Final answer:
The 3rd stage of the host response to tuberculosis is the formation of tubercles in the lungs. Bacteria continue to multiply within the tubercles, resulting in tissue damage and the formation of a caseous center. Tubercles may eventually rupture and bacteria can spread to other organs.
Step-by-step explanation:
The 3rd stage of the host response to tuberculosis (TB) is the formation of a solid state granuloma. After the bacterium enters the alveoli in the lungs, it is phagocytized by macrophages. If not eliminated by macrophages, the infection can progress and cause an inflammatory response, leading to the formation of small round lesions called tubercles. Bacteria continue to be released into the center of the tubercles, resulting in tissue damage and the formation of a caseous center. Tubercles may eventually rupture and bacteria can spread through the bloodstream to other organs.