Lecture 33: GIT 2

Question 0

Mastication

Answer 0

• Initiates mechanical breakdown of food and allows mixing with saliva
• Under voluntary control
• Cutting and grinding of food with teeth
• Tongue and buccal muscles position food within mouth
• Trigeminal nerve (CN V) – sensory to teeth and motor to jaw muscles
• Facial nerve (CN VII) – motor and sensory to tongue and pharynx
• Glossopharyngeal nerve (CN IX) – sensory to caudal 1/3 of tongue
• Hypoglossal nerve (CN XII) – motor to tongue

Question 1

What is prehension?

How does it happen?

Answer 1

• Bringing food into mouth
• Involves lips, teeth and tongue + head and jaw movements
• Voluntary
• Facial (CN VII), hypoglossal (CN XII) and trigeminal (CN V) nerves provide motor innervation to lips, tongue, and muscles of jaw, respectively
• Sensory input important, involving olfactory nerve (CN I) (smell), optic nerve (CN II) (vision) and trigeminal nerve (sensation to rostral oral mucosa, lips and teeth)
• To drink, draw fluid into oral cavity by suction

Question 2

Salivary glands

Answer 2

• Some secretion from multiple small glands in wall of oral cavity
• Most secretion from paired parotid, mandibular and sublingual salivary glands
• Parotids produce serous secretion
• Secretion from mandibular and sublingual glands is mixed

Question 3

Formation of saliver. 2 step process

Also what is the effect of flow rate on saliva composition

Answer 3

1.Acini secrete fluid containing amylase, lysozyme, mucin, and electrolytes in similar concentrations to plasma
2.During passage through ducts, ionic composition of saliva modified
ØNa+ and Cl- reabsorbed
ØK+ and HCO3- secreted

Effects of flow rate on saliva composition
•High flow – less time for modification in ducts (isotonic)
•Low flow – less Na+ and Cl- and more K+ (hypotonic)
•Saliva HCO3- > plasma HCO3-, except at very low flow rates

Question 4

What is the composition of saliva and what is each of its functions?

Answer 4

• 98% water
• Mucin – forms mucus when mixed with water – acts as lubricant
• Amylase – initiates starch breakdown
• Bicarbonate – neutralises acids produced by oral bacteria – prevents acid damage to dental enamel
• Lysozyme and antibodies – protection against oral bacteria

Question 5

How do you regulate salivary secretion?

Answer 5

• Regulated exclusively by autonomic nervous system
• Volume and composition = balance between parasympathetic and sympathetic activity
• Parasympathetic stimulation – high volume; watery consistency
• Sympathetic stimulation causes constriction of blood vessels supplying glands – low volume; viscous consistency + increased amylase
• During meals, parasympathetic predominates
• Reflex activity – tactile stimuli from mouth, and sight or smell of food

Question 6

Deglutition: swallowing

What are the different phases?

Answer 6

• Initial phase voluntary – food bolus moved against pharynx
• Remaining phases involuntary – reflex activity

VOLUNTARY
•Oral
INVOLUNTARY (REFLEX)
•Pharyngeal
•Oesophageal
•Gastro-oesophageal