What are the 3 main functions of saliva?
• Lubricates and wets food
• Starts digestion of carbs (salivary amylase)
• Protects oral environment
How does saliva protect the oral environment?
o Mucosa kept moist
o Maintains alkaline environment to neutralise acid produced by bacteria
o High calcium concentration stops teeth from dissolving in saliva.
What is zerostomia? What happens in zerostomia?
• Poor production of saliva
• Teeth and mucosa degrade very quickly
What are the constituents of saliva?
• Water – Saliva is hypotonic (less electrolytes than body cells) to prevent mucosa wet without drawing water out of them
• Electrolytes – Na¬ and Cl at lower conc than plasma. Ca, K, and iodide at higher concs than plasma. Iodide is a bacteriocide.
• Alkali – HCO3 higher conc than plasma
• Mucus – Mixture of mucopolysaccharides
• Enzymes – salivary amylase
Name the 3 salivary glands, where they are located and their type of secretion
Parotid - serous. Near ears
Sublingual - mucus. Under tongue
Submaxillary - Mucus and Serous. Under maxilla.
Explain the structure of an exocrine gland. What part of the gland produces the fluid?
Exocrine glands are blind ended tubes with acini on one side and ductal cells lining the duct to the outside world.
Acinar cells produce something which the ductal cells modify.
Explain the mechanism of secretion of serous saliva
1. Acini produce secretion which is isotonic with the ECF with addition of enzymes and higher [I-]
2. Ductal cells decrease [Na] and increase [K] and [HCO3]:
a. As solution goes down duct, sodium removed generating electrochemical gradient which chloride follows. K conc increases as Na K ATPase used to remove Na.
b. At rest pH of saliva is slightly alkaline. During mastication more HCO3 added, solution more alkaline.
3. Since ductal cells have a maximum rate of modification; the more rapidly saliva is produced, the less modified it is, except for HCO3.
What are the features of resting and stimulated saliva and how do they differ?
• Low volume, very hypotonic
• Few enzymes and neutral pH.
• Highly modified acinar secretions
• Less modified secretions
• High volume, less hypotonic
• More enzymes, more alkaline.
What receptors are located on an acinar cell to produce saliva?
What controls volume of salivary secretion? What controls composition of salivary secretion?
Volume – Controlled by acinar cells
Composition – Controlled by duct cells
What is the sympathetic and parasympathetic innervation for the salivary glands?
Sympathetic – Superior cervical ganglion
Parasympathetic – Glossopharyngeal
How does parasympathetic APs result in more salivary secretion? What receptors do parasympathetic APs act on?
o Acetylcholine released, which acts on acinar cells to promote formation of primary secretion
o Also acts on duct cells to promote HCO¬3 secretion
o Composed of muscarinic receptors which can be blocked by drugs
Describe the process of swallowing
1. Mastication produces bolus which moves to pharynx and stimulates a swallowing reflex
2. Reflex split into voluntary phase and pharyngeal phase.
3. Voluntary – Separation of bolus and movement into pharynx
4. Pharyngeal phase – Pressure receptors in palate and anterior pharynx detect food and send nerve impulse to brain to:
a. Inhibit respiration
b. Raise larynx
c. Close glottis
d. Open upper oesophageal sphincter.
5. Rapid peristaltic wave of the oesophageal muscles takes food from pharynx to stomach in 10 seconds
6. Lower oesophageal sphincter opens.
How can dysphagia occur?
Can occur from obstruction or compression of oesophagus by tumours or achalasia (failure of sphincters to open).
From what vertebral levels does the oesophagus extend?
C6 to T11
What are the 3 layers of the oesophagus?
3) muscularis externa
What type of muscle is each third of the muscularis externa of the oesophagus made up of?
1. Superior third – Voluntary striated muscle
2. Middle third – Voluntary striated and smooth muscle
3. Inferior third – Smooth muscle
What is the purpose of the upper oesophageal sphincter?
prevents air entrance into oesophagus
What is the purpose of the lower oesophageal sphincter?
Prevents acid reflux of stomach
What is the lower oesophageal sphincter classified as? What is it comprised of?
Classified as a physiological sphincter
This is comprised of:
• Oesophagus entering stomach at an acute angle
• Diaphragm exerts pressure on the oesophagus, leading to a ‘pinch cock’ effect
• Positive intra-abdominal pressure compresses walls of oesophagus
• Folds of mucosa aid in occluding lumen at the gastro-oesophageal junction.
What 2 categories are there in dysphagia?
1) Oesophageal dysphagia – dysphagia for solids
2) Oropharyngeal dysphagia – dysphagia for liquids
What is barrett's oesophagus? Why is it clinically relevant?
Acid reflux results in metaplasia of the oesophageal from non-keratinised stratified squamous epithelia to columnar epithelium and goblet cells.
Leads to increased risk of adenocarcinoma resulting from the goblet cells.