Salivary Glands and Saliva Glossary Salivary Glands and Saliva Saliva is produced in and secreted from salivary glands. The basic secretory units of salivary glands are clusters of cells called an acini. These cells secrete a fluid that contains water, electrolytes, mucus and enzymes, all of which flow out of the acinus into collecting ducts. Within the ducts, the composition of the secretion is altered. Much of the sodium is actively reabsorbed, potassium is secreted, and large quantities of bicarbonate ion are secreted. Bicarbonate secretion is of tremendous importance to ruminants because it, along with phosphate, provides a critical buffer that neutralizes the massive quantities of acid produced in the forestomachs. Small collecting ducts within salivary glands lead into larger ducts, eventually forming a single large duct that empties into the oral cavity.

Most animals have three major pairs of salivary glands that differ in the type of secretion they produce: parotid glands produce a serous, watery secretion submaxillary (mandibular) glands produce a mixed serous and mucous secretion sublingual glands secrete a saliva that is predominantly mucous in character The basis for different glands secreting saliva of differing composition can be seen by examining salivary glands histologically. Two basic types of acinar epithelial cells exist: serous cells, which secrete a watery fluid, essentially devoid of mucus mucous cells, which produce a very mucus-rich secretion Acini in the parotid glands are almost exclusively of the serous type, while those in the sublingual glands are predominantly mucus cells. In the submaxillary glands, it is common to observe acini composed of both serous and mucus epithelial cells. In the histologic sections of canine salivary gland shown above, the cells stained pink are serous cells, while the white, foamy cells are mucus-secreting cells. Secretion of saliva is under control of the autonomic nervous system, which controls both the volume and type of saliva secreted.

This is actually fairly interesting: a dog fed dry dog food produces saliva that is predominantly serous, while dogs on a meat diet secrete saliva with much more mucus. Parasympathetic stimulation from the brain, as was well demonstated by Ivan Pavlov , results in greatly enhanced secretion, as well as increased blood flow to the salivary glands. Potent stimuli for increased salivation include the presence of food or irritating substances in the mouth, and thoughts of or the smell of food. Knowing that salivation is controlled by the brain will also help explain why many psychic stimuli also induce excessive salivation - for example, why some dogs salivate all over the house when it's thundering What then are the important functions of saliva? Saliva serves many roles, some of which are important to all species, and others to only a few: Lubrication and binding: the mucus in saliva is extremely effective in binding masticated food into a slippery bolus that (usually) slides easily through the esophagus without inflicting damage to the mucosa. Saliva also coats the oral cavity and esophagus, and food basically never directly touches the epithelial cells of those tissues.

Solubilizes dry food: in order to be tasted, the molecules in food must be solubilized. Oral hygiene: The oral cavity is almost constantly flushed with saliva, which floats away food debris and keeps the mouth relatively clean. Flow of saliva diminishes considerably during sleep, allow populations of bacteria to build up in the mouth -- the result is dragon breath in the morning. Saliva also contains lysozyme, an enzyme that lyses many bacteria and prevents overgrowth of oral microbial populations. Initiates starch digestion: in most species, the serous acinar cells secrete an alpha-amylase which can begin to digest dietary starch into maltose. Amylase is not present, or present only in very small quantities, in the saliva of carnivores or cattle. Provides alkaline buffering and fluid: this is of great importance in ruminants, which have non-secretory forestomachs. Evaporative cooling: clearly of importance in dogs, which have very poorly developed sweat glands - look at a dog panting after a long run and this function will be clear.

Diseases of the salivary glands and ducts are not uncommon in animals and man, and excessive salivation is a symptom of almost any lesion in the oral cavity. The dripping of saliva seen in rabid animals is not actually a result of excessive salivation, but due to pharyngeal paralysis, which prevents saliva from being swallowed. Medical Physiology/Gastrointestinal Physiology/Secretions - Wikibooks, open books for an open world Medical Physiology/Gastrointestinal Physiology/Secretions 1.15.1 Diarrhea Secretions in the GI tract[ edit ] About 9 liters of fluid pass through the GI system each day, and only about 2 liters are ingested, the rest represent secretions from the system itself. About half, 3.5, liters is secreted from the exocrine glands, the salivary glands, the pancreas and the liver, the other half is secreted by the epithelial cells of the of the digestive tract it self. Nearly all this fluid is absorbed, so the pellets of feces only contain a significant amount of fluid in diarrhea.

To put this in perspective a 70 Kilogram man has about 42 liters of fluid, so the secretions represent about a sixth of the body's volume. The circulation contains about 3.5 liters, so these secretions represent twice the body's circulating volume! Failures of absorption of the intestinal secretions can thus lead to rapid dehydration and electrolyte imbalance. The secretions consist of digestive enzymes, mucous and substantial amounts of fluid and ions. Daily Volume Several different types of gland are found in the GI Tract: Single cell mucous glands and goblet cells. Pit glands. Invaginations of the epithelia into the submucosa. In the small intestine these are called Crypts of Lieberkuhn. Deep tubular glands. These are found in the stomach - the gastric glands, and the upper duodenum - Brunners glands. Complex glands, the salivary glands, the pancreas, and the liver. The salivary glands and the pancreas are compound acinous glands. Mechanisms of stimulation[ edit ] Local effects[ edit ] The mechanical presence of food causes stimulation not only locally but also adjacent regions. This may either be a direct effect, or via.

the enteric nervous system. Autonomic stimulation[ edit ] Stimulation of parasympathetic nerves invariably serve to increase secretion. Stimulation of sympathetic nerves may increase some secretions, but usually diminishes blood flow, which will usually decrease overall secretion. Digestive Enzymes[ edit ] Digestive enzymes are secreted by glandular cells which will store the enzyme in secretory vesicles until they are ready to be released. These cells are characterised by a robust rough endoplastic reticulum and numerous mitochondria. Passage of materials from the ribosomes, through the endoplasmic reticulum and Golgi body to the secretory vesicles takes about 20 minutes. Note the presence of nerve fibers on the basal side of the cell. Water & Electrolyte secretions[ edit ] Glandular secretions must also secrete water and electrolytes to go along with the organic substances. The following illustration shows the most likely mechanism for this. In its resting state the membrane resting potential is about -30-40 mV Neural stimulation causes an influx of -ve chloride ions decreasing resting potential by 10-20 mV Sodium ions follow down the electrical gradient. Cell contents become hyper osmotic.

