Physiology of the Mouth, Pharynx, and Oesophagus

Question 1

Give 8 functions of saliva.

Answer 1

Lubricates and wets food for swallowing

Helps with taste

Begins digestion of starch (via a-amylase) and lipids (via lingual lipase)

Washes away bacteria and food particles

Keeps mucosa moist

Cools hot food

Contents destroy bacteria

Maintains alkaline environment

Question 2

How much saliva is produced each day?

Answer 2

800 – 1500ml per day

Question 3

What is the pH range of saliva?

Answer 3

pH 6.2 – 8

Question 4

Describe the tonicity of saliva.

Answer 4

Hypotonic

Question 5

List the 6 components of saliva.

Answer 5

Water

Mucous

High concentration of potassium and bicarbonate

Low concentration of sodium and chloride

Digestive enzymes

Antibacterial agents – proteolytic enzymes (lysozyme) and antibodies (IgA)

Question 6

List the 5 main types of salivary glands.

Answer 6

Parotid gland

Sublingual gland

Submandibular gland

Von Ebner’s glands of the tongue

Many tiny buccal glands

Question 7

What type of saliva do the parotid glands secrete?

Answer 7

Serous – watery and rich in a- amylase

Question 8

What type of saliva do the sublingual glands secrete?

Answer 8

Mucous

Question 9

What type of saliva do the submandibular glands secrete?

Answer 9

Mixed serous and mucous

Question 10

What do Von Ebner’s glands of the tongue secrete?

Answer 10

Lingual lipase

Question 11

What are the 3 main cell types found in salivary glands?

Answer 11

Acinar cells

Ductal cells

Myoepithelial cells

Question 12

What is the function of acinar cells?

Answer 12

Produce an initial saliva which is isotonic and has approximately the same composition as plasma

Question 13

What is the function of ductal cells?

Answer 13

Modify the initial saliva by altering the concentrations of various electrolytes to produce the final, hypotonic saliva

Question 14

What is the function of myoepithelial cells?

Answer 14

Contract to eject saliva into the mouth

Question 15

Where are myoepithelial cells found?

Answer 15

Acini and intercalated ducts

Question 16

After saliva is secreted from the acini and passes through the intercalated ducts, where does it pass through next?

Answer 16

Striated ducts

Question 17

Describe the epithelium of the intercalated ducts.

Answer 17

Simple cuboidal and myoepithelial cells

Question 18

Describe the epithelium of the striated ducts.

Answer 18

Simple cuboidal to simple columnar epithelium

Question 19

Describe the innervation of the salivary glands.

Answer 19

Have both parasympathetic and sympathetic innervation, but parasympathetic is dominant

Question 20

Explain how there is a net absorption of solute in the ductal cells.

Answer 20

Because more NaCl is absorbed than KHCO3 is secreted

Question 21

Why does water not follow the absorption of the solute in the ductal cells?

Answer 21

The ductal cells are relatively impermeable to water, so water remains trapped in the lumen

Question 22

The degree of modification of saliva is dependent on what?

Answer 22

Flow rate

Question 23

Describe how resting saliva compares to stimulated saliva in terms of its tonicity.

Answer 23

Resting saliva is more hypotonic than stimulated saliva, as the ductal cells have more time to modify the saliva

Question 24

Describe how resting saliva compares to stimulated saliva in terms of its bicarbonate content.

Answer 24

Resting saliva contains less bicarbonate than stimulated saliva – bicarbonate is selectively stimulated, so its concentration increases with increasing flow rate, making stimulated saliva more alkaline than resting saliva

Question 25

Give 4 things which increase parasympathetic activity to the salivary glands.

Answer 25

Food

Smell

Nausea

Conditioned reflexes (e.g. Pavlov’s dogs)

Question 26

Give 3 things which decrease parasympathetic activity to the salivary glands.

Answer 26

Fear

Sleep

Dehydration

Question 27

What is xerostomia?

Answer 27

A dry mouth from reduced / absent salivary secretion or change in the composition of saliva

Question 28

Give 5 causes of xerostomia.

Answer 28

Dehydration

Anxiety

Medication side effect

Sjogren’s syndrome

Damage to salivary glands or their innervation e.g. trauma, surgery, radiotherapy

Question 29

List the 5 classifications of taste.

Answer 29

Sweet, sour, salty, bitter, umami.

Question 30

Which 3 cell types comprise taste buds?

Answer 30

Taste receptor cells

Supporting cells

Basal cells

Question 31

What kind of receptors are taste receptor cells?

Answer 31

Chemoreceptors

Question 32

What 3 features of the lower oesophageal sphincter prevent reflux of gastric contents into the oesophagus?

Answer 32

Right crus of the diaphragm

Acute angle at which the oesophagus enters the stomach

Mucosal folds present at the gastro-oesophageal junction

Question 33

Give 2 complications of GORD.

Answer 33

Oesophageal stricture – scarring and narrowing of the oesophagus.

Barrett’s oesophagus – metaplasia of squamous epithelium to gastric mucosa (columnar epithelium), associated with an increased risk of oesophageal cancer.

Question 34

Describe the oral phase of swallowing.

Answer 34

Initiated when the tongue forces a bolus of food back toward the oropharynx, which contains a high density of somatosensory receptors. Activation of these receptors initiates the involuntary swallowing reflex in the medulla via vagus (CN X) and glossopharyngeal (CN IX) nerves.

Question 35

Describe the 4 steps in the pharyngeal phase of swallowing.

Answer 35

The soft palate is pulled upward, blocking food from entering the nasopharynx.

The epiglottis moves to cover the opening of the larynx, and the larynx moves upward against the epiglottis to prevent food from entering the trachea.

The upper oesophageal sphincter relaxes.

A peristaltic wave of contraction is initiated in the pharynx and propels food through the open sphincter.

Question 36

Describe the 4 oesophageal phase of swallowing.

Answer 36

The upper oesophageal sphincter closes.

Larynx falls, glottis opens, and respiration recommences.

Lower oesophageal sphincter relaxes.

If the primary peristaltic wave does not clear the oesophagus of food, a secondary peristaltic wave mediated by the enteric nervous system is initiated by the continued distension of the oesophagus.