3.7
Tuberculose Pulmonar II: Fisiopatologia
A tuberculose, ou TB, é uma doença infecciosa bacteriana causada pelo Mycobacterium tuberculosis. Embora seu principal impacto seja nos pulmões, levan…
A fisiopatologia da tuberculose começa quando um hospedeiro suscetível inala gotículas aerossolizadas contendo Mycobacterium tuberculosis.
As gotículas atingem os alvéolos dos pulmões, onde as bactérias se multiplicam e encontram macrófagos alveolares, que as engolfam.
No entanto, em vez de destruir as bactérias, os macrófagos permitem que elas sobrevivam e se repliquem em seu interior.
Após 2-6 semanas, o corpo inicia uma resposta imune mediada por células, formando uma estrutura especializada chamada granuloma para conter a disseminação bacteriana.
O granuloma compreende células imunes, células bacterianas vivas e mortas, células T e macrófagos.
A bactéria pode permanecer dormente dentro do granuloma, não causando sintomas e não sendo contagiosa. Este estágio é conhecido como infecção latente por tuberculose.
Se o sistema imunológico estiver comprometido, a tuberculose latente pode progredir para a doença ativa da tuberculose por meio do processo de caseação, onde o centro de um granuloma se necrosa, formando uma substância semelhante ao queijo chamada caseum.
Esse material caseoso então corrói em um brônquio, criando uma cavidade que facilita a rápida proliferação bacteriana e a disseminação potencial da infecção pelo sangue ou linfa.
View the full transcript and gain access to JoVE Core videos
Q1: How does Mycobacterium tuberculosis survive inside alveolar macrophages?
When susceptible hosts inhale aerosolized droplets containing Mycobacterium tuberculosis, the bacteria reach the lungs' alveoli where alveolar macrophages engulf them. However, instead of destroying the bacteria, the macrophages allow them to survive and replicate within. This intracellular survival mechanism enables the infection to establish and persist in the host.
Q2: What is a granuloma and why does the body form one?
A granuloma is a specialized immune structure that forms 2-6 weeks after infection when the body initiates a cell-mediated immune response. It comprises immune cells, live and dead bacterial cells, T-cells, and macrophages clustered together. The granuloma's primary function is to contain and prevent the spread of Mycobacterium tuberculosis throughout the body.
Q3: What is the difference between latent and active tuberculosis infection?
In latent tuberculosis infection, bacteria remain dormant within the granuloma, causing no symptoms and being non-contagious. Active tuberculosis disease develops when the immune system is compromised, allowing bacteria to multiply and spread, causing tissue damage and symptoms. About 5-10% of individuals with latent TB infection progress to active disease, particularly if their immune system becomes weakened.
Q4: How does caseation lead to cavity formation in tuberculosis?
Caseation occurs when the center of a granuloma becomes necrotized, forming a cheese-like substance called caseum. If this caseous material erodes into a bronchus, it creates a cavity that facilitates rapid bacterial proliferation. This cavitation process worsens symptoms and increases the potential for bacterial spread through blood or lymph.
Q5: How is tuberculosis transmitted from one person to another?
Tuberculosis transmission begins when a person inhales droplet nuclei containing Mycobacterium tuberculosis. These droplets are typically released into the air when an individual with pulmonary or laryngeal TB coughs, sneezes, or speaks. The inhaled bacteria then reach the alveoli in the lungs, where the infection cycle begins.
Q6: What role does the cell-mediated immune response play in tuberculosis infection?
Approximately 2-6 weeks post-infection, the body mounts a cell-mediated immune response where T cells recognize mycobacterial antigens presented by infected macrophages. This triggers cytokine release, activating other immune cells and processes that lead to granuloma formation. This immune response aims to contain bacterial spread and is essential for controlling the infection.
Q7: Can tuberculosis spread to organs outside the lungs?
Yes, from the lungs, Mycobacterium tuberculosis can spread through the bloodstream, causing miliary TB, or through the lymphatic system to other organs, resulting in extrapulmonary tuberculosis. This dissemination occurs when bacteria escape the primary infection site and establish secondary infections in various body systems, complicating the disease presentation and nursing management and prevention strategies.