Salivary Glands- histology — Transcript

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1. 0:06Salivary glands are exocrine glands present  in the oral cavity which release saliva. If
2. 0:11we study their classification, salivary glands  have been classified according to their size,
3. 0:15as major salivary glands and minor salivary glands  or according to the type of saliva they secrete,
4. 0:20serous salivary glands, mucous salivary  glands and mixed salivary glands.
5. 0:24Development. Salivary glands are ectodermal in  origin. During embryogenesis, the epithelial
6. 0:30cells proliferate into the underlying  ectomesenchyme. This epithelial bud grows
7. 0:34with development of clefts, which results in the  formation of branches. This process of growth,
8. 0:40clefting and branching continues and is called  'branching morphogenesis' which requires the
9. 0:45epithelial mesenchymal interaction. The central  cells of this solid epithelial structure,
10. 0:49then undergoes degeneration for lumen formation.  The central cell degeneration occurs first in the
11. 0:55distal and proximal portion of the chords  and then in the middle portion. Finally,
12. 0:59the central cells of the acini undergo  degeneration for completing the lumen formation.
13. 1:05The first salivary gland to initiate development  is parotid gland around 5 weeks in utero,
14. 1:09then submandibular gland around 6 weeks in utero,  sublingual gland at 8 weeks in utero and all minor
15. 1:16salivary glands initiate development during the  3rd month of fetal life. Histologically speaking,
16. 1:21salivary glands have two main components, first  component is the secreting end pieces or acini,
17. 1:27which are small sac-like cavity. And second  component is the duct system. The acini produces
18. 1:33the saliva and the duct system carries the saliva  from the acini to the oral cavity. These secreting
19. 1:39end pieces or acini can be serous acini, mucus  acini or a serous demilune, which is a combination
20. 1:45of both. Whereas the duct system includes the  intercalated ducts, striated ducts and excretory
21. 1:51ducts. Apart from these, there are some cells  located adjacent the acini and intercalated ducts
22. 1:58called the Myoepithelial cells. The whole salivary  structure is lined by a basement membrane.
23. 2:04Let us start with the serous acini. Serous acini  are spherical in shape. On looking inside we see,
24. 2:118 to 12 serous cells, which are pyramidal in  shape, with their broad bases at the basement
25. 2:16membrane and apex towards the lumen. Now the  lumen is small and has finger like extensions
26. 2:21between the adjacent cells called intercellular  canaliculi. Serious cells are connected to each
27. 2:27other by various intracellular junctions and  to the basement membrane by hemidesmosomes.
28. 2:32If we take a closer look, the cell membrane of  these cells towards the lumen is not smooth but
29. 2:38shows numerous short microvilli. On looking inside  the cells we see a spherical nucleus placed at the
30. 2:44basal region, with most of the cell organelles,  like rough endoplasmic reticulum and gogli
31. 2:49complex, in the apical part. There is accumulation  of secretory granules, which are rich in proteins.
32. 2:56During routine staining these granules take up  stains strongly, making the cytoplasm appear dark.
33. 3:03Serous acini are seen in parotid glands,  von Ebner glands and submandibular gland.
34. 3:09Next, mucus acini. Mucous acini are usually  tubular in shape. On looking inside we see 10
35. 3:16to 16 mucous cells. The lumen is larger in size  but lacks the intercellular canaliculi. Mucous
36. 3:23cells are connected to each other by various  intercellular junctions and to the based membrane
37. 3:27by hemidesmosomes. If we look closely, we see the  cell membrane towards the lumen shows numerous
38. 3:33short microvilli. On looking inside the cell, the  major part of the cell is filled with accumulation
39. 3:38of secretory products. This secretary product  is mucus, which is rich in carbohydrates and it
40. 3:45pushes the nucleus in the basal part against the  cell membrane. Where it is oval and flattened in
41. 3:51shape, along with the rest of the cell organelles.  During routine staining mucuos does not take up
42. 3:57stain, as a result of which the cytoplasm appears  empty. Mucuos acini are seen in sub-mandibular
43. 4:04gland, sublingual gland and all minor  salivary glands, except the von Ebner glands.
44. 4:10Serous demilune. Serous demilune is formed  when serious acini and mucous acini are
45. 4:15present together. Serous demilune consist of a  mucous acini which is capped by a crescent-shaped
46. 4:20serous acini. It is always mucous acini capped  by a serious acini and never the serous acini
47. 4:26capped by a mucous acini. The mucous acini in  serous demilune, have intercellular canaliculi,
48. 4:33which are not normally seen in mucous acini. The  saliva from the serious acini passes through these
49. 4:40intracellular canaliculi and enters the lumen  of mucous acini, from where it enters the ducts.
