Phlegm

Japanese: 痰

Concept/Mechanism Even healthy individuals produce approximately 10-100 mL of airway secretions per day, which are mainly produced by bronchial glands and goblet cells in the bronchi. Bronchial glands are mixed glands consisting of mucus cells and serous cells. Mucus cells secrete glycoproteins to increase viscosity. Serous cells secrete water, electrolytes, secretory IgA, secretory IgM, lysozyme, etc. to decrease viscosity. The produced mucus thinly covers the surface of the airway epithelium, preventing the airway from drying out and trapping inhaled dust and microorganisms. It is then transported to the central airway by the ciliary movement of the airway epithelial cells and is unconsciously swallowed in the larynx. When bronchial glands or goblet cells are stimulated by various causes, or when their hypertrophy or proliferation is promoted, the amount of airway secretions increases, and is perceived as phlegm. In other words, phlegm is excess secretion from the airways. Sputum may occasionally be expectorated as postnasal drip, aspirated saliva, purulent secretions from the lung parenchyma, or leakage or exudate into the alveoli.
When phlegm becomes stuck in the airway or gets stuck in the larynx, it causes a productive cough. It often obstructs the airway, causing dyspnea, atelectasis, obstructive pneumonia, and hypoxemia due to hypoventilation.
The most important cause of phlegm is airway infection. In particular, bacterial infections mobilize neutrophils, which turn the phlegm yellow-green due to the peroxidase contained in neutrophils. Such phlegm is called purulent. If the phlegm has an odor, anaerobic bacterial infection is suspected. Among non-purulent sputum, highly viscous sputum is called mucous, and that which is not is called serous. Mucous sputum is seen in asthma and acute bronchitis, while serous sputum is seen in pulmonary edema, laryngitis, and alveolar cell carcinoma, and purulent sputum is often observed in bronchiectasis, diffuse panbronchiolitis, chronic bronchitis, and pulmonary abscess. In asthma, the amount of viscous sputum increases during attacks, further narrowing the lumen of the contracted airways. In pulmonary edema, plasma components leak into the alveoli, causing serous and sometimes frothy sputum to be expectorated. In alveolar cell carcinoma, very large amounts of serous sputum may be produced, a condition known as bronchorrhea.
Clinical examinations Sputum contains a lot of information about lesions in the airways and lung parenchyma. To identify the causative bacteria of infection, sputum is used for bacterial smears, culture, and identification. It is important to evaluate whether sputum is from the lower respiratory tract and is suitable for bacteriological examination. The Miller-Jones classification, which indicates the macroscopic characteristics of sputum, is shown in Table 2-35-1. The more purulent it is, the more useful it is for bacteriological examination. From the morphology and staining of bacteria by Gram staining, it is possible to infer that Streptococcus pneumoniae, Staphylococcus aureus, Moraxella catarrhalis, Haemophilus influenzae, and Pseudomonas aeruginosa are the causative bacteria. If there is an image of phagocytosis of these bacteria by white blood cells, it is highly likely that they are the causative bacteria. Even if there is no image of phagocytosis, if the quantitative culture shows 10 ⁶ to 10 ⁷ CFU (colony forming units)/mL or more, it is highly likely that they are the causative bacteria. In addition, the presence or absence of malignant cells is examined by cytology of sputum. Furthermore, if the majority of inflammatory cells in the sputum are neutrophils, the causative pathology is likely to be infectious disease, and if they are eosinophils, the element of allergy is large.
Treatment Treatment is centered on identifying the cause of phlegm production and administering appropriate treatment. If it is a bacterial infection, an appropriate antibiotic is administered. As a symptomatic treatment, mucolytics are used for viscous phlegm. β2 agonists are also sometimes used in the hope that they will expand narrowed airways, promote the expectoration of phlegm, and suppress coughing. However, caution is required as they can also stimulate the bronchial glands and increase mucus secretion. [Yamaguchi Etsuro]
■References <br /> Kimura Hiroshi, Yamada Yoshihito: Sputum, hemoptysis, hemoptysis. Learn Pathophysiology with Charts, 2nd ed. (Kawakami Yoshikazu, et al. eds.), pp40-41, Chugai Igakusha, Tokyo, 2000. Nagai Atsushi: Sputum. Today's Diagnostic Guidelines, 5th ed. (Kameyama Masakuni, et al. eds.), pp337-338, Igaku-Shoin, Tokyo, 2002.

