鼻涕

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鼻涕是指鼻中的粘液。鼻涕由鼻粘膜的杯狀細胞分泌，功能在於保護呼吸道。鼻涕的分泌是持續性的，但因鼻腔與食道相通，所以一般都在不知不覺中被嚥下。

呼吸道中粘液分泌增加是許多常見疾病，如感冒的症狀，在鼻腔和喉嚨中存在粘液是正常的，但是數量增多會影響舒適的呼吸並需要通過擤鼻涕或吐痰來排出咽喉後部的粘液。鼻涕也可以通過傳統的方法鼻沖洗來去除。在西方社會中，治療粘液過多的更常用的方法是使用藥物如解充血藥。

在醫學術語中，一小塊乾的或半乾的鼻涕被稱為鼻石或鼻屎。當粘液捕獲住塵土或其他空氣中的微粒就會形成鼻屎，粘液在微粒周圍變乾並變硬，有些像牡蠣中珍珠的形成。由於捕捉外部微粒是鼻涕的主要功能之一，鼻屎的存在是功能正常的鼻子（與鼻炎相反）的指示器。

乾燥的鼻涕被稱為鼻屎，通常可以通過摳鼻子去除，但在不少文化中，在公眾場合摳鼻子被視為不雅的行為。比較文明的做法，是透過用衛生紙大力的抹鼻涕，以刺激鼻腔分泌鼻涕，把鼻屎順道沖走。

  此條目介紹的是the biological substance。关于其他用法，请见「鼻涕 (消歧义)」。

Mucous cells of the stomach lining secrete mucus (pink) into the lumen

In vertebrates, mucus (/mkəs/ MYOO-kəss; adjectival form: "mucous") is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is rich in glycoproteins and water. It is typically produced from cells found in mucous glands. Mucous fluid may also originate from mixed glands, which contain both serous and mucous cells. It is a viscous colloid containing antiseptic enzymes (such as lysozymes), immunoglobulins, inorganic salts, proteins such as lactoferrin, and glycoproteins known as mucins that are produced by goblet cells in the mucous membranes and submucosal glands. This mucus serves to protect epithelial cells (that line the tubes) in the respiratory, gastrointestinal, urogenital, visual, and auditory systems; the epidermis in amphibians; and the gills in fish. A major function of this mucus is to protect against infectious agents such as fungi, bacteria and viruses. The average human nose produces about a liter of mucus per day. Most of the mucus produced is in the gastrointestinal tract.

Bony fish, hagfish, snails, slugs, and some other invertebrates also produce external mucus. In addition to serving a protective function against infectious agents, such mucus provides protection against toxins produced by predators, can facilitate movement and may play a role in communication.

The rest of this article deals with the production and function of mucus in humans.

Respiratory system

Illustration depicting the movement of mucus in the respiratory tract.

In the human respiratory system, mucus aids in the protection of the lungs by trapping foreign particles that enter them, in particular, through the nose, during normal breathing. "Phlegm" is a specialized term for mucus that is restricted to the respiratory tract, whereas the term "nasal mucus" describes secretions of the nasal passages.

Nasal mucus is produced by the nasal mucosa; and mucosal tissues lining the airways (trachea, bronchus, bronchioles) is produced by specialized airway epithelial cells (goblet cells) and submucosal glands. Small particles such as dust, particulate pollutants, and allergens, as well as infectious agents and bacteria are caught in the viscous nasal or airway mucus and prevented from entering the system. This event along with the continual movement of the respiratory mucus layer toward the oropharynx, helps prevent foreign objects from entering the lungs during breathing. This explains why coughing often occurs in those who smoke cigarettes. The body's natural reaction is to increase mucus production. In addition, mucus aids in moisturizing the inhaled air and prevents tissues such as the nasal and airway epithelia from drying out. Nasal and airway mucus is produced continuously, with most of it swallowed subconsciously, even when it is dried.

Increased mucus production in the respiratory tract is a symptom of many common illnesses, such as the common cold and influenza. Hypersecretion of mucus can occur in inflammatory respiratory diseases such as respiratory allergies, asthma, and chronic bronchitis. The presence of mucus in the nose and throat is normal, but increased quantities can impede comfortable breathing and must be cleared by blowing the nose or expectorating phlegm from the throat.

Diseases involving mucus

In general, nasal mucus is clear and thin, serving to filter air during inhalation. During times of infection, mucus can change color to yellow or green either as a result of trapped bacteria or due to the body's reaction to viral infection. The green color of mucus comes from the heme group in the iron-containing enzyme myeloperoxidase secreted by white blood cells as a cytotoxic defense during a respiratory burst.

