anatomy of salivary glands Flashcards
1
Q
What are the 3 pairs of major salivary glands?
A
-parotid
-submandibular
-sublingual glands
2
Q
Parotid gland location
A
-wedged between mandibular ramus and its associated muscles in front and the mastoid process and sternocleidomastoid muscle behind
-superficial part of gland has inverted triangular outline and extends from zygomatic arch to angle of mandible
3
Q
How does parotid gland secrete saliva?
A
via parotid duct which opens into mouth through parotid papilla on buccal mucosa adjacent to upper second molars
4
Q
Submandibular gland location
A
-consists of a large superficial part, located in the neck on medial surface of mandible
-small deep part lying in posterior part of floor of the mouth on lateral part of tongue
5
Q
How does submandibular gland secrete saliva
A
-via submandibular duct which opens into the floor of the mouth through the sublingual papilla on one side of the attachment of lingual frenulum
6
Q
Location of sublingual gland
A
-found entirely on floor of mouth in front of deep lobe of submandibular gland
-in the second to the premolar region
-lies directly under the lining mucosa of floor of mouth which is raised as sublingual fold
7
Q
How does submandibular gland secrete saliva
A
onto floor of mouth through several tiny ducts on crest of sublingual fold
8
Q
Minor salivary glands
A
small collections of secretory issue embedded within submucosa through most of oral cavity
9
Q
How many salivary glands are there
A
450-1,000
10
Q
Where are salivary glands they not found??
A
-gingiva/dorsum of anterior 2/3 tongue
11
Q
How do salivary glands develop?
A
-proliferation of oral epithelial cells, forming localised thickening that grows into underlying ectomesenchyme
-continued growth leads to epithelial bud connected to surface by cord of epithelial cells, with mesenchymal cells condensing around bud
-oral-epithelium derived tissue forms the ducts and secretory elements of salivary gland
12
Q
Where do surrounding mesenchymal connective tissues of salivary glands derived from
A
neural crest
13
Q
What 2 elements do salivary glands consist of?
A
-glandular secretory tissue (parenchyma)
-supporting connective tissue (stroma)
14
Q
How do glandular secretory tissue and supporting connective tissue interact? In major salivary glands
A
-connective tissue forms a capsule that surrounds and protects the gland and septa subdivide the gland into major lobes
-secretory units in each lobe consist of clusters of grape-like structures 9acini) positioned around lumen
15
Q
What is acini?
A
-composed of secretory cells can produce the primary secretion which varies according to secretory cells within
16
Q
What does duct system do?
A
-collects and modifies the secretion through progressively larger ducts to a main duct which carries saliva to mucosal tissue
17
Q
What type of cells does acini contain?
A
-Acini contain either serous cells, mucous cells, or may be mixed.
18
Q
What is serous demilune?
A
-When mixed, the serous cells, in histologic sections, appear to form a cap termed a ‘serous demilune’, this arrangement has been shown to be the result of an artefact of preparation.
19
Q
What shape are acini?
A
-Acini tend to be spherical in shape, although those composed only of mucous cells appear to form tubes rather than spheres.
20
Q
What is intercalated duct
A
-first part
-Each group of secretory cells surround a lumen and empty into a small, duct termed an intercalated duct.
21
Q
What is striated duct
A
2nd part
22
Q
Serous acini vs mucous acini
A
-by the nature of the secretion they produce They produce a watery fluid that is more protein rich and has less carbohydrate than mucous cells. The mucous cells produce a more viscous, mucin-rich product.
23
Q
How can you distinguish serous and mucous by histology
A
- serous cells which appear darker from the paler mucous cells.
24
Q
What are contractile cells?
A
-Around the acini and intercalated ductal cells, contractile cells with several processes are present and represent the myoepithelial cells.
25
Appearance of serous acini
-Serous cells have a characteristic dark granular appearance with haematoxylin and eosin staining when viewed under a light microscope.
-The granular appearance results from the numerous refractile granules in the part of the cell adjacent to the lumen.
-The cells have a wedge-shaped outline, and are arranged like pizza slices around a narrow central lumen.
26
Inside cell structure
The nuclei, and rough endoplasmic reticulum, are located at the basal end of the cell next to the connective tissue from which they are separated by a basal lamina.
