Lecture 20: The Basic Structure of the GI System Flashcards
what is the primary function of the GI system?
bring nutrients into internal environment so they can be used
what functions is the GI system specialised for?
- motility
- secretion
- digestion
- absorption
what is the overall structure of the GI system?
- long tube with outgrowths
- closed off at both ends (sphincters)
- lined by epithelium
what are the major organs of the digestive tract?
- oral cavity
- pharynx
- esophagus
- stomach
- small intestine
- large intestine
what are the accessory organs of the GI system?
- teeth
- tongue
- salivary glands
- gallbladder
- pancreas
where is stratified squamous epithelium found? why?
- mouth/oral cavity
- esophagus
- anus
for protection against abrasion
where is simple columnar epithelium found?
- stomach
- small intestine
- large intestine
what is an example of unicellular glands? what are the features of it?
goblet cells
- columnar
- goblet shape
- has apical mucous granules
- has basal nucleus
what are the multicellular glands?
simple
- gland with single duct (e.g. stomach and small intestine)
compound
- gland with 2 or more ducts (e.g. salivary glands)
what are the 4 layers of the gut tube?
- mucosa
- submucosa
- muscularis externa
- adventitia
what does the mucosa consist of?
- epithelium
- lamina propria (FCT with lymphatics and blood vessels)
- muscularis mucosae
- sometimes glands
what does the submucosa consist of?
- glands
- blood vessels
how is secretion regulated in the submucosa?
secretion is regulated by the submucosal nerve plexus (part of the ENS)
what does the muscularis externa consist of?
Smooth muscle:
2 main layers
- inner circular
- outer longitudinal
Myenteric plexus:
- part of ENS
- found in between muscle layers
- regulates motility
What is the adventitia?
- outermost layer of the gut tube
- made of FCT
what happens to the layers when organs are in the peritoneal cavity?
there is an additional outer covering called the serosa (not one of the 4 layers)
what is the peritoneum? what are the layers of it?
a serous membrane
parietal layer - lines the body wall
visceral layer - lines the organs
there is a fluid filled space between this layer
what is a mesentery?
double layer of visceral peritoneum that connects organ to body wall
what is an omentum?
double layer of visceral peritoneum that connects an organ to another organ
what are the omentas
lesser omentum
- connects liver to stomach
greater omentum
- connects stomach to transverse colon
what are the features of the mouth and oral cavity?
it is where food is ingested and digestion begins
- needs stratified squamous epithelium for protection
- needs enzymes for digestion
- food travels through fauces, into oropharynx then into esophagus
what are the salivary glands and their secretions?
3 pairs connected to oral cavity via ducts
- parotid (secretes serous fluid with amylase)
- sublingual (secretes mucus only)
- submandibular (mixed)
what is the structure of salivary glands?
- compound salivary glands
- have acinar cells that secrete enzymes (amylase)
- have duct cells that secrete bicarbonate (buffering)
what is the esophagus? where is it? how is the epiglottis involved?
- a long tube located posterior from the trachea and extends from pharynx to the stomach
- the epiglottis ensures food enters the esophagus and not the trachea
what is the structure of the esophagus?
- higher folded submucosa and mucosa (stratified squamous) with the capacity to expand
- the muscularis externa moves bolus by peristalsis
- the first third is skeletal muscle, the second third is a mixture, and last third is smooth muscle
how does mucous work in the esophagus?
the esophagus needs mucus for lubrication and protection, but it doesn’t have goblet cells
- instead it has mucous secreting glands in the submucosa with ducts to the surface
how does mucous work in the esophagus?
the esophagus needs mucus for lubrication and protection, but it doesn’t have goblet cells
- instead it has mucous secreting glands in the submucosa with ducts to the surface