Water follows. Intracellular pressure increases Increased pressure opens ports on apical side of cell flushing water and electrolytes Micro electrode studies indicate that the whole process lasts about a second! Digestive Enzymes of the GI tract[ edit ] The following table shows a summary of the digestive enzymes of the GI tract: Location Stimulates gastric contractions (hunger pangs) Secretin is of particular historical interest as it was the first hormone discovered in 1902 Mucus Secreting Cells[ edit ] Mucous is a viscous secretion used for protection and lubrication. It consists mainly of Glycoproteins. It is made by mucous cells in the stomach and Goblet cells in the small intestine. Up to 25% of the intestinal epithelial cells are goblet cells.In the mouth about 70% of the mucous is secreted by the minor salivary glands. Mucous has the following properties: Adherent properties, it sticks well to surfaces Enough body to prevent contact of most food particles with tissue Lubricates well - has a low resistance to slippage Strongly resistant to digestive enzymes Neutralizing properties.

As well as a buffer like effect, mucous can also contain large quantities of bicarbonate. Blue staining Goblet cells Control of secretion is by a variety of neuropeptides in the enteric nervous system; parasympathetic innervation; and cytokines from the immune system. Transverse section of Villus showing goblet cells Electrolytes and Fluids[ edit ] A large portion of the 7 liters is composed of water and ions. The ionic composition varies from region to region. The acini of the salivary glands secrete a sodium and chloride rich secretion, this is then turned to a potassium, bicarbonate rich secretion as it travels down the lumen and ducts of the glands The Oxyntic cells of the stomach secret Hydrochloric acid The mucous cells of the stomach secrete a mucous rich in bicarbonates The pancreatic ducts and ductules secrete a solution rich in bicarbonate the Crypts of Liberkuhn of the small intestine secrete a solution almost indistinguishable from interstitial fluid.

Mouth[ edit ] The Salivary glands consist of the parotid, submandibular, and sublingual glands as well as numerous smaller buccal glands secreting both serous and mucoid secretions. The parotid secretions are mainly serous, the buccal glands mucus, and the sublingual and submandibular are a mixture of the two. The acini secrete proteins and a fluid similar in consistency to interstitial fluid, and the ducts exchange the sodium for potassium and Bicarbonate for chlorine leaving saliva that is rich in Potassium and bicarbonate ions. The glands secrete between 800-1500 mls a day Salivary Glands, From Grays Anatomy The sodium ions are actively reabsorbed, and the potassium ions are actively secreted at the luminal side of the cell with an excess of sodium reabsorbtion causing a -70mV gradient. This causes passive reabsorbtion of chlorine ions. Bicarbonate ions are both passively exchanged , and actively secreted in exchange for chlorine. This is illustrated in the diagram below.

The saliva contains the enzyme Ptyalin, an amylase for breaking down carbohydrates as well as a lipase. Anti-bacterial action of Saliva[ edit ] The mouth contains numerous bacteria, and an important function of saliva is oral hygine. The saliva contains thiocyanate, a potent antibacterial. The lipase in the saliva will also breakdown bacteria cell walls and facilitates the passage of thiocyanate into the bacteria. The lipase in fact is not very important for the digestion of food, most fat digestion occours with the pancreatic enzymes, but is important in its anti-bacterial and oral hygiene role. Regulation of Salivary Secretion[ edit ] Salivation is controlled viathe parasympathetic system from the salivary nuclei in the brain stem. Factors that induce salivation include: Taste stimuli, especially sour taste Higher centers especially appetite anticipation, smells and visual clues In response to signals from the stomach and upper GI tract, particularly irritating stimuli. Salivation can also occour as a prelude to vomiting. Clinical Note - Sjögren's syndrome[ edit ] Histopathologic image of focal lymphoid infiltration in the minor salivary gland associated with Sjögren syndrome. Lip biopsy.

H & E stain Sjögren's syndrome is an auto immune disorder where immune cells attack the salivary and tear glands. This can play havoc with oral hygiene and lead to rampant caries. Esophagus[ edit ] Esophageal secretions are entirely mucous in character, and assist passage of food as well as protecting the lower end of the esophagus from gastric reflux. Stomach[ edit ] The adult stomach secretes about 1500 cc in a normal day consisting of hydrochloric acid, bicarbonate rich mucous, and the digestive hormone precursor pepsinogen. Pepsinogen is activated to its active form pepsin by the acidity of the stomach. G cells also secrete the hormone gastrin. The gastric pits of the stomach open on to branching glands: pyloric glands in the antral part of the stomach; gastric or oxyntic (acid forming) glands in the fundus and body of the stomach. A schematic diagram of an oxcyntic gland is shown here (see also anatomy).

The parietal or oxcyntic cells secrete hydrochloric acid; the peptic or chief cells secrete pepsinogen; the mucous cells secrete a bicarbonate rich mucous; and the G cells (found only in the antral glands) secrete the hormone Gastrin. Hydrochloric Acid secretion[ edit ] The oxcyntic or parietal cell contains a large number of of intracellular canaliculi shown schematically here: The pH of the secreted acid is about 0.8, and has a hydrogen ion concentration of about 3 million times that of arterial blood. To achieve this level of concentration requires a lot of energy, about 1500 calories per liter of secretion. The mechanism of hydrogen ion formation is illustrated schematically here. Carbon dioxide and water enter the cell and combine to form carbonic acid under the influence of the enzyme carbonic anhydrase. Bicarbonate is actively excreted at the basal side of the cell and is exchanged for chlorine. Potassium is exchanged for hydrogen ions at the apical side of the cell Chlorine ions (not shown in diag.) are also actively secreted.