27
Where are capillaries
Capillaries are seen in close proximity to this surface
28
What is at the other end of these cells
The other end of these cells contain many dense, round secretory granules, in which the molecular components of saliva are stored and later release into lumen by exocytosis.
29
What happens during mastication
During mastication, the number of granules decreases significantly as they are discharged into the lumen due to reflex stimulation of salivation.
30
What re gap junctions
Gap junctions allow communication and coordination between adjacent serous cells and tight junctions control passage of water and certain ions between the cells.
31
Appearance of mucous acini
In routine light microscopy with haematoxylin and eosin staining, mucous acini appear as collections of pale cells since their mucin content does not readily take up these stains.
-However, when stains that reveal acidic glycoproteins, such as the periodic acid–Schiff stain, are used the secretory material is strongly stained.
32
Structure of mucous cells and lumen
-Secretory acini that are composed of mucous cells often have a tubular arrangement; when cut in cross section, these tubules have round profiles with mucous cells surrounding a central lumen of larger size than that of serous end pieces
33
Secretory granules
-the mucous cells display numerous secretory granules that are easily distinguished from those of serous cells by their pale appearance.
34
Nuclei of mucous cells
-The nuclei of mucous cells are round and centrally located when secretory granules have been discharged following stimulation of salivary secretion.
35
Unstimulated mucous cells nucleus
are filled with secretory granules and their nuclei are more peripherally placed. (pushed away)
36
What is demilune?
* -mucous acini have it at end of cell
Serous demilunes are the serous cells at the distal end of mucous tubuloalveolar secretory unit of certain salivary glands. These demilune cells secrete the proteins that contain the enzyme lysozyme, which degrades the cell walls of bacteria.
* -small portion of serous cells arranged in demilune, only at end of tubules
-Note that conventional fixation methods result in distension of the mucous secretory granules and cells; the nuclei are flattened and compressed into the basal part of the cell, and in mixed acini, the serous cells are displaced towards the basal portion of the acinus to form demilunes.
37
What are myoepithelial cells
-contractile cells associated with. the secretory acini and intercalated ducts of the salivary glands
-produce self contraction
38
Where are my-epithelial cells located
-between the basal lamina and the secretory or duct cells and are joined to the cells by desmosomes.
39
Structure of my-epithelial cells
-Myoepithelial cells around acini have a stellate-shaped body and branching processes which extend to surround the acinus. Around the intercalated ducts, the myoepithelial cells are elongated and have few, short, processes.
40
What is inside the my-epithelial cells
-The ultrastructure of these cells typically shows a flattened nucleus and bundles of contractile actin filaments within dendritic processes.
41
What do they do in parasympathetic and sympathetic stimulation?
-Myoepithelial cells have many similarities to smooth muscle cells but are derived from epithelium, they contract as a result of activity of both parasympathetic and sympathetic stimulation.
42
What does this contraction result in
-Contraction of the myoepithelial cells is believed to provide support for the acini during active secretion of saliva.
-They may also aid salivary flow from the acini into the duct system, control lumen volume and secretory pressure.
43
Duct system structure
-The duct system within salivary glands is a network of tubules that gradually increase in diameter, beginning at the secretory acini and extending to the oral cavity.
44
What are the Three types of duct
-the intercalated, striated and collecting ducts.
Intercalated and striated ducts role
-The intercalated and striated ducts are intralobular and affect the composition of the secretion passing through them.
-They modify the composition of the secretion (as well as transport it) and may be termed secretory ducts.
45
The function of the collecting ducts
-is the transport of saliva
46
Intercalated duct
-The intercalated duct is the smallest of the ducts and is usually compressed between several acini which drain into it.
-These ducts are lined by simple cuboidal epithelial cells which have prominent nuclei but little cytoplasm.
-Cells nearest to the acini contain secretory granules near their luminal surface, these contain macromolecular components, including lysozyme and lactoferrin, which they contribute to the primary secretion of saliva.
- Intercalated ducts vary in length within the different major and minor salivary glands.
-houses potential stem cells
47
Collecting ducts
-The collecting duct is the largest of the three ducts.
-It is located in the interlobular connective tissue.
-These ducts often have a pseudostratified epithelium with columnar and basal cells; only the columnar cells reach the lumen. In small glands e.g., minor glands these ducts drain directly onto the oral epithelium.
48
What are basal ducts
-As we have seen, basal cells are present in the collecting ducts; but these are also found less frequently in the striated ducts.
