physiology of mouth and esophagus

1. Mouth and Oesophagus
by
Dr. Taher F T Elshami

2. Salivary Secretions
• The different salivary glands have varying proportions of
two types of secretory cells, serous cells and mucous cells
• Serous cells produce a watery fluid with a digestive
enzyme called salivary amylase
• Mucous cells secrete mucous
• Parotid glands
• Secrete clear watery, serous fluid
• Rich in salivary amylase
• Submandibular glands
• Secrete primarily serous fluid and some mucus
• Sublingual glands
• Secrete primarily mucus

3. Major Salivary Glands
3
Sublingual gland
Mandible (cut)
Parotid
gland
Masseter
muscle
Submandibular
gland
Tongue
Submandibular
duct
Duct
(a)
Serous cell
Duct Mucous cell
(c)
Serous cell
Duct
(b)
Serous
cell
Mucous
cell
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4. Saliva Compositon
Water (99.5%) Solid (0.5%)
Organic Inorganic
Ptyalin
Mucin
Lysozyme
IgA
Lactoferrin
Na+
K+
Ca+
Cl-
HCO3
Mg
• Main function of Salivary
Gland-secretion of saliva
• Daily secretion -800 to
1500 ml
• pH : 6-7

5. Functions of Saliva
Salivary
Families
Anti-
Bacterial
Buffering
Digestion
Mineral-
ization
Lubricat-
ion &Visco-
elasticity
Tissue
Coating
Anti-
Fungal
Anti-
Viral
Carbonic anhydrases,
Histatins
Amylases,
Mucins, Lipase
Cystatins,
Histatins, Proline-
rich proteins,
Statherins
Mucins, Statherins
Amylases,
Cystatins, Mucins,
Proline-rich proteins, Statherins
Histatins
Cystatins,
Mucins
Amylases, Cystatins,
Histatins, Mucins,
Peroxidases

6.  Under neural control
 Mainly by parasympathetic signals from
Sup & Inf salivatory nuclei
Control of Salivary Secretion
Sup Salivatory Nu
Inf Salivatroy Nu
Facial N
Otic Ganglion
Chorda tympani N
Submandibular G
Parotid Gland

7.  Control of salivary secretion:
 - Mainly nervous regulation, through 2 reflexes:
 [I] Conditioned reflexes:
 - Acquired reflexes.
 - Developed by learning & training.
 - Need an intact cerebral cortex.
 Mechanism of conditioned reflexes:
 (A) Stimulus:
 - Seeing, smelling or hearing, or even thinking of food.

8.  (B) Reflex arc (pathway):
 1- Receptors in the eye, nose & ear.
 2- Afferent cranial nerves (optic, olfactory & auditory).
 3- Center cerebral cortex salivary nuclei (MO).
 4- Efferent
 a) Parasympathetic nerves to salivary gland.
 b) Sympathetic nerves to salivary gland.
 5- Effector organs salivary glands.
 (C) Response salivary secretion:
 a) Parasympathetic large amount, watery & rich in electrolytes.
 b) Sympathetic small amount, viscid & rich in enzymes.

9.  [II] Unconditioned (simple) reflexes:
 - Inborn reflex.
 - Does not depend on training.
 (A) Stimulus:
 - Presence of food in the mouth
 (B) Reflex arc (pathway):
 1- Receptors:Taste buds present on the tongue
 2- Afferent:
 - Chorda tympani “facial nerve” (VII)
 - Glossopharyngeal nerve (IX).
 3- Center: Salivary nuclei in the medulla oblongata.
 4- Efferent:
 a- Parasympathetic nerves to salivary gland.
 b- Sympathetic nerves to salivary gland.
 5- Effector: Salivary glands.
 (B) Response: Salivary secretion.
 a) Parasympathetic large amount, watery & rich in electrolytes.
 b) Sympathetic small amount, viscid & rich in enzymes.

11. Muscles of mastication
 Primary muscles of mastication:
 Masseter
 Temporalis
 Lateral pterygoid
 Medial pterygoid
 Secondary muscles of mastication:
The suprahyoid group of muscles being used as secondary or
supplementary muscles. They are:
 Digastric
 Mylohyoid
 Geniohyoid

12. Food ingestion: stimulated by hunger & Appetite.
Mastication
swallowing.
Mastication(chewing):
By incisors & molar teeth controlled by:
Chewing reflex: stimulated by bolus presence in the mouth causing
reflex inhibition of mastication muscles , lower jaw drops & initiating
a stretch reflex of jaw mastication muscles leading to their rebound
contraction & repeating again the same series of events until the
bolus in fully masticated for easy swallowing.

13. Importance of chewing:
1.Exposing the total surface area of foods specially the raw vegetables
to GIT secretions & enzymes.
2.Prevents excoriation of GIT mucosal surfaces.
3.Increasing the easiness of food emptying from stomach to the
s.intestine.

14. Pharynx Function
 Passageway for air and
food
 Epiglottis is fold of tissue
that determines the
pathway
 Food movement continues
to esophagus via
peristalsis.

