Salivary Glands Histology PDF

Salivary glands Majd ismail sarairh Chapter 16 * Definition and description : Salivary glands are glands the ducts of which open into the oral cavity. 1- compound refers to the fact that a salivary gland has more than one tubule entering the main duct 2- tubuloa...

Salivary glands Majd ismail sarairh Chapter 16 * Definition and description : Salivary glands are glands the ducts of which open into the oral cavity. 1- compound refers to the fact that a salivary gland has more than one tubule entering the main duct 2- tubuloacinar describes the morphology of the secreting cells 3- merocrine indicates that only the secretion of the cell is released 4- exocrine describes a gland that secretes fluid on to a free surface  *Salivary glands may be classified ❖ according to size : 1- major : parotid ,, sub mandibular ,, sublingual 2- minor : scattered throughout the oral mucosa and include the labial , buccal, palatoglossal, palatal and lingual glands. ❖ According to the types of secretion : mucous, serous or mixed. Note : Salivary glands are not present in the gingiva or the dorsum of the anterior two-thirds of the tongue *  PAROTID SUBMANDIBULAR SUBLINGUAL Type of Pure serous in adults, Mixed mostly serous Mixed mostly mucous Mixed serous in infant (80% serous) secretion and old Stenson’s duct Wharton’s duct bartholines duct Main duct Opposite U7 At side of lingual floor of mouth frenum Capsule Encapsulated Encapsulated Poor or non capsulated Secretion at rest 30% 60% 5% Notes -Fat cells spaces -The human sublingual gland is seen not a single unit : 1- a posterior -Lymph nodes are part (the greater sublingual situated both on the gland) usually drains into a main surface and within duct ( bartholin duct ) the parotid gland but 2- anterior part (the lesser are not found within sublingual gland) of 8–30 small the other salivary salivary glands drain through glands. (rivinus ducts) which are ( 8-20 ) smaller ducts that open directly into the overlying oral mucosa.  Parotid gland The largest salivary gland.  25% amount of secretion which is mainly serous in adults.  In newborn >>> mixed predominantly serous.  Duct: Stenson’s duct  Has capsule  Fat cells spaces seen  Submandibular gland Location : angle of mandible.. 60% of secretion The second largest of the salivary glands. Duct:Wharton’s duct  produces a mixed secretion , *serous more than mucous “ The gland has a well formed connective tissue capsule. The serous cells, duct system, myoepithelial cells and basal cells as described for the parotid gland also apply to the submandibular gland.  Sublingual gland Anterior floor of the mouth ,,, 5% secretion. The sublingual gland has been conventionally considered to be a mixed gland but with the majority of mucous elements. secrete spontaneously and continuously.  Minor salivary glands  -The minor salivary glands are classified by their anatomical location: -The palatoglossal glands are located in the region of the pharyngeal isthmus. --The palatal glands lie in both the soft and the hard palate. --The anterior lingual glands are embedded within muscle near the ventral surface of the tongue and have short ducts opening near the lingual frenulum. --The posterior lingual glands are located in the root of the tongue.  - It has been estimated that they may number between 450 and 750. and their secretion around 5-10%  -They are primarily mucous except for the serous glands of von Ebner, which drain into the trench of the circumvallate papillae  However, the minor salivary glands secrete spontaneously and continuously  - mucous secretion here is entirely mediated by parasympathetic nerve impulses. * Composition of Saliva is : over 99% water very small amount of additional inorganic and organic compounds (such as proteins, glycoproteins and enzymes) allows it to perform many important function  *Functions of saliva : 1. Lubrication: a major role is related to the production of mucin, which acts as a lubricant during mastication, swallowing and speech. The mucous film protects the mucosa and keeps it moist. 2.Taste : saliva brings substances into solution so that they can be tasted. 3. Buffering and maintenance of tooth integrity : limits the activity of bacteria by causing their aggregation. Saliva contains minerals and acts as a buffer; both features help to maintain the integrity of the dental enamel. 