The term "foci of TB" refers primarily to the Ghon focus, which is the initial site of infection in the lung when a person, typically a child, is first exposed to Mycobacterium tuberculosis, the bacteria that causes tuberculosis (TB).
Here's a breakdown:
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Ghon Focus: This is the primary lesion that develops in the lung, usually in the lower or middle zones, just beneath the pleura (the lining of the lung). It represents the body's initial immune response to the TB bacteria.
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Ghon Complex: The Ghon focus often occurs in conjunction with infected hilar lymph nodes (lymph nodes near the lung's root). The combination of the Ghon focus and the affected lymph nodes is known as the Ghon complex. This complex represents the complete primary infection site.
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Ranke Complex: In many cases, the Ghon complex heals. As it heals, it can calcify (become hardened with calcium deposits). The calcified Ghon complex is known as the Ranke complex. While the TB bacteria may remain dormant within the Ranke complex, it indicates a prior TB infection.
So, in summary, the foci of TB, in the context of primary infection, are the Ghon focus (the initial lung lesion) and the associated infected lymph nodes that make up the Ghon complex. Later, a calcified Ghon Complex would be considered a Ranke Complex.
