Salivary gland
Encyclopedia
The salivary glands in mammal
s are exocrine gland
s, gland
s with ducts, that produce saliva
. They also secrete amylase
, an enzyme
that breaks down starch
into maltose
. In other organisms such as insects, salivary glands are often used to produce biologically important proteins like silk
or glues, and fly
salivary glands contain polytene chromosome
s that have been useful in genetic
research.
. Blood vessel
s and nerve
s enter the glands at the hilum
and gradually branch out into the lobules.
s, which in turn join to form striated duct
s. These drain into ducts situated between the lobes of the gland (called interlobar duct
s or secretory ducts).
All of the human salivary glands terminate in the mouth, where the saliva proceeds to aid in digestion. The saliva that salivary glands release is quickly inactivated in the stomach by the acid that is present there.
s. The secretion produced is a mixture of both serous fluid
and mucus
, and enters the oral cavity via Wharton's ducts. Approximately 70% of saliva in the oral cavity is produced by the submandibular glands, even though they are much smaller than the parotid glands.
of the oral mucosa
. They are 1-2mm in diameter and unlike the other glands, they are not encapsulated by connective tissue only surrounded by it. The gland is usually a number of acini connected in a tiny lobule. A minor salivary gland may have a common excretory duct with another gland, or may have its own excretory duct. Their secretion is mainly mucous in nature (except for Von Ebner's glands) and have many functions such as coating the oral cavity with saliva. Problems with dentures are usually associated with minor salivary glands.
of the tongue. They secrete a serous fluid that begin lipid hydrolysis. They facilitate the perception of taste
.
and sympathetic
arms of the autonomic nervous system
. Both result in increased amylase output and volume flow.
Salivary duct calculus may cause blockage of the ducts, causing pain and swelling of the gland because of cyst
s.
Many anti-cancer
treatments may impair salivary flow. Radiation therapy
may cause permanent xerostomia
, whereas chemotherapy
may cause only temporary salivary impairment. Graft versus host disease after allogeneic bone marrow transplantation may manifest as dry mouth and many small mucocele
s.
Tumor
s of the salivary glands may occur.
A sialogram
is a radiocontrast
study of a salivary duct.
Saliva production may be pharmacologically stimulated by so called sialagogue
s (e.g., pilocarpin, cevimeline). It can also be suppressed by so called antisialagogue
s (e.g., tricyclic antidepressant
s, SSRI, antihypertensives, polypharmacy
).
s, although there are often individual mucus-secreting cells. Amphibian
s have a single salivary gland, the intermaxillary gland, located in the forward part of the palate
. Reptile
s and bird
s normally have only very small glands on the lips, palate, and base of the mouth, although there are some birds with large glands, which produce a sticky saliva that helps in nest-building. The distinct parotid, submandibular, and sublingual glands are only developed in mammals.
The salivary glands of some species, however, are modified to produce enzymes; salivary amylase is found in many, but by no means all, bird and mammal species (including humans, as noted above). Furthermore, the venom
glands of poisonous snake
s, Gila monster
s, and some shrew
s, are modified salivary glands.
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s are exocrine gland
Exocrine gland
Exocrine glands are a type of ductal glands that secrete their products into ducts that lead directly into the external environment...
s, gland
Gland
A gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...
s with ducts, that produce saliva
Saliva
Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...
. They also secrete amylase
Amylase
Amylase is an enzyme that catalyses the breakdown of starch into sugars. Amylase is present in human saliva, where it begins the chemical process of digestion. Food that contains much starch but little sugar, such as rice and potato, taste slightly sweet as they are chewed because amylase turns...
, an enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
that breaks down starch
Starch
Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...
into maltose
Maltose
Maltose , or malt sugar, is a disaccharide formed from two units of glucose joined with an αbond, formed from a condensation reaction. The isomer "isomaltose" has two glucose molecules linked through an α bond. Maltose is the second member of an important biochemical series of glucose chains....
. In other organisms such as insects, salivary glands are often used to produce biologically important proteins like silk
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...
or glues, and fly
Fly
True flies are insects of the order Diptera . They possess a pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax...
salivary glands contain polytene chromosome
Polytene chromosome
To increase cell volume, some specialized cells undergo repeated rounds of DNA replication without cell division , forming a giant polytene chromosome...
s that have been useful in genetic
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
research.