Table 2-35-1
Miller-Jones classification of sputum macroscopic properties ">

Table 2-35-1

Source : Internal Medicine, 10th Edition About Internal Medicine, 10th Edition Information

Japanese:

概念・機序
　健常者でも1日約10～100 mLの気道分泌物があり，おもに気管支の気管支腺や杯細胞から産生される．気管支腺は粘液細胞と漿液細胞からなる混合腺である．粘液細胞は糖蛋白を分泌し粘稠度を増加させる．漿液細胞は水分，電解質，分泌型IgA，分泌型IgM，リゾチームなどを分泌し，粘稠度を低下させる．産生された粘液は気道上皮表面を薄く覆い，気道の乾燥を防ぐとともに，吸入された塵埃や微生物をとらえる．その後，気道上皮細胞の繊毛運動により中枢気道に送られ，喉頭で無意識に嚥下されている．種々の原因により気管支腺や杯細胞が刺激されたり，それらの肥大化や増生が促されると気道分泌物量が増加し，痰として自覚される．すなわち痰とは気道の過剰分泌物である．ときに後鼻漏や気道に吸引された唾液，肺実質の化膿性分泌物，肺胞への漏出物や滲出物が痰として喀出されることがある．
　痰が気道に滞留したり，喉頭でからむとぜろぜろとした咳となり，いわゆる湿性咳嗽となる．またしばしば気道を閉塞し，呼吸困難や無気肺，閉塞性肺炎，低換気による低酸素血症の原因となる．
原因
　痰を生じる原因で最も重要なものは気道感染である．特に細菌性では好中球が動員され，その結果好中球に多く含まれるペルオキシダーゼにより痰は黄緑色となる．そのような痰は膿性とよばれる．痰に臭気を伴う場合には嫌気性菌感染が疑われる．非膿性痰のうち，粘稠度の高いものは粘液性とよび，そうではないものは漿液性とよぶ．粘液性の痰は喘息，急性気管支炎などでみられ，漿液性痰は肺水腫，喉頭炎，肺胞上皮癌などで，膿性痰は気管支拡張症，びまん性汎細気管支炎，慢性気管支炎，肺化膿症などで観察されることが多い．喘息では発作時に特に粘稠な痰が増加し，攣縮を起こした気道の内腔をさらに狭める．肺水腫では肺胞へ血漿成分が漏出するために，漿液性からときに泡沫状の喀痰が喀出される．肺胞上皮癌ではきわめて大量の漿液性喀痰が産生されることがあり，気管支漏とよばれる．
臨床検査
　痰には気道や肺実質の病変に関する多くの情報が含まれている．感染症の原因菌同定のために，痰を用いた細菌の塗抹検鏡，培養，同定が行われる．痰が下気道由来で細菌学的検査に適しているか否かの評価は重要である．そのための痰の肉眼的性状を表すMiller-Jones分類を表2-35-1に示す．膿性が強くなるほど細菌学的検査には有用である．Gram染色による細菌の形態や染色性から，肺炎球菌，黄色ブドウ球菌，モラクセラ・カタラーリス菌，インフルエンザ菌，緑膿菌などは推定可能である．白血球によるそれらの菌の貪食像があれば，原因菌である可能性が高い．貪食像がなくとも定量培養で10⁶～10⁷ CFU （コロニー形成単位）/mL以上であれば，原因菌である可能性が高い．また痰の細胞診により，悪性細胞の有無を検査する．さらに痰中の炎症細胞の主体が好中球であれば原因病態が感染症の可能性が高く，好酸球であればアレルギー性の要素が大きい．
治療
　治療は，痰を産生する原因を明らかにし，それに対して適切な治療をすることが主体となる．細菌感染であれば，適切な抗菌薬を投与する．対症療法として粘稠な痰に対して粘液溶解剤を使用する．β2刺激薬も狭窄した気道を拡張させて痰の喀出を促進し，咳を鎮める働きを期待して使用されることがある．しかし，逆に気管支腺を刺激して粘液分泌を増強させることがあるので注意が必要とされる．［山口悦郎］
■文献
木村　弘，山田嘉仁：喀痰，血痰，喀血．チャートで学ぶ病態生理学，第2版（川上義和，他編），pp40-41，中外医学社，東京，2000．永井厚志：痰．今日の診断指針，第５版（亀山正邦，他編），pp337-338，医学書院，東京，2002．

表2-35-1
Miller-Jones による痰の肉眼的性状分類">

表2-35-1

出典　内科学第10版内科学第10版について　情報

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