Lecture 5 - Salivation & Swallowing

Question 1

Describe the composition of saliva

Answer 1

• Mostly water
• Hypotonic, rich in K+ and HCO3- (depending on flow rate)
• Slightly alkaline (typically)
• Mucins - help with lubrication to move bolus (as osmotically active)
• Amylase (from salivary glands)
• Lingual lipase (from lingual glands)
• Immune proteins (IgA, lysozyme, lactoferrin)

Question 2

What are the primary functions of saliva?

Answer 2

1) Lubrication - due to mucus content, helps with swallowing & speech
2) Protection - saliva has cooling effect on hot food/water, buffers acid, washes away debris stuck in teeth & has immune function
3) Digestion - via salivary amylases & lingual lipases

Question 3

What are the 3 major salivary glands and where are they located?

Answer 3

1) Parotid gland - beside the ear, communicates with aural cavity via duct
2) Sublingual gland - under the tongue
3) Submandibular gland - split into superficial & deep

Question 4

Describe the mechanism of secretion of saliva from salivary glands, and why the solution is hypotonic.

Answer 4

• Saliva produced by acinus lined with acinar cells, roughly isotonic with plasma.
• Passes into duct via contraction of myoepithelial cells
• Ductal cells have transporters which remove Na & Cl- ions, and secrete in K+ and HCO3- but to a much lesser extent, so solution becomes hypotonic.

Question 5

How does flow rate affect the tonicity of the saliva?

Answer 5

At rest (low flow rate):

• More contact time with ductal cells = Most hypotonic solution

When active (high flow rate):

• Less contact time with ductal cells = Least hypotonic solution

Question 6

Describe the neural control of the 3 main salivary glands

Answer 6

• All are under primary control of parasympathetic nervous system (increases production)
• Sympathetic also increases production, but causes vasoconstriction so is less watery (hence dry mouth when nervous)
• Parotid gland receives PNS innervation from glossopharyngeal nerve (CN9) and the other two from branches of the facial nerve (CN6)

Question 7

What is xerostomia + how is it caused?

What are the consequences?

Answer 7

• Lack of saliva, due to medications, autoimmune, dehydration etc.
• Leads to infections, tooth decay, halitosis (think about functions of saliva)

Question 8

Name 3 other pathologies associated with the salivary glands?

Answer 8

1) Mumps - viral infection leading to parotiditis
2) Sjogrens - autoimmune disorder leading to swollen/painful salivary glands
3) Sialoliths - salivary (calcified) stones , causes pain when salivating so associated with eating

Question 9

What is the composition of saliva produced by each salivary gland?

Answer 9

1) Parotid - produces 25% of saliva, serous/water with lots of enzymes
2) Submandibular - produces 70% of saliva, mixed serous and mucous
3) Sublingual - produces 5% of saliva, mucous secretion, less enzymes

Question 10

What occurs in the oral phase of swallowing?

Answer 10

Voluntary phase (around 7ish seconds)

1) Preparation of bolus by chewing/tasting
2) Bolus pushes towards oropharynx via tongue movements
3) Kicks in reflex to start pharyngeal phase

Question 11

What occurs during the pharyngeal phase of swallowing?

Answer 11

Involuntary phase (roughly 0.2s)

1) Soft palate blocks off nasal cavity so not food/liquid can enter
2) Pharyngeal constrictors push bolus downwards
3) Larynx elevates , closing epiglottis
4) Vocal chords become closed together as extra safety mechanism to prevent inhaling food
5) Opening of upper oesophageal sphincter

Question 12

What occurs during the oesophageal phase of swallowing?

Answer 12

Involuntary phase

• Closure of upper oesophageal sphincter
• Peristaltic wave carries bolus down oesophagus to stomach

Question 13

What is dysphagia?

What are the potential causes?

Answer 13

• Problems coordinating swallowing
• Can lead to dribbling and material entering respiratory tract causing coughing and choking. Fluid particularly hard to swallow
• Cerebrovascular accident (stroke), parkinsons disease, oesophageal tumour

Question 14

Describe the muscular composition of the oesophagus

What are the 4 positions in the oesophagus where material can lodge?

Answer 14

• Top 1/3 is skeletal muscle, bottom 1/3 is smooth muscle, middle 1/3 is mixed

1) Junction of the pharynx with oesophagus
2) Where the arch of aorta crosses over the tube
3) Where the left main bronchus compresses tube
4) At oesophageal hiatus (point of narrowing at diaphragm)

Question 15

What mechanism are in place to prevent gastro-oesophageal reflux?

Answer 15

• Smooth muscle of distal oesophagus and part of diaphragm form sphincter to prevent reflux
• Oesophagus enters stomach at acute angle so when pressure rises in stomach flap valve is shut to prevent reflux.