Mucus in the context of Mucociliary clearance

Human feces (American English) or faeces (British English), commonly and in medical literature more often called stool, are the solid or semisolid remains of food that could not be digested or absorbed in the small intestine of humans, but has been further broken down by bacteria in the large intestine. It also contains bacteria and a relatively small amount of metabolic waste products such as bacterially altered bilirubin, and the dead epithelial cells from the lining of the gut. It is discharged through the anus during a process called defecation.

Human feces has similarities to the feces of other animals and varies significantly in appearance (i.e. size, color, texture), according to the state of the diet, digestive system, and general health. Normally, human feces are semisolid, with a mucus coating. Small pieces of harder, less moist feces can sometimes be seen impacted in the distal (final or lower) end. This is a normal occurrence when a prior bowel movement is incomplete, and feces are returned from the rectum to the large intestine, where water is further absorbed.

A respiratory droplet is a small aqueous droplet produced by exhalation, consisting of saliva or mucus and other matter derived from respiratory tract surfaces. Respiratory droplets are produced naturally as a result of breathing, speaking (speech droplet), sneezing, coughing, or vomiting, so they are always present in our breath, but speaking and coughing increase their number.

Droplet sizes range from < 1 μm to 1000 μm, and in typical breath there are around 100 droplets per litre of breath. So for a breathing rate of 10 litres per minute this means roughly 1000 droplets per minute, the vast majority of which are a few micrometres across or smaller. As these droplets are suspended in air, they are all by definition aerosols. However, large droplets (larger than about 100 μm, but depending on conditions) rapidly fall to the ground or another surface and so are only briefly suspended, while droplets much smaller than 100 μm (which is most of them) fall only slowly and so form aerosols with lifetimes of minutes or more, or at intermediate size, may initially travel like aerosols but at a distance fall to the ground like droplets ("jet riders").

Sputum is mucus that is coughed up from the lower airways (the trachea and bronchi). In medicine, sputum samples are usually used for a naked-eye examination, microbiological investigation of respiratory infections, and cytological investigations of respiratory system.

A naked eye exam of the sputum can be done at home by a patient in order to note the various colors (see below). Any hint of yellow or green color (pus) suggests an airway infection (but does not indicate the type of organism causing it). Such color hints are best detected when the sputum is viewed against a bright white background, such as white paper, a white pot, or a white sink surface.

Digestion is the breakdown of large insoluble food compounds into small water-soluble components so that they can be absorbed into the blood plasma. In certain organisms, these smaller substances are absorbed through the small intestine into the blood stream. Digestion is a form of catabolism that is often divided into two processes based on how food is broken down: mechanical and chemical digestion. The term mechanical digestion refers to the physical breakdown of large pieces of food into smaller pieces which can subsequently be accessed by digestive enzymes. Mechanical digestion takes place in the mouth through mastication and in the small intestine through segmentation contractions. In chemical digestion, enzymes break down food into the small compounds that the body can use.

In the human digestive system, food enters the mouth and mechanical digestion of the food starts by the action of mastication (chewing), a form of mechanical digestion, and the wetting contact of saliva. Saliva, a liquid secreted by the salivary glands, contains salivary amylase, an enzyme which starts the digestion of starch in the food. The saliva also contains mucus, which lubricates the food; the electrolyte hydrogencarbonate (HCO₃), which provides the ideal conditions of pH for amylase to work; and other electrolytes (Na, K, Cl). About 30% of starch is hydrolyzed into disaccharide in the oral cavity (mouth). After undergoing mastication and starch digestion, the food will be in the form of a small, round slurry mass called a bolus. It will then travel down the esophagus and into the stomach by the action of peristalsis. Gastric juice in the stomach starts protein digestion. Gastric juice mainly contains hydrochloric acid and pepsin. In infants and toddlers, gastric juice also contains rennin to digest milk proteins. As the first two chemicals may damage the stomach wall, mucus and bicarbonates are secreted by the stomach. They provide a slimy layer that acts as a shield against the damaging effects of chemicals like concentrated hydrochloric acid while also aiding lubrication. Hydrochloric acid provides acidic pH for pepsin. At the same time protein digestion is occurring, mechanical mixing occurs by peristalsis, which is waves of muscular contractions that move along the stomach wall. This allows the mass of food to further mix with the digestive enzymes. Pepsin breaks down proteins into peptides or proteoses, which are further broken down into dipeptides and amino acids by enzymes in the small intestine. Studies suggest that increasing the number of chews per bite increases relevant gut hormones and may decrease self-reported hunger and food intake.

Saliva (commonly referred as spit or drool) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can be extracted), enzymes (such as lingual lipase and amylase), and antimicrobial agents (such as secretory IgA, and lysozymes).

The enzymes found in saliva are essential in beginning the process of digestion of dietary starches and fats. These enzymes also play a role in breaking down food particles trapped within dental crevices, thus protecting teeth from bacterial decay. Saliva also performs a lubricating function, wetting food and permitting the initiation of swallowing, and protecting the oral mucosa from drying out.

