
What are the four functions of the GI system?
Motility, secretion, digestion, absorption
What is the function of the motility of the GI tract?
To transport food into and through the body, mixing luminal contents and transporting waste out
What is the function of the secretion of the GI tract?
To synthesise and release enzymes, mucus and serous fluid into the lumen
What is the function of the digestion of the GI tract?
To break nutrients into smaller pieces, mechanically and chemically
What is the function of the absorption of the GI tract?
To bring nutrients and water from the lumen to the internal environment
What are the sphincters and what is their function in the GI system?
Rings of smooth muscle that close off ends and separate sections of the tube
What do the sphincters allow?
Different environments within different organs
What is the GI system lined by?
Epithelium
What type of epithelia is found in the mouth, oral cavity and esophagus?
Stratified squamous to protect from abrasions
What type of epithelia is found in the stomach, small and large intestines?
Simple columnar for secretion and absorption
What type of epithelia is found in the anus?
Stratified squamous to protect from abrasion
What are unicellular glands?
Glands with single cells to perform a function. Columnar, goblet-shaped, mucous-producing cells with apical mucous granules and a basal nucleus.
What are the two functions of the unicellular glands?
Lubrication and protection
What are multicellular glands?
Invaginated epithelium to form glands, this increases the surface area for more secretion
What are the two types of multicellular glands?
Simple and Compound
What is a simple multicellular gland?
A gland with a single duct
Where are the simple multicellular glands found?
In the stomach and small intestine
What is a compound multicellular gland?
A gland with 2 or more ducts
Where are the compound multicellular glands found?
Salivary glands
What are the four layers of the gut tube, deep to superficial?
Mucosa, submucosa, muscularis, adventitia
What does the mucosa consist of?
Epithelium, basement membrane, lamina propria (FCT), muscularis mucosae and sometimes glands
What does the submucosa consist of?
FCT, glands, blood vessels and submucosal plexus
What is the function of the submucosal plexus?
To regulate secretion through the enteric nervous system (ENS)
What is the muscularis?
A layer of smooth muscle
What are the two main layers of the muscularis?
Inner circular and outer longitudinal
How is the inner circular muscularis structured?
Cells wrap around the tube
How is the outer longitudinal muscularis structured?
Cells run up and down the tube
What is the myenteric plexus?
Part of the ENS, located between the inner circular and outer longitudinal muscle layers. It regulates motility (contractions)
What is the adventitia composed of?
Fibrous connective tissue to hold things together
Where does digestion begin?
The mouth and oral cavity
What are the two forms of digestion?
Mechanical and chemical
Where does food flow through to get to the stomach?
The fauces, into oropharynx and laryngopharynx and then into the esophagus
What does the mouth and oral cavity need?
Lubrication
How is the mouth and oral cavity lubricated?
Through salivary glands
What are the three salivary glands?
Parotid, sublingual, submandibular
What does the parotid salivary gland secrete?
Serous fluid with amylase
What does the sublingual salivary gland secrete?
Mucous only
What does the submandibular salivary gland secrete?
Mixed of mucous and serous fluid
Where is the parotid glad positioned?
In front of the ear
Where is the sublingual gland located?
Below the tongue
Where is the submandibular gland located?
Around the mandible
What type of glands are the salivary glands?
Compound secretory glands
What is an acinus?
Cluster of cells
What do acinus cells secrete?
In the salivary glands
Serious fluid, enzymes and mucus
What do duct cells secrete?
In the salivary glands
Bicarbonate, a pH buffer
What is the esophagus?
Long tube of about 25cm made from stratified squamous epithelium
Where is the esophagus located?
Posterior to the trachea and extends from the pharynx to the stomach
What does the epiglottis ensure?
Food does not enter the trachea
What is the function of the muscularis externa?
To move food bolus
What is the composition of muscle along the muscularis externa? (In the esophagus)
First 1/3 = skeletal muscle
Second 1/3 = mixture
Third 1/3 = smooth muscle
What component of the esophagus is highly folded?
The submucosa and mucosa which expands for food passage
How does the esophagus secrete mucus without goblet cells?
Through glands with ducts in submucosa and the mucosa close to the stomach
Why does the esophagus need mucus?
For lubrication and protection
Why is the structure of the esophagus so different to the stomach?
To preform different functions
