L3: functions and secretions of saliva Flashcards
General functions of saliva (6)
- Moistens and cleanses oral mucosa
- Cools food and aids chewing, making bolus
- Lubrication by mucins (sticky glycoproteins) - makes food food easier to chew/swallow, aids speech, and protects oesophagus
- Solubilises food, taking it deep into the tastebuds - aids taste
- Digestion - alpha amylase, lingual lipase (important in newborns)
- Anti-bacterial - lysozymes, antibodies, lactoferrin
Dental relevant functions of saliva (3)
Buffer - saliva is an alkaline buffer, containing bicarbonate ions. Neutralises acid in food/vomit.
Minerals - mineralises teeth by containing high levels of calcium and phosphate. Prevents enamel demineralisation by acid.
Secretes protective pellicle - protein rich film covering the teeth. Adsorbed onto teeth after cleaning and protects against acid. Stained by tea/coffee/cigarettes. Colonised by bacteria easily aiding plaque formation.
How can the pellicle aid plaque formation?
Pellicle allows ‘pioneer’ bacteria to colonise
Bacteria multiply
Secondary colonisation and multiplication means species diversity increases
Forms mature dental plaque
Causes of salivary hypofunction
Head and neck cancer radiotherapy can damage salivary glands
Autoimmune diseases like Sjogren’s, Lupus, Rheumatoid Arthritis
Drug therapy, e.g., antihistamines, antihypertensives, antidepressants etc.
Symptoms of salivary hypofunction
Reduced or totally absent saliva Dry mouth - xerostomia Difficulty swallowing dry foods Loss of taste Constant thirst
Dental problems due to salivary hypofunction
- oral bacterial/yeast overgrowth
- pH drops due to lack of bicarbonate ions and bacteria producing acid
- bacteria cause caries formation
- acid causes enamel demineralisation
- periodontal disease
- difficulty wearing dentures
More dental symptoms of salivary hypofunction
Xerostomia Burning mouth Fissured lobulated tongue Candida/oral yeast infection Lichen planus - whitish streaks Aphthous ulcers Dental caries - tooth decay (Images at min 20)
3 major salivary glands
Parotids - serious (watery) secretion. Found in cheeks.
Submandibular - mixed serous and mucous secretion (more serious). Found under jawbone.
Sublingual - mixed serous and mucous secretion (more mucous). Found under tongue,
What are the salivary glands composed of?
Exocrine glands - composed of acini (cluster of cells) and ducts
What is the composition of saliva from each of the 3 glands?
25% parotid
70% submandibular
5% sublingual secretions
(Pic at 25:40)
What is mumps?
Viral infection typically infecting the salivary glands - particularly the parotid glands
Composition of saliva
> 99% water
Ions: sodium, potassium, bicarbonate, chloride, calcium, magnesium, phosphate, iodide
Proteins: alpha amylase, lipase, mucins, immunoglobulins
pH range: 6.1-8.0
What does the pH of saliva depend on?
pH depends on bicarbonate ion content and flow rate
Is saliva hypertonic, isotonic or hypotonic in relation to plasma?
Hypotonic compared to plasma - facilitates taste
Generally saliva has less ions in it than the plasma but as more saliva is required in the mouth (like during eating), more bicarbonate is added to it (stays hypotonic throughout)
What is osmolality?
Concentration of ions.
What happens to osmolality when salivary secretion increases?
When salivary secretion increases, osmolality increases since more bicarbonate is secreted so concentration of ions increases.
What happens to pH of saliva during eating?
pH changes from being slightly acidic at rest to basic. Increase in alkalinity due to increased increased bicarbonate.
How is saliva made?
Acinar cell secretion:
- capillary filtration occurs and plasma gets picked up by acinar cells
- ions from the surrounding blood vessels move into the acinus cells and then into the lumen
- the primary saliva secretion is isotonic to plasma - isotonic saliva
- water follows by osmosis from plasma into acinar lumen
- then duct cell reabsorption
(Pic at 35:18)
How is the primary saliva secretion modified?
Ductal cell reabsorption
- there are lots of ion channels in the duct cells that remove sodium and chloride but add potassium and bicarbonate ions
- the ducts are relatively impermeable to water. Because more solutes are removed then water, a hypotonic saliva is formed
Why might xerostomia be a common side effect of many drugs?
Because there are so many ion channels involved in the ductules, so which may be the target of many drugs
How does saliva composition vary at different times?
- when a lot of saliva is needed, the blood vessels in the salivary glands will vasodilate. So there is a high hydrostatic pressure in the surrounding capillaries forcing more plasma into the acini. It passes through the ducts faster so there is less time to reabsorb sodium but more bicarbonate is added - which is needed for eating to neutralise acid. Saliva is still hypotonic but almost if you plasma.
- when asleep e.g., there is a lower hydrostatic pressure in the surrounding capillaries which forces less plasma into acini. So slower flow through ducts and more time to absorb sodium. Hypotonic saliva keeps the mouth lubricated for talking etc.
Why does saliva have to be hypotonic?
If saliva were hypertonic, then we would lose water from the tongue, cheeks etc as it would move from high to low water potential.
How is secretion controlled?
- pressure and chemoreceptors (chewing, taste, tactile stimulation)
- input from cerebral cortex (thought, sight, smell of food)
- exclusively under ANS control
- predominantly parasympathetic
- flow rate depends on type of stimulus
Role of parasympathetic nerves in controlling saliva secretion
- vasodilatation - hyperaemia (increased blood flow
- increase transport into acinar cells
- release of ACh acts directly on membrane receptors on acinar cells to cause saliva secretion - e.g., increased mucins/enzyme synthesis
- increased transport of bicarbonate from duct cells
- increased amylase and enzymes
- increased extrusion of saliva from ducts
