Session 2 - Saliva and the Salivary glands Flashcards
What structures facilitate mastication?
- Teeth
* Muscles of mastication
What is the purpose of the teeth?
- Cut (incisors)
- Crush (molars)
- Mix with saliva
What are the muscles of mastication?
- Masseter
* Innervated by branch of trigeminal nerve
How many litres of saliva produced per day?
1.5
What are the functions of saliva?
- Lubricates and wets food
- Starts digestion of carbohydrate
- Protects oral environment
Give four ways saliva protects the oral environment?
• Keeps mucosa moist • Washes teeth • Maintains alkaline environment ○ Neutralises acid produced by bacteria • High calcium concentration (?) ○ Soluble in acidic solution, not in alkaline and thus do not degrade
What is the condition when you do not have enough saliva, and what occurs?
- Zerostomia (stomeeyah)
* Can still eat food, but teeth and mucosa degrade very quickly
What is the tongue?
A collection of 8 muscles that work to manipulate food for mastication and form it into a bolus
Aids in swallowing
What are the six main constituents of saliva?
• Water • Electrolytes • Alkali • Bacteriostats • Mucus ○ Mixture of mucopolysaccharides • Enzymes - Salivary amylase
What is meant by “hypotonic” water?
• More water in saliva than in rest of body (osmotic potential body –> saliva)
How does the concentration of Na+ and Cl- in the saliva compare to that in the plasma?
• Lower concentration in saliva
How does concentration of Ca2+, K+ and I- in saliva compare to plasma?
• High concentration in saliva as compared to plasma
○ K+ as by product from production of saliva
○ I- helps control population of bacteria
What makes saliva alkaline?
• The addition of HCO3
What are the three paired salivary glands?
- Parotid
- Sub Mandibular
- Sub-lingual
What is the structure of the salivary glands?
• Ducted, exocrine glands
What are ducted exocrine glands made up of?
- Blind ended tubes
* Connected system of ducts
What cells line the acini, or the blind ended part of the salivary glands?
• Acinar cells
What cells line the ducts of the salivary glands
• Duct cells
What kind of secretion is produced by the parotid?
- Watery secretion rich in enzymes, but little mucus (serous)
- 25%
What types of secretions are produced by the sublingual glands?
- Viscous secretion
- No enzymes
- Lots of mucus
- 5%
What secretion are produced by the sub-maxillary glands?
- All components of saliva, mix serous and mucous
- Gland made up of mixture of serous and mucous acini, leading to common ducts
- 70% of all saliva
How is saliva produced to be hypotonic, despite being made form extra-cellular fluid
• Glands secrete more concentrated solution and remove solute
Why isn’t saliva secreted directly in its final state?
• No cellular mechanism to secrete water
How is saliva secreted?
• Ïn a concentrated substance, from which solute is reabsorbed
What do acinar cells secrete?
• An isotonic fluid containing enzymes
What do duct cells do to pre-saliva?
- Remove Na+ and Cl-
* Add HCO3-
Why does water not follow the electrolytes removed from saliva by the duct cells
• Gaps between duct cells very tight
Why is saliva more concentrated at a higher flow rate?
• Duct cells have a limit on how much Na+ and Cl- they can remove
Smaller fraction removed
What happens to the pH of saliva at higher flow rates?
- Stimulus for secretion promotes HCO3- secretion
* Saliva becomes more alkaline
Outline the mechanism of acinar secretion
- Cl- actively secreted into lumen of cut
* Water and other ions then follow passively
How do the duct cells remove Na+ from the lumen of the duct?
- Na+/K+-ATPase antiporter on ECF membrane secretes Na+ out of cell
- This generates conc gradient from Na+ from duct lumen to duct cell
How do the duct cells remove Cl- from the lumen?
- Na/K+-ATPase also increases conc of K+ within the cell
- This drives expulsion of Cl- into the ECF via a K+/Cl- symport transporter
- Cl- high in lumen, low in cell. Conc grad, diffusion
How is HCO3- secreted into the duct lumen?
- Cl-/HCO3- antiporter
* Cl- moves into cell down conc grad, HCO3- moves into lumen
What part of the nervous system controls salivary secretion?
