3.7
肺結核 II: 病態生理学
結核は、マイコバクテリウム・ツベルクローシスによって引き起こされる細菌感染症です。主な影響は肺に及び、肺結核を引き起こしますが、肺外結核と呼ばれる状態の他のさまざまな臓器にも影響を及ぼす可能性もあります。
病態生理学の詳細な説明は次のとおりです。
感染: 感染過程は、人がマイコバクテリウム・ツベルク…
結核の病態生理学は、感受性の高い宿主が結核菌を含むエアロゾル化した液滴を吸い込むときに始まります。
液滴は肺胞に到達し、そこで細菌が増殖して肺胞マクロファージに遭遇し、細菌を飲み込みます。
しかし、マクロファージは細菌を破壊する代わりに、細菌が生き残り、内部で複製することを可能にします。
2〜6週間後、体は細胞性免疫応答を開始し、細菌の広がりを封じ込めるために肉芽腫と呼ばれる特殊な構造を形成します。
肉芽腫は、免疫細胞、生細胞と死細胞、T細胞、およびマクロファージで構成されています。
細菌は肉芽腫内で休眠状態のままであり、症状を引き起こさず、非伝染性である可能性があります。この段階は、潜伏性結核感染症として知られています。
免疫系が損なわれると、潜伏性結核は、肉芽腫の中心が壊死してカゼムと呼ばれるチーズのような物質を形成するケースゼーションプロセスを通じて活動性結核疾患に進行する可能性があります。
次に、この乾酪質材料は気管支に侵食され、細菌の急速な増殖と血液やリンパ液を介した感染の潜在的な広がりを促進する空洞を形成します。
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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.