Histology
The gland is internally divided into lobulesLobe (anatomy)
In anatomy, a lobe is a clear anatomical division or extension that can be determined without the use of a microscope This is in contrast to a lobule, which is a clear division only visible histologically....
. Blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s and nerve
Nerve
A peripheral nerve, or simply nerve, is an enclosed, cable-like bundle of peripheral axons . A nerve provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons. Nerves are found only in the peripheral nervous system...
s enter the glands at the hilum
Hilum (anatomy)
In human anatomy, the hilum is a depression or fissure where structures such as blood vessels and nerves enter an organ.-Examples of hila:* Hilum of kidney, admits the renal artery, vein, ureter, and nerves...
and gradually branch out into the lobules.
Ducts
In the duct system, the lumina are formed by intercalated ductIntercalated duct
The intercalated duct, also called intercalary duct, is the portion of an exocrine gland leading directly from the acinus to a striated duct. The intercalated duct forms part of the intralobular duct...
s, which in turn join to form striated duct
Striated duct
A striated duct is a gland duct which connects an intercalated duct to an interlobular duct. It is characterized by the basal infoldings of its plasma membrane, characteristic of ion-pumping activity by the numerous mitochondria...
s. These drain into ducts situated between the lobes of the gland (called interlobar duct
Interlobar duct
A interlobar duct is a gland duct which connects more than one anatomic lobe.Examples of where it can be found include the parotid gland and submandibular gland....
s or secretory ducts).
All of the human salivary glands terminate in the mouth, where the saliva proceeds to aid in digestion. The saliva that salivary glands release is quickly inactivated in the stomach by the acid that is present there.
Anatomy
Parotid glands
The parotid gland is the largest salivary gland and is found wrapped around the mandibular ramus. The secretion produced is mainly serous in nature and enters the oral cavity via Stensen's duct.Submandibular glands
The submandibular glands are a pair of glands located beneath the lower jaws, superior to the digastric muscleDigastric muscle
The digastric muscle is a small muscle located under the jaw. so digastric muscles are muscle fibers in ligament of treitz ,omohyoid , occipitofrontalis....
s. The secretion produced is a mixture of both serous fluid
Serous fluid
In physiology, the term serous fluid is used for various bodily fluids that are typically pale yellow and transparent, and of a benign nature, that fill the inside of body cavities. Serous fluid originates from serous glands, with secretions enriched with proteins and water. Serous fluid may also...
and mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
, and enters the oral cavity via Wharton's ducts. Approximately 70% of saliva in the oral cavity is produced by the submandibular glands, even though they are much smaller than the parotid glands.
Sublingual gland
The sublingual glands are a pair of glands located beneath the tongue, anterior to the submandibular glands. The secretion produced is mainly mucous in nature, however it is categorized as a mixed gland. Unlike the other two major glands, the ductal system of the sublingual glands do not have striated ducts, and exit from 8-20 excretory ducts. Approximately 5% of saliva entering the oral cavity come from these glands.Minor salivary glands
There are over 600 minor salivary glands located throughout the oral cavity within the submucosaSubmucosa
In the gastrointestinal tract, the submucosa is the layer of dense irregular connective tissue or loose connective tissue that supports the mucosa, as well as joins the mucosa to the bulk of underlying smooth muscle .-Contents:Blood vessels, lymphatic vessels, and nerves will run through...
of the oral mucosa
Oral mucosa
The oral mucosa is the mucous membrane epithelium of the mouth. It can be divided into three categories.*Masticatory mucosa, para-keratinized stratified squamous epithelium, found on the dorsum of the tongue, hard palate and attached gingiva....
. They are 1-2mm in diameter and unlike the other glands, they are not encapsulated by connective tissue only surrounded by it. The gland is usually a number of acini connected in a tiny lobule. A minor salivary gland may have a common excretory duct with another gland, or may have its own excretory duct. Their secretion is mainly mucous in nature (except for Von Ebner's glands) and have many functions such as coating the oral cavity with saliva. Problems with dentures are usually associated with minor salivary glands.
