L13

Question 1

Notes:Regardless of whether the gland is serous, mucous, or mixed, the acinus or secretory endpiece has several common features:

Answer 1

it is comprised of a cluster of acinar cells surrounding a central lumen. There are spaces between the cells (called inter-cellular spaces) and the cells are also joined by tight junctions. Together the tight junctions and intercellular spaces allow the passage of water and small ions but restrict the passage of larger molecules.

Question 2

You should also notice that the end of the acinar cell that faces the lumen contains

Answer 2

secretory granules. Surrounding the acinar cells is another type of cell called a myoepithelial cell. Finally, the entire endpiece is surrounded by a basal lamina.

Question 3

Notes:Serous cells in the parotid secrete

Answer 3

amylase,

Question 4

serous cells in multiple glands secrete

Answer 4

PRP’s; however,

Question 5

serous cells do not secrete

Answer 5

mucins in appreciable amts.

Question 6

Just remember, ducts have the larger most obvious

Answer 6

lumen and the lumen associated with the acini are very small, virtually imperceptible at this magnification.

Question 7

A major job of the mucous cell is to secrete

Answer 7

mucins, high MW, heavily glycosylated glycoproteins, that are NOT secreted by serous cells but which are CRITICAL for lubricating the oral surface. Because of the biochemical characteristics of mucins, the secretory granules that contain them are more pale-staining (in both H&E stained sections and electron micrographs) than the secretory granules of serous cells.

Question 8

Mucous granules occupy most of the

Answer 8

apical part of the cell facing the lumen.

Question 9

Note that in several cases, multiple mucous granules appear to be

Answer 9

fused. This apparent fusion is probably an artifact of the fixation technique; in reality, mucous granules are thought to remain as separate entities within the cell.

Question 10

There are parts of 3 mucous cells, topped by

Answer 10

Notes:More detail of this arrangement at the EM level There are parts of 3 mucous cells, topped by 3 serous cells; because of their position on top of the mucous cells, this arrangement is called a “serous demilune”. Note that this section, like most of those that we view in this class, were prepared by conventional fixation in a formaldehyde-based solution. It turns out that the serous demilune, as well as some of the other classically-described differences in the appearance of serous and mucous cells may be an artifact of these conventional fixation techniques.

Question 11

As the name implies, a myoepithelial cell is a

Answer 11

specialized epithelial cell with contractile properties. *It typically has a number of processes and these wrap around the acini and ducts.

Question 12

Myoepithelial cells are said to be

Answer 12

innervated & function in expelling saliva into the ductal system

Question 13

Three types of ducts are associated with salivary glands:

Answer 13

In the major glands the acini open into the intercalated ducts, which lead to the striated ducts (also called secretory) and then finally to the excretory (which are also called collecting) ducts. The excretory ducts empty directly into the oral cavity.

Question 14

The intercalated duct is the

Answer 14

smallest duct- often several different acini drain into a given intercalated duct. Intercalated ducts are usually quite short. The cells that make up the intercalated duct are cuboidal in shape with a centrally placed nucleus. The major function of the intercalated duct is simply to convey saliva, but they do secrete a few antimicrobial proteins (Interestingly, but FYI only: 2 antimicrobial proteins are secreted by the intercalated duct– lysozyme, which acts on bacteria by breaking down cell walls & lactoferrin– which exhibits antiviral and antifungal, in addition to antibacterial activity).

Question 15

Intercalated ducts lead directly to

Answer 15

striated ducts. Not only are striated ducts longer, they are also more active. Importantly, they are a site of reabsorption- they take up sodium & chloride from the primary secretion & are thus are responsible for the fact that the saliva that reaches the mouth is hypotonic. Because this reabsorption is against a concentration gradient, it is an energy-requiring process for which ATP is critical.

Question 16

Not only are the striated ducts a site of

Answer 16

reabsorption, like intercalated ducts, they secrete a few proteins, and important to remember, they ALSO secrete bicarbonate, which is vital for the buffering action of saliva.

Question 17

Morphology of striated duct cells is distinctive-

Answer 17

tall columnar cells that are highly polarized. At their apical end, they have short microvilli & but their basal end is characterized by numerous infoldings of the basolateral membrane which give rise to a somewhat striped or striated appearance. These striations provide a large surface area for the reabsorption that takes place in these ducts. At the EM level it is also obvious that these cells have particularly prominent mitochondria; I’ll just mark a few of them here*.

Question 18

Finally, we come to the excretory ducts- these have the primary purpose of

Answer 18

simply carrying the saliva to the oral cavity- no notable secretion or reabsorption occurs here. The excretory ducts consist of a series of ducts that become progressively wider as they get closer to the oral cavity. As they get wider and closer to their junction with the oral epithelium, their histologic character also changes from a single epithelial layer to pseudostratified epithelium.

Question 19

Sometimes the final part of the excretory duct becomes .

Answer 19

stratified and keratinized