Gut Histology Flashcards
What are the structures of the digestive system ?
- oral cavity
- pharynx
- oesophagus
- stomach
- small intestine
- large intestine
What are the 3 parts of the small intestine ?
- duodenum
- jejenum
- ileum
What are the parts of the large intestine ?
- caecum
- colon
- rectum
- anal canal
What are the large glands associated with the small intestine ?
- pancreas
- liver
What is the lining of the oral cavity known as ?
The oral mucosa
What are the 3 parts of the oral mucosa ?
- masticatory mucosa
- ordinary lining mucosa
- specialised mucosa of the tongue
Where is masticatory mucosa found ?
Gingiva and hard palate
Summarise the structure of masticatory mucosa
- made up of stratified squamous keratinised epithelium
- firmly bound to the underlying bone by collagen fibres in the submucosa
Describe the masticatory mucosa on the gingiva
- the epithelium is very thick
- very wavy to give a large surface area
What are the 2 zones of the hard palate known as ?
Fatty zone and glandular zone
What is the line running down the centre of the hard palate known as ?
Raphe - covered by masticatory mucosa
Where is lining mucosa found in the oral cavity ?
Everywhere apart from the top surface of the tongue, gingiva and hard palate
- inside of lips
- underside of the tongue
- cheeks (may have lines of masticatory mucosa)
- soft palate
- gums away from the gingiva
Summarise the structure of the lining mucosa
Made up of stratified squamous non keratinised epithelium
What does the submucosa of the oral cavity contain ?
Lots of small salivary glands
Where is the specialised mucosa of the tongue found ?
On the anterior 2/3 of the tongue (in front of the sulcus terminalis)
What are the different types of lingual papillae ?
- circumvallate papillae
- filliform papillae
- fungiform papillae
- foliate papillae
Where are the circumvallate papillae found ?
Along the sulcus terminalis
Where did the thyroid gland develop ?
Foramen caecum on the tongue
Describe the structure of the circumvallate papillae
- big about the size of a match head
- connective tissue core
- surrounded by epithelium - stratified squamous non keratinised epithelium
- contains taste buds
- embedded in a groove which is flooded with saliva from the Von Ebner glands
Describe the structure of the foliate papillae
- elongated folds
- connective tissue core
- surrounded by stratified squamous non keratinised epithelium
- contains taste buds
Describe the structure of the fungiform papillae
- connective tissue core
- surrounded by epithelium
- contains taste buds
Which of the lingual papillae contain taste buds ?
- circumvallate papillae
- foliate papillae
- fungiform papillae
Describe the structure of filiform papillae
- pointed
- connective tissue core
- surrounded by stratified squamous keratinised epithelium
- no taste buds
Which cells are found in taste buds ?
- sensory cells
- supporting cells
- basal cells
Where are minor salivary glands found and how often do they secrete ?
- lips
- cheek
- tongue
- palate
- secrete continuously
Where are major salivary glands found and how often do they secrete ?
- parotid gland
- submandibular gland
- sublingual glands
- secrete on appropriate stimulation
What is the contents of the saliva ?
- water
- calcium
- phosphates
- carbohydrates
- amylase
- various inorganic ions
What is the function of the saliva ?
- can repair small amounts of damage to the enamel
- digestion
- lubrication
- cleanses oral cavity
Which parts of the digestive system are known as the hollow parts of the gut ?
Parts of the digestive tract beyond the pharynx
Describe the general structure of the hollow tube parts of the gut
Innermost layer - mucosa which has 3 layers :
1) epithelium
2) lamina propria
3) muscularis mucosae - contains Meissner’s plexus
- Mucosal glands and extrinsic glands pertrude out of this layer
Second layer - submucosa (connective tissue layer)
- submucosal glands pertrude
Third layer - muscularis externa which has 2 layers of smooth muscle :
• inner circular layer
• outer longitudinal layer
[muscularis externa contains Auerbach’s plexus]
Outermost layer - adventitia
What is the functions of the Meissner’s plexus and Auerbach’s plexus ?
