Salivation And Swallowing Flashcards
What processes happen in the mouth?
Salivation, mastication, bolus formation and swallowing.
How does mastication take place?
The incisors cut food; the molars crush it. Mixed with saliva.
Which muscle is heavily involved in mastication? What is it innervated by?
The masseter - trigeminal nerve.
Why is production of saliva important?
Lubricates and moistens food, initiates carbohydrate digestion and it protects the oral environment. 1.5L is produced each day.
How does saliva protect the oral environment?
Keeps mucosa moist, Cleans teeth, Slightly alkaline, neutralising acid produced by bacteria. Has a high [Ca2+].
What is the clinical condition where no saliva is produced? What is its clinical significance?
Xerostomia. Teeth and mucosa will degrade very quickly but one can still eat moistened food.
What is saliva composed of?
Water - more H2O than plasma
Electrolytes - less Na+/Cl-, more Ca2+/K+/I-
Alkali - more HCO3-.
Bacteriostats - e.g. I-
Mucus - mixture of mucopolysaccharides
Enzymes - salivary amylase
How many salivary glands are there?
Three paired, ducted exocrine glands:
Parotid, Sub-maxillary, Sub-lingual
What are the two prominent cells in exocrine glands?
Acinar cells and ductal cells.
What do exocrine glands consist of?
The acini (lined with acinar cells) and a connected system of ducts (lined with duct cells) which lead to a single outlet.
What is an acini?
In an exocrine gland, the acinar is the berry-shaped termination where the secretion is produced. They are also found in alveoli.
What do each of the salivary glands produce?
Parotid - serous; watery - rich in enzymes Sub-lingual - mucous; viscous - lots of mucus Sub-maxillary - mixed; mixture of serous and mucus acini leading to common ducts
What proportions of volume are secreted from each salivary gland?
Parotid (serous) - 25% Sub-lingual (mucous) - 5% Sub-maxillary (mixed) - 70%
Saliva is hypotonic. What does this mean?
It is of a lower osmotic pressure than the extra-cellular fluid. This will mean it is less likely to take in water - it has a higher water content than ECF.
How is hypotonic saliva manufactured?
Must start with ECF and remove solute to make it more dilute. This is because there is no cellular mechanism to actively secrete water.
What is the composition of the fluid that the acinar cells secrete?
Isotonic to the ECF with enzymes present.
Saliva then undergoes ductal modification. What happens here?
[Na+] and [Cl-] decrease; [HCO3-] is added.
Why does water not follow the electrolytes out of the saliva?
The gaps between the duct cells are tight.
What controls the volume of saliva?
Acinar secretion.
What controls the composition of saliva?
Ductal modification.
Is the rate of ductal modification limited?
Yes, there is a maximum rate. The more rapidly saliva is produced, the less modified it is n.b. will not apply to HCO3-
How will ductal modification be affected by low flow rate (resting saliva)? What about a high flow rate (stimulated saliva)?
At a low flow rate, the duct cells have the opportunity to remove most Na+ ([Na+] = ~10mmol/L), however as the rate of ductal modification is saturable at a high flow rate the duct cells will remove the same amount (a lesser proportion) of Na+ ([Na+ = <80mmol/L]). These changes in flow will also mean [K+] changes (opposite direction to Na+, ranging from 8-20mmol/L).
What is the mechanism of acinar secretion?
Cl- are secreted directly into the lumen of the duct - water and Na+ will follow.
Visualise the ion channels on the basolateral and apical surfaces of the duct cell. What does it look like?
What is the mechanism of ductal secretion?
Basolateral side
Na+-K+-Pump: lowers [Na+] in duct cell, increases [K+]
K+-Cl- Symporter: effluexes [K+] and [Cl-] - key for AE
NHE (Na+-H+-Exchanger) - effluxes [H+] (H+ + HCO3- <–> CO2 + H2O - catalysed by carbonic anhydrase).
Apical side:
AE (Anion exchanger) - [Cl-] must move into the duct cell, [HCO3-] otherway = alkali saliva: ideal
Passive transport of Na+ and K+
What is salivary secretion controlled by?
Nervous system - Autonomic Nervous System…
Sympathetic - Superior cervical ganglion - reduces blood flow to the glands, thus less salive = dry mouth.
Parasympathetic - Glossopharyngeal Nerve (IX Cranial Nerve), Otic ganglion (Parotid); Facial Nerve (VII Cranial Nerve), Submaxillary ganglion (Sub-lingual and maxillary).
With regards to salivary secretion, what afferent inputs affect the parasympathetic output? Where do these afferent inputs go to?
Taste receptors (especially acid) in the tongue and mouth. the nose (e.g. smells), conditioned reflexes (e.g. Pavlov’s dogs).
These afferent inputs will be sent to centres in the medulla.
What receptors are the parasympathetic system mediated by? What drugs might affect saliva production?
Muscarinc receptors - sensitive to ACh. Acts on acinar cells to promote formation of primary secretion, duct cells to promote HCO3- secretion. Atropine-like drugs may affect these processes.
How else can the sympathetic nervous system affect saliva?
Aldosterone, released from the adrenal cortex, will upregulate the Na+-K+-Pump. This will cause saliva to become even more hypotonic.
When does the swallowing reflex take place?
Normally when food has reached the larynx.
What are the phases of swallowing?
Voluntary phase - separation of bolus, moves into pharynx
Pharyngeal phase - pressure receptors (palate and anterior pharynx) send afferent input to brain stem swallowing centre. (Inhibits respiration, raises larynx, closes glottis, opens UOS)
Oesophageal phase - Upper 1/3 of oesophagus is voluntary muscle (rest is smooth). A rapid peristaltic wave is coordinated by extrinsic nerves in the swallowing centre, transferring food to the stomach in ~9s. … LOS opens.
What is dysphagia? How does this differ from odynophagia?
Difficulty in swallowing, a brainstem function. Absent in brain death - must be checked in head injuries (risk of aspiration). Odynophagia is the sensation of pain whilst swallowing.
What can cause dysphagia?
Motility problems, e.g. achalasia - failure of smooth muscle to relax. Primary (oesophageal) cause.
Obstruction or compression of oesophagus, e.g. tumours. Secondary (non-oesophageal) cause.
Broadly, what are the two types of dysphagia? How would you investigate in each case?
Difficulty swallowing food - Oesophageal dysphagia
Barium swallow/endoscopy
Difficulty swallowing liquids - Oropharyngeal dysphagia
Flexible endoscopy - allows you to view the entire oesophagus and trachea.
What is aspiration?
When food or drink is swallowed and enters the trachea or lungs.
What is dysphagia of liquids commonly associated with and why?
Strokes - the patient may have reduced sensation and not realise they have aspirated (silent aspiration).
