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A mucous membrane or mucosa is a
membrane A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membranes include cell membranes (outer coverings of cells or organelles that all ...
that lines various cavities in the body and covers the surface of internal organs. It consists of one or more layers of
epithelial cells Epithelium () is one of the four basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume ...
overlying a layer of
loose connective tissue Loose connective tissue is a category of connective tissue Connective tissue is one of the many basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological ...
. It is mostly of
endoderm Endoderm is the innermost of the three primary germ layer A germ layer is a primary layer of cell (biology), cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazo ...
al origin and is continuous with the skin at body openings such as the
eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light L ...

eye
s,
ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear The outer ear, external ear, or auris externa is the external part of the ear, which consists ...

ear
s, inside the nose,
inside the mouth
inside the mouth
,
lip Lips are a visible body part at the mouth of many animals, including humans. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Human lips are a tactile sensory organ, and can be an ...

lip
,
vagina In mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Female#Mammalian female, femal ...

vagina
, the
urethra The urethra (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appro ...

urethra
l opening and the
anus The anus (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in ...

anus
. Some mucous membranes secrete
mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membrane A mucous membrane or mucosa is a biological membrane, membrane that lines various cavities in the body and covers the surface of internal organs. It consists o ...
, a thick protective fluid. The function of the membrane is to stop
pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a Germ theory ...
s and dirt from entering the body and to prevent bodily tissues from becoming dehydrated.


Structure

The mucosa of organs are composed of one or more layers of
epithelial cells Epithelium () is one of the four basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume ...
that secrete
mucus Mucus ( ) is a slippery aqueous secretion produced by, and covering, mucous membrane A mucous membrane or mucosa is a biological membrane, membrane that lines various cavities in the body and covers the surface of internal organs. It consists o ...
, and an underlying
lamina propria The lamina propria is a thin layer of connective tissue Connective tissue is one of the four basic types of animal tissue (biology), tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesoderm. Connectiv ...
of
loose connective tissue Loose connective tissue is a category of connective tissue Connective tissue is one of the many basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological ...
. The type of cells and type of mucus secreted vary from organ to organ and each can differ along a given tract. Mucous membranes line the digestive, respiratory and reproductive tracts and are the primary barrier between the external world and the interior of the body; in an adult human the total surface area of the mucosa is about 400 square meters while the surface area of the skin is about 2 square meters. They are at several places contiguous with
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have differ ...

skin
: at the
nostril A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for Respiration (physiology), respiration alongside ...
s, the
lip Lips are a visible body part at the mouth of many animals, including humans. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Human lips are a tactile sensory organ, and can be an ...

lip
s of the
mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...

mouth
, the
eyelids An eyelid is a thin fold of skin that covers and protects an eye Eyes are organs of the visual system The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photorecepto ...

eyelids
, the
ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear The outer ear, external ear, or auris externa is the external part of the ear, which consists ...

ear
s, the genital area, and the
anus The anus (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be in ...

anus
. Along with providing a physical barrier, they also contain key parts of the immune system and serve as the interface between the body proper and the
microbiome A microbiome () is the community (ecology), community of microorganisms that can usually be found living together in any given habitat. It was defined more precisely in 1988 by Whipps ''et al.'' as "a characteristic microbial community occupyi ...
.


Examples

Some examples include: *
Bronchial mucosa A bronchus is a passage or airway in the respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animal A ...
and the lining of
vocal folds In humans, vocal cords, also known as vocal folds or voice reeds, are folds of tissue in the throat that are key in creating sounds through vocalization. The size of vocal cords affects the pitch of voice. Open when breathing and vibrating for ...

vocal folds
*
Endometrium The endometrium is the inner epithelial Epithelium is one of the four basic types of animal Tissue (biology), tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly pack ...

Endometrium
: the mucosa of the
uterus The uterus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the ...

uterus
*
Esophageal mucosaEsophageal can refer to: * The esophagus The esophagus (American English) or oesophagus (British English; American and British English spelling differences#ae and oe, see spelling differences) (), informally known as the food pipe or gullet, i ...
*
Gastric mucosa The gastric mucosa is the mucous membrane layer of the stomach, which contains the glands and the gastric pits. In humans, it is about 1 mm thick, and its surface is smooth, soft, and velvety. It consists of simple columnar epithelium, lamina ...
*
Intestinal mucosa The gastrointestinal wall of the human gastrointestinal tract, gastrointestinal tract is made up of four layers of specialised tissue. From the inner cavity of the gut (the Lumen (anatomy), lumen) outwards, these are: *Mucosa *Submucosa *Muscular l ...
*
Nasal mucosa The nasal mucosa lines the nasal cavity The nasal cavity is a large, air-filled space above and behind the nose A nose is a protuberance in vertebrates that houses the nostrils, or nares, which receive and expel air for Respiration (physio ...
*
Olfactory mucosa The olfactory mucosa is located in the upper region of the nasal cavity The nasal cavity is a large, air-filled space above and behind the human nose, nose in the middle of the face. The nasal septum divides the cavity into two cavities, also kno ...
*
Oral mucosa The oral mucosa is the mucous membrane A mucous membrane or mucosa is a biological membrane, membrane that lines various cavities in the body and covers the surface of internal organs. It consists of one or more layers of Epithelium, epithelial c ...

