The Physiology of Salivary Glands

Question 1

What type of glands are salivary glands?

Answer 1

Exocrine (require a duct).

Question 2

What do salivary glands secrete onto?

Answer 2

Mucosal surfaces

Question 3

What happens without salivary glands?

Answer 3

Tongue papillae have become very sore
Cervical caries
Dental mirror sits to ventral surface of tongue (underside surface)

Question 4

Explain the main ducts of each of the major salivary glands

Answer 4

Major duct of the parotid gland is the Stenson’s duct.

Main duct for submandibular is the Wahrtin’s duct.

Sublingual gland has a series of ductal opening. These are the ducts of Rivinus.
Sublingual caruncles deliver the saliva from the sublingual gland to the oral cavity.

Question 5

What does the ductal system look like?

Answer 5

Main duct arising and then as it reaches the body of the gland, it branches into the ductal tree.
Secretary units at the end of the ducts that give rise to saliva.

Question 6

Explain the basic function of the salivary gland

Answer 6

The acinar cells produce saliva and secrete saliva initially into thin ducts (intercalated duct). Saliva moves through the ductal system passing through the striated ducts and then into the excretory ducts.

Striated ducts have invaginations of the basal plasma membrane and have lots of mitochondria in basal cytoplasm.

Acinar cells are surrounded by myoepithelial cells. Myo-epithelial cells stabilise the acinus when is secretes, preventing the acinar cells becoming expanded due to pressure, important in maintaining the stable structure of the acinar units.

The acinar cells are filled with dark staining granules which are secreter granules containing salivary proteins which are secreted into saliva.

Question 7

Explain the location of the minor salivary glands

Answer 7

Minor salivary glands are present in the submucosal surface.
They are therefore close to the epithelium with short ducts delivering saliva.
They are present in the lamina propria and consist of secretory units of 1-2mm and present under most mucosal surfaces.

Labial minor glands have beads of saliva representing one minor labial gland. These are used for diagnosing Sjogrens syndrome.

Question 8

Explain the reflex of salivary secretion

Answer 8

1. Begins by oral stimuli - taste, mastication, olfactory, thermal or painful stimuli.
2. This can activate taste buds and this gives rise to afferent signals in sensory signals which are conducted to the brain stem.
3. From here, to the CNS and delivers signals to the salivary nuclei or down the thoracic spinal cord.
   This process is modulated by signals from the cortex of the brain.
4. From the salivary nuclei, they are parasympathetic efferent nerves delivering signals to the different major glands.
   From the thoracic spinal cord, nerve signals sending efferent sympathetic nerves deliver signals to the submandibular and parotid glands.
5. Saliva is then secreted from the glands into the mouth.

Question 9

What types of nerves work together to cause saliva secretion?

Answer 9

Parasympathetic and sympathetic autonomic nerves work together (online the rest of body) to enhance saliva secretion. There is no peripheral inhibition of salivary secretion.

Question 10

Where do signals come which inhibit salivary secretion?

Answer 10

From the cortex.

Question 11

What cranial nerves are important in salivary secretion signals?

Answer 11

5, 9 and 12

Question 12

Which gland only receives parasympathetic innervation?

Answer 12

Sublingual

Question 13

Explain the slide on autonomic nerves supplying different structures in the salivary gland

Answer 13

Autonomic nerves innervate the acini that produce the secretion.
Myoepithelial cells contract with innervation to hold the acinar cell when secreting saliva.
They also innervate the duct.

Autonomic nerves also control blood flow through vessels. They dilate blood vessels as water in base of saliva is from blood vessels so we need more blood supply.

Question 14

What are some parasympathetic effects of reflex stimuli?

Answer 14

• Evoke most fluid secretion
• Evoke some protein secretion
• Contract myoepithelial cells
• Cause vasodilation as part of the secretary process
• Denervation casues gland atrophy

Question 15

What are some sympathetic effects of nerve stimuli?

