Seminar part 2 salivary gland

Presented by

Dr. Shrikant Sonune

Guided by

Dr Ashok Patil,

Dr Shilpa Kandalgaonkar,

Dr Mayur Choudhari,

Dr Suyog Tupsakhare,

Dr Mahesh Gabhane.

Content Introduction Histology of salivary glands.

Parotid gland Submandibular gland Sublingual gland Minor salivary gland

Structure of terminal end pieces Ductal system Formation of saliva Composition of saliva Function of saliva. Clinical considerations. References

Histology of major salivary glandsSalivary glands consist of secretory end pieces that are composed of

1. Serous cells

2. Mucous cells

3. Mucous end pieces capped by serous demilunes

Histology of major salivary glands

System of ducts

1. Intercalated, intralobar

2. Striated

3. Excretory– interlobular.

that modify the saliva produced by the end pieces and convey it to the oral cavity.

Contractile myoepithelial cells are distributed around the end pieces & intercalated ducts.

The gland is supported by connective tissue, which carries the nerve, vascular & lymphatic supplies to the parenchymal component

Histology of major salivary glands

Parotid glands The spherical secretory

end pieces are all serous

Pyramidal shaped acinar cells have a spherical, basally situated nucleus & surround a small, central lumen.

Fat cell spaces often are seen in sections of the parotid gland.

Parotid glands The intercalated ducts

lined by Cuboidal epithelial cells & have Lumina that are larger than those of acini.

The striated ducts -numerous and appear as singly acidophilic, round or elongated tubules of larger diameter than the end pieces.

The duct consist of simple columnar epithelium, with round centrally placed nuclei.

The Lumina are large relative to the overall size of the ducts.

Parotid glands

Submandibular Serous end pieces &

mucous tubules capped with serous demilunes, thus it is mixed gland.

Serous cells significantly outnumber the mucous cells.

Pyramidal shaped acinar cells have a spherical, basally situated nucleus & surround a small, central lumen.

The mucous cells are filled with pale staining secretory material & little cytoplasm is usually visible.

Lumina of mucous tubule are larger than those of serous end pieces.

Submandibular

Serous demilune cells are similar in structure but discharge their secretions into small intercellular canliculi that extend between the mucous cells to reach the tubule lumen.

The intercalated and striated ducts are less numerous than those in the parotid gland, but otherwise they are structurally similar.

Submandibular

Sublingual

It is also a mixed gland, but mucous secretory cells predominate.

Serous end pieces may be present, they are rare.

The intercalated ducts are short and difficult to recognize.

Interlobar ducts are fewer in number than in the parotid or submandibular glands.

Minor salivary glands Minor salivary glands are found

throughout the oral cavity, except in the anterior part of the hard palate & the gingiva.

These glands consist of aggregates of secretory end pieces & ducts, organized into small lobule like structure located in the submucosa or between muscle fibers of the tongue.

The minor gland saliva typically rich in mucins

Minor salivary glands The ducts draining individual glandular aggregates

usually open directly onto the mucosal surface.

The secretory end pieces of most minor glands are mucous or have a small serous component arranged as occasional demilune.

In contrast to the usual situation in minor glands, the lingual serous glands (of vonEbner) in the tongue below the circumvallate papillae are pure serous glands

Minor salivary glands Functional importance

The minor glands exhibits a continuous slow secretory activity & thus have important role in protecting and moistening the oral mucosa, especially at night when the major salivary glands are mostly inactive.

Serous acini They are predominant in parotid gland. The acini are

made up of serous cells.

They have all the features of a cell specialized for the synthesis, storage, and secretion of protein.

Serous cells produces proteins & glycoproteins many of which have well defined enzymatic, antimicrobial, calcium binding, or other activities.

Serous acini Serous cells are approximately

pyramidal in shape with broad base resting on a thin basal lamina & its narrow apex bordering on the lumen.

Nucleus is spherical located in basal region of cell occasionally binucleate cells are observed.

Their nuclei vary in shape and position, but are more rounded and situated less basally than in mucous cells.

Most prominent feature of the serous cell is the accumulation of secretory granules in the apical cytoplasm.

In routine histological preparations, apical portion of the cell may appear as an acidophilic mass.

