3.1 Mucosal protection in the gut Flashcards
What are the two anti-microbial substances produced by the normal gut flora?
Short chain fatty acids and bacreriocins
Name three chemical defences and how are the protective?
Bile, pepsin and gastric acid
All antimicrobial
What is the major component of mucus
glycoproteins
What are the mucus secreting cells in the stomach?
Surface and neck mucus cells
What are the mucus secreting cells in the small and large intestine?
Brunners glands and goblet cells
what are two ways mucus cells protect epithelial cells from microbial insult?
They form a barrier for clonization and they contain IgA which will expel the organism
What are the three types of protective mechanisms in the gut?
Microbiological
Chemical
Physical
How does the normal gut flora protect the host against pathogens?
It will compete with the pathogenic organisms for nutrients and attachment sites on epithelial cells
It will also produce antimicrobial substances that can kill or inhibit growth of invading pathogens and prevent their colonization (short chain fatty acids and bacteriocins)
What is the physical mucosal protection of the gut?
A single layer of intestinal epithelial cells providing a physical barrier between the lamina propria and intestinal lumen that contains the normal gut flora and pathogens
What functions do tight junctions play?
They hold together the epithelial cells forming a seal against the external environment - infection can only occur
What is the role of epithelial cell turnover and peristalsis?
Intestinal epithelial cell turnover is constant shedding of cells damaged by microbial infection or stresses and replenishment by neighbouring epithelial cells - this will help expel pathogens and prevent overgrowth of normal gut flora
What is the role of gastic mucus?
It is acid resistant preventing the HCl from breaking down he epithelium - secreted bicarbonate ions establishing a pH gradient
how does H.pylori cause infection?
It can swim through teh gastric mucus in teh stomach and attach to epithelial cells beneath where it can cause inflammation
How does pathogneic E.Coli cause infection?
Produces proteins that specifically degrade mucin to gain access to intestinal epithelium
What cell types are present in Peyers patches and what is its structure?
B cell follicles with germinal centres and smaller T cell area
There is a sunepithelial dome which is rich in dendritic cells B and T cells
Layer of follicle associated epithelium containing conventional intestinal epithelial cells (enterocytes) and fewer specialised cells (microfold M cells)
What are isolated lymphoid follicles composed of
composed of epithelium containing M cells but with mainly B cells (develop after birth)
How do peyers patched uptake antigens?
M cells take up antigen by endocytosis and phagocytosis
Antigen is transported across the M cells in vesicles and released at the basal surface
Antigen is bound by dendritic cells which activates T cells
How do dendritic cells directly uptake antigens?
They extend their processes across the epithelial layer to capture the antigen from the lumen of the gut
What are the two forms of antigen uptake?
Uptake by peyers patched mediated by M cells
Direct uptake by dendritic cells
Where are CD8 and CD4 T cells mainly located?
CD4 in the lamina propria
CD8 in the epithelium
What are the immunologic properties of the lamina propria?
CD4 T cells, IgA producing plasma cells, macrophages, dendritic cells and mast cells
What are the immunological properties of the epithelium?
CD8 T cells
What is the role of epithelial cells in immune response and what is their structure?
contain receptors on their basal surface allowing them to recognise bacteria that have invaded the epithelial barrier
The basolateral surface contain toll like receptors
The cytoplasm contain nuceltotide binding oligomerisation proteins (NODs)
What occurs when epithelial cells recognise pathogens?
There is an influx of inflammatory cells/lymphocytes into the mucosa from the blood stream
- Endocytosed bacteria are recognise by TLRs
- Bacteria or their products in the cytosol recognised by NOD1 and NOD2