In the case of bacterial infection, the bacterium becomes trapped in already-clogged sinuses, breeding in the moist, nutrient-rich environment. Sinusitis is an uncomfortable condition which may include congestion of mucus. A bacterial infection in sinusitis will cause discolored mucus and would respond to antibiotic treatment; viral infections typically resolve without treatment. Almost all sinusitis infections are viral and antibiotics are ineffective and not recommended for treating typical cases.

In the case of a viral infection such as cold or flu, the first stage and also the last stage of the infection cause the production of a clear, thin mucus in the nose or back of the throat. As the body begins to react to the virus (generally one to three days), mucus thickens and may turn yellow or green. Viral infections cannot be treated with antibiotics, and are a major avenue for their misuse. Treatment is generally symptom-based; often it is sufficient to allow the immune system to fight off the virus over time.

Cystic fibrosis

主条目：Cystic fibrosis

Cystic fibrosis is an inherited disease that affects the entire body. Symptoms begin mostly in the lungs, with viscous (thick) mucus that is difficult to expel.

Mucus as a medical symptom

Increased mucus production in the upper respiratory tract is a symptom of many common ailments, such as the common cold. Nasal mucus may be removed by blowing the nose or by using nasal irrigation. Excess nasal mucus, as with a cold or allergies, due to vascular engorgement associated with vasodilation and increased capillary permeability caused by histamines, may be treated cautiously with decongestant medications. Excess mucus production in the bronchi and bronchioles, as may occur in asthma, bronchitis or influenza, may be treated with anti-inflammatory medications as a means of reducing the airway inflammation, which triggers mucus over-production. Thickening of mucus as a "rebound" effect following overuse of decongestants may produce nasal or sinus drainage problems and circumstances that promote infection.

Cold weather and nasal mucus

During exposure to cold weather, the cilia, which normally sweep mucus away from the nostrils and toward the back of the throat (see respiratory epithelium), become sluggish or completely cease functioning. This results in mucus running down the nose and dripping (a runny nose). Mucus also thickens in cold weather; when an individual comes in from the cold, the mucus thaws and begins to run before the cilia begin to work again.

Digestive system

In the human digestive system, mucus is used as a lubricant for materials that must pass over membranes, e.g., food passing down the esophagus. Mucus is extremely important in the intestinal tract. It forms an essential layer in the colon and in the small intestine that helps reduce intestinal inflammation by decreasing bacterial interaction with intestinal epithelial cells. A layer of mucus along the inner walls of the stomach is vital to protect the cell linings of that organ from the highly acidic environment within it. Mucus is not digested in the intestinal tract. Mucus is also secreted from glands within the rectum due to stimulation of the mucous membrane within.

Reproductive system

In the human female reproductive system, cervical mucus prevents infection and provides lubrication during sexual intercourse. The consistency of cervical mucus varies depending on the stage of a woman's menstrual cycle. At ovulation cervical mucus is clear, runny, and conducive to sperm; post-ovulation, mucus becomes thicker and is more likely to block sperm. Several Fertility Awareness methods, such as the Creighton Model and Billings method rely on this fact to prevent or to improve the odds of pregnancy.

In the human male reproductive system, the seminal vesicles contribute up to 100% of the total volume of the semen and contain mucus, amino acids, prostaglandins, vitamin C, and fructose as the main energy source for the sperm.

鼻涕的成分

鼻涕的主要成分：水份、无机盐、少量糖、脂肪、蛋白质、少量脱落的粘膜细胞、吸附的灰尘和空气中的化学物质等。这也是生病时大量细菌会寄生其中， 使鼻涕呈现黄色或绿色的原因。

有色鼻涕

鼻涕一般是無色透明黏液，但鼻涕顏色若呈現淡黃色或淡綠色，且變濃稠狀，這代表鼻腔可能受到細菌或病毒感染。當細菌感染時，細菌在鼻腔內大量滋生，免疫反應導致鼻黏膜腫脹，因而產生鼻塞。据英国彼士顿研究所一个研究人体分泌液的研究小组调查，在3000名志愿者身上发现有5%的志愿者有其他颜色的鼻涕，如红色，棕色，紫色等。该研究小组解释，可能是因为人类个体免疫系统变异导致该结果，而这种结果又是由于病菌和病毒的进化导致的。

參見

• 空鼻症候群
• Alkaline mucus
• Empty nose syndrome
• Mucoadhesion
• Mucophagy
• Snail slime
• Sniffle
• Spinnbarkeit