Serous acini

The basal portion of the cytoplasm is filled with rough endoplasmic reticulum. Specially cells that produces large amount of protein for secretion, the rough endoplasmic reticulum is well develop & arranged in parallel stacks, usually basal & lateral to nucleus.

Serous acini

Golgi apparatus is located apical or lateral to the nucleus.

The newly synthesized secretory proteins within RER are transported to the Golgi apparatus via small vesicles.

Serous acini

Proteins are packed into vacuoles of different size & density of these granules are forming secretory granules & are called immature granules, presecretory granules, condensing vacuoles.

After that the increase in density of the secretory material suggests that it is being concentrated as it is being transported & packed for storage in granules.

Serous acini

After variable period of storage in cell apex, they are discharge by exocytosis at the secretory surface of the cell.

Serous acini

Apically, the cytoplasm is filled by proteinaceous secretory (zymogen) granules with high amylase activity.

Serous acini

MUCOUS ACINI Mucous acini are made

up mucous cells and are present in mucous and mixed salivary glands.

They produce store, and secrete proteinaceous material and smaller enzymatic component.

Mucous cells typically have tubular configuration when cut in cross section these tubules appears as round profile with mucous cell surrounding a central lumen of larger size than that of serous end pieces.

MUCOUS ACINI

In routine histological preparations the apex of the cell appears empty except for thin strands of cytoplasm compressed against the base of the cell.(empty appearance to the supra-nuclear cytoplasm.)

MUCOUS ACINI

Most prominent feature of mucous cells is the accumulation in the apical cytoplasm of large amounts of secretory product (mucus).

Droplets are usually larger than serous granules & may be irregular or compressed in shape.

MUCOUS ACINI

Secretory product differ from those of serous cell in

They have little or no enzymatic activity.

Contains more amount of carbohydrate.

They serve mainly for lubrication & protection of oral tissue.

MUCOUS ACINI

The nucleus of mucous cell is oval or flattened in shape located just above the basal plasma membrane

The rough endoplasmic reticulum is limited to narrow band of cytoplasm along the base & lateral borders of cell & to an occasional patch of cytoplasm, mitochondria, Golgi apparatus are dispersed in the same loci.

MUCOUS ACINI

Golgi apparatus plays an important role in these cells because of the large amount of carbohydrates that it adds to the secretory products.

MUCOUS ACINI

Mucous cells have large Golgi complex, located mainly basal to the mass of secretory granules. Small granules form at the trans face of Golgi complex, increase in size, & join the rest of granules stored in the apical cytoplasm.

MUCOUS ACINI

Mucous cells are joined by a verity of intercellular junctions. Unlike serous cells, however mucous cells lack intercellular canliculi, except for those covered by deminule cells.

MUCOUS ACINI

SEROUS DEMILUNE: crescents of Giannuzzi ,(crescents of Heidenhain) Occasionally and in particular in glands located relatively

close to the oral cavity, serous cells and mucous cells may form compound or mixed acini.

The serous cells form in these cases small half-moon or crescent-shaped structures, which is known as serous demilune.

It is attached to mucus producing acini and empties their secretory product into interstices between the mucus-producing cells.

These serous deminule cells are in all respects similar to the serous end piece cells present in the same gland.

Their secretions reach the lumen of the end piece through intercellular canliculi extending between the mucous cells at the end of tubule.

MYOPITHELIAL CELL: Myoepithelial cells are

contractile cells associated with secretory end pieces and with much of the ductal system.

They lie between the basal lamina and the epithelial cells proper. They extend numerous cytoplasmic processes around serous acini and are often termed basket cells.

MYOPITHELIAL CELL: Myoepithelial cells

associated with ducts are more fusiform in shape, and are aligned along the length of the duct.

Their cytoplasm contains abundant actin microfilaments which mediate contraction under the control of both sympathetic and parasympathetic stimulation.

MYOPITHELIAL CELL: The outflow of saliva is

thus accelerated through reduction in the luminal volume of secretory end pieces and ducts, contributing to the secretory pressure.

Contraction of the myoepithelial cells thought to provide support for the end pieces during active secretion of saliva.