Answer 15

• Act collaboratively with parasympathetic
• Seldom cause much fluid secretion
• Cause protein secretion
• Contract myoepithelial cells
• Do not cause vasoconstriction as part of secretory process
• Denervation causes some gland atrophy

Question 16

Explain the 2 stage process of saliva formation

Answer 16

Stage 1: Formation of primary saliva
- Acinar cells receive signals from parasympathetic nerves and from sympathetic nerves giving rise to the secretion of water, salts and protein.
Acetylcholine binding to muscarinic receptors on the acinar cells gives rise to the secretion of NaCl and then water will follow.
The NT for sympathetic is noradrenaline binding to beta adrenergic receptor on the acinar cells, we get exocrine secretion of protein by the acinar cells. NT can also bind to alpha receptor giving rise to a small amount of water secretion.

Stage 2: Modification of saliva in ducts
- Ductal epithelium is impermeable to the movement of water so no water can follow out the duct. This is due to the junctions of the ductal cells being really tight.
Secretion of saliva has a lower ionic strength than the primary saliva. This is called hypotonic saliva.
Minor glands have no sympathetic innervation! How do minor glands secrete protein? This is reliant on other molecules called neuropeptides released by parasympathetic nerves to allow protein secretion.

Question 17

Explain the biological reactions behind salivary secretion

Answer 17

Ach binds to muscarinic receptor leads to phospholipase C increasing IP3 concentration. This causes an increase in intracellular calcium concentration. This gives rise to the secretion of electrolyte and fluid form acinar cells.

Release of noradrenaline binging to beta adrenergic receptors activates adenylate cyclase, increase in cAMP, gives rise to secretion of proteins through exocytosis.
This secretion is across the apical membrane of the acinar cells which faces the lumen of the duct.

Question 18

How does secretion take place in an acinar cell?

Answer 18

Process of secretion depends on the gradient of sodium across acinar cells.

Intracellularly, there is a low sodium concentration. This is due to the sodium-potassium ATPase pump in the basal-lateral membrane pumping sodium out the cell.

Question 19

Explain how salivary secretion is dependant on opening of apical chloride channels

Answer 19

1. Ach binding to a muscarinic receptor.
2. This increase calcium concentration in the cell.
3. This opens up an apical channel allowing chloride into the acinar lumen.
4. This creates a negative charge in the acinar lumen. Sodium follows into the lumen between the acinar cells across the tight junction.
5. This gives NaCl in the lumen. This creates an osmotic gradient so water follows in.
6. Water travels between tight junction of cells and can travel across cells through an aquaporin.
7. This process is maintained by the Na+/K+ ATPase which increases its rate when stimulus arises. The chloride within the cell is replaced by chloride into the cell across the basal-lateral membrane by a co-transporter.
8. When Ach stops binding, the whole process will stop. The Ca2+ is taken. Back up into the endoplasmic reticulum of the acinar cell.

Question 20

How does protein secretion from the acinar cell work?

Answer 20

Most of the protein in saliva is secreted from acinar cells from storage granules.
They contain a variety of proteins, amylase, mucins, proline rich proteins and statherins and more.

IgA is also put into the lumen here. This is not produced by acinar cells like the other proteins, but instead by plasma cells that are outside the gland.
Transporter protein picks up the IgA and transports it across the acinar cells instead.

Small number of blood proteins present in saliva.

Question 21

What different glands produce different proteins?

Answer 21

Different glands have acinar cells that are slightly different. They are characterised by producing different amounts of protein.
Parotid gland produces lots of amylase.
Submandibular have serous cells that dont produce mucin proteins.
Sublingual gland produces mucin.

Question 22

When the flow rate is fast, what is the difference in ion concentrations?

Answer 22

Stimulated
Stage 1 = larger volume of salvia produced
Fast flow rate of salvia.
Stage 2 = removal of sodium and chloride but this is less. Less potassium uptake. As well as this, bicarbonate is secreted into the lumen for buffering.