They are networks of nerves that control the contraction of the gut muscle and coordinate muscles in peristalsis
What is the function of the oesophagus ?
- transport of material from the throat to the stomach
Why is the mucosa and submucosa of the oesophagus folded ?
Allows the oesophagus to stretch without causing damage
What type of epithelium is found in the oesophagus ?
Stratified squamous non keratinised epithelium
What are the muscle types found in the muscularis externa of the oesophagus ?
- top 1/3 of the oesophagus is skeletal muscle because swallowing is a voluntary activity
- middle 1/3 is mixed
- bottom 1/3 is smooth muscle
What is the function of the mucus glands of the oesophagus ?
- mucus glands at the top important in the lubrication of material
- mucus glands at the bottom protect oesophagus from acids and enzymes of the stomach
How is the structure of the stomach different to the other hollow tube parts of the gut ?
There is an additional layer of oblique muscle in the muscularis externa between the circular and longitudinal layer
What are the folds in the stomach known as and what is their function ?
Rugae - allow the stomach to expand
What are the sphincters of the stomach ?
The opening and exit point of the stomach
Describe the lining of the stomach
- The surface layer is made of simple columnar epithelium and every cell in the columnar epithelium is a mucous secreting cell and so it is known as a secretory sheet
- This makes a layer of mucous on the epithelium which keeps the stomach contents away from the epithelium
- The lining forms indents known as gastric pits which have gastric glands
Which types of cells are found in the walls of the gastric glands and what is the function of the gastric glands ?
- parietal (oxyntic) cells which make HCl
- chief (zymogen) cells which make pepsin
What is the length of the duodenum ?
~ 25 cm and it is C shaped
What is the function of the duodenum ?
Takes bile from the liver and digestive enzymes from the pancreas
Describe the 3 structural levels of the small intestine
- the submucosa is folded into plicae circulares and this is the first level of increasing the surface area of the small intestine
- the mucosa is folded into villi
- the apical plasma membrane is folded into micro villi which forms a brush border
What are crypts of lieberkuhn ?
Depressions at the base of each villus and the epithelium of the crypt is continuous with the epithelium of the villi
Why are epithelial cells replaced ?
The gut lining is in a very hostile environment and so cells can only live a few days
What are Peyer’s patches in the ileum ?
Lymph nodules, B cells and T cells in the lamina propria which monitor the contents of the gut floor
What type of epithelium is found in the large intestine ?
A single layer of columnar cells
Why is there an abundance of goblet cells in the epithelium of the large intestine ?
They produce mucous so the faeces which is formed can be lubricated for exit
What are the 3 ribbons of muscle in the longitudinal muscle layer of the musularis externa in the large intestine known as ?
Taeniae coli
What are the appendices epiploicae of the large intestine ?
Fatty tissue deposits which allow the gut to slide over other components
What are the 2 types of epithelium found in the anal canal ?
The top of the canal contains simple columnar epithelium
Lower down is stratified squamous non keratinised epithelium
What are the types of muscle found in the anal canal ?
The top contains smooth muscle
The bottom contains skeletal muscle for voluntary action
What type of epithelium is found on the bottom surface of the tongue ?
Stratified squamous epithelium with some keratinisation
Where do the Von Ebner glands open ?
In the base of the groove around the papilla
What is the function of the Von Ebner glands ?
They flush out the groove surrounding the papilla which allows for the renewal of taste sensations
Why is the oesophagus not lined with simple epithelium ?
- the gut lining is very hostile and so the epithelium has only a short lifespan of a few days
- so the epithelium needs to have many layers to protect the oesophagus from the acidic contents of the stomach
- the oesophagus is not involved in absorption
What is the role of the crypts of Lieberkuhn ?
They contain stem cells for the epithelium and allow for the continual replacement of intestinal epithelial cells
Why does the large intestine not contain villi ?
The large intestine is involved in the absorption of water and ions and this doesn’t require a large surface area to be efficient
What are the infoldings of the large intestine ?
Haustrae