-They have been implicated as potential stem cells during turnover and/or cell regeneration in salivary glands.
-Basal cells may contain actin filaments similar to myoepithelial cells.
49
Where do striated ducts receive primary secretion from?
-The striated ducts receive the primary secretion from the intercalated ducts and make up the largest portion of the duct system.
50
Cells of striated ducts shape and charge
-The cells of the striated ducts have a large, centrally positioned nucleus copious pale staining cytoplasm.
-Columnar cells of striated duct
-The columnar cells of the striated duct are highly polarised.
51
What do the columnar cells luminal surfaces have? (striated)
their luminal surfaces have short microvilli while
52
What dot heir basal surfaces have
their basal surfaces, adjacent to the basal lamina, separating it from the adjacent connective tissue, provides a large surface area, supplied with high levels of energy (large numbers of mitochondria).
53
What happens at striated ducts
-modification of saliva
-The striated ducts are the site of electrolyte resorption (especially of sodium and chloride) and secretion (potassium and bicarbonate) without loss of water.
-The primary secretion is converted from isotonic or slightly hypertonic (with concentrations similar to those in the plasma) to hypotonic.
54
Where is parotid gland enclosed in?
-parotid capsule
55
What do parotid gland connective tissues form?
-septa, containing blood vessels, nerves, lymph nodes and collecting ducts
56
Acini of the gland
-are serous, although mucous cells are occasionally present
-Fat cell spaces and nuclei of myoepithelial cells may be visible.
57
Intercalated ducts
-Intercalated ducts are numerous and long in the parotid gland. The striated ducts are numerous and appear as round, or elongated tubules of larger diameter.
58
Submandibular glands type of secretion
-The second largest of the salivary glands, the submandibular gland, produces a mixed serous/mucous secretion.
-Serous cells produce a watery protein-rich fluid whereas mucous cells produce a more viscous, mucin-rich product containing proteins linked to a greater amount of carbohydrate.
59
What do their connective tissues form?
-The submandibular gland has a well-formed connective tissue capsule.
60
The serous acini are
more numerous and have similar structure to those found in the parotid gland.
61
The mucous secretory cells in the submandibular gland
-are pale-staining and form tubular acini. The intercalated ducts are shorter, and the striated ducts are longer and more noticeable
62
What is the sublingual gland and how is it enclosed
-The sublingual gland is the smallest of the major salivary glands and is not completely enclosed by a connective tissue capsule.
63
What does sublingual glands consist of
-The gland is said to consist of 7 to 15 small salivary glands, each having its own duct system
How do they empty
emptying via the crest of the sublingual fold.
64
Is sublingual glands serine/mucous?
-The sublingual gland is usually considered to be a mixed gland in which mucous acini predominate. -Histologically, at the light microscope level, it is seen to consist of many groups of pale staining mucous cells with darker staining so-called serous acini and demilunes.
-However, recent research has shown that the serous cells in this gland may be immature mucous cells.
65
Duct system sublingual
The duct system is much less well developed than in the other major salivary glands
-Striated ducts are usually absent.
66
How do acini drain in sublingual?
-The acini sometimes drain into intercalated ducts, but these may also be absent; the acini therefore usually drain directly via collecting ducts to the mucosal surface on the floor of the mouth.
-The sublingual gland tissue therefore drains through several small ducts (ducts of Rivinus) that open directly into the overlying oral mucosa. Part of the gland tissue may drain via the submandibular duct and into the sublingual papilla.
67
What are minor glands
-comprise small aggregates of secretory acini and associated duct(s
-organised into lobule-like structures and located in the submucosa or between the muscle fibres of the tongue.
68
Duct system of minor glands
-These glands have collecting ducts, but intercalated and striated ducts are usually absent. The short ducts draining individual glandular aggregates open directly onto the mucosal surface.
69
Are minor glands mucous/serine?
-They are mucous glands except for the serous glands of von Ebner, which drain into the trench of the circumvallate papillae, which are located in front of the sulcus terminalis on the dorsum of the tongue. Note that their secretions are released in regions with significant numbers of taste buds.
70
The anterior lingual glands location
-are embedded within muscle near the ventral surface of the tongue and have short ducts opening near the lingual frenum.
71
The posterior glands location
in the root of the tongue.
