GI physiology - The Mouth

Question 1

How much saliva does the body produce each day?

Answer 1

1.5 litres

Question 2

What is the function of saliva?

Answer 2

• Lubricates food
• Begins digestion of carbohydrates
• Protection of the oral environment
• Keeping mucosa moist
• Washing teeth
• Maintaining an alkaline environment
• Contains a high concentration of calcium

Question 3

Constituents of saliva.

Answer 3

Water

Electrolytes – sodium and chloride ions are usually at a lower concentration than the plasma (hypotonic). Potassium, calcium and iodide ions are usually at a higher concentration than plasma (hypertonic)

Bicarbonate – present at a higher concentration than in plasma to maintain an alkaline environment

Bacteriostats

Mucus

Enzymes – salivary amylase

Question 4

Which glands produce saliva? What are the acinar and suct cells responsible for?

Answer 4

The parotid, submandibular and sublingual glands. Within the glands, the acinar cells are responsible for the volume of saliva secreted, and the duct cells are responsible for the composition of saliva.

Question 5

What type of saliva do each of the paried salivary glands produce?

Answer 5

• The parotid glands produce serous saliva: a watery secretion that is rich in enzymes.
• The sub-lingual glands produce mucous saliva: a viscous secretion containing no enzymes and large amounts of mucus.
• The sub-mandibular glands produce a mixed secretion, that is both serous and mucous.

Question 6

Characteristics of resting saliva.

Answer 6

At rest, the acinar secretion is highly modified and has the following characteristics:

• Low volume
• Very hypotonic
• Neutral or slightly acidic
• Few enzymes

Question 7

Characteristics of stimulated saliva.

Answer 7

When the production of saliva is stimulated, flow exceeds the ductal cells maximum rate of modification and so the acinar secretion is modified less:

• High volume
• Less hypotonic than resting saliva
• Alkaline
• Many enzymes

Question 8

Nervous control of saliva.

Answer 8

Under the control of the autonomic nervous system, comprised of sympathetic and parasympathetic nerve fibres.

Question 9

What provides sympathetic control of salivary production?

Answer 9

Superior cervical ganglion.

Question 10

Sympathetic stimulation of the salivary system mechanism.

Answer 10

Sympathetic stimulation results in the release of noradrenaline, which acts upon alpha- and beta-adrenergic receptors.

Question 11

Effects of symathetic stimulation of the salvary glands.

Answer 11

• Decreased production of saliva by acinar cells
• Increased protein secretion
• Decreased blood flow to the glands

Question 12

What provides parasympatheic control of salivary glands?

Answer 12

The parasympathetic outflow is coordinated via centres in the medulla, and innervation occurs via the facial and glossopharyngeal nerves.

Question 13

What triggers parasympathetic stimulation?

Answer 13

The presence of food in the mouth.

Question 14

Parasympathetic stimulation of the salivary system mechanism.

Answer 14

Parasympathetic outflow results in the release of acetylcholine (ACh) onto M3 muscarinic receptors.

Question 15

Effects of parasymathetic stimulation of the salvary glands.

Answer 15

• Acinar cells increase secretion of saliva
• Duct cells increase HCO3– secretion
• Co-transmitters result in increased blood flow to the salivary glands
• Contraction of myoepithelium to increase the rate of expulsion of saliva

Overall, increased parasympathetic stimulation results in an increased flow of saliva that is more watery in composition.

Question 16

What are the phases of swallowing?

Answer 16

• Voluntary phase
• Pharyngeal phase
• Oesophageal phase

Question 17

Voluntary phase of swalowing.

Answer 17

• Mastication leads to a bolus of food being produced
• During this stage the back of the tongue is elevated and the soft palate pulled anteriorly against it. This keeps the food within the oral cavity and allows the airway to remain open.
• Following this, inspiration is inhibited and the bolus of food is moved to the pharynx by the tongue. This leads to the stimulation of the swallowing reflex.

Question 18

Pharyngeal phase of swallowing - Pressure receptors are activated and signal the swallowing center in the brain which:

Answer 18

• Inhibits respiration
• Raises the larynx
• Closes the glottis
• Opens the upper oesophageal sphincter

Question 19

Pharyngeal phase of swallowing - what measures ensure that the food only moves towards the oesophagus?

Answer 19

• The soft palate is elevated to close the nasopharynx
• The true vocal cords close to prevent aspiration.

Question 20

Oesophageal phase of swallowing.

Answer 20

• The larynx lowers, returning to its normal position.
• The cricopharyngeus muscle then contracts to prevent reflux and respiration begins again.
• The bolus is moved down the oesophagus via peristalsis.
• Transit time to the stomach takes around 9 seconds.