Clinical Note: Intrinsic factor and Pernicious anaemia[ edit ] The oxcyntic or parietal cells also secrete intrinsic factor, a substance essential for the absorption of Vitamin B12 in the small intestine. In chronic gastritis, this may not be secreted, and the medical condition pernicious anaemia will develop. Bicarbonate Rich Mucous Secretion[ edit ] Mucous secretion rich in alkaline bicarbonate protects the stomach from the Hydrochloric acid of the gastric juice. Bicarbonate ions are generated by the mechanism illustrated below: Carbon dioxide and water enter the cell and combine to form carbonic acid under the influence of the enzyme carbonic anhydrase. Hydrogen ions are actively secreted on the basal side of the cell in exchange for sodium. Bicabonate ions are actively secreted on the apical or lumen side of the cell in exchange for chlorine Secretion and Activation of Pepsinogen[ edit ] Pepsinogen is secreted by the peptic or chief cells of the gland. When first secreted pepsinogen is inactive, but contact with acid converts it to the active form pepsin by splitting the pepsinogen molecule.

Pepsin functions best at a pH between 1.8 and 3.5 Stimulation of Gastric Acid secretion.[ edit ] The Oxcyntic cells function in close association with histamine producing cells called enterochromaffin-like cells (ECL) which secrete histamin. These cells release histamin in direct contact with the oxcyntic glands and promote the secretion of HCl. The activation of this complex is under hormonal (Gastrin) and nervous control. Gastrin, secreted by the G cells in the antrum of the stomach in response to the presence of protein is the most potent stimulator of the Histamine/Acid complex. The gastrin is not only carried by the blood stream, but is also carried directly into the lumens of the gastric pits an has a direct stimulating action. The Histamin/HCl complex is also activated by acetylcholine released by the vagus nerve Other substances also control Acid secretion, mainly through their action on Gastrin production. Inhibition of Gastric Acid secretion.[ edit ] Factors which slow stomach emptying, which was discussed when considering motility will also reduce gastin production and hence Acid secretion.

Regulation of Pepsinogen Secretion[ edit ] Pepsinogen secretion occours in response to two signals: Acetylcholine release from the vagus nerve stimulation of peptic cell secretion in response to acid in the stomach, probably not directly but through the enteric nervous system Small Intestine[ edit ] The upper small intestine secretes the hormones Cholecystokinase and secretin, mucous, Intestinal digestive juices, and possibly enzymes. The Digestive enzymes are secreted by the small intestine at a rate of about 1800 ccs a day. The pH of the small intestine secretions averages 7.5 to 8.0. Hormone Secretion[ edit ] Cholecystokinin (CCK)is secreted in response to fats and peptides in the upper small intestines, particularly the duodenum. Actions of CCK include: Secretion of Pancreatic Enzymes Relaxation of the sphincter of Oddi increased tension in the pyloric sphincter, inhibiting stomach emptying Secretin is released in response to the presence of Acid in the duodenum.

Actions of Secretin include: Secretion of Copious amounts of bicarbonate rich fluid by the biliary and gall bladder ducts Secretion of alkaline rich mucous by Brunners glands increased tension in the pyloric sphincter, inhibiting stomach emptying Brunner's Glands[ edit ] The first few centimeters of the Duodenum, between the pylorus of the stomach and the Ampulla of Vater, contain numerous compound mucous glands called Brunner's Glands. These secrete an Alkaline rich mucous - pH between 8.0 & 8.9 - in response to various stimuli: Local irritation and the presence of Acid Vagal Stimulation Gastrointestinal hormones, particularly secretin. The mechanism for secreting the alkaline rich mucous is similar to that already discussed for the stomach. Clinical Note - Peptic Ulcers[ edit ] Gastric and duodenal ulcers are due mainly to the breakdown of the protective barrier of alkaline mucous. The following factors have been identified as causes: Non Steroidal Anti-inflamatory Drugs (NSAIDs). The bacteria Heliobacter Pylori. Excess acid secretion which can over whelm the defences.

This can occour particularly in Zollinger-Ellison syndrome, caused by benign gastrin secreting tumors which may develop in the stomach or duodenum. It is of interest that Brunner Cell secretion is inhibited by sympathetic stimulation, thus this may be a connection between the 'hyper' personality and their disposition to duodenal ulcers. Less mucous may be secreted making the duodenum more vulnerable to stomach acid and stomach pepsin. Crypts of Lieberkuhn[ edit ] These are located over the entire surface of the small intestine adjacent to the villi. They secrete a copious solution almost identical to interstitial fluid. The mechanism for secretion is not well understood but one hypothesis is illustrated here which differs only slightly from the hypothesis described earlier: Sodium and chlorine ions are pumped into the cell; water follows by osmosis; the chlorine ions are actively pumped into the lumen; water and sodium follows from the cell itself or possibly passes through 'leaky' tight junctions. Mucous Cells[ edit ] The villi are covered with goblet cells. About a quarter to a half of the villi cells are mucous producing.

Enzyme Secretion[ edit ] Small intestine secretions that are free of cellular debris contains almost no enzymes! Thus the enzymes are either secluded within the cell, or possibly they are attached to the brush border. In any case they are not flushed down the lumen, and they remain local. Regulation of Small Intestine Secretions[ edit ] Secretions are produced almost entirely from local enteric nervous reflexes in response to local stimuli. Islet of Langerhans surrounded by Acini showing relationship of Islet of Langerhans and exocrine gland The pancreas is a large endocrine and exocrine gland situated retroperitonealy beneath the stomach. The endocrine portion of the gland secretes Insulin and glucagon from the Islets of Langerhans (see thumbnail of histology). This function of the pancreas will be looked at else where. The microscopic structure of the pancras is similar to the salivary glands, the acini secrete enzymes, and the ductules and ducts secrete large quantities of a bicarbonate rich juice.

