2. Steps in pathogenesis - overview Flashcards
What are the 7 stages of pathogenesis?
- Entry into the host
- Attain a niche
- Avoid constitutive or non specific host defences
- Circumvent specific induced host responses
- Grow and persist within the host
- Cause damage to the host
- Exit from the host
What are the five possible entry routes a micro-organism may use to gain entry?
- Skin
- Eyes
- Gastrointestinal tract
- Respiratory tract
- Urinogenital tract
Which of the aforementioned entry routes are the most often infected?
The gastrointestinal and respiratory tract are most often infected, followed by the other mucosal surfaces and eyes. The skin is the least often infected.
How are the alveoli protected from micro-organisms?
No cilia or mucus is present here but macrophages line the alveoli to phagocytose invading micro-organisms.
How does the upper and lower respiratory tract prevent micro-organism entry into the body?
- Hairs lining the notstrils trap larger pathogens.
- Ciliated cells, goblet cells and subepithelial mucus-secreting glands. The latter two secrete mucus to entrap invaders allowing them to be wafted back up the respiratory tract by ciliary action, or in the case of the upper respiratory tract to the back of the throat to be swallowed and killed in the stomach.
- Antibodies
What are the predominant antibodies present in the upper and lower respiratory tract?
IgA - Upper RT
IgG - Lower RT
How does mucus membrane help protect infection in the gastrointestinal tract?
Mucus acts as a mechanical barrier to cells which may become infected and contains secretory IgA antibodies that protect the immune individual against infection.
How does the normal intestinal microflora serve to protect from gastrointestinal infection?
- Killing other bacteria by bacteriocins
- Competition for nutrition and attachment sites
- The production of bacterial inhibitors e.g acetic and propionic acids
What do pathogens attach to in the oral cavity?
- Mucosal surfaces
- Teeth
- Epithelial cells of cheek
- Tongue
What are the natural defence mechanisms of the oral cavity?
Saliva is secreted continually allowing for mechanical removal of micro-organisms and release of antimicrobial agents such as lysozyme and secretary antibodies.
Why is it difficult for micro-organisms to establish a niche in the urinary tract?
Due to the continual flushing of urine.
Why are urinary infections more common in woman than men?
The female urethra is 5cm long compared to the 20cm of the male urethra. In addition its close proximity to the anus exposes it to more pathogenic micro-organisms.
Name a commensal microorgansim which colonises the vagina?
Lactobacillus
Mention a protective defence mechanism established to prevent vaginal infections.
Oestrogen allows the secretion of glycogen in the vagina which is metabolised by lactobacilli to produce lactic acid making the vagina slightly acidic and thus prevents its colonisation by harmful microorganisms.
What happens after menopause when glycogen is no longer being secreted like it used to be?
The vaginal secretions become alkaline due to the lack of glycogen and microorganisms such as staphylococci and streptococci can establish themselves in the vagina.
