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In animal
anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of concerned with the study of the structure of s and their parts. Anatomy is a branch of natural science which deals with the structural organization of living things. It is an old scie ...

anatomy
, the mouth, also known as the oral cavity, buccal cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the
alimentary canal The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system The human digestive system consists of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, di ...
, bounded on the outside by the lips and inside by the
pharynx The pharynx (plural: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, thou ...

pharynx
and containing in
higher vertebrates Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade A clade (; from grc, , ''klados'', "bran ...
the tongue and teeth. This cavity is also known as the buccal cavity, from the Latin ''bucca'' ("cheek"). Some animal phyla, including
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic ma ...
s, have a complete
digestive system The human digestive system consists of the gastrointestinal tract The gastrointestinal tract, (GI tract, GIT, digestive tract, digestion tract, alimentary canal) is the tract from the mouth to the anus which includes all the organs of th ...

digestive system
, with a mouth at one end and an
anus The anus (from Latin ''wikt:en:anus#Latin, anus'' meaning "ring", "circle") is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that ...

anus
at the other. Which end forms first in
ontogeny Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the ovum, egg to adult. The term can also be used to refer to th ...
is a criterion used to classify animals into
protostome Protostomia () is the clade A clade (), also known as a monophyletic group or natural group, is a group of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ...
s and
deuterostome Deuterostomia (; in 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 app ...
s.


Development

In the first multicellular animals, there was probably no mouth or gut and food particles were engulfed by the cells on the exterior surface by a process known as
endocytosis Endocytosis is a in which are brought into the cell. The material to be internalized is surrounded by an area of , which then buds off inside the cell to form a containing the ingested material. Endocytosis includes (cell drinking) and (cell ...

endocytosis
. The particles became enclosed in
vacuole A vacuole () is a membrane-bound organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts o ...
s into which enzymes were secreted and digestion took place
intracellular This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemic ...
ly. The digestive products were absorbed into the cytoplasm and diffused into other cells. This form of digestion is used nowadays by simple organisms such as ''
Amoeba An amoeba (; less commonly spelt ameba or amœba; plural ''am(o)ebas'' or ''am(o)ebae'' ), often called an amoeboid, is a type of cell Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Cl ...
'' and ''
Paramecium '' ''Paramecium'' ( , ; also spelled ''Paramoecium'') is a genus of eukaryotic Eukaryotes () are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system ...

Paramecium
'' and also by
sponges Sponges, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the Diploblasts. They are Multicellular organism, multicellular organisms that have bodies full of pores and channels allowing water ...

sponges
which, despite their large size, have no mouth or gut and capture their food by endocytosis. The vast majority of other multicellular organisms have a mouth and a gut, the lining of which is continuous with the epithelial cells on the surface of the body. A few animals which live parasitically originally had guts but have secondarily lost these structures. The original gut of multicellular organisms probably consisted of a simple sac with a single opening, the mouth. Many modern invertebrates have such a system, food being ingested through the mouth, partially broken down by enzymes secreted in the gut, and the resulting particles engulfed by the other cells in the gut lining. Indigestible waste is ejected through the mouth. In animals at least as complex as an
earthworm An earthworm is a terrestrial invertebrate that belongs to the phylum . They exhibit a tube-within-a-tube , are externally segmented with corresponding internal segmentation, and usually have on all segments. They occur worldwide where soil, wa ...

earthworm
, the
embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism that consists of more than one cell (biology), cell, in contrast to a unicellular organism. All species of animals, Embryophyte, la ...

embryo
forms a dent on one side, the
blastopore Gastrulation is the stage in the early embryonic development An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism that consists of more than one cell (biology), cell, in contrast to a ...
, which deepens to become the
archenteron The primary gut that forms during gastrulation Gastrulation is the stage in the early embryonic development ''Embryonic'' is the twelfth studio album by experimental rock Experimental rock, also called avant-rock, is a subgenre of rock music tha ...
, the first phase in the formation of the gut. In deuterostomes, the blastopore becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. In the protostomes, it used to be thought that the blastopore formed the mouth ('' proto–'' meaning "first") while the anus formed later as an opening made by the other end of the gut. More recent research, however, shows that in protostomes the edges of the slit-like blastopore close up in the middle, leaving openings at both ends that become the mouth and anus.


Anatomy


Invertebrates

Apart from sponges and
placozoa The Placozoa are a basal Basal or basilar is a term meaning ''base'', ''bottom'', or ''minimum''. Science * Basal (anatomy), an anatomical term of location for features associated with the base of an organism or structure * Basal (medicine), a ...

placozoa
ns, almost all animals have an internal gut cavity which is lined with gastrodermal cells. In less advanced invertebrates such as the
sea anemone Sea anemones are the marine, predation, predatory animals of the order (biology), order Actiniaria. They are named after the anemone, a terrestrial flowering plant, because of the colourful appearance of many. Sea anemones are classified in the p ...