These travel down the pancreatic duct to the second part of the duodenum where it exits via the Ampulla of Vater, protected by the Sphincter of Oddi. Enzymes secreted by the acini include proteolytic enzymes, amylases and lipases. The proteolytic enzymes are all secreted in an inactive form to prevent auto-digestion(see below). Pancreatic Digestive Enzymes[ edit ] The following table summarizes the digestive enzymes secreted by the pancreas: Group Lipase converts fats to fatty acids and monoglycerides Phospholipase splits fatty acids from phospholipids Cholesterol esterase hydrolises cholesterol esters Inhibition and Activation of Enzymes[ edit ] The cells that secrete proteolytic enzymes also secrete another substance called tripsin inhibitor. This prevents any tripsin that may form in the cells or ducts from becoming active, or activating the other enzymes. If however the pancreas becomes damaged or the pancreatic ducts become blocked then the action of tripsin inhibitor can be over whelmed, and the very serious condition acute pancreatitis can develop.

This can also occur if there is regurgitation of intestinal contents through the Ampulla of Vater. Wiki Article on Acute Pancreatitis Secretion of Bicarbonate ions[ edit ] Copious quantities of Bicarbonate ion rich solutions are secreted by the ducts and ductules of the pancreas in response to the hormone Secretin. The mechanisms are similar to that of the mucous cells of the stomach, except that large quantities of fluid are also produced. Carbon dioxide and water enter the cell and combine to form carbonic acid under the influence of the enzyme carbonic anhydrase. Hydrogen ions are actively secreted on the basal side of the cell in exchange for sodium. Bicabonate ions are actively secreted on the apical or lumen side of the cell in exchange for chlorine Sodium and Water ions follow either passively through 'leaky' tight junctions, or through cell by the mechanism described above in 'Water & Electrolyte secretions'. Phases of Digestion[ edit ] Like Gastic secretions, Pancreatic secretions can be divided into three phases: Cephalic Gastric Intestinal The Cephalic phase occurs when we think about or anticipate food.

It is mediated by the vagus nerve. It causes secretion of about 20% of the enzymes, but as this secretion is not accompanied by fluid secretions, the enzymes are not flushed out and tend to remain in the ducts. The gastric phase occurs when food enters the stomach, and again is mediated by neural stimuli. This accounts for another 5-10%, and again in the absence of serous flow these secretions tend to remain in the ducts. The Intestinal phase occurs when food enters the small intestine and both serous pancreatic secretion becomes copious due to the hormone secretin. Regulation of pancreatic Secretion[ edit ] Three basic stimuli control pancreatic secretion Acetylcholine from the parasympathetic nerves of the vagus and the cholinergic nerves of the enteric nervous system. Cholecystokinin secreted in the duodenum and the uopper small intestine Secretin, also secreted in the duodenum and upper jejunum. The following diagram summarizes the factors controlling pancreatic secretions. Acetylcholin and Cholecystokinin cause secretion of digestive enzymes, but these tend to remain in the gland, as there are no secretions to flow them out.

Secretin causes copious secretions of sodium bicarbonate rich fluids which wash the enzymes into the small intestine, and also neutralize the Hydrochloric acid from the stomach. 2HCl + Na2CO3 --> 2NaCl + H2CO3 --> H2O + CO2 The carbonic acid (a weak acid) immediately dissociates into Carbon Dioxide and water The Carbon dioxide is absorbed into the blood stream. Pancreatic enzymes work best between a pH of 7-8. Sodium Bicarbonate has a pH of about 8. Biliary System[ edit ] Basic anatomy of the biliary system About 1500 mLs of bile are secreted every day. The bile is secreted continuously by the hepatocytes of the liver, and if not immediately required for digestion are stored in the gall bladder. Here they are concentrated up to 15 times. Initally bile fluid has about the same electrolyte concentration of interstitial fluid, but during concentration large quantities of electrolytes (but not Ca ions) are reabsorbed.

In the presence of fats in the duodenum, cholesystokinin is secreted which causes strong contractions of the gall bladder and relaxation of the Sphincter of Oddi, propelling the bile into the small intestine. Vagal stimulation can have a similary but secondary effect. Bile contains Bile salts, an emulsifying agent neccessary for the digestion and absorption of fats; as well as bilirubin, cholesterol and fatty acids Composition of Human Hepatic Duct Bile Water 0.1% Manufacture of Bile and Structure of Hepatic Lobule[ edit ] The illustration below shows a schematic diagram of a liver lobule. Blood is conveyed to the lobules by branches of the hepatic portal vein and the hepatic artery. It then flows through sinuses, bathing the hepatocytes, to the central vein of the lobule, a branch of the Hepatic vein which drains into the Inferior Vena Cava. The hepatocytes secrete bile into bile canuliculi running between the hepatocytes, and these drain into branches of the bile duct. Bile is continuously secreted by the hepatocytes.

The fluid part of the secretion, a watery substance rich in sodium and bicarbonate is added by the ducts of the biliary system, and this secretion is stimulated by Secretin. Histology slide from the University of Ottawa Recycling of Bile Salts[ edit ] Bile salts are recycled by the GI System. About 95% of bile salts are are reabsorbed from the terminal ilium and returned to the liver via the portal system. In addition, some salts are produce by bacterial action in the Large intestine, and these too are returned to the liver. About 0.2 gm per day of bile salts are manufactured by the Liver, and the total pool of salts is about 3.5gm, so recycling is very important. recycling occurs 6-8 times per day or about twice per meal. If the terminal ilium is resected, or affected by disease such as Crohn's, fat digestion is seriously compromised, and mal-absorption of fat soluble vitamins can occur. Regulation of Bile Secretion[ edit ] The following Diagram summarizes the regulation of Bile secretion: Large Intestine[ edit ] The chief function of the large intestine is absorption of fluids and the formation of faeces.

