Mastication (Chewing)
 To grind & break food into small parts.
 Function
 Facilitate swallowing
 Mix food with saliva
 Stimulate tastebuds that affect secretion of saliva, stomach & pancreas
 Mechanism:
 Can be done voluntary.
 Most chewing is reflex in response to the present of food in mouth.
Salivary Secretion
 3 pairs of glands
2 parotids
20%
Serous sec.
Rich in enzymes
2 submandibular
70%
Mixed secretion
(mucous + enzymes)
2 sublingual
5%
Mucous
Buccal glands
5%
Mucous
 Nerve supply:
Symp. 1st & 2nd thoracic seg.
relay in cervical ganglia
Parasymp. 7th & 9th cranial cranial
nerve facial glosso-phary.
Composition of Saliva:
 Volume
 pH
 Tonicity
1-1.5 lit/day
6-7 i.e. acidic
Hypotonic than plasma
99.5%
0.5%
Water
Solids
Organic
Mucous to
lubricate food
Enzymes
Ptylin
(S.amylase)
Lingual lipase
Lysozymes
(antibacterial)
Inorganic
Na & cl less than plasm.
K+ & HCO3- more than plasm.
Functions of Saliva:
1. Swallowing moisten food particles lubrication by
mucous.
2. Speech help movement of tongue & lips.
3. Solvent for substance to stimulate taste bicarbonate.
4. Antibacterial due to presence of lysozymes.
5. Buffer action due to presence of bicarbonate to
prevent dental caries.
6. Excretion of drugs as Hg & I2.
7. Regulation of osmolality by sensation of thirst.
8. Digestion Saliva is not essential for digestion Starch
 amylase maltose
Xerostomia:






 or arrested salivary secretion
Dry mouth.
Bad odor.
Dysphagia (difficult swallowing).
Dental caries.
Difficulty in speech.
Mechanism of Salivary Secretion:
[1] Primary sec. = (Acini stage) contains
enzymes mucous electrolytes very near
to ECF




[2] Secondary sec.
= (Duct stage)
Na+
K+
actively
actively
reabsorbed
secreted


 Na+ in Saliva
 K+ in Saliva
Na reab. > K+ secretion  -ve 70 mv. inside duct.
HCO3- are secreted by duct into lumen.
HCO3- is exchanged with cl-.
Duct is impermeable to H2O  hypotonic.
Characters of Saliva under Resting condition:
Hypotonic
Rich in K+ &
HCO3-
Poor in Na+ & cl-
Characters of Saliva under Activity:
 Salivary flow is rapid
   time for electrolyte exchange
Saliva
Hypotonic
(closer to isotonic)
Less K+ & HCO3that of plasma
Aldosterone hormone:
  Na+ & cl-  K+ secretion reab.
 N.B.: If rate of salivary flow is rapid 




 K+ loss.
  K+ in plasma.
 Hypokalemia.
 Muscle weakness & paralysis.
High Na+ & cl- but
still less than plasma
Control of Salivary Secretion:
 Under nervous control Only why there is No hormonal control
 The hormonal control needs
 Time, while food in mouth
 Stay for very short time
Basal Secretion of Saliva:
 Continuous & spontaneous.
 Occurs even in absence of stimuli.
 Is due to parasymp. Tone
 Control of secretion
 Unconditioned reflex (simple)
 Conditioned reflex (acquired)
Unconditioned reflex:
 Food in mouth stimulate
Chemoreceptors
Pressure receptors
 Afferent 7, 9, 10 cranial nerves.
 Centre M.O.
 Efferent 7 & 9 cranial nerves.
 Response   salivary secretion.
 N.B.: During dental procedures, salivary secretion is
 due to stimulation of pressure receptors.
Conditioned Reflex (Acquired):
 Before food enters mouth.
 Sight, smell, odor, hearing thinking.
 Centre:
Cerebral cortex

