Physiology of Mastication Swallowing

Question 1

Describe the mechanisms involved in chewing.

Answer 1

1. Mechanical breakdown:
   - Grinds and breaks up food into smaller pieces.
   - ^ surface area for salivary enzymatic digestion

Question 2

Describe the mechanisms involved in salivation.

Answer 2

1. Lubrication:
   - Mix food with saliva (salivary amylase), starts enzymatic digestion.
   - Facilitates swallowing softens and lubricates food (mucus).
   - Stimulates taste buds: reflex= ^ in salivary, gastric, pancreatic and bile secretion to prepare for arrival of food.

Question 3

List the salivary glands.

Answer 3

• Parotid glands 20-25% largest and saliva is serous/ watery
• Submandibular glands 70-75% (major and mixed serous + viscous)
• Sublingual glands 3-5% most viscous saliva
• Minor glands
  *Total production = 1-2 Litres/ day.

Question 4

List the composition of saliva.

Answer 4

• 99.5% H2O; 0.5% electrolytes and protein.
• Proteins:
  1. Salivary α-amylase (starch)
  2. Lingual lipase (dietary lipids)
  3. Mucins (glycoproteins)
  4. IgA and lysozyme (immune defence)
• Hypotonic: Low Na+ and Cl-, high K+ and HCO3-
• pH 6.0 - 8.0

Question 5

List the functions of saliva.

Answer 5

• Begins digestion of dietary starches
• Lubrication facilitates swallowing
• Oral Hygiene:
  1. Antibacterial action: Lysozymes: lyses and destroys certain bacteria. IgA: respond to bacteria and maintain homeostasis of oral microbiota.
  2. Buffering: rich in bicarbonate buffers, neutralise acids from food and bacteria
  3. Flushes away food particles, epithelia etc.

Question 6

Explain the control of salivary secretion and xerostomia.

Answer 6

• Xerostomia: dry mouth resulting from reduced or absent saliva flow.
  1. Simple (unconditioned) salivary reflex:
• Chemoreceptors and pressure receptors respond to pressure of food.
• Initiate impulses in afferent nerves to salivary center.
• Parasympathetic efferent impulses via extrinsic autonomic nerves transmitted to salivary glands = ^ salivation.
  2. Acquired (conditioned) salivary reflex:
• Occurs without stimulation
• Learned response based on experience (thinking, smelling)

Question 7

Outline the oral phase of swallowing/ deglutination.

Answer 7

• Oral / Buccal (voluntary) bolus is rolled from mouth to pharynx.
• Involves: Masticatory, buccinator, floor of mouth, lips (orbicularis oris muscle), tongue.

Question 8

Outline the pharyngeal phase of swallowing/ deglutination.

Answer 8

• Pharyngeal reflex: bolus moves from pharynx to oesophagus.
• Involves palate, pharynx, larynx, and tongue.

Question 9

Outline the oesophageal phase of swallowing/ deglutination.

Answer 9

• Oesophageal reflex: bolus moves from oesophagus to stomach.
• Involves UES, LES, closure of nasopharynx, raising of larynx, epiglottis closing, peristalsis.
  *LES= lower oesophageal sphincter.

Question 10

Describe the control of the lower oesophageal sphincter and its role in achalasia.

Answer 10

• Impaired swallowing due to excess LES tone, weak oesophageal peristalsis and failure of LES relaxation.

Question 11

Identify the causes of vomiting and the reflexes involved.

Answer 11

• Defence mechanism of GI tract to elimination of harmful substances.
• Pharyngeal (gag) reflex (vagus nerve).
• Stimulation of vomiting (emetic) centre in medulla, integrates input and modulates response
  to noxious stimuli, multiple pathways