About 1-2 liters of fluid enter the large intestine, and these are mainly absorbed, only about 200 cc being egested each day. The large intestine secretes about 200 cc of fluid a day, mainly in the form of mucous. Diarrhea[ edit ] The large intestine can produce large quantities of water and electrolytes in response to irritation, such as occurs in infections. This can lead to dehydration, but also has the beneficial effect of flushing out the irritants. Salivary Glands Salivary Glands Date: 20/07/2007 Description The major salivary glands (together accounting for about 90% of the fluid production) include the paired parotid glands, which are located opposite the maxillary first molars, and the submandibular and sublingual glands, which are found in the floor of the mouth. Minor glands (that produce less than 10% of the total volume of saliva) are found in the lower lip, tongue, palate, cheeks, and pharynx. The terms major and minor refer to the anatomic size of the glands.

Major glands do produce more saliva than minor glands, but the quality of content and thus the type of protection varies. Paradoxically, it could be argued that the minor salivary glands are the most important because of their protective components. 􀂉 The parotid glands are "serous" glands, for their acinar cells contain only serous-secreting cells, whose secretions are devoid of mucin compared to that of the submandibular and sublingual glands, which contain both serous- and mucin-secreting cells. The parotid glands produce a thin, watery, and amylase-rich fluid on stimulation which accounts for up to 50% of the mouth volume of saliva under stimulated conditions, whereas it contributes much less (20%) to the unstimulated saliva secretion. 􀂉 As compared with the parotid, the submandibular glands (comprising both serous and mucous acinar cell types) secrete a more viscous, mucin-rich saliva. They contribute predominantly (65%) to the unstimulated saliva secretion, and less (35%) to saliva under stimulated conditions.

The viscosity of the submandibular saliva usually decreases with increasing flow rate since the serous cells have a greater response to stimulation than do the mucin-secreting cells. 􀂉 The sublingual glands, which contribute with 1–2% of the unstimulated volume of whole saliva, mainly consist of mucous acinar cells and also produce a thick, viscous mucin-rich saliva. 􀂉 The minor glands, although they produce less than 10% of the total volume of saliva, play an important role in lubricating the mucosa, as even in the absence of local stimuli they produce saliva. The minor glands, which are distributed throughout the oral mucosa (labial, buccal, lingual, palatinal mucosa), are mixed glands largely comprising mucous acinar cells. However, the palatinal glands are strictly mucous, whereas the lingual von Ebner’s glands are strictly serous. Figure The types of cells found in the salivary glands are acinar cells, various duct system cells, and myoepithelial cells. 􀂾 Acinar cells, in which saliva is first secreted, determine the type of secretion produced from the different glands.

Two basic types of acinar epithelial cells exist: serous cells secrete a watery fluid, essentially devoid of mucus, whereas mucous cells produce a very mucus-rich secretion. Secretion can be classified as serous, mucous, or mixed; serous secretions are produced mainly from the parotid gland, mucous secretions from the minor glands, and mixed serous and mucous secretions from the submandibular and sublingual glands (in sublingual glands secretion is mostly mucous). 􀂾 Duct system cells found in the salivary ducts are classified as intercalated, striated, and excretory. Intercalated duct cells are the first duct network connecting acinar secretions to the rest of the gland. These cells are not involved in the modification of electrolytes, as are the remaining duct cells. Striated cells are second in the network, functioning as electrolyte regulation in resorbing sodium. The final duct cells, the excretory duct cells, contribute by continuing sodium resorption and secreting potassium. Excretory duct cells are the last part of the duct network before saliva reaches the oral cavity.

􀂾 Myoepithelial cells, which are long cell processes wrapped around acinar cells, contract on stimulation to constrict the acinar. This function, secreting or “squeezing out” accumulating fluid, is the result of a purely neural process. The acinar cells secrete the salivary fluid, and the ductal cells secrete some protein and modify the ionic composition of the saliva as they convey it to the mouth. The zonula occludens, a tight junction that resides at the apical pole of the cell, separates the apical and basolateral plasma membranes. Within this zonula occludens, the lateral membranes of adjacent cells closely approximate one another. These sites of intimate contact, colloquially termed membrane "kisses", are thought to represent the physical sites at which diffusion of molecules across the zonula occludens is impeded. Junctions between acinar cells are highly permeable, those between intercalated duct cells are less permeable, and junctions between striated duct cells are essentially impermeable. The tight junctions in the resting rat parotid gland are impermeable to tracers of molecular weight > 1,900.

Salivary glands have a high blood flow. The external carotid arteries enter the submandibular and sublingual glands along with the main ducts and nerves, thereby creating a hilum, although this hilum is not as clearly defined as in larger organs such as the kidney. Within the glands, the vessels follow the subdivision of the secretory duct tree so that each lobule has a distinct and separate blood supply. The direction of the blood flow is countercurrent to the direction of the salivary flow. Salivary fluid secrection Ematic circulation of salivary glands is very important for saliva formation. Actually only in cells where there is blood passage there can be saliva formation. Important studies suggest that preassure generted by salivary secrction is dependent on blood preassure. Parasympathetic stimulation of salivary glands causes a higher blood flow. The current secretion model predicts that, when stimulated, salivary acinar cells lose KCl. The loss of K+ and Cl-, across basolateral and apical membranes, respectively, creates a large transepithelial potential difference.