sea anemone
, the mouth also acts as an anus. Circular muscles around the mouth are able to relax or contract in order to open or close it. A fringe of tentacles thrusts food into the cavity and it can gape widely enough to accommodate large prey items. Food passes first into a
pharynx The pharynx (plural: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, thou ...

pharynx
and digestion occurs extracellularly in the
gastrovascular cavity The gastrovascular cavity is the primary organ of digestion Digestion is the breakdown of large insoluble food Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plant, animal or Fung ...
. Annelids have simple tube-like guts and the possession of an anus allows them to separate the digestion of their foodstuffs from the absorption of the nutrients. Many molluscs have a
radula The radula (, ; plural radulae or radulas) is an anatomical structure used by mollusks Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks (). Around 85,000 e ...
which is used to scrape microscopic particles off surfaces. In invertebrates with hard exoskeletons, various mouthparts may be involved in feeding behaviour. Insects have a range of mouthparts suited to their mode of feeding. These include mandibles, maxillae and labium and can be modified into suitable appendages for chewing, cutting, piercing, sponging and sucking.
Decapods The Decapoda or decapods (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crabs, lobsters, crayfish, Caridea, shrimp and Dendrobranchiata, prawns. Most decapods are scave ...
have six pairs of mouth appendages, one pair of mandibles, two pairs of maxillae and three of
maxilliped An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In invertebrate biology, an appendage refers to any of the homology (biology), homologous body parts that may extend from a b ...
s. Sea urchins have a set of five sharp calcareous plates which are used as jaws and are known as Aristotle's lantern.


Vertebrates

In vertebrates, the first part of the digestive system is the
buccal cavity Buccal may refer to: * Buccal, or buccal cavity, an oral body cavity (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 org ...
, commonly known as the mouth. The buccal cavity of a fish is separated from the opercular cavity by the gills. Water flows in through the mouth, passes over the gills and exits via the operculum or
gill slit Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as shark Sharks are a group of elasmobranch fish characterized by a Chondricht ...
s. Nearly all fish have jaws and may seize food with them but most feed by opening their jaws, expanding their pharynx and sucking in food items. The food may be held or chewed by teeth located in the jaws, on the roof of the mouth, on the pharynx or on the
gill arch Branchial arches, or gill arches, are a series of bony "loops" present in fish, which support the gills. As gills are the primitive condition of vertebrates, all vertebrate embryos develop pharyngeal arch The pharyngeal arches, also known as ...
es. Nearly all amphibians are carnivorous as adults. Many catch their prey by flicking out an elongated tongue with a sticky tip and drawing it back into the mouth where they hold the prey with their jaws. They then swallow their food whole without much chewing. They typically have many small hinged
pedicellate teethPedicellate teeth are a tooth morphology today unique to modern amphibians Amphibians are ectotherm File:Junonia lemonias DSF by Kadavoor.JPG, ''Junonia lemonias'' is basking under the sun. An ectotherm (from the Ancient Greek, Greek ἐκτ ...
, the bases of which are attached to the jaws while the crowns break off at intervals and are replaced. Most amphibians have one or two rows of teeth in both jaws but some frogs lack teeth in the lower jaw. In many amphibians there are also vomerine teeth attached to the bone in the roof of the mouth. The mouths of reptiles are largely similar to those of mammals. The
crocodilia Crocodilia (or Crocodylia, both ) is an Order (biology), order of mostly large, predatory, List of semiaquatic tetrapods, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous Period (g ...

crocodilia
ns are the only reptiles to have teeth anchored in sockets in their jaws. They are able to replace each of their approximately 80 teeth up to 50 times during their lives. Most reptiles are either carnivorous or insectivorous but turtles are herbivorous. Lacking teeth that are suitable for efficiently chewing of their food, turtles often have
gastrolith gastroliths from Tropic Shale The Tropic Shale is a Mesozoic geologic Formation (geology), formation. Dinosaur remains are among the fossils that have been recovered from the formation,Weishampel, ''et al.'' (2004). "Dinosaur distribution." Pp. 517 ...
s in their stomach to further grind the plant material. Snakes have a very flexible lower jaw, the two halves of which are not rigidly attached, and numerous other joints in their skull. These modifications allow them to open their mouths wide enough to swallow their prey whole, even if it is wider than they are. Birds do not have teeth, relying instead on other means of gripping and macerating their food. Their
beak The beak, bill, and/or rostrum is an external anatomical structure found mostly in birds Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves , characterised by feathers, toothless beaked jaws, the Ovi ...

beak
s have a range of sizes and shapes according to their diet and are composed of elongated mandibles. The upper mandible may have a nasofrontal hinge allowing the beak to open wider than would otherwise be possible. The exterior surface of beaks is composed of a thin, horny sheath of
keratin Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin (α-keratin) is a type of keratin found in vertebrates. It is the key structural material making up Scale (anatomy), scales, hair, Nail ...

keratin
. Nectar feeders such as
hummingbird Hummingbirds are birds Birds are a group of s constituting the Aves , characterised by s, toothless beaked jaws, the of eggs, a high rate, a four-chambered , and a strong yet lightweight . Birds live worldwide and range in size fr ...