50. 4:46They are predominantly seen in mixed  salivary glands like submandibular gland.
51. 4:51So that was about the various types of secretory  end pieces or acini. Now about the duct system.
52. 4:57The duct system of salivary glands is a varied  network of hollow tubules which connects the lumen
53. 5:03of secretary end pieces to the oral cavity. Let's  begin with the intercalated ducts. Intercalated
54. 5:09ducts are present just adjacent to the secretary  end pieces and are first to receive the saliva.
55. 5:14Their lumen is just wider than that of the acini.  In histology they sometimes appear pressed between
56. 5:21the acini, hence the name intercalated. These  ducts are lined by simple cuboidal epithelium.
57. 5:28That is, a single layer of cuboidal cells. Though  myoepithelial cells may be present adjacent to
58. 5:34these cells. The ductal cells have intercellular  junctions and desmosomes with myoepithelial cells.
59. 5:40On looking closely the apical surface or the surface towards the lumen has few short
60. 5:46microvilli. On looking inside the cells we see  a large rounded nucleus in the center, with cell
61. 5:52organelles around it. Few secretory granules are  present in the apical part of the cell which plays
62. 5:58a role in saliva modification. Striated ducts.  Saliva from the intercalated ducts drains into
63. 6:05these striated ducts and form the largest portion  of the duct system. The lumen is larger than that
64. 6:12of the intercalated ducts and are lined by simple  columnar epithelium. That is, a single layer of
65. 6:18tall columnar cells. They are joined together by  intercellular junctions and have short microvilli
66. 6:23on the apical surface of the cells. On looking  inside the cells the nucleus is spherical and
67. 6:29centrally placed with cell organelles around it.  Few secretory granules are present in the apical
68. 6:34part of the cell. The basal part of the cell shows  numerous elongated infoldings of cell membranes.
69. 6:41These cytoplasmic partitions are full of elongated  mitochondria, giving the cell an appearance of
70. 6:47having striations, hence the name striated  duct. Excretory ducts. Saliva from striated
71. 6:55ducts drains into the excretory ducts which then  open into the oral cavity. The overall diameter
72. 7:01of the ducts and the lumen is largest. These  ducts are lined by pseudostratified epithelium.
73. 7:06That is, a single layer of tall columnar cells,  which reach the lumen and basal cells, which do
74. 7:12not reach the lumen. They are joined together by  intercellular junctions and have short microvilli
75. 7:17in the apical surface. On looking inside, the  nucleus is spherical and centrally placed,
76. 7:22with cell organelles around it. The infoldings  of basal cell membrane is less pronounced.
77. 7:29Some other types of cells are also present in  the excreted ducts. Like, goblet cells, which
78. 7:34contain mucin. Tuft cells or brush cells with long  stiff microvilli and a nerve ending near its base.
79. 7:42As the excretory duct reaches the oral  cavity, the pseudostratified epithelium
80. 7:46transforms into stratified epithelium  and merges with the oral epithelium.
81. 7:52So that was about the various types of ducts  in the duct system. Now about the myoepithelial
82. 7:58cells. These cells are closely related to the secretary  cells and intercalated duct cells. They lie
83. 8:04between the acini or duct cells and the basement  membrane and are attached by desmosomes. Adjacent
84. 8:10the acini the myoepithelial cells are stellate  shaped, that is, they have long processes. If
85. 8:16we take a look at the acini from the outside,  the myoepithelial cells are present around it.
86. 8:21Imagine a player's hand around a ball. Due to  this shape they are sometimes also called as the
87. 8:27basket cells. Myoepithelial cells that are present  adjacent to the intercallated ducts are fusiform.
88. 8:34If we take a look inside the myoepithelial cells,  we see a flattened nucleus surrounded by most of
89. 8:40the organelles. The cytoplasm has actin filaments  just like smooth muscles and cytokeratin filaments
90. 8:46just like epithelial cells. These actin filaments  give myoepithelial cells the ability to contract.
91. 8:53Myoepithelial cells support the acini and prevent  any backflow of saliva. And when required,
92. 8:59by their contractile movement, squeeze the  secretary acini to increase the outflow of saliva.