MYOPITHELIAL CELL: They provide signals to the acinar secretory cells that

are necessary for maintaining cell polarity & the structural organization of secretory end piece.

Myoepithelial cells produces a number of proteins that have tumour suppressor activity such as proteinases inhibitors (tissue inhibitor of metalloproteinase) & anti angiogenesis factors & these cells may provide a barrier against invasive epithelial neoplasms.

Ductal System A salivary gland consists of a series of branched

ducts, terminating in spherical or tubular secretory end pieces or acini.

The main excretory duct, which empties into oral cavity, divides into progressively smaller interlobar and intralobular excretory ducts that enter lobes and lobules of the gland.

Ductal system The three classes of

ducts are intercalated, striated & excretory each with differing structure & function.

Ductal system actively participates in the production & modification of saliva.

Intercalated Ducts The first cells of the intercalated duct are directly

adjacent to the secretory cells of the end pieces, and the lumen of the end pieces is continuous with the lumen of the intercalated duct.

The intercalated ducts are lined by a simple Cuboidal cells, & myoepithelial cell bodies & their process typically are located along the basal surface of the duct.

The overall diameter of the intercalated ducts is smaller than that of the end pieces, & their Lumina are larger than those of the end pieces.

Intercalated Ducts Several ducts draining individual end pieces join to

form larger intercalated ducts before empting into the striated ducts.

The intercalated ducts cells have centrally placed nuclei & a small amount of cytoplasm containing some rough endoplasmic reticulum & small Golgi complex.

Intercalated ducts often are difficult to identify in routine histologic sections.

Intercalated Ducts

The intercalated ducts contribute macromolecules which are stored in their secretory granules to the saliva. These components involve lysozyme and lactoferrin, along with the other unknown component.

A portion of the fluid component of the primary saliva likely is added in the intercalated duct region.

Undifferentiated cells, thought to represent salivary stem cells, are believed to present in the intercalated ducts. These cells may proliferate & undergo differentiation to replace damage or drying cells in the end pieces & striated ducts.

Striated Ducts The striated duct, constitute the largest portion of

ducts are the main Ductal component located within the lobules of the gland, that is intralobular.

The overall diameter of the ducts is greater than that of the secretory end pieces & lumen is larger than those of the secretory end pieces & intercalated ducts.

The basal lamina encloses the striated duct, & a capillary plexus is present in the surrounding connective tissue.

Striated duct cells are columnar with centrally placed nucleus & pale, acidophilic cytoplasm.

Striated Ducts The apical cytoplasm may contain small secretory granules

& electron lucent vesicles.

The presence of vesicles suggests that the cells may participate in endocytosis of substances from the lumen.

Numerous lysosomes and peroxisomes and deposits of glycogen frequently are present in perinuclear cytoplasm.

Adjacent cells are joined by well developed tight junctions & junctional complexes but lack gap junctions.

An important function of striated duct cell is modification of the primary saliva by reabsorption and secretion of electrolytes.

Excretory ducts The excretory ducts are located in the connective

tissue septa between the lobules of the gland, thus it is having extra lobular & inter lobular locations.

These ducts are larger in diameter & than striated ducts and typically have Pseudostratified epithelium with columnar cells extending from the basal lamina to the Ductal lumen

Small basal cells that sit on the basal lamina but do not reach the lumen.

Excretory ducts The epithelium of main excretory duct may become

stratified near the oral opening.

In the smaller excretory ducts the structure of the columnar cells is similar to that of the striated duct cells.

The basal cells have a high rate of proliferation.

Other type of cell include1. Tuft (caveolated or brush) cells, with long stiff microvilli &

apical vesicles, are thought to be receptor cells of some type. Nerve endings occasionally are found adjacent to the basal portion of these cells.

2. Lymphocytes & macrophages- cells with pale cytoplasm an dense nuclear chromatin may be found toward the base of the duct epithelium.

3. Dendritic cells – the cells have long branching processes that extend between the epithelial cells. These are antigen presenting cells, that are involved in immune surveillance & the processing & presentation of foreign antigens to T lymphocytes.

Connective tissue The connective tissue of salivary glands includes a

surrounding capsule, variably developed, that demarcates the gland from adjacent structure.

