Salivary Secretion and Control

Question 1

What are the 4 major parts of the main secretory unit?

Answer 1

• acinus: end point of ductal system - series of cells which produce saliva, connected directly to intercalated duct
• intercalated duct: in between acinus and striated duct, very thin walled
• striated duct: invaginations on basal layer os cells giving stripey appearance
• secretory duct - leads into mouth

Question 2

What are the types of acinar cells?

What are myoepithelial cells?

Answer 2

• serous acinus - rounded nucleus at basal part of cell, many vesicles near middle
• mucous acinus - nuclei squeezed towards basal layer, pale cytoplasm
• mucous acinus and serous demilune

Myoepitheial cells: surround acini and intercalated ducts

• squeeze acinus, may assist secretion of saliva
• regulate diameter of lumen
• support and protect acinus and intercalated duct from pressure-related damage

Question 3

Give an overview of striated ducts:

Secretory ducts:

Answer 3

Striated duct: none in sublingual gland, only serous glands

• columnar shaped cells
• active modification of primary saliva
• massive basal membrane folding
• high metabolic activity, lots of mitochondria

Secretory ducts: large lumen

• pseudostratified columnar epithelium
• stratified near termination - merges with stratified squamous oral epithelium

Question 4

What are the 4 stages of formation of constituents of primary saliva?

Answer 4

Formation of an isotonic solution in the acinus (primary saliva)

1. Increased permeability of K into lumen and interstitial fluid
2. K in interstitial fluid activates transporter mechanism to transport Na, K and Cl, moving Na and excess K, Cl back into the cell
3. Cl moves through the apical membrane into the lumen of the acinus
4. Activation of acinar cell - increased concentration of Cl in acinar fluid drags Na to balance the charge, water follows between the cells

Question 5

What happens when saliva enters the striated duct?

Answer 5

Conversion of isotonic solution to a hypotonic solution

• active reabsorption of Na and Cl from the lumen
• active secretion of K and HCO3 into the lumen
• no reabsorption of water
• as the duct is impermeable to water this stays in the lumen –> resulting in a more hypotonic solution

Question 6

How is salivary secretion largely controlled?

Which parts of the gland do salivary efferent nerves innervate?

Myoepithelial cells are innervated by which autonomic branches?

Answer 6

Salivary secretion dependant on reflex activity

• reflex: innate, automatic, predictable, goal-directed response involving the CNS to a known stimulus
• adequate stimulus - usually associated with feeding
• complex secretomotor and vasomotor innervation
• lack of uniformity of response between glands and species

Salivary efferent nerves:

• affect acinar, ductal and myoepithelial cells

Myoepithelial cells - both sympathetic and parasympathetic neurones

Question 7

What is the gustatory-salivary reflex?

What is the masticatory-salivary reflex?

Comment on the olfactory-salivary reflex:

Answer 7

Gustatory-salivary reflex: triggered by taste

• stimuli delivered to gustatory receptors in taste buds
• sour > salt > bitter and sweet

Masticatory-salivary reflex: chewing

• mechanoreceptive afferent neurones innervating: PDL, oral mucosa
• ipsilateral increase in production (same side as chewing)

Olfactory-salivary reflex: does not exist in humans in parotid, but does in the submandibular gland

Question 8

What could be the initiating signal for salivation?

Comment on psychic stimuli:

Answer 8

Higher centres:

• facilitate
• also inhibit i.e. dry mouth with anxiety
• but cannot enhance response

Psychic stimuli:

• mouthwatering - sight of food - not been demonstrated to cause significant increase in flow
• may be due to a sidden awareness of saliva already present in mouth
• or contraction of myoepithelial cells or facial musculature of the FOM