Wk 1 - Pathology: Mucosal Barrier Flashcards
What is the mucosal barrier?
- Mucosa = epithelium + lamina propria + muscularis mucosae
- Specialised tissue which lines or coats other tissues and protects them from potentially injurious agents
- Mucosa often has additional functions
List some of the main functions of the gut’s epithelia.
-
Defence i.e. part of mucosal barrier
- Lining organs and ducts
-
Glandular i.e. secretion
- e.g. gastric glands
- Other specialised functions
- e.g. temperature control (skin)
- e.g. food absorption (GI tract)
List some of the possible agents that can cause tissue injury.
- Mechanical
- Chemical
- Thermal
- Microbial
- Iatrogenic
- Other (e.g. IBS not sure what the cause is)
What are the main ways that the GI tract can get injured? List some examples for each mechanism of injury.
-
Mechanical
- Hard food material in oesophagus
- Hard faeces in rectum and anal canal
-
Chemical
- Acid and bile in stomach
- Alcohol in stomach
- Digestive enzymes
-
Thermal
- Hot food in oesophagus
-
Microbial
- Bacteria anywhere in GI tract
-
Iatrogenic
- Drugs damaging mucosa
Describe the sequelae of GI mucosal injury.
- Inflammation
- Mucosal damage
- Interference with function e.g. absorption
- Ulceration (defect in epithelium)
- Complications
- Metaplasia
- Neoplasia
How does the GI tract mucosa maintain its integrity?
- Different mucosa at different sites
-
Mucosa type associated with
- Specialised function of site
- Ability to maintain integrity
- Commonest injurious agent(s) at site
What are the main features of oesophageal mucosa?
- Stratified squamous epithelium with mucus glands
- Bc main function of oesophagus is passage of food
- Making if most susceptible to mechanical injury (thermal injury in specific)
What are the features of the gastric mucosa?
Features:
- Specialised glandular epithelium
- Mucus secretion
- Hydrochloric acid secretion
Because the stomach’s functions include food storage and initial digestive function, and du to the nature of injury (bacterial and chemical).
List some agents that cause gastric mucosal injury.
- Acid, pepsin, Helicobacter pylori
- Other chemical
- Bile, alcohol
- Drugs
- Aspirin
- Inflammatory
- Pernicious anaemia (due to damage of cells that absorb B12)
- Other
- Cigarette smoking
How does the gastric mucosa defend itself against injury-causing agents? (nb also in physiology lecs stomach and secretions)
-
Physical
- Mucus, intact cell junctions
- High epithelial cell turnover
-
Chemical
- Bicarbonate secretion
- Mechanism for acid & pepsin secretion (degrades mucus as well as food digestion)
-
Waste disposal
- Good blood supply (in case acid ‘spills over’ into blood – it is cleared away quickly as to not cause damage)
What are the features of the small intestinal mucosa?
Features:
- Large surface area
- Villi & mucosal folds
- Columnar epithelium
- Microvilli ++
- Mucus secretion
Because main job of small intestine is food digestion and nutrient absorption so key injurious agent is bacteria.
List the features of the large intestinal mucosa.
Features:
- Columnar epithelium
- Some microvilli (to facilitate water resorption)
- Mucus secretion ++
The main job of large intestine is water resorption and faecal storage (rectum). This makes it prone to bacterial injury and also mechanical injury.
What are the main features of the anal canal mucosa?
Features:
- Stratified squamous epithelium
- Mucus gland
Main job of anal canal is passage of faeces so prone to mechanical injury (if hard stool) and also possible bacterial injury.
What is metaplasia?
- Change of one mature tissue into another mature tissue
- May involve mucosa or other tissues
- Occurs due to change in environment
- Indicator of chronic tissue damage
- ‘New’ tissue may better suit new environment
Is metaplasia neoplastic?
- Not neoplastic in its own right
- Mucosal metaplasias often represent relatively unstable tissues
- May be associated with progression to neoplasia i.e. dysplasia & malignancy