Vaginal lubrication is a naturally produced fluid that lubricates the vagina. Vaginal lubrication production increases significantly during sexual arousal in anticipation of sexual intercourse. Vaginal dryness is the condition in which this lubrication is insufficient, and sometimes artificial lubricants are used to augment it. Without sufficient lubrication, sexual intercourse can be painful. The vaginal lining has no glands, and therefore the vagina must rely on other methods of lubrication. Plasma from the vaginal walls due to vascular engorgement is considered to be the chief lubrication source, and the Bartholin's glands, located slightly below and to the left and right of the introitus (vaginal opening), also secrete mucus to augment vaginal wall secretions. Near ovulation, cervical mucus provides additional lubrication.

A mucous membrane or mucosa is a membrane that lines various cavities in the body of an organism and covers the surface of internal organs. It consists of one or more layers of epithelial cells overlying a layer of loose connective tissue known as the lamina propria. It is mostly of endodermal origin and is continuous with the skin at body openings such as the eyes, eyelids, ears, inside the nose, inside the mouth, lips, the genital areas, the urethral opening and the anus. Some mucous membranes secrete mucus, a thick protective fluid. The function of the membrane is to stop pathogens and dirt from entering the body and to prevent bodily tissues from becoming dehydrated.

Amphibians, fish, snails, slugs, and some other invertebrates also produce external mucus from their epidermis as protection against pathogens, to help in movement, and to line fish gills. Plants produce a similar substance called mucilage that is also produced by some microorganisms.

The adjective secretomotor refers to the capacity of a structure (often a nerve) to induce a gland to secrete a substance (usually mucus or serous fluid).

Secretomotor nerve endings are frequently contrasted with sensory neuron endings and motor nerve endings. An example of secretomotor activity can be seen with the lacrimal gland, which secretes the aqueous layer of the tear film. The lacrimal branch of the ophthalmic nerve (itself a branch of trigeminal nerve V1) supplies secretomotor innervation to the lacrimal gland, stimulating its secretion of the aqueous layer. However, these nerves fibers originate from the facial nerve (VII) and only travel briefly with fibers from the trigeminal nerve.

Swallowing, also called deglutition or inglutition in scientific and medical contexts, is a physical process of an animal's digestive tract (e.g. that of a human body) that allows for an ingested substance (typically food) to pass from the mouth to the pharynx and then into the esophagus. In colloquial English, the term "swallowing" is also used to describe the action of gulping, i.e. taking in a large mouthful of food without any biting.

Swallowing is performed by an initial push from back part of the tongue (with the tongue tip contacting the hard palate for mechanical anchorage) and subsequent coordinated contractions of the pharyngeal muscles. The portion of food, drink and/or other material (e.g. mucus, secretions and medications) that moves into the gullet in one swallow is called a bolus, which is then propelled through to the stomach for further digestion by autonomic peristalsis of the esophagus.

Respiratory epithelium, or airway epithelium, is ciliated pseudostratified columnar epithelium a type of columnar epithelium found lining most of the respiratory tract as respiratory mucosa, where it serves to moisten and protect the airways. It is not present in the vocal cords of the larynx, or the oropharynx and laryngopharynx, where instead the epithelium is stratified squamous. It also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by the secretion of mucus and the action of mucociliary clearance.

An epiphragm (from the Ancient Greek ἐπί, epi " upon, on, over " and φράγμα, -phrágma "fence") is a temporary structure which can be created by many species of shelled, air-breathing land snails, terrestrial pulmonate gastropod mollusks. It can also be created by freshwater snails when temporary pools dry up.

In most species, the epiphragm is made of dried mucus, and although it is elastic, it is fairly easily torn when forcibly removing a snail from its substrate. In a few species, the epiphragm is thick and quite rigid, being reinforced with calcium carbonate. This kind of epiphragm is very strong and may be difficult to break.

A cervical mucus plug (operculum) is a plug that fills and seals the cervical canal during pregnancy. It is formed by a small amount of cervical mucus that condenses to form a cervical mucus plug during pregnancy.

The cervical mucus plug (CMP) acts as a protective barrier by deterring the passage of bacteria into the uterus, and contains a variety of antimicrobial agents, including immunoglobulins, and similar antimicrobial peptides to those found in nasal mucus.The CMP inhibits the migration of vaginal bacteria towards the uterus, protecting against opportunistic infections that can lead to pelvic inflammatory disease and the onset of preterm labor. Ensuring the presence and proper function of the CMP is essential in reducing severe infections and promoting overall reproductive health.

A hormonal intrauterine device (IUD), also known as an intrauterine system (IUS) with progestogen and sold under the brand name Mirena among others, is an intrauterine device that releases a progestogenic hormonal agent such as levonorgestrel into the uterus. It is used for birth control, heavy menstrual periods, and to prevent excessive build of the lining of the uterus in those on estrogen replacement therapy. It is one of the most effective forms of birth control with a one-year failure rate around 0.2%. The device is placed in the uterus and lasts three to eight years. Fertility often returns quickly following removal.

