Non-specific defence

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Physical Barriers

The skin and other membranes are rather good at keeping stuff out. Very few organisms can pass through intact skin, and mucous on membranes in places like the nose trap other microbes in the stickiness. Hairs in the nose do the trick, actting as a filter, and cilia in the respiratory tract move stuff to the throat for it to be swallowed and mashed up. The bladder only allows urine out one way, which minimises amount of microbes getting inside.


Inflammation

This baby is pretty good at stopping stuff. There are several common symptoms of inflammation:

  • redness
  • pain
  • swelling
  • heat
  • loss of function

Back in the day when people used to latin, the used to remember, rubor, dolor, tumor, calor and loss of function. This makes it slightly easier to remember although that's only if you know what they all mean. Also, "loss of function" doesn't half-rhyme. May be this was less helpful than I thought it would be.

Anyway, here are the stages of inflammation:

Tissue damage

Microbes damage tissues, which release chemical mediators.

Chemicals cause... vasodilation

Some of the chemical mediators make blood vessels wider. The vasodilation increases blood flow to the area, which brings more cells and proteins to the area, but also causes the redness and the heat.

Chemicals cause... permeability to plasma.

This makes the endothelial cells contract in the microcirculation, making gaps that allow plasma proteins to escape (this also increases leakage of tissue fluid, causing swelling - the swelling isnt useful, it just happens). The sswelling can also cause the pain, by compressing sensory nerve endings.

Chemicals cause... chemotaxis

The chemicals attract neutrophils, which are passing through the blood, slowly since the loss of fluid has thickened it. They detect the chemicals, and bind to the wall of the blood vessels (aka. margination). They then work through the gaps between the endothelial cells (aka. diapedesis), and end up in the interstitial fluid by the injury. This way loads of neutrophils end up at the site (and some other leukocytes).


Tip: Use PVC (like the plastic) to remember what the chemicals cause...

Microbe MASHUP!

The microbes are destroyed through phagocytosis, from complement attack and release of antimicrobial substances, a weedkiller style attack.

Tissue Heal

The tissues heal, but you should read about that here