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    What are tubercles and how do they cause damage and what is tuberculosis?
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    (Original post by Jennifer50)
    What are tubercles and how do they cause damage and what is tuberculosis?
    Tubercules are like masses of dead lung tissue that act as reservoirs for infection as it's hard for white blood cells to penetrate them
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    so how do they form?
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    (Original post by Jennifer50)
    so how do they form?
    When you introduce the TB bacteria into the lungs, specifically the alveoli, white blood cells in the membrane detect this and will try to destroy the bacteria.

    Normally what happens is that the white blood cells engulf the bacterium via phagocytosis and then fuse the bacteria with a lysosome to create a phagolysosome. The enzymes will normally break down the bacterium.

    However the bacterium has a very thick slime capsule that allows it survive the immune response and harbour within the white blood cell. This effectively creates an inactive white blood cell, and when several of these group together, they form a granuloma. It gets bigger and bigger due to more white blood cells and then triggers the death of lung cells. These dead cells are known as a tubercule
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    (Original post by Jennifer50)
    so how do they form?
    When TB bacilli enter the lungs they go to the alveoli where they are engulfed by alveolar macrophages. This tends to occur along fissures between the lobes of the lungs. These alveolar macrophages secrete hydrolytic enzymes on to the bacilli to try to digest them however, the bacilli have a thick fatty layer of mycolic acid which is in the cell wall (not the capsule) which prevents it from being destroyed. Some macrophages migrate to and drain in local lymph nodes and transmit the mycobacteria to the lymph nodes. The bacilli are able to survive and reproduce in the macrophages and eventually kill the macrophages which initiates an inflammatory response. These macrophages begin to aggregate and form giant multinucleated cells which form the granuloma. A granuloma is a collection of immunological cells. These granulomas contain lots of dead macrophages and dead lung tissue and the death of the macrophages and the lung tissue is known as caseous necrosis (caseous = cheese-like appearance, necrosis = tissue death). The granuloma seals off the infection and prevents the bacilli from spreading.

    Over time, the tubercle may undergo fibrosis (scarring) and calcification - allowing it to be seen on an X-ray. The granuloma in the lung tissue would be referred to as a Ghon focus histologically, however, the granuloma in the lung AND in the lymph node would be histologically referred to as the Ghon complex.

    Hopefully that helps.
 
 
 
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