Production of saliva Flashcards
Describe the functional unit of a salivon and its four components
Salivons are the basic unit of a salivary gland. They consist of:
Acinus:
• It is a rounded secretory unit
• There are two types of secretions, serousandmucous
• Aserous acinussecretes proteins in an isotonic watery fluid (isotonic when compared to plasma)
• Amucous acinussecretes mucin - lubricant
Intercalated duct:
• Connects the acinus to the striated duct
• Contains secretory granules
Striated duct:
• Modifies the secretory product
Excretory duct:
• Modify the composition of saliva
Describe the 2 stages of saliva production
Primary secretion:
• Acinar cells are surrounded by myoepithelium, which contracts, thus moving the fluid produced by acinar cells towards the duct
Secondary secretions (ductal secretion): • As the fluid moves along the duct, the duct cells absorb NaCl from the fluid (but not water), resulting in saliva becoming hypotonic • The ducts are water impermeable, thus water is not lost • Simultaneously, they secrete bicarbonate into the saliva
Explain the process of fluid secretion in the acinar
- This process is dependent on active transport
- Basically, at the base/ outer wall of the acinar cells are the Na+K+-ATPase and Na+K+Cl transporters
- Na and K enter the cell. This naturally causes water to come in as well
- Water eventually travels to the acinar lumen
Explain the process of ion transport in the striated and excretory ducts
- The secretory ducts have apical membrane antiporters
- These absorb Na+ and Cl- from the lumen, but secret K+ and HCO3 - into the lumen
- These cells are impermeable to water, thus water is not lost
List the 4 stimulants of salivary secretion
- Taste, temperature and smell (gustatory)
- Tactile stimulation of the buccal mucosa
- Mastication and chewing
- Nausea
Describe unstimulated saliva in terms of:
- Flow rate
- pH
- Secretory organs
Unstimulated saliva
Flow rate:
• 0.3-0.5 mL/min
• Lower lip hydration should be less than 60 seconds
pH:
• 6.8-7.8
Secretory organs:
• Submandibular gland: 69%
• Parotid gland: 26%
• Sublingual gland: 5%
Describe stimulated saliva in terms of:
- Flow rate
- pH
- Secretory organs
Stimulated saliva
Flow rate:
• 1.0-2.0 mL/min
• Or, more than 5mL at 5 minutes
pH:
• 7.4, with strong acid buffering capacity
Secretory organs:
• Parotid gland: 53%
• Submandibular gland: 35%
• Sublingual gland: 5%
Briefly describe how salivary production (secretion and composition) is controlled
• It is controlled by the ANS, and hormones may modify the composition of the saliva
ANS:
• In the brain stem near the pons and medulla region lies the superior and inferior salivary nuclei
• Both parasympathetic and sympathetic act simultaneously and synergistically to produce saliva
Hormones may modifying the composition:
• Aldosterone increases Na+ reabsorption and K+ secretion
• Interesting observations: oestrogen and progesterone role = postmenopausal hyposalivation, and excessive salivation during pregnancy
Describe how the parasympathetic system contributes to salivary secretion, in terms of the responsible nerves, signalling and the type of saliva produced
- Glossopharyngeal nerve CN IX: originates from the inferior salivary nuclei. It synapses at the otic ganglion, where it innervates the parotid gland and facial nerve
- Facial nerve CN VII: Comes from the superior salivary nucelli in the pons. It (passes through the parotid gland) and synapses at the submandibular ganglion, where it innervates the submandibular and sublingual glands
- Signalling is carried out through the neurotransmitter, acetylcholine (Ach), which binds to muscarinic receptors on the surface of acinar cells and ductal cells
- This causes fluid and electrolyte secretion, resulting in the final product of water saliva
Describe how the sympathetic system contributes to salivary secretion, in terms of the responsible nerves/ arteries signalling and the type of saliva produced
• The sympathetic nervous system affects salivary gland secretions indirectly by innervating the blood vesselsthat supply the glands, resulting in vasoconstriction= lessening the saliva’s water content
Nerves and arteries: • Superior cervical ganglion travel with arteries • External carotid artery: parotid • Lingual artery: submandibular • Facial artery: sublingual
- Signalling is carried out through the neurotransmitter, noradrenaline which binds to adrenergic receptors. When they bind, it causes contraction of myoepithelial cells to increase salivary flow
- Results in short-lived, smaller increase in salivary secretion
- Saliva is more viscous: less water content but more protein content
Detail the neurological control of salivary secretion by mentioning the two stimuli responsible, the nerves involved and the sympathetic/ parasympathetic activation
Stimuli:
· Masticatory stimuli: message travels via trigeminal nerve (V) and stimulates the salivation centre in the medulla oblongata
· Gustatory stimuli: message travels via CN VII, IX and X (facial, glossopharyngeal and vagus nerves) and stimulates the salivation centre in the medulla oblongata
Parasympathetic activation:
· CN VII (facial nerve) releases acetylcholine neurotransmitters to bind with muscarinic rectors in the submandibular and sublingual glands
· CN IX (glossopharyngeal nerve) releases acetylcholine neurotransmitters to bind with muscarinic rectors in the parotid glands
Sympathetic activation:
· The salivation centre in the medulla oblongata sends a message to the superior cervical ganglion
· These release noradrenaline which binds to adrenergic receptors on acinar and ductal cells
· Mucous saliva is produced
Describe how stress and anxiety impacts salivary flow
- Stress/ depression/ sleep stimulates the higher centres in the brain (cortex and limbic system)
- This then stimulates the inhibitors neurotransmitters in the salivation centre within the medulla oblongata
- It is NOT primarily due to sympathetic activation
State the 6 causes of reduced/ inhibited salivary flow
- Physiological causes : sleep, fear, dehydration
- Medication: “Anti drugs” such as anticholinergics, antihistamines, antihypertensives, antidepressants, some illicit drugs
- Psychogenic disorders and mental illnesses such as depression, and anxiety
- Irradiation to the head and neck
- Autoimmune disorders, e.g. Sjogren’s syndrome
- Salivary gland infection causing inflammation and obstruction
List the 10 implications of long term hyposalivation
- Dryness of the lips, oral mucosa
- Burning mouth syndrome
- Mucosal ulceration
- Problems with eating, speech
- Altered taste perception
- Halitosis
- Difficulty in wearing removable dentures
- High caries risk
- Atrophy of the filiform papillae
- Increased frequency of opportunistic infections (e.g. thrush)