Von Ebner's glands
Von Ebner's glands are glands found in circumvallate papillaeCircumvallate papillae
The circumvallate papillae are dome-shaped structures on the human tongue that vary in number from eight to twelve....
of the tongue. They secrete a serous fluid that begin lipid hydrolysis. They facilitate the perception of taste
Taste
Taste is one of the traditional five senses. It refers to the ability to detect the flavor of substances such as food, certain minerals, and poisons, etc....
.
Innervation
Salivary glands are innervated, either directly or indirectly, by the parasympatheticParasympathetic nervous system
The parasympathetic nervous system is one of the two main divisions of the autonomic nervous system . The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously...
and sympathetic
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
arms of the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
. Both result in increased amylase output and volume flow.
- Parasympathetic innervation to the salivary glands is carried via cranial nerves. The parotid gland receives its parasympathetic input from the glossopharyngeal nerveGlossopharyngeal nerveThe glossopharyngeal nerve is the ninth of twelve pairs of cranial nerves . It exits the brainstem out from the sides of the upper medulla, just rostral to the vagus nerve...
(CN IX) via the otic ganglionOtic ganglionThe otic ganglion is a small, oval shaped, flattened parasympathetic ganglion of a reddish-gray color, located immediately below the foramen ovale in the infratemporal fossa. It gives innervation to the parotid gland for salivation....
, while the submandibular and sublingual glands receive their parasympathetic input from the facial nerveFacial nerveThe facial nerve is the seventh of twelve paired cranial nerves. It emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity...
(CN VII) via the submandibular ganglionSubmandibular ganglionThe submandibular ganglion is part of the human autonomic nervous system. It is one of four parasympathetic ganglia of the head and neck...
. These nerves release acetylcholine and substance P, which activate the IP3 and DAG pathways respectively.
- Direct sympathetic innervation of the salivary glands takes place via preganglionic nerves in the thoracic segments T1-T3 which synapse in the superior cervical ganglionSuperior cervical ganglionThe superior cervical ganglion , the largest of the cervical ganglia, is placed opposite the second and third cervical vertebræ. It contains neurons that supply sympathetic innervation to the face....
with postganglionic neurons that release norepinephrine, which is then received by β-adrenergic receptors on the acinar and ductal cells of the salivary glands, leading to an increase in cyclic adenosine monophosphate (cAMP) levels and the corresponding increase of saliva secretion. Note that in this regard both parasympathetic and sympathetic stimuli result in an increase in salivary gland secretions. The sympathetic nervous system also affects salivary gland secretions indirectly by innervating the blood vesselBlood vesselThe blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s that supply the glands.
Role in disease
- See mumpsMumpsMumps is a viral disease of the human species, caused by the mumps virus. Before the development of vaccination and the introduction of a vaccine, it was a common childhood disease worldwide...
(parotiditis epidemica), Sjögren's syndromeSjögren's syndromeSjögren's syndrome , also known as "Mikulicz disease" and "Sicca syndrome", is a systemic autoimmune disease in which immune cells attack and destroy the exocrine glands that produce tears and saliva....
, MucoceleMucoceleA "mucous cyst of the oral mucosa" is a clinical term that refers to two related phenomena: mucus extravasation phenomenon, and mucus retention cyst...
, Graft versus host disease and Salivary gland neoplasm.
Salivary duct calculus may cause blockage of the ducts, causing pain and swelling of the gland because of cyst
Cyst
A cyst is a closed sac, having a distinct membrane and division on the nearby tissue. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, a cyst could go away on its own or may have to be removed through surgery.- Locations :* Acne...
s.
Many anti-cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
treatments may impair salivary flow. Radiation therapy
Radiation therapy
Radiation therapy , radiation oncology, or radiotherapy , sometimes abbreviated to XRT or DXT, is the medical use of ionizing radiation, generally as part of cancer treatment to control malignant cells.Radiation therapy is commonly applied to the cancerous tumor because of its ability to control...
may cause permanent xerostomia
Xerostomia
Xerostomia is the medical term for the subjective complaint of dry mouth due to a lack of saliva. Xerostomia is sometimes colloquially called pasties, cottonmouth, drooth, or doughmouth. Several diseases, treatments, and medications can cause xerostomia. It can also be exacerbated by smoking or...