This lumen-negative potential difference drives Na+ flux between acinar cells into the lumen, and H2O follows the resulting NaCl osmotic gradient. Sustained secretion is dependent on the activation of K+ and Cl- reuptake mechanisms located in the basolateral membranes. The net effect of simultaneously activating Cl- efflux and Cl- reuptake mechanisms is transepithelial Cl- movement, the driving force for fluid secretion. It is interesting to note that little desensitization occurs, i.e., in the continuous presence of a muscarinic agonist, salivary glands can secrete for hours. A salivary acinar cell contains four ion transporters, the Na+/K+ adenosine triphosphatase (ATPase), a Na+-K+-2Cl- cotransporter and a Ca2+-activated K+ channel, all located in the basolateral membrane, and a Ca2+-activated Cl- channel located in the apical membrane. Fluid secretion is thought to arise from the concerted actions of these four transporters.

Figure:Salivary fluid secrection Upon stimulation, saliva is initially formed as a near isotonic plasma-like primary secretion in the acinar lumen (the first stage). The acinar cells forming the secretory endpiece of the salivary gland actively pump sodium ions from the blood into the lumen of the endpiece. The resulting osmotic pressure difference between the blood and the fluid in the endpiece causes water to flow from the blood, through the tight junctions between the acinar cells, and into the lumen of the endpiece. Thus, the primary secretion (as it leaves the endpiece) is thought to be almost isotonic with plasma. When this fluid passes along through the duct system it is modified by selective and energy-dependent reabsorption of sodium and chloride (without water, as the salivary ducts are impermeable to water) and secretion of potassium and bicarbonate – the latter especially occurring under stimulated conditions. The resulting saliva becomes increasingly hypotonic as it moves down the ductal system: the final saliva secreted to the oral cavity contains concentrations of sodium and chloride much below that of primary saliva.

Saliva modulation in sistemic deseases Immune general reaction, like the ones we have in transplant rejection, can act on salivary glands, reducing secrection speed and increasing Na+ e Cl- concentration. Cystic Fibrosis is an illness that has as targets lung and pancreas and is caracterised by a defective Cl- transporter. It causes a reduction in the salivary production and increases the quantity of Ca++ in saliva. Thyroid and Saliva Innervation of Salivary Glands Secretion of saliva is under control of the autonomic nervous system, which controls both the volume and type of saliva secreted. A dog fed dry dog food produces saliva that is predominantly serous, while dogs on a meat diet secrete saliva with much more mucus. Parasympathetic stimulation from the brain results in greatly enhanced secretion, as well as increased blood flow to the salivary glands. Stimulated saliva is reported to contribute as much as 80% to 90% of the average daily salivary production. The secretion of saliva is controlled by a salivary center composed of nuclei in the medulla, but there are specific triggers for this secretion.

Salivary glands are innervated by both sympathetic and parasympathetic nerve fibers. Various neurotransmitters and hormones stimulate different receptors, different salivary glands, and different responses. When sympathetic innervations dominate, the secretions contain more protein from acinar cells, whereas predominant parasympathetic innervations produce a more watery secretion. Stimulation of one receptor often enhances and complements another receptor. Therefore, the separation of contributing stimuli and resulting secretory products is not absolute. Three types of triggers, or stimuli, for this production are mechanical (the act of chewing), gustatory (with acid the most stimulating trigger and sweet or bitter the least stimulating), and olfactory (a surprisingly poor stimulus). Other factors affecting secretion include psychic factors such as pain, certain types of medication, and various local or systemic diseases affecting the glands themselves. Salivary secretion is regulated by a reflex arch comprising afferent receptors and nerves carrying impulses induced by actions on gustation and mastication, a central connection (salivation center), and an efferent part consisting of parasympathetic and sympathetic autonomic nerve bundles that separately innervate the glands. The secretory reflex arch is also under influence of higher centers in the brain.

Saliva may be secreted in the absence of exogenous stimuli referred to as the resting or unstimulated salivary flow. Initiation of salivation by an unconditioned reflex. The afferent part is activated by stimulation of various sensory receptors including chemoreceptors in the taste buds and mechanoreceptors in the periodontal ligament. The afferent nerves carrying impulses to the salivary nuclei (salivation center) in the medulla oblongata are the facial, glossopharyngeal and vagal nerves (taste) and the trigeminal nerve (chewing). Olfaction and stretch of the stomach are other afferent inputs that can initiate formation of saliva. Initiation of salivation by a conditioned reflex. The sight and thought of food may lead to some formation of saliva. The salivary nuclei also receive impulses from other centers of the brain resulting in facilatory or inhibitory effects on salivation depending on, for example, the emotional state. Efferents. The salivary nuclei direct signals to the efferent part of the reflex consisting of parasympathetic (facial and glossopharyngeal nerves) and sympathetic autonomic nerves that separately innervate the glands.

The sympathetic nerves, running from the sympathetic trunk, follow the blood vessels supplying the glands. Release of neurotransmitters from postganglionic neurons of both branches of the autonomic nervous system elicits secretion of saliva to the oral cavity. The facial nerve provides parasympathetic control of the submandibular, sublingual, and minor glands (except von Ebner’s gland), whereas the glossopharyngeal nerves control the parotid glands. Increased salivary secretion in response to chewing is the result of a masticatory-salivary reflex, which has been found to be primarily unilateral and dependent on the applied stimulus intensity. In the oral cavity chewing activates mechanoreceptors in the periodontal membrane. Chewing compresses the teeth into the periodontal membrane, which activates the mechanoreceptors, followed by transmission of impulses through the trigeminal nerve to the salivation center. Salivary secretion increases with the hardness and the size of the object being chewed as well as the chewing force by the chewing muscles. Increased salivary secretion in response to taste stimulation is, like chewing, induced reflexly.