4.Wound healing and upper GI mucosal integrity : Peptide growth factors (e.g. epidermal growth factor, nerve growth factor) are produced by the submandibular gland. epidermal growth factor may be involved in wound healing and (together with mucin) maintaining gastro- oesophageal epithelial integrity. 5.Antimicrobial effect : Immunoglobulins (mainly IgA) are produced by plasma cells within the stroma of the salivary glands and secreted into saliva to function as part of a widespread mucosal immune system that also includes lymphoid tissue in the gut and bronchi 6.Digestion : amylase is present in saliva to aid digestion. Also present in saliva are kallikrein ( serine protease ) and blood group substances Saliva contains small quantities of numerous other proteins : 1-cystatin : inhibitors of harmful cysteine-proteinases produced by bacteria and dying neutrophils 2- lysozyme histatin and lactoferrin : antibacterial agents 3- statherin : inhibitor of mineralization 4-gustin : detection of taste. *Saliva flow rate There is a low level of secretion of saliva throughout the day, with periodic large additions from the major glands ( at meal times) an average salivary flow rate of 0.3ml/min  it has been calculated that 500–750 ml of saliva is secreted each day (with about 90% derived from the major salivary glands).  Methods of salivary secretion: Main regulated pathway constitutive pathway. Need stimuli Always active (no stimuli). Need 3.5 hour for synthesis Continuous flow. Proteins stored in granules Proteins Not stored in granules , but use vesicles ( Vesicular mechanism ) Mechanism of secretion : 1- The sublingual gland and the minor salivary glands spontaneously secrete saliva “ small amounts “ , but the bulk of this secretion is nerve-mediated. 2- The parotid and submandibular glands do not secrete saliva spontaneously and their secretion is entirely nerve- mediated. *Structure of salivary glands Salivary glands consist of two main elements: 1- the glandular secretory tissue (the parenchyma). 2- the supporting connective tissue (the stroma) ❖From the stroma of the capsule surrounding and protecting the gland pass septa that subdivide the gland into major lobes; lobes are further subdivided into lobules. ❖septa : 1- carry blood supply and nerve into the parenchyma 2- contain fibroblast,collagen,fat cells,plasma cells(secrete immunoglobulins) ❖Each lobe contains numerous secretory units consisting of clusters of grape-like structures (the acini) positioned around a lumen. ❖The acini of the parenchyma are responsible for the production of the saliva  The acinus, via its lumen, empties into an intercalated duct lined with cuboidal epithelium, which in turn joins a larger striated duct formed of columnar cells. The striated ducts empty into the collecting ducts  Both the intercalated and striated ducts affect the composition of the secretion passing through them.  Stroma of capsules >>> septa >>> lobes >>> lobules >>> acini >>> intercalated duct >>> striated duct >>> collecting duct >>> main duct A secretory acinus may be: 1- serous: (source of amylase ).. watery.. has more protein ,, less carbohydrate 2- mucous : viscous..proteins linked to a greater amount of carbohydrate, forming a more viscous, mucin-rich product. 3-mixed : the serous cells have been forming a cap outside the mucous cells ( serous demilunes) *Serous cell  Serous cells 1 - The cells have a wedge-shaped outline 2- The cell membrane shows numerous microvilli and infoldings and connect by Desmosomes , gap and tight junction 3 - The prominent nuclei are round and located in the basal third of the cell, which is basophilic (because of the presence of rough endoplasmic reticulum). 4- The luminal part of the cell contains dense, round secretory granules. 5- Over 99% of saliva is water. 6- Mitochondria within the cell supply the energy for the synthetic and secretory process. 7- The appearance of serous cells will clearly vary with the levels of secretory activity 8-Both parasympathetic and sympathetic fibers innervate the acini. NOTE >> Parasympathetic causes formation and secretion of secretory granules. sympathetic drive usually increases the output of preformed components from the cells. 9- have intercellular canaliculi *Mucous cell  Mucous cells 1- the cells are tubular in shape , The cell membrane shows fewer microvilli and infoldings. 