72
Minor glands names
present in the buccal and labial mucosa, as well as the soft palate, lateral zones of the hard palate, and the floor of the mouth.
73
When do minor glands secrete
-The minor salivary glands secrete spontaneously and continuously and have an important role in protecting and moistening the oral mucosa, especially at night when the major salivary glands are mostly inactive (except the sublingual glands which also secrete spontaneously).
74
How are salivary glands specified?
-according to their size (major and minor) and/or the types of secretion they produce (mucous, serous or mixed).
75
Types of secretion
-two types of secretion; a watery or ‘serous’ secretion or a more viscous ‘mucous’ secretion (or a mixture of both). This can constitute a simple form of classification, i.e., serous, mucous or mixed.
76
Size specification
-The classification according to size divides the glands into ‘major’ or ‘minor’.
-The major glands are essentially discrete structures which are completely or largely enclosed by a connective tissue capsule and can be isolated as distinct structure.
-The minor glands are found throughout the oral mucosa and are small, less discrete structures.
77
Parotid type
-100% serous
78
Submandibular type
mixed, ratio of serous to mucous is 10:1
79
Sublingual
Mixed, serous to mucus is 1:10
80
Minor glands
-100% mucous excepts glands of von Ebner which are minor serous producing glands
How are minor salivary glands classified?--by anatomical location e.g. buccal/labial
81
Compostiijn of saliva
-Saliva is over 99% water, yet the very small amount of additional inorganic and organic compounds allows it to perform many important functions.
82
Digestion
It initiates digestion via the amylase which it contains, although it is worth noting that this may be more to do with breaking up food remnants between and around teeth than initiated digestion itself.
83
Protection against bacteria
It contains numerous substances which combat bacterial colonisation (by bacterial killing or by inhibiting binding of bacteria to oral surfaces)
-mucosal immunity via immunoglobulins (mainly IgA)
- maintenance of oral homeostasis via various other proteins,
-enzymes and growth factors (may be important in wound healing).
84
remineralisation
Saliva helps to maintain the integrity of the dental enamel via its content of minerals to aid remineralisation (calcium and phosphate) and its bicarbonate ions (buffering plaque acid)
85
lubrication
-It contains lubricants to aid mastication, swallowing and speech and also provides a medium for food to dissolve to allow constituent compounds to enter the taste buds.
86
wound healing
saliva contains high levels of certain growth factors, for example epidermal growth factor. This potentiates epithelial cell proliferation and may be a significant factor in wound healing.
87
Change of saliva gland due to age
-generalised reduction in the amount of secretory tissue
-a proportional increase in connective tissue.
-Fat and inflammatory cells are also seen to increase with age.
88
Changes in duct system
-an increase in non-striated intralobular ducts
-dilatation of extralobular ducts as well as generalised degenerative changes.
89
Is there a reduction in saliva?
-In healthy, unmedicated individuals, there does not appear to be a reduction in the amount of saliva produced in older individuals possibly due to salivary glands capacity to produce more saliva than is required under normal circumstances.
90
Clinical diagnosis
-Age changes need to be taken into account when examining the salivary glands histologically in clinical diagnosis;
-changes such as infiltration by lymphocytes to form lymphocytic foci can affect the histological picture, when tissue samples taken from patients by biopsy, are examined thus making diagnosis of some conditions more challenging.
91
Blockage
Blockage may occur of the main collecting duct of a major salivary gland.
-The cause may be a sialolith (stone).
-The patient may report transient painful swelling on the affected side of the jaw at mealtimes.
-On examination you may notice that saliva cannot be expressed from the parotid or submandibular papilla.
92
Sjogren's syndrome
dry mouth due to Sjögren's syndrome, an autoimmune condition affecting exocrine glands.
-This causes progressive loss of salivary function from lymphocyte infiltration of the gland and the gradual replacement of acinar cells.
-Loss of gland function can also occur following radiation therapy for head and neck cancer
93
Submucosal swelling
Damage to the ducts of minor and sublingual salivary glands may result in the escape of mucus into the surrounding soft tissues.
-When this persists, a mucocele is formed and presents as a submucosal swelling.
94
Facial paralysis:
Accidental injection into the parotid gland capsule while administering mandibular block anaesthesia can result in anaesthesia of the facial nerve and transient facial paralysis.
-Therefore, knowledge of the anatomy and careful technique are vital for safe clinical practice.
