L9 - Mouth and oesophagus physiology

Question 1

What are the names of the 3 salivary glands located in the mouth?

Answer 1

Parotid:
- watery saliva
- a-amylase

Sublingual:
- thick saliva
- mucus

Submandibular:
- watery saliva
- a-amylase

• ~1500mL saliva secreted each day!

Question 2

How is saliva formed?

Answer 2

Isotonic fluid produced by acinar cells in the salivary glands

• acinar cells - secrete electrolytes + water

Question 3

What are the components of saliva and their functions?

Answer 3

1. Water:
   - moistens food + dissolves food molecules
2. Mucus:
   - lubrication of food - easy to swallow
3. HCO3-:
   - neutralises acids in food + bacterial metabolites
4. Lysozymes:
   - kills bacteria (health maintenance of teeth + gums)
5. Amylase:
   - breakdown of carbohydrates (initial)
6. Lipase:
   - breakdown of fats (initial)

Question 4

What are the neuronal inputs of the regulation of saliva secretion?

Answer 4

• Reflexes mediated via ANS - sympathetic + parasympathetic
• Both systems stimulate salivary secretion - parasympathetic produces greater response
• Stimuli (taste/smell) triggers response in chemoreceptors + pressure receptors in walls of mouth + tongue
• ↑ saliva production, as ↑ blood flow from ↑ parasympathetic activity
• Response from parasympathetic - saliva produced is watery with mucus + amylase
• Response from sympathetic - ↑ thicker mucus + ↓ blood flow to glands - overall reduction of secretion of watery saliva (causing dry mouth)

Question 5

How is swallowing (deglutition) achieved? - 3 stages

Answer 5

1. Voluntary stage:
   - tongue pushes bolus (food ball) backwards to orthopharynx
2. Pharyngeal stage (involuntary reflex):
   - receptors send afferent impulses to deglutition centre in medulla oblongata
   - centre send signal via efferent fibres to muscles in pharynx + oesophagus
   - soft palate + uvula moves up to seal of nasopharynx (preventing food going up nasal cavity)
   - impulses from deglutition centre: - inhibit respiration
   - raise the larynx
   - close the glottis
   - food further into trachea - epiglottis is tilted backward to cover glottis (causing suspended breathing for 1-2s)
3. Oesophageal stage:
   - food moves down the oesophagus via peristalsis

Question 6

What are the components of the oesophagus and their neuronal control?

Answer 6

Oesophagus - tube connecting laryngopharynx (last 3rd part of pharynx) to stomach

Upper portion 1/3:
- striated muscular layer (skeletal muscle) - assist in swallowing
- somatic (voluntary) input

Middle portion 2/3:
- mixture of skeletal (striated) and smooth muscle
- both somatic + autonomic

Lower portion 3/3:
- only smooth muscle (connected to stomach)
- autonomic input