2- their nuclei tend to be compressed into the basal part of the cell. 3- mucous cells have a more Golgi apparatus (because of the greater amount of carbohydrate that is added ). 4- the mucous acini are paler since their mucin content does not readily take up routine stains. 5- lack intercellular canaliculi. * Myoepithelial cells Location : lie between the basal lamina and the basal membranes of the acinar cells and the intercalated duct cells. Myoepithelial cells have : - desmosomal attachments with underlying parenchymal cells - gap junctions with adjacent myoepithelial cells - hemidesmosomal attachments with the basal lamina.  Myoepithelial cells around acini are : dendritic cells, consisting of a stellate- shaped body containing the nucleus and a number of long tapering processes radiating from it.  Around intercalated ducts : elongated, run longitudinally along the duct and have few, short, processes. Flattened nucleus Functional studies clearly indicate that myoepithelial activity can: support the underlying parenchyma. accelerate the initial outflow of saliva reduce luminal volume contribute to the secretory pressure help salivary flow to overcome increases in peripheral resistance.  the cell contains numerous contractile actin microfilaments about 7 nm in diameter Myoepithelial cells contract as a result of activity of both parasympathetic and sympathetic stimulation. Cell division may occur because CD44 is expressed on cell membrane  Duct system Intralobular : “inside” 1- Intercalated duct : A-The smallest and most distal , compressed between the acini. B- It drainages several acini and appears to contribute to the primary secretion. C-It is lined by cuboidal epithelial cells with secretory granules and small amounts of the organelles. D-The nuclei in the duct cells appear prominent and centrally located. E- Both luminal and basal surfaces of the duct cells are smooth and desmosomes unite adjacent cells. F -modify saliva by antimicrobial portion “ lysozyme and lactoferrin” 2- the striated ducts A. form a much longer and more active component of the duct system than the intercalated ducts. B. Lined by simple columnar epithelium C. The cells have a large amount of cytoplasm and a large spherical centrally positioned nucleus that makes them easy to identify D. anchored together by desmosomes and tight junction E. Basal surfaces separated from ct by basal lamina F. basal membrane > striation , Luminal surfaces > microvilli G. This large surface area, supplied with high levels of energy from the mitochondria, is clearly involved in active transport. H. The cells of the striated duct show small secretory granules on the luminal side that may contain epidermal growth factor, lysozyme, kallikrein and IgA.  Effect of striated ducts  The striated ducts are the site of electrolyte resorption (especially of sodium and chloride) and secretion (potassium and bicarbonate) without loss of water.  The effect on the material in the lumen is to convert an isotonic or slightly hypertonic fluid into a hypotonic fluid  Interlobular :  In addition to the columnar layer (which now lacks striations), the collecting duct situated in the interlobular region may have a layer of basal cells( bi-layered epi)  Have a ct adventitia  Near its termination the lining of the main duct becomes stratified as it merges with the stratified squamous epithelium of the surface oral epithelium. ❖ the intercalated and striated ducts modify the composition of the saliva (as well as transport it) and may be termed secretory ducts, the main function of the collecting ducts is to transport it. Parotid gland: intercalated ducts and striated ducts are long, narrow and branching Submandibular gland : The intercalated ducts are shorter and difficult to locate while the striated ducts are longer and more obvious , they both are less numerous compared to parotid Sublingual gland: the duct system is much less well developed than in the other major salivary glands and striated ducts are usually absent. The acini sometimes lead to intercalated ducts but these may be absent and the acini lead to collecting ducts, which lack the basal striations that characterize striated ducts. Minor salivary glands : have collecting ducts, but intercalated and striated ducts are generally absent. As a result >>no salt removal >>saliva is isotonic and rich in sodium  SALIVARY GLYCOPROTEINS The salivary glands contain a mixture of salivary glycoproteins that range from neutral to acidic.  