Taste sensation is traditionally divided into the four classical basic taste modalities: sweet, salty, sour, and bitter. Each modality is based on distinct transductional systems in the single receptor cell leading to depolarization of the receptor potential and generation of action potentials. This facilitates the release of neurotransmitters, stimulating gustatory afferent nerve fibers that then carry the taste signal onto the higher-order systems. Each taste receptor cell responds, however, in varying degrees to substances that fall into more than one taste category. Among additional taste modalities that have been identified is umami, which is elicited by monosodium glutamate and certain ribonucleotides. Moreover, perception of taste is affected by general sensory impulses arising from pain (‘hot spices’), food temperature and texture through the trigeminal nerve. The highest saliva stimulation is obtained with sour taste, followed by salt (NaCl), sweet, and bitter. There is no additive effect on salivary flow by giving a mixture of different taste stimuli. In fact, it elicits a lower flow rate than the sum of the separate stimuli. Furthermore, salivary flow increases with increasing concentration and amount of a separate taste stimulus.

Continuous taste stimulation usually leads to varying degrees of adaptation, which is highest for sweet taste, but lowest for sour taste. Taste impulses are carried to the brain by parasympathetic nerves, many of which travel with branches of the trigeminal nerve. The sensory nerves, which carry signals in response to stimulation of taste receptors are, with regards to the tongue, the facial nerve (in particular sweet, salty and acid stimuli), whereas the glossopharyngeal nerve innervates the circumvallate papillae, the back of the tongue and also the palate. Fibers of the vagal nerve innervate taste buds in the tonsillar region, the epiglottis, the pharyngeal wall and esophagus. The taste pathway activated by inputs from the facial, glossospharyngeal and vagal nerves have ipsilateral reflex connections to the salivatory center in the brain stem. The first neurons synapse in the tractus solitarius and its nucleus, where the secondary neurons cross the midline and travel to the thalamus. Also in this region, the third neurons communicate with the postcentral gyrus-facial area and there are also projections to the olfactory cortex.

Salivary gland disorders refer to conditions that cause swelling or pain in the saliva-producing tissues around the mouth. Items secretion - Dictionary Definition : Vocabulary.com secretion A secretion is a substance made and released by a living thing, like when your skin sweats. Secretions don't have to do with secrets, but with secreting: synthesizing and then producing a substance. A machine can't make a secretion — only living things can. Many secretions are harmless, while others are dangerous to other animals. For example, the secretions of some frogs are a type of poison. Some secretions stay within an animal, like the bile secreted by our livers. Saliva is another secretion. The word comes from the Latin root secretionem, "separation." Salivary Glands and Saliva Salivary Glands and Saliva Sign Up for Our Free Newsletters Thanks, You're in! Health Tip of the Day Recipe of the Day There was an error. Please try again. Please select a newsletter. Please enter a valid email address. Did you mean ?

salivary gland | anatomy | Britannica.com Salivary gland human digestive system Salivary gland, any of the organs that secrete saliva, a substance that moistens and softens food, into the oral cavity of vertebrates. Salivary glands may be predominantly serous , mucous, or mixed in secretion. Mucus is a thick, clear, and somewhat slimy substance. Serous secretion is a more liquid opalescent fluid composed of water and proteins, such as the digestive enzyme amylase . Depending on the types of cells present, the glands may be specific, giving off only one of these two substances; or they may be mixed, giving off combinations of both secretions. Secretions can be increased by the presence, thought, or smell of food and also by thermal stimulation. In addition to numerous small glands in the tongue , palate , lips , and cheeks, human beings have three pairs of major salivary glands that open into the mouth through well-developed ducts. The parotid salivary glands, the largest of the three, are located between the ear and ascending branch of the lower jaw.

Each gland is enclosed in a tissue capsule and is composed of fat tissue and cells that secrete mainly serous fluids. Each gland’s major duct ( Stensen’s duct) opens in the rear of the mouth cavity near the second upper molar. The second pair, the submaxillary glands , also called submandibular glands, are located along the side of the lower jawbone. The major duct of each ( Wharton’s duct) opens into the floor of the mouth at the junction where the front of the tongue meets the mouth’s floor. A capsule of tissue also surrounds each of these glands, which give off mixed secretions mostly serous in nature. The third pair, the sublingual glands , are situated beneath the mucous membrane of the floor of the mouth, near the chin region. They are not covered by a capsule and are therefore more dispersed throughout the surrounding tissue. They have many ducts ( Rivinus’s ducts) that empty near the junction of the tongue and the mouth’s floor; several unite to form Bartholin’s duct, the major duct of the sublingual gland, which empties into or near the submaxillary duct. These glands secrete a mixed fluid that is mainly mucus. See also saliva .

Learn More in these related articles: An Examination Of The Bodily Fluids And Excretions An Examination Of The Bodily Fluids And Excretions (especially as regards their possible consumption by ritualists) by Asa Rhadon Semen - the primary male sexual fluid, which like blood is composed of both cellular and non-cellular material. Though blood consists of numerous differentiated cells floating in a plasma, the only cells swimming in seminal plasma are sperm. These cells, the only human cells that move under their own power, are in fact almost too archetypically male, consisting basically of a warhead containing 23 chromosomes (half the usual cell's complement) which is driven toward destiny by its engine's whiplike propeller. The plasmas of red blood and white blood (semen) are also quite different. While both types are a complex mix of organic and inorganic chemicals, blood plasma feeds and interacts with a multitude of varying cells and tissues; seminal plasma, on the other hand, serves only to nourish and assist the spermatozoa. Also, it is unique among human substances in its high levels of fructose (as opposed to glucose), for which fact science can presently find no proven explanation.