hummingbird
s have specially adapted brushy tongues for sucking up nectar from flowers. In mammals the buccal cavity is typically roofed by the hard and
soft palate The soft palate (also known as the velum, palatal velum, or muscular palate) is, in mammals, the soft biological tissue, tissue constituting the back of the roof of the mouth. The soft palate is part of the palate of the mouth; the other part is t ...
s, floored by the
tongue The tongue is a muscular MUSCULAR (DS-200B), located in the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use Brita ...

tongue
and surrounded by the
cheek The cheeks ( la, buccae) constitute the area of the face below the human eye, eyes and between the Human nose, nose and the left or right ear. "Buccal" means relating to the cheek. In humans, the region is innervated by the buccal nerve. The are ...

cheek
s,
salivary glands The salivary glands in mammals are exocrine glands that produce saliva through a system of Duct (anatomy), ducts. Humans have three paired major salivary glands (Parotid gland, parotid, Submandibular gland, submandibular, and sublingual gland, subl ...

salivary glands
, upper and lower
teeth A tooth (plural teeth) is a hard, calcified Calcification is the accumulation of calcium salts in a Tissue (biology), body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. ...

teeth
. The upper teeth are embedded in the
upper jaw The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the var ...

upper jaw
and the lower teeth in the
lower jaw In 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 any ind ...

lower jaw
, which articulates with the
temporal bone The temporal bones are situated at the sides and base of the skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the vertebrate skeleton in animals. Bones protect the various organs of ...

temporal bone
s of the
skull The skull is a bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones protect the various organs of the body, produce red blood cell, red and white blood cells, sto ...

skull
. The
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 ...
are soft and fleshy folds which shape the entrance into the mouth. The buccal cavity empties through the
pharynx The pharynx (plural: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea – the tubes going down to the stomach and the lungs. It is found in vertebrates and invertebrates, thou ...

pharynx
into the
oesophagus The esophagus (American English) or oesophagus (British English; both ), informally known as the food pipe or gullet, is an Organ (anatomy), organ in vertebrates through which food passes, aided by Peristalsis, peristaltic contractions, from t ...

oesophagus
.


Other functions of the mouth

Crocodilia Crocodilia (or Crocodylia, both ) is an Order (biology), order of mostly large, predatory, List of semiaquatic tetrapods, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous Period (g ...

Crocodilia
ns living in the tropics can gape with their mouths to provide cooling by
evaporation Evaporation is a type of that occurs on the of a as it changes into the gas phase. The surrounding gas must not be saturated with the evaporating substance. When the molecules of the liquid collide, they transfer energy to each other bas ...

evaporation
from the mouth lining. Some mammals rely on panting for
thermoregulation Thermoregulation is the ability of an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxo ...
as it increases evaporation of water across the moist surfaces of the lungs, the tongue and mouth. Birds also avoid overheating by gular fluttering, flapping the wings near the gular (throat) skin, similar to panting in mammals. Various animals use their mouths in threat displays. They may gape widely, exhibit their teeth prominently or flash the startling colours of the mouth lining. This display allows each potential combatant an opportunity to assess the weapons of their opponent and lessens the likelihood of actual combat being necessary. A number of species of bird use a gaping, open beak in their fear and threat displays. Some augment the display by hissing or breathing heavily, while others clap their beaks. Mouths are also used as part of the mechanism for producing sounds for communication. To produce sounds, air is forced from the lungs over
vocal cord In humans, vocal cords, also known as vocal chords, 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 ...
s in the larynx. In humans, the pharynx, the soft palate, the hard palate, the
alveolar ridge A sagittal or side view image of a human head. The upper alveolar ridge is located between numbers 4 and 5. The alveolar ridge (; also known as the alveolar margin) is one of the two jaw ridges, extensions of the mandible or maxilla, either on the ...
, the tongue, the teeth and the lips are termed articulators and play their part in the production of speech. Varying the position of the tongue in relation to the other articulators or moving the lips restricts the airflow from the lungs in different ways producing a range of different sounds. In frogs, the sounds can be amplified using sacs in the throat region. The vocal sacs can be inflated and deflated and act as resonators to transfer the sound to the outside world. A bird's song is produced by the flow of air over a vocal organ at the base of the
trachea The trachea, also known as the windpipe, is a tube that connects the to the bronchi of the s, allowing the passage of , and so is present in almost all air- s with lungs. The trachea extends from the larynx and branches into the two primary . ...
, the
syrinx In classical Greek mythology, Syrinx (Greek language, Greek Σύριγξ) was a nymph and a follower of Artemis, known for her chastity. Pursued by the amorous god Pan (god), Pan, she ran to a river's edge and asked for assistance from the Pota ...
. For each burst of song the bird opens its beak and closes it again afterwards. The beak may move slightly and may contribute to the resonance but the song originates elsewhere.


See also

*
Human mouth In human anatomy The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis In biology Biology is the natu ...

Human mouth
* Oral manifestations of systemic disease


References


External links

* * * {{Authority control Human head and neck Animal anatomy Digestive system Facial features