Mastication Flashcards
What is mastication?
chewing - solid food is chewed, cut, torn and ground into smaller pieces
What structures are involved in chewing?
- upper and lower jaws with teeth 2. the striated mandibular muscles 3. the tongue and cheeks
Course of the food during mastication?
food is forced from oral cavity to the vestibule and back, crossing and recrossing the occlusional surfaces
Importance of chewing?
- exposing starches in food to salivary amylase
- increase surface area of ingested material for enzymatic attack
- Taste sensations are enhanced by mastication by dissolving or suspensions of solid components in the saliva
- prevent injury to the lining of the pharynx and eosophagus by reducing size of ingesta
What stimulates salivation?
- taste sensations - also stimulate gastric secretions 2. chewing
Centres integrating chewing lie where?
- lower brainstem in the basal ganglia
2. cerebral cortex
Function of the tongue after mastication and salivation?
the tongue compacts food into a bolus
What structures produce saliva?
- buccal glands
- 3 pairs of extrinsic salivary glands
- produce 1 litre
Structure of extrinsic glands?
connected to oral cavity via ducts
Describe the kinds of saliva?
- serous - producing saliva rich in protein, water and electrolytes (parotid gland)
- mucous gland (sublingual gland) - produce mucus
- mucus + protein - submandibular gland
What is the composition of saliva?
- Constitutes 99% Water, hypoosmotic to plasma
- Electrolytes: Na+, K+ , Ca2+, Cl- and bicarbonate (HCO3-)
- Digestive enzymes: α-amylase, lysozymes
- Proteins: mucus (mucins), IgA and IgM
What are the functions of saliva?
- keeps mouth moist
- facilitates speaking
- health of the mouth
- facilitates swallowing
- digestion of starches
- facilitates food taste
- immunity
How does saliva maintain the health of the mouth?
- contains substances that limit and regulate bacterial growth 2. contains alkali that neutralises acid
How does saliva aid in the digestion of starch?
- Saliva contains salivary amylase (ptyalin or alpha-amylase) 2. Mediates starch digestion in the mouth
How does saliva ease swallowing?
Saliva moistens and lubricates food so that it can be broken down by chewing before being swallowed : 1. the water in the saliva moistens the food particles 2. salivary mucins bind masticated food into coherent and slippery bolus that can easily slide through the esophagus without damaging the mucosa
What regulates secretion of saliva?
autonomic nervous sytem - sympathetic + parasympathetic
Sympathetic stimulation causes?
secretion of small amounts of viscous saliva
Parasympathetic stimulation causes?
profuse secretion of watery saliva with a relatively low content of organic material
Where does the parasympathetic outflow originate?
salivary nuclei of the medulla oblongota
The salivary nuclei receives afferent signals from?
- mouth + palate - taste and touch 2. nose - smell 3. higher centres - brain stem nuclei
What causes reflex secretion of saliva?
- food in the mouth 2. stimulation of the vagal afferent fibres at the gastric end of the oesophagus
What accelerates salivary production?
- chewing with an empty mouth
- smell
- irritating stimuli
What is swallowing/deglutition?
the movement of food from the mouth through oesophagus into the stomach - facilitated by saliva and mucus
What structures are involved in swallowing?
mouth, pharynx + esophagus
What are the 3 reflex stages involved in swallowing?
- oral 2. pharyngeal 3. oesophageal
What is the oral (buccal) phase?
the voluntary phase where food is moved from mouth to pharynx
Describe the oral stage?
food is compressed into a bolus against the hard palate by the tongue and the bolus is then moved backwards into the pharynx - once the bolus enters the oropharynx it stimulates touch receptors that initiate the swallowing reflex
Describe the pharyngeal stage?
the upper oesophageal sphincter relaxes and it lasts less than a second - Elevation of the larynx and folding of the epiglottis direct the bolus over the closed glottis while the uvula and soft palate block passage back to the nasopharynx
How do the swallowing reflexes begin?
as tactile receptors on the palatal arches and uvula are stimulated by the passage of the bolus
Describe the swallowing reflex?
- The information is relayed to the swallowing centre of the medulla oblongata via the trigerminal and glossopharyngeal nerves
- Motor commands originating at this point cause the soft palate and uvula to close nasopharynx, and epiglottis to close opening to larynx
- During this period, the respiratory centres are inhibited, and breathing stops
Describe the oesophageal stage?
- Food enters the oesophagus and initiates peristaltic wave that sweeps the bolus to the stomach in 5 to 6 seconds
- Once within the oesophagus, the bolus is pushed toward the stomach by a peristaltic wave
- The approach of the bolus triggers the opening of the lower oesophageal sphincter, and the bolus proceeds to the stomach
Name the types of peristalsis in the oesophagus?
- primary 2. secondary
Describe primary peristalsis?
- Initiated by swallowing and reflexely controlled by medullary swallowing centres 2. Coordinated by afferent and efferent fibres within the grossopharyngeal and vagus nerves
Describe secondary peristalsis?
- Occurs in the absence of pharyngeal phase
- Sweeps the oesophagus clean of material left after previous swallow or refluxed from stomach
- Driven by local reflexes triggered by the stimulation of sensory receptors in the oesophageal walls
- May be caused by dry or poorly lubricated bolus
- These receptors relay information by way of the submucosal and myenteric plexus
When can food enter the stomach?
when the lower oesophageal sphincter relaxes