Septa that extends inward from the capsule divide the gland into lobes and lobules and carry blood vessels and nerves that supply the parenchymal components and the excretory ducts that convey saliva to the oral cavity

The cells of connective tissue include fibroblasts, macrophages,mast cells, plasma cells, adipose cells and occasionally granulocytes and lymphocytes.

Connective tissue Collagen and elastic fibers along with the

glycoproteins and proteoglycans of the ground substance constitute the extracellular matrix of the connective tissue.

Within the lobules of the gland, finer partitions of connective tissue extend between adjacent secretory end pieces and ducts.

These partitions carry the arterioles, capillaries and venules of the microcirculation & the finer branches of the autonomic nerves that innervate the secretory & Ductal cells.

Nerve supply

Within the gland lobule, branches of the nerves follow the blood vessels, eventually forming a plexus of unmyelinated fibers adjacent to arterioles, ducts and secretory end pieces.

Blood supply Salivary glands necessities an extensive blood supply.

One or more arteries enter the gland & give rise to smaller arteries & arterioles, exist around the excretory ducts.

The arterioles break up into capillaries that are distributed around the secretory end pieces & striated ducts.

An extensive capillary plexus also arising from separate arterioles exist around the excretory ducts.

The endothelium of the capillaries & post capillary venules is fenestrated.

The venous return generally follows arterial supply.

Formation of saliva. The formation of saliva occurs in two stages

In 1ststage cells of secretory end pieces & intercalated ducts produce primary saliva.

In the second stage the primary saliva is modified as it passes through the striated and excretory ducts, mainly by reabsorption & secretion of electrolytes.

The final saliva that reaches the oral cavity is hypotonic.

MACROMOLECULAR COMPONENTS The cells of the secretory end pieces, Secretory

proteins are synthesized by ribosome attached to the Cisternae of the endoplasmic reticulum and translocated to the lumen of the endoplasmic reticulum.

The proteins are transferred by small vesicles to the Golgi complex, where they undergo further modification, followed by condensation as packaging into secretory granules.

MACROMOLECULAR COMPONENTS The secretory granules are stored in the apical

cytoplasm until the cell receives an appropriate secretory stimulus. The contents are released into lumen by process of exocytosis.

The effective stimulus for exocytosis is nor epinephrine (sympathetic neurotransmitter).

Fluid & electrolytes Secretion of water by the cells of the secretory end

pieces is regulated by the parasympathetic innervations.

Hypertonic secretion draws ions in to the luminal spaces. That draws the water from the cells to luminal spaces by active mechanism.

Composition of saliva

Parameter Characteristics

Volume 600-1000 ml/day

Electrolytes Na+ ,K+ ,Cl- , HCO3- ,Mg++

HPO4-- ,SCN- , F-

Secretory proteins Amylase, proline richproteins,mucins,histatins,cystatins,peroxidase, lysozyme, lactoferrin

Immunoglobulins IgA, IgG, IgM

Small organic molecules Glucose, amino acids, urea, uric acid and lipids

Other components Insulin, serum albumin

Function of saliva Protection-Clearance, lubrication, thermal & chemical

insulation, pellicle formation, tannin binding.

Buffering – ph maintenance, neutralization of acids.

Tooth integrity- enamel maturation & repair.

Antimicrobial activity- physical barrier, immune defense, non immune defense.

Tissue repair -wound healing, epithelial regeneration.

Digestion -bolus formation, amylase, lipase

Taste-solution of molecules, maintenance of taste buds

Clinical consideration Age changes

Disease

Structural (histogenesis of various diseases).

Functional condition

Age changes Generalized loss of parenchymal tissue.

Lost salivary cells often replaced by adipose cells.

Increase in fibrous connective tissue.

Decrease in production of saliva.

Diseases Affected by local, systemic disease

Endocrine, autoimmune, infectious disease.

Developmental malformation Aplasia.

Atresia.

Stafnnes cyst.

Fordyce's granules.

Functional condition Xerostomia

Ptylism

References Ten Cate’s Oral histology Development, Structure and

Function Sixth Edition

General Anatomy 3rd vol. by B. D. Chaurasia

Textbook of Human Histology Inderbir Singh

Textbook of Oral and maxillofacial Surgery by NeelimaMalik

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