The remainder of the seminal fluid consists of various proteins, the functions of which are also unclear. The spermatozoa are formed in the testicles and lodge in the epididymis until they are ejaculated through the vas deferens and the urethra, mixing with a rich variety of glandular secretions along the way. There can be no doubt that, considered from a purely nutritional perspective, fresh semen is a highly nourishing food. As with all the substances discussed in this essay, there may be infectious agents like human immunodefiency virus or various of the hepatitis viruses present in semen. Most of these agents are inactivated by the hydrochloric acid that does the digesting in human stomachs; however, there is a danger of an infection passing through a sore or irritation on the mucus membranes of one's mouth or throat. The safest way to do any ritual involving the bodily fluids is to know in detail the medical status of your partner(s). Menstrual blood - one of the very most important bodily fluids used in the performance of advanced sex magick techniques.

It is the normal quasi-monthly discharge of ovulating women, and consists of a mixture of ordinary blood, the sloughed-off layer of endometrium, and the virtually microscopic remains of (usually) two unfertilized human eggs . The blood is made up of plasma (a pale brownish aqueous solution) in which is suspended a myriad of cells and chemicals . The endometrium is a mucus membrane which lines the uterus. It thickens in response to the release of certain hormones, its mucus glands and cells swelling and the circulation of blood increasing. After a period of time, if a fertilized egg fails to implant itself, the blood vessels in this waiting endometrium go into spasm. The outer layer of the thickened membrane falls apart and is expelled in the process called menstruation. Each egg is a specialized single cell containing only half the chromosomes of a normal human cell; it is tens of thousands of times larger than a sperm, though at around an eighth of a millimeter one could easily fit inside this next period. Most of the egg is made up of what is called yolk, a nutrient-rich cell plasma used up during the egg's development.

If an egg is not fertilized within about 24 hours it begins to disintegrate, and is usually expelled as part of the menstrual blood. Female sexual fluids - the vaginal fluid is composed of mucus, the remains of dead cells, white blood cells, and a complex liquid that is sweated by the vaginal walls. Sexual excitation almost invariably causes some increase in the production of vaginal fluids, primarily mucus and sweat, though the amount may range greatly for different individuals and at different times. The exact sources of all the components of human vaginal fluid is still not certain, but the list of ingredients is long: inorganic salts, urea, amino acids and other proteins , and a number of volatile fatty acids. These acids evaporate easily making them ideal for conveying messages by smell; in fact, their role in sexual attraction among rhesus monkeys is well established. All women produce some of the two major human fatty acids, acetic acid (the major constituent of vinegar) and lactic acid (an element of sour milk). Around a third of them also produce significant amounts of other volatiles. The exact role of these aromas in human sexuality is not understood, but the smell of the vagina is known to affect many men quite strongly.

Also, there are some women who produce vaginal fluid quite copiously during orgasm (the so-called 'female ejaculation'); the source and composition of this orgasmic fluid has not been sufficiently studied to enable a report on their significance at this time. Sweat - there are two different types of sweat gland, and they are both found only in mammalian animals. The eccrine glands help our bodies to regulate temperature by secreting water (with a mix of inorganic salts) whenever our internal temperature rises. As this water evaporates from our skins some of the excess heat is dissipated into the atmosphere. During sex the increased respiration and circulation, along with some perhaps vigorous physical activity, usually causes a rise in internal body temperature, and therefore produces sweat from the eccrine glands. However, there is also another type of sweat gland which is more important in creating a specifically sexual type of sweat. These are the apocrine glands, generally situated around the hair follicles in the armpits and groin, which secrete a fatty kind of sweat into tiny tubes in the skin.

In response to various strong emotional stimuli (anger, stress, lust, etc.) the walls of the tubes contract, pushing the fatty substance up to the surface of the skin; here bacteria soon break it down into a variety of aromatic fatty acids. Some of these fatty acids smell good to humans while others are considered unpleasant, even offensive. The influence of sex magick practices upon the specific odor and amount of apocrine sweat produced by sexual activity has not yet been thoroughly scientifically investigated, though anecdotal evidence is copious enough to form a basis for at least one Thelemic ritual practice. Saliva - a somewhat viscous fluid which normally is constantly present in the mouths of human beings, being secreted by their variously surrounding salivary glands . The fluid itself is mainly simple water, but it also contains mucus, numerous proteins and digestive enzymes , and inorganic salts. Once in the mouth it mixes with the remains of food, bacteria, dead cells, and white blood cells (as well as red blood cells if there are any openings in the mucus membrane of the mouth).

Saliva has multiple functions; moistening and lubricating the mouth to help with speech and swallowing, beginning the digestive process with enzymes which break down complex carbohydrates into sugars, removing organic debris, and it also plays an important part in the sequence of dehydration->thirst->potation. Mucus - the one human bodily fluid which is a constituent of most of the other substances listed here. Its usual function is to form a generalized protective layer which also serves to dampen and lubricate much of the respiratory, reproductive, and digestive systems. It consists of various cells and chemicals suspended in varying amounts of water . In a few cases (i.e., the lining of the stomach, the endometrium or uterine lining, etc.) the mucus' thickness is such that it takes on a semisolid appearance. Urine - consists mostly of ordinary water, but at least 158 different chemicals have been found in normal, healthy samples. Urea and other nitrogenous wastes, along with the inorganic salts of sodium, potassium, magnesium, and calcium make up by far the largest part of the substances present, but urine is a veritable soup of organic and inorganic compounds.

Some of these chemicals may be good for you, and the toxins are usually present in such low concentrations that the daily consumption of one's morning urine (a yogic practice of long standing) is doubtless far safer than the ordinary use of tobacco. Feces - its exact composition varies widely depending upon the diet and health of the defecator, but broadly speaking fecal matter consists of water, inorganic salts, food residues, amino acids and digestive enzymes, cellulose and fiber; mucus, blood, bacteria, and parasites are also commonly present. We have seen no reports of any scientific study undertaken to determine the health effects of customary shit-eating, but from the standpoint of contagion it is probably not a great deal more (though certainly it is not any less) dangerous than the consumption of semen, menstrual blood, etc., all of which, as noted above, may be risky.

Question: Which bodily fluid is secreted by the parotid glands?
Answer: Saliva