, whereas chemotherapy
Chemotherapy
Chemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....
may cause only temporary salivary impairment. Graft versus host disease after allogeneic bone marrow transplantation may manifest as dry mouth and many small mucocele
Mucocele
A "mucous cyst of the oral mucosa" is a clinical term that refers to two related phenomena: mucus extravasation phenomenon, and mucus retention cyst...
s.
Tumor
Tumor
A tumor or tumour is commonly used as a synonym for a neoplasm that appears enlarged in size. Tumor is not synonymous with cancer...
s of the salivary glands may occur.
A sialogram
Sialogram
Sialogram or sialography is imaging of the salivary glands using x-ray-Technique:A baseline radiograph of the required salivary gland would be taken , a cannula then is inserted in this salivary gland duct's opening in the mouth, then a Radio-opaque fluid is injected in the duct through a small...
is a radiocontrast
Radiocontrast
Radiocontrast agents are a type of medical contrast medium used to improve the visibility of internal bodily structures in an X-ray based imaging techniques such as computed tomography or radiography...
study of a salivary duct.
Saliva production may be pharmacologically stimulated by so called sialagogue
Sialagogue
A herb with sialagogue action stimulates the secretion of saliva from the salivary glands.Herbs with sialagogue action include:*Bloodroot *Blue Flag *Cayenne pepper...
s (e.g., pilocarpin, cevimeline). It can also be suppressed by so called antisialagogue
Antisialagogue
Antisialagogues are substances that decrease the production of saliva and their effect is opposite to that of sialagogues. Their origin may be both natural and synthetic. Classic antisialagogues:* atropine,* opium,* alkalies,* belladonna,* hyoscyamus,...
s (e.g., tricyclic antidepressant
Tricyclic antidepressant
Tricyclic antidepressants are heterocyclic chemical compounds used primarily as antidepressants. The TCAs were first discovered in the early 1950s and were subsequently introduced later in the decade; they are named after their chemical structure, which contains three rings of atoms...
s, SSRI, antihypertensives, polypharmacy
Polypharmacy
Polypharmacy is the use of multiple medications by a patient, especially when too many forms of medication are used by a patient, when more drugs are prescribed than is clinically warranted, or even when all prescribed medications are clinically indicated but there are too many pills to take ....
).
In other animals
In most vertebrates, saliva does not contain any enzymes, consisting of mucus and water only, and its primary function is to moisten food while eating. As a result, true salivary glands are rarely found in fish or aquatic tetrapodTetrapod
Tetrapods are vertebrate animals having four limbs. Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods by descent. The earliest tetrapods evolved from the lobe-finned fishes in the Devonian...
s, although there are often individual mucus-secreting cells. Amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s have a single salivary gland, the intermaxillary gland, located in the forward part of the palate
Palate
The palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
. Reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s and bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s normally have only very small glands on the lips, palate, and base of the mouth, although there are some birds with large glands, which produce a sticky saliva that helps in nest-building. The distinct parotid, submandibular, and sublingual glands are only developed in mammals.
The salivary glands of some species, however, are modified to produce enzymes; salivary amylase is found in many, but by no means all, bird and mammal species (including humans, as noted above). Furthermore, the venom
Venom
Venom is the general term referring to any variety of toxins used by certain types of animals that inject it into their victims by the means of a bite or a sting...
glands of poisonous snake
Snake
Snakes are elongate, legless, carnivorous reptiles of the suborder Serpentes that can be distinguished from legless lizards by their lack of eyelids and external ears. Like all squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales...
s, Gila monster
Gila monster
The Gila monster is a species of venomous lizard native to the southwestern United States and northwestern Mexican state of Sonora...
s, and some shrew
Shrew
A shrew or shrew mouse is a small molelike mammal classified in the order Soricomorpha. True shrews are also not to be confused with West Indies shrews, treeshrews, otter shrews, or elephant shrews, which belong to different families or orders.Although its external appearance is generally that of...
s, are modified salivary glands.