+++ superior & inferior
Salivary nuclei

 Afferent:
7th & 9th cranial nerves
 Response:  Salivary secretion
 This reflex needs previous experience.
 Removal of cortex  Loss of Cond. Re.
Role of Autonomic Nerves:
Parasymp.
Symp.
Dominant role
Visicid
True secretion
Concentrated
High volume ( water)
Small volume
Rich in enzymes
Rich in mucous
Cause dry mouth during stress
N.B.: VIP is cotransmitter with ac. ch.
VIP  V.D not blocked by atropine
 The smooth muscles of G.I.T. are arranged in bundles.
 They are electrically connected with one another through gap
junctions that allow low-resistance movement of ions from one
cell to the next.
 So, each muscle layer functions as functional a syncytium.
 The pace maker cells of G.I.T smooth muscle are present in the
circular muscle layer.
 These cells are called:
 Interstitial cells of Cajal
 These Cajal cells are self excitable like SA-node
 Electrical activity of G.I.T
is divided into
Basic electric rhythm
= Slow wave potential
= Resting membrane potential
 It is the passage of food from mouth to stomach.
 Started: Voluntary (Buccal phase)
 Completed: Involuntary (Pharyngeal & oesoph.)
 Controlled by: Deglutition Centre in M.O.
 Involves 3 phases
 Buccal (oral)
1 sec.
 Pharyngeal phase
2 sec.
 Oesophageal phase
8-10 sec.
1.Buccal phase (Oral phase):
 Voluntary lasts for 1 sec.
 Passage of food from mouth to phary. by contraction
Hard palate
of myelohyoid muscle.
 The bolus is on the dorsum of tongue
 The tip of tongue is in contact to hard palate.
Bolus
Tongue
 Tongue moves upward & backwards
 To push bolus into pharynx.
 We can stop deglutition in this buccal phase (bec. it
voluntary).
2. Pharyngeal phase:
 Involuntary lasts 2 sec.
 Passage of food from pharynx to oesoph.
 When bolus is at oropharyngeal junction
 It stimulates:
Pressure receptors
 Afferent : 5 & 9 cranial nerves.
 Centre
: Deglutition centre in M.O.
 Efferent : 5, 9, 10 & 12 cranial n.
Events:
Palatopharyngeal folds:
 Approximate to prevent passage of large bolus into pharynx.
Soft palate (uvula):
 Moves upwards to close posterior nasal cavity to prevent food
entrance into nasal cavity.
Respiration:
 Is inhibited
 i.e. reflex apnea for 2 sec.
Vocal cords:
 Approximated.
Larynx:
 Moves upwards & anterior to be covered by epiglottis.
 Anterior movement will open upper oesoph. sphincter.
Pharyngeal muscles:
 Fast pharyngeal peristalsis to  intrapharyngeal pressure to move
bolus into oesophagus.
 It is Primary Peristalsis.
Upper oesophageal sphincter:
 Is relaxed by the anterior movement of larynx.
3.Oesophageal phase:
 Involuntary.
 Passage of food from oesophagus into stomach.
 2 types of peristalsis.
Primary Peristalsis
Secondary Peristalsis
 Continuation of peristaltic wave
initiated in pharynx.
 Takes 8-10 sec.
 Occurs with each swallowing
 Controlled by swallowing centre in
M.O.
 If food is remained in oesoph. wall.
 Food attached to oesph. wall will
stimulate.
 Pressure receptors

 Local
reflex
from
oesophageal
myenteric plexus

 Very strong Powerful peristalsis to
push food till reached to stomach.
 Sec. peristalsis occurs when primary
fails to move food into stomach.
Lower esophageal sphincter LES:
 Formed of circular muscle.
 It is Tonically contracted to prevent reflux of Hcl from
stomach into oesoph.
 When peristalsis reaches lower end of esophagus, LES is
relaxed to allow bolus to pass into stomach.
Esophageal secretion:
Only
To lubricate food
mucous
No enzymes.
To protect wall of esoph. from Hcl
of stomach
Motor disorders of esophagus:
(1) Achalasia
Failure of relaxation of LES.
Due to:
Damage of myenteric plexus.
 Accumulation of food in esophagus.
 Distension of esoph.
Treatment:
Antispasmotics to relax sphincter
Surgical myotomy to dilate sphincter.
(2) LES incompetence
 If LES is incompetent Hcl reflux from
stomach to esoph.
 Heart burn.
(3) Dysphagia:
 i.e. difficulty in swallowing
 Ex.
 Myasthenia gravis
 Paralysis of 5, 9, 10 cranial nerves.