Lecture 20: BASIC STRUCTURE OF THE GI SYSTEM Flashcards
What is the primary function of the GI system?
Bring nutrients into the internal environment (blood) so that they can be used for growth and energy. Waste is excreted
What functions is the GI system specialised for?
Motility, secretion, digestion and absorption
What are the key structures of the GI system?
Long tube with outgrowths, closed off at both ends, lined by epithelium
How is the GI system closed off at both ends?
Sphincters - thickened regions of circular smooth muscle
Why is the GI system lined by epithelium?
Because it is exposed to the outside
Where in the GI system is there stratified squamous epithelium?
Mouth/oral cavity, oesophagus, anal canal
What is the purpose of stratified squamous epithelium?
Protection from abrasion
Where in the GI system is there simple columnar epithelium?
Stomach, small intestine and large intestine
What is the purpose of simple columnar epithelium?
Secretion and absorption
What are unicellular glands?
Goblet cells
What is the shape of goblet cells?
Columnar, goblet
What is on the apical side of goblet cells?
Mucous granules
What is on the basal side of goblet cells?
Nucleus and other organelles because the mucous granules push them down
What can the epithelium do?
Invaginate to form glands
What are the types of multicellular glands?
Simple and compound
What are simple glands?
Gland with a single duct
What are compound glands?
Gland with two or more ducts, have more surface area for secretion
What are the layers of the gut (from inner to outer)?
Mucosa, submucosa, muscular (externa/proper) and adventitia
What is in the mucosa?
Epithelium, lamina propria (FCT), muscularis mucosa and sometimes glands
What is between the epithelium and lamina propria?
Basement membrane
What does the lamina propria of the mucosa contain?
Blood vessels and lymphatics
What is the muscular mucosa?
Thin layer of smooth muscle
What is in the submucosa?
Glands and blood vessels
How is secretion in the submucosa regulated?
By the submucosal nerve plexus which is part of the enteric nervous system (ENS)
What is the ENS?
The nervous system of the gut which can work independently of the CNS
What does the muscularis made of?
Smooth muscle under involuntary control and the myenteric plexus
What are the layers of smooth muscle in the muscularis?
Inner circular and outer longitudinal
What is the myenteric plexus part of?
ENS
Where is the myenteric plexus found?
In between the muscle layers of the muscularis
What does the myenteric plexus do?
Regulate motility
What is the outermost layer of the gut tube?
Adventitia
What do organs have when in the peritoneal cavity?
An additional covering called the serosa which is not considered to be one of the four layers
What is the peritoneum?
A serous membrane
What does the parietal layer of the peritoneum line?
The body wall
What does the visceral layer of the peritoneum line?
The organs
What is between the visceral and parietal peritoneum?
A fluid filled space (peritoneal space/cavity)
What does retroperitoneal mean?
Posterior to the peritoneum
What is retroperitoneal?
Organs which don’t move when functioning - these organs still have visceral peritoneum
What are mesenteries?
Double layers of visceral peritoneum that connect the organ to the body wall
What are omentas?
Double layers fo visceral peritoneum that connect organ to another organ
Where is food ingested?
At the mouth/oral cavity
What happens in the moth?
Digestion begins (mechanical and chemical - requires enzymes) and lubrication
Where does the food go from the mouth?
Through fauces, into oropharynx, then into esophagus
How many pairs of salivary glands are there?
3 which are connected to the oral cavity via ducts
What are the 3 salivary glands?
Parotid, sublingual and submandibular
What is secreted by the parotid glands?
serous fluid with amylase
What is secreted by the sublingual glands?
Mucous only
What is secreted by the submandibular glands?
Mix of serous fluid with amylase and mucous
What is the total volume of salivary secretions?
1L per day
What type of glands are salivary glands?
Compound secretory
What are cells in clusters?
Acinus
What do acinar cells do?
Secrete enzymes (amylase)
What do duct cells do?
Secrete bicarbonate (buffering)
How long is the oesophagus?
Approximately 25 cm
Where is the oesophagus located?
Posterior to the trachea and extends from the pharynx to the stomach
What is the oesophagus?
A basic tube modified to pass food
What is within the oesophagus?
Highly folded submucosa and mucosa with the capacity to expand
What is the mucosa of the oesophagus?
Stratified squamous epithelium
What does the muscularis in the oesophagus do?
Move food
What is the first third of the muscularis of the oesophagus?
Skeletal muscle
What is the second third of the muscularis of the oesophagus?
mixture of smooth and skeletal muscle
What is the last third of the muscularis of the oesophagus?
Smooth muscle
What is mucous needed for in the oesophagus?
Lubrication and protection
How is the mucous in the oesophagus made?
No goblet cells, instead have glands with ducts to the surface
