lecture 20 - GI system basic structure Flashcards
What are the 4 fundamental functions of the GI system?
Motility, secretion, digestion, absorption
What closes off the ends of the GI tracts?
Sphincters
What lines the GI tract?
Epithelium
What are the major organs of the GI system?
oral cavity/mouth, pharynx, oesophagus, stomach, small intestine, large intestine
What are the accessory organs of the GI system?
Teeth, tongue, salivary glands, liver, gall bladder, pancreas
In the GI tract, what is stratified squamous epithelium adapted for?
Protection from abrasion
In the GI tract, what is simple columnar epithelium adapted for?
Secretion & absorption
What type of epithelium lines the mouth/oral cavity and oesophagus?
Stratified squamous
What type of epithelium lines the stomach, small intestine and large intestine?
Simple columnar
What type of epithelium lines the anus?
Stratified squamous
What cells make up the unicellular glands of the GI system?
goblet cells
What is the shape of goblet cells?
Columnar, with a wide apical aspect
How are multicellular glands formed in the GI tract?
When epithelium invaginates to form ducts
What are the 2 types of multicellular glands?
Simple & compound
What is a simple multicellular gland?
A gland with a single duct
What is a compound multicellular gland?
A gland with 2 or more ducts
What type of gland is a salivary gland?
Compound multicellular gland
What are the 4 layers of the gut tube?
Mucosa, sub-mucosa, muscularis externa/proper, adventitia
What are the layers (top to bottom) of the GI mucosa?
Epithelium, basement membrane, lamina propria (FCT), muscularis mucosa. Sometimes contains glands.
What layer of the GI mucosa contains blood vessels and lymphatics?
Lamina Propria (FCT)
What are the components of the GI submucosa?
Glands, blood vessels, the submucosal nerve plexus
What layer of the gut tube contains the submucosal nerve plexus?
Submucosa
What body system is the submucosal nerve plexus part of?
the Enteric Nervous system (ENS), the gut’s local nervous system
What is the function of the enteric nervous system?
Allows local coordination of gut reflexes without significant contribution from the CNS
What type of muscle is found in the muscularis externa/muscularis proper
Smooth muscle
What are the 2 layers of smooth muscle in the muscularis proper?
Inner circular, outer longitudinal
Is the circular smooth muscle of the gut tube the inner or outer layer of muscle?
Inner
Is the longitudinal smooth muscle of the gut tube the inner or outer layer of muscle?
Outer
What is the structure and function of the inner circular muscle of the muscularis?
Circumferential smooth muscle fibres that control gut tube diameter
What is the structure and function of the outer longitudinal muscle of the muscularis?
Longitudinal/‘lengthways’ smooth muscle fibres that control gut tube length
What feature of the muscularis in the GI tract regulates and stimulates motility?
The myenteric plexus
What is the location of the myenteric plexus?
In the muscularis proper of the gut tube
What is the function of the myenteric plexus?
Regulates gut tube motility, as part of the enteric nervous system
What is the tissue type of the GI adventitia?
Fibrous connective tissue
What is the additional outermost layer found on GI organs within the peritoneal cavity?
Serosa
What type of membrane is the peritoneum?
Serous membrane
What are the 2 layers of the peritoneum?
Parietal and Visceral
What is the peritoneum?
A tissue/membrane that lines the abdominal wall and encloses most of the abdominal and GI organs
What does the parietal layer of the peritoneum line?
The body wall
What does the visceral layer of the peritoneum line?
The organs
What sits between the parietal and visceral layers of the peritoneum?
Fluid filled space called the peritoneal cavity/space
What is the term for abdominal organs that sit outside the peritoneum?
Retroperitoneal
What is the most notable retroperitoneal GI organ?
The pancreas
What is mysentery?
A double layer of visceral peritoneum that connects an organ to the body wall
What is omenta?
Double layer of visceral peritoneum that connects an organ to another organ
What are the similarities and differences between mesentery and omentum?
Both double layers of visceral peritoneum, but mysentery connects organ to body wall and omentum connects organ to organ
What is the approximate volume of daily salivary secretions?
1L
How many pairs of salivary ducts are connected to the oral cavity?
3 pairs - 6 in total
How are salivary glands connected to the oral cavity?
Via ducts
What are the 3 salivary glands?
parotid, sublingual, submandibular
What do the parotid salivary glands secrete?
Serous fluid containing amylase
What do the sublingual salivary glands secrete?
Mucous
What do the submandibular salivary glands secrete?
Mixture of serous fluid with amylase and mucous
What type of gland are salivary glands?
Compound secretory glands
What are components of a compound gland?
Duct and acini
What is an acinus?
A cluster of cells ( often within a compound duct)
What does an acinus of a salivary duct secrete?
Enzymes, such as amylase
What do the duct cells of salivary gland secrete?
bicarbonate for buffering
What is the function of the bicarbonate secreted by the duct cells of salivary glands?
Buffering
What is the approximate length of the esophagus?
~25cm
What is the location of the oesophagus, in relation to the trachea?
Posterior to the trachea
What feature ensures that food enters the oesophagus and not the trachea?
The epiglottis
Why is the submucosa and mucosa of the oesophagus highly folded?
To give it the capacity to expand when a food bolus passes through
What is the epithelium type in the esophagus?
Stratified squamous
How does the muscle type in the muscularis externa change along the oesophagus?
1st third is skeletal muscle, 2nd third is mixture of skeletal and smooth muscle, 3rd third is smooth muscle
Why does the oesophagus need mucus?
Protection and lubrication
What secretes the mucus of the oesophagus?
Glands with ducts to the surface, rather than goblet cells