15. Structure of the Pharynx
• The pharynx can be divided into the following parts:
• Nasopharynx
• Oropharynx
• Laryngopharynx
Superior
Middle
Inferior
Tongue
Epiglottis
Trachea
Nasopharynx
with mucosa
removed to
show muscles
Pharyngeal
constrictor
muscles:
(a) The tongue forces food into the pharynx.
Food
mass
Hard
palate

16. The Esophagus
 A hollow collapsible tube
 Length- 10 inches
 The upper third contains skeletal
muscles
 The middle third contains mixed
skeletal and smooth muscles
 The lower third contains smooth
muscles and the esophago-
gastric/ cardiac sphincter is found
here
 Functions to carry or propel foods
from the oropharynx to the
stomach

17. Physiology of esophagus
 Upper esophageal sphincter (UES)
 Lower esophageal sphincter (LES)
 High-pressure zone (HPZ)
 UES
 3 cm long zone of increased pressure at upper end of esophagus
 Relaxes with swallowing – normally remains closed (prevents
swallowing of air with inspiration)
 Contracts thereafter Contraction of UES in sequence with
pharynx above and esophagus below
 Essentially same as criopharyngeus muscle

18. LES (functional sphincter)
 3-5 cm zone of increased pressure at lower end of esophagus
 Relaxes with swallowing
 Contracts thereafter in sequence with transmitted pressure increases –
prevents reflux
 Sphincter tone provided by intrinsic myogenic activity
 Sphincter relaxation due to neural activity
HPZ
 Classically believed to be equivalent to LES
 Now felt to be determined by esophageal environment (Not entirely
a result of active motor tone of LES; HPZ results primarily from
exposure of segment of distal esophagus to intraabdominal positive
pressure)

19. Physiology of Swallowing
19

20. Introduction
 Swallowing involves co-ordinated activity of muscles of oral
cavity, pharynx, larynx and esophagus
 The whole process is partly under voluntary control & partly
reflexive in nature
 Swallowing by definition involves passage of bolus of food
(solid / liquid) from the oral cavity to stomach via the
pharynx and esophagus, passing over the entrance to
laryngeal vestibule.
 Voluntary control of Swallowing involves control of jaw,
tongue, degree of constriction and length of pharynx and
closure of laryngeal inlet.
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21. 21

22. Components of deglutition
 Deglution has 3 components
 Passage of bolus from oral cavity to stomach
 Protection of airway
 Inhibition of air entry into the stomach
22

23. Deglutition - phases
Three stages have been traditionally described for the sake of convenience. They
help in the better understanding of the physiological process involved.
 Oral
 Pharyngeal
 Esophageal
23

24. Oral phase
 (I) The first or buccal phase:
 - It is voluntary & consists of
passage of food from mouth to
pharynx. When food is masticated
& mixed with saliva, it collects in
the form of bolus on the dorsum
of the tongue. The tongue then
elevates by contraction of
mylohyoid muscle forcing the
bolus into the pharynx.
24

25. Pharyngeal phase (Pumping action of tongue &
hypopharyngeal suction)
 (II) The second or pharyngeal phase:
 - It is involuntary & consists of passage of
food through pharynx.
 - It begins when food touches the tonsillar &
pharyngeal region.
 - Protective reflexes which prevent food from
entering the respiratory passages. These are:
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a- Reflex elevation of the larynx to be covered by epiglottis & root of the tongue. So, opening of
larynx is closed & food cannot enter the trachea.
b- Reflex inhibition of respiration (apnea). The swallowing center in medulla inhibits the
respiratory center.
c- Reflex elevation of soft palate which becomes in contact with posterior pharyngeal wall & shuts
the posterior nasal openings from the pharynx. So, food cannot enter the nose.

26. Role of epiglottis in the pharyngeal phase
 The movement of epiglottis occurs
in two stages
 The epiglottis moves from vertical –
horizontal position
 The upper third of epiglottis moves
below the horizontal to a slightly
lower level to cover the narrowed
laryngeal inlet
26

27. Esophageal stage
 (III) The third or esophageal phase:
 - It is involuntary & consists of passage
of food down the esophagus to the
stomach.
 - Immediately after semisolid food
enters the upper esophagus, a
peristaltic wave starts & propels food
down the esophagus to the stomach.
 - This phase is helped by mucin & gravity
in erect position.
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28. Neural control of swallowing
 Two areas of brain are involved
 Cerebral cortex
 Brain stem
28
 Neural control of swallowing involves a number of different regions of the
CNS, extending from the motor nuclei within the brainstem, up to the
cortex. The act of swallowing is regulated by sensory feedback.
 The initiation of swallowing can either be as a voluntary act, or a reflex as
the result of stimulation of the mucosa in the oral cavity. The latter may
occur during saliva accumulation or by presence of food or liquid.
 Due to anatomical & physiological close relationship between swallowing,
ventilation & mastication, there is extensive overlap in the brainstem
areas controlling these functions.