• Autonomic nervous system
What does parasympathetic stimulation of the salivary glands do?
• Increases production of primary secretion and increases addition of HCO3
Outline the pathway of parasympathetic stimulation of salivary glands
o Parotid Gland
Glossopharyngeal Nerve (9th cranial nerve)
Otic ganglion
o Submandibular and Sublingual Glands
Facial Nerve (7th cranial nerve)
Submandibular ganglion
o Muscarinic receptors
Blocked by atropine like drugs
o Co-transmitters stimulate extra blood flow
Outline the parasympathetic outflow surrounding saliva stimulation
• Afferent information from ○ Mouth and tounge - taste receptors ○ Nose ○ Conditioned reflexes • All goes to medulla
Outline sympathetic stimulation of salivary glands?
• Occurs via superior cervical ganglion
○ Reduces blood flow to the salivary glands
○ Limits salivary flow
Where is the oropharynx found?
- Behind the oral cavity
- Below the nasopharynx
- Above the laryngopharynx
From what structures does the oropharynx extend to and from?
• The uvula to the hyoid bone
What structure closes over the glottis to prevent aspiration?
• The epiglottis
What is the oesophagus?
- A muscular tube that passes food from the pharynx to the stomach
- Continuous with the lower part of the laryngopharynx
Outline the tissue structure of the oesophagus
• Mucosa
○ Composed of non-keratinized stratified squamous epithelium, lamina propria and a layer of smooth muscle
• Submucosa
○ Containing mucous secreting glands
• Muscularis externa
○ Upper third of oesophagus has striated skeletal muscle under somatic control for swallowing
○ Lower two thirds are smooth muscle under autonomic control
What does the brain stem swallowing centre do when pressure felt of pharyngeal plate
- Inhibits respiration
- Raises larynx
- Closes the glottis
- Can open upper oesophageal sphincter
What are the three phases of swallowing?
- Voluntary phase
- Pharyngeal phase
- Oesophageal phase
What happens in the voluntary phase of swallowing?
• Tongue moves bolus back onto the pharynx
What happens in the pharyngeal phase of swallowing?
- Afferent information from pressure receptors in the palate and anterior pharynx reaches the swallowing centre in the brain stem.
- A set of movements is triggered
- Inhibition of breathing
- Raising of the larynx
- Closure of the glottis
- Opening of the upper oesophageal ‘sphincter’
What happens in the oesophageal phase of swallowing?
- The muscle in the upper third of the oesophagus is voluntary striated muscle under somatic control
- The muscle of the lower two thirds is smooth muscle under control of the parasympathetic nervous system.
- A wave of peristalsis sweeps down the oesophagus, propelling the bolus to the stomach in ~9 seconds.
- Coordinated by extrinsic nerves from the swallowing centre of the brain
- Lower oesophageal ‘sphincter’ opens
What is dysphagia?
• The symptom of difficulty in swallowing
What is odynophagia
• The symptom of pain whilst swallowing
What is achalasia?
- Motility problems of the smooth muscle preventing peristalsis
- Caused by damage and loss of nerves in gullet wall
What are the two main types of dysphagia?
- Oesophageal dysphagia
* Oropharyngeal dysphagia
What is oesophageal dysphagia and how is it investigated?
- Dysphagia for solids
* Investigate with barium swallow/endoscopy
What Oropharyngeal dysphagia?
• Investigate with a flexible endoscopy evaluation of swallowing, allowing you to view entire trachea
What causes dysphagia?
• Obstruction or compression of oesophagus
- Tumours
What is Barrett’s oesophagus?
- An abnormal change of the epithelial cells of the oesophagus
- Metaplasia from non-keratinised stratified squamous epithelia to columnar epithelium and goblet cells
- Strong association with adenocarcinoma
What is gastro-oesophageal reflux disease?
• Reflux of stomach’s content’s into the oesophagus and pharynx causes cough, hoarseness and asthma
Why does gastro-oesophageal reflux damage the oesophagus?
• Does not have the same protective mucosa as the stomach
What features protect the oesophagus from reflux?
- The lower oesophageal sphincter
- Angle of his (acute angle of entry of oesophagus
- Positive intra-abdominal pressure compresses the oesophagus