This is easily demonstrated by staining with Alcian blue at pH 2.5, which stains any acidic groups present in the glycoproteins. This technique has shown that: 1) serous cells in the parotid gland contains neutral glycoproteins. 2.) mucous cells in the submandibular, sublingual and minor salivary glands contain mainly acidic glycoproteins. 3) serous cells in the submandibular gland contain a mixture of neutral and acidic glycoproteins 4) intercalated duct cells often contain glycoproteins that are a mixture of both neutral and acidic forms and 5) striated duct cells often contain neutral glycoproteins.  Calcium  Calcium is incorporated into the secretory granule during its formation in order that the negatively charged parts of the glycoprotein can be neutralized by the positive charge on the calcium. The more acidic the glycoprotein, the more calcium is needed.  the secretory granules of the mucous acini and the serous acini of the submandibular gland contain more calcium than those of the serous acini in the parotid gland.  the secretory granules of the striated ducts contain no demonstrable calcium.  The calcium in the secretory granules, when released, may precipitate on exposed phospholipids of damaged membranes to form sialomicroliths  Sialomicroliths  are small, hard masses that are only evident microscopically in the salivary glands and may occur in the parenchymal cells,lumina and stroma.  They contain variable amounts of both mineral (in the form of calcium phosphates, including hydroxyapatite) as well as non-mineralized components in the form of condensed organic secretory material. They remain small following their formation in small spaces and may be flushed away in saliva or removed by macrophages.  often associated with atrophic foci , and both increase in number with age. present in all normal submandibular glands and 20% of normal parotid glands. This frequency appears to relate to the higher concentration of calcium in the submandibular gland.  rare in sublingual glands and minor salivary glands where secretion is continuous and stagnation is less likely  BASAL CELLS  Basal cells have been implicated as potential stem cells during turnover and/or cell regeneration in salivary glands.  They are sparsely distributed in the striated ducts and more densely distributed in the collecting ducts, in which they form a continuous layer as the ducts pass further towards the hilum.  However, some cell division is seen in all parenchymal cell types, including myoepithelial cells and all these cells may be involved in salivary gland regeneration.  These cells can be distinguished from other parenchymal cells by a combination of their morphology, their coexpression of cytokeratin 14 and the antiapoptotic factor bcl-2, and a proliferative index of about 3% that is the highest of any cell in the region  Oncocytes Oncocytes are epithelial cells occurring singly or in small groups in the acini and ducts of normal salivary glands. This increase in numbers of mitochondria is accompanied by a great reduction in other types of organelle.  They are acidophilic , granular due to a large increase in the number of mitochondria.  Oncocytes increase with age and are thought to arise as the result of degeneration of normal cells.  AGE changes A wide range of age changes has been documented in salivary glands : 1- decrease in the amount of glandular tissue (number of secretory cells) 2- an increase in the amount of fibrous tissue, fat cells, inflammatory cells and oncocytes. 3- An increase in duct volume has also been described, although some of this increase may be due to shrinkage of acini. 4- With such a significant loss of parenchyma , it might be assumed that there would be a reduction in the amount of saliva ( hyposalivation) produced “ xerostomia ”. 5- there is an infiltration by lymphocytes to form lymphocytic foci in salivary glands that increases with age. What is the best statement describing these histological structures? 1. They are present in parotid gland. 2. Their secretion is rich in amylase. 3. They are carbohydrates secreting cells. 4. They contain numerous mitochondria. Resorption and secretion of electrolytes happened in ? 1.Main duct. 2.Intercalated duct. 3.Collecting duct. 4.Striated duct. Potential stem cells are? 1.Myoepithelial cells. 2.Basal cells. 3.Acini. 4.Oncocytes.