Side effects include irregular periods, benign ovarian cysts, pelvic pain, and depression. Rarely uterine perforation may occur. Use is not recommended during pregnancy but is safe with breastfeeding. The IUD with progestogen is a type of long-acting reversible birth control. It works by thickening the mucus at the opening of the cervix, stopping the buildup of the lining of the uterus, and occasionally preventing ovulation.

Spitting is the act of forcibly ejecting saliva, sputum, nasal mucus and/or other substances from the mouth. The act is often done to get rid of unwanted or foul-tasting substances in the mouth, or to get rid of a large buildup of mucus. Spitting of small saliva droplets can also happen unintentionally during talking, especially when articulating ejective and implosive consonants.

Spitting in public is considered rude, disgusting, and a social taboo in many parts of the world including the West, while in some other parts of the world it is considered more socially acceptable.

Mucins (/ˈmjuːsɪn/) are a family of high molecular weight, heavily glycosylated proteins (glycoconjugates) produced by epithelial tissues in most animals. Mucins' key characteristic is their ability to form gels; therefore they are a key component in most gel-like secretions, serving functions from lubrication to cell signalling to forming chemical barriers. They often take an inhibitory role. Some mucins are associated with controlling mineralization, including nacre formation in mollusks, calcification in echinoderms and bone formation in vertebrates. They bind to pathogens as part of the immune system. Overexpression of the mucin proteins, especially MUC1, is associated with many types of cancer.

Although some mucins are membrane-bound due to the presence of a hydrophobic membrane-spanning domain that favors retention in the plasma membrane, most mucins are secreted as principal components of mucus by mucous membranes or are secreted to become a component of saliva.

The gastric mucosa is the mucous membrane layer that lines the entire stomach. The mucus is secreted by gastric glands, and surface mucous cells in the mucosa to protect the stomach wall from harmful gastric acid, and from digestive enzymes that may start to digest the tissue of the wall. Mucus from the glands is mainly secreted by pyloric glands in the lower region of the stomach, and by a smaller amount in the parietal glands in the body and fundus of the stomach.

The mucosa is studded with millions of gastric pits, which the gastric glands empty into. In humans, it is about one millimetre thick, and its surface is smooth, and soft. It consists of simple secretory columnar epithelium, an underlying supportive layer of loose connective tissue called the lamina propria, and the muscularis mucosae, a thin layer of muscle that separates the mucosa from the underlying submucosa. The gastric mucosa serves as a gastric barrier, reinforced by tight junctions between the epithelial cells.

Meconium is the earliest stool of a mammalian infant resulting from defecation. Unlike later feces, meconium is composed of materials ingested during the time the infant spends in the uterus: intestinal epithelial cells, lanugo, mucus, amniotic fluid, bile, and water. Meconium, unlike later feces, is viscous and sticky like tar – its color usually being a very dark olive green and it is almost odorless. When diluted in amniotic fluid, it may appear in various shades of green, brown, or yellow. It should be completely passed by the end of the first few days after birth, with the stools progressing toward yellow (digested milk).

Rhinorrhea (American English), also spelled rhinorrhoea or rhinorrhœa (British English), or informally, runny nose, is the free discharge of a thin mucus fluid from the nose; it is an extremely common condition. It is a common symptom of allergies (hay fever) or certain viral infections, such as the common cold or COVID-19. Rhinorrhea varies in color and consistency depending upon the underlying cause. It can be a side effect of crying, exposure to cold temperatures, cocaine abuse, or drug withdrawal, such as from methadone or other opioids. Treatment for rhinorrhea may be aimed at reducing symptoms or treating underlying causes. Rhinorrhea usually resolves without intervention, but may require treatment by a doctor if symptoms last more than 10 days or if symptoms are the result of foreign bodies in the nose.

The term rhinorrhea was coined in 1866 from the Greek rhino- ("of the nose") and -rhoia ("discharge" or "flow").

Chronic obstructive pulmonary disease (COPD) is a type of progressive lung disease characterized by chronic respiratory symptoms and airflow limitation. GOLD defines COPD as a heterogeneous lung condition characterized by chronic respiratory symptoms (shortness of breath, cough, sputum production or exacerbations) due to abnormalities of the airways (bronchitis, bronchiolitis) or alveoli (emphysema) that cause persistent, often progressive, airflow obstruction.

The main symptoms of COPD include shortness of breath and a cough, which may or may not produce mucus. COPD progressively worsens, with everyday activities such as walking or dressing becoming difficult. While COPD is incurable, it is preventable and treatable. The two most common types of COPD are emphysema and chronic bronchitis, and have been the two classic COPD phenotypes. However, this basic dogma has been challenged as varying degrees of co-existing emphysema, chronic bronchitis, and potentially significant vascular diseases have all been acknowledged in those with COPD, giving rise to the classification of other phenotypes or subtypes.