Oral mucosa
* Penile mucosa *
Vaginal mucosa In mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in Female#Mammalian female, femal ...
*
Frenulum of tongue The frenulum of tongue or tongue web (also lingual frenulum or frenulum linguæ; also fraenulum) is a small fold of mucous membrane A mucous membrane or mucosa is a membrane that lines various cavities in the body and covers the surface of intern ...
*
Tongue The tongue is a muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper surfa ...

Tongue
*
Anal canal The anal canal is the terminal segment of the large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remaining ...
* Palpebral conjunctiva


Development

Developmentally, the majority of mucous membranes are of
endoderm Endoderm is the innermost of the three primary germ layer A germ layer is a primary layer of cell (biology), cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazo ...
al origin. Exceptions include the
palate The palate () is the roof of the mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ...

palate
, cheeks, floor of the
mouth In animal anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is ...
,
gums The gums or gingiva (plural: ''gingivae'') consist of the mucosal A mucous membrane or mucosa is a membrane Image:Schematic size.jpg, up150px, Schematic of size-based membrane exclusion A membrane is a selective barrier; it allows some things ...
,
lips Lips are a visible body part at the mouth of many animals, including humans. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Human lips are a tactile sensory organ, and can be an e ...
and the portion of the
anal canal The anal canal is the terminal segment of the large intestine The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remaining ...
below the
pectinate line The pectinate line (dentate line) is a line which divides the upper two thirds and lower third of the anal canal The anal canal is the terminal segment of the large intestine, between the rectum and anus, located below the level of the pelvic diaph ...
, which are all
ectoderm The ectoderm is one of the three primary germ layer A germ layer is a primary layer of cell (biology), cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoans ( ...

ectoderm
al in origin.


Function

One of its functions is to keep the tissue moist (for example in the respiratory tract, including the mouth and nose). It also plays a role in absorbing and transforming
nutrients A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, anything that has mass and ta ...
. Mucous membranes also protect the body from itself; for instance mucosa in the stomach protects it from stomach acid, and mucosa lining the bladder protects the underlying tissue from urine. In the
uterus The uterus (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the ...

uterus
, the mucous membrane is called the
endometrium The endometrium is the inner epithelial Epithelium is one of the four basic types of animal Tissue (biology), tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly pack ...

endometrium
, and it swells each month and is then eliminated during
menstruation Menstruation (also known as a period and many other Colloquialism, colloquial terms) is the regular discharge of blood and Mucous membrane, mucosal tissue from the endometrium, inner lining of the uterus through the vagina. The menstrual cycl ...
.


Nutrition

Niacin Niacin, also known as nicotinic acid, is an organic compound and a form of vitamin B3, vitamin B3, an essential nutrient, essential human nutrient. It can be manufactured by plants and animals from the amino acid tryptophan. Niacin is obtaine ...

Niacin
and
vitamin A Vitamin A is a group of unsaturated nutritional organic compounds that includes retinol, retinal, (also known as retinaldehyde), retinoic acid and several provitamin A carotenoids (most notably Beta-Carotene, beta-carotene). Vitamin A has mul ...

vitamin A
are
essential nutrient A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, anything that has mass and ta ...
s that help maintain mucous membranes.


See also

*
Alkaline mucusAlkaline mucus is a thick fluid produced by animals which confers tissue protection in an acidic environment, such as in the stomach. Properties Mucus that serves a protective function against acidic environments generally has a high viscosity, th ...
*
Mucin Mucins () are a family of high molecular weight A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical ph ...

Mucin
*
Mucociliary clearance Mucociliary clearance (MCC), mucociliary transport, or the mucociliary escalator, describes the self-clearing mechanism of the airways in the respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biol ...
* Mucocutaneous boundary * Mucosal immunology *
Rete pegs Rete pegs (also known as rete processes or rete ridges) are the epithelial extensions that project into the underlying connective tissue in both skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate anima ...


References

{{Authority control Membrane biology Anatomy