Transcript No. 4

NO.4
1. Introduction of Alimentary System
2. Oral Cavity
Chapter 2
The Alimentary System
Introduction
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Every cell in the body requires a constant source of
energy in order to perform its particular functions—
these functions are contraction, secretion, synthesis,
or any other. Ingested food provides the basic
materials from which this energy is produced and
new molecules are synthesized. Most food, however,
cannot enter the bloodstream and be used by the
cells of the body until it is broken down into simpler
molecules. The digestive system alters the ingested
food by mechanical and chemical processes so that
it can ultimately cross the wall of the
gastrointestinal tract and enter the blood vascular
and lymphatic systems. The vascular system then
carries these food molecules through the hepatic
portal vein to the liver before distributing them to
cells throughout the body. After entering the cells,
the digested food molecules may be reassembled
into proteins, carbohydrates, and lipids, or they may
be used in the production of energy to support body
activity.
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Constitution:
1. Alimentary canal and certain
accessory organs.
2. Alimentary glands.
The alimentary system (or digestive
system) comprises the alimentary canal
(gastrointestinal tract) and certain
accessory organs including lips and cheeks,
palate, tongue, and teeth, as well as
glands (salivary glands, liver and
pancreas).
Functions:
Ingestion of food into the mouth
Movement of food along the digestive tract
Mechanical preparation of food for digestion
Chemical digestion of food
Absorption of digested food into the circulatory and
lymphatic systems
Elimination of indigestible substances and waste
products from the body by defecation
Alimentary canal
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The alimentary canal about 9 m long
extends from the mouth to the anus.
It consists of the following 6 parts:
The mouth
The pharynx
The esophagus
The stomach
Small intestine: is divided into three parts:
the duodenum, jejunum, and ileum.
Large intestine
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Section 1 The Oral Cavity
The oral cavity
(mouth) is the
first part of the
digestive tract.
It extends from
the lips to the
oropharynx.
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Division:
Oral vestibule and Oral cavity proper:
Oral vestibule: an outer, smaller part. It is
a slit-like space, bounded externally by
the oral lips and cheeks, internally by the
gums and teeth. It communicates with the
exterior by the oral fissure.
When the teeth are occluded it
communicates with the oral cavity proper
by an aperture behind the 3rd molar teeth
on each side, and by narrow clefts
between contiguous teeth.
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On the inner surface of the cheek, opposite the
crown of 2nd upper molar tooth, a small papilla
marks the opening of the parotid duct.
Oral cavity proper: an inner, large part. It is
bounded laterally and in front by the alveolar
arches, the teeth and gums; behind, it
communicates with the pharynx by isthmus of
fauces (the oropharyngeal isthmus) between the
palatoglossal arches.
The roof of the oral cavity consists of the hard
palate and soft palate, while the greater part of
the floor is formed by the tongue.
Ⅰ. The Oral Lips
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Construction: Each lip consists
mainly of muscle covered by skin
externally and mucous membrane
internally. The red margin of the lips
is seen where the skin meets the
mucous membrane.
Ⅱ. The Cheeks
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They have a structure similar to the
lips –an outer skin, an inner mucous
membrane and a layer of muscle in
between.
The parotid duct opens on the inside
of the cheeks opposite the upper
second molar tooth.
Ⅲ. The Palate
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It constitutes the roof of the mouth
and the floor of the nasal cavity.
Composition: two regions;
The hard palate: an anterior twothirds. The hard palate is formed by
palatine processes of the maxillae
and the horizontal plates of the
palatine bones. It is covered with a
dense tissue, formed by the
periosteum and mucous membrane.
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The soft palate: a posterior one-thirds.
The soft palate hangs like a curtain
between the mouth and the oropharynx.
Uvula,
Palatoglossal arch,
Palatopharyngeal arch,
Isthmus of fauces: The palatoglossal
arch runs downward to the side of the
base of the tongue and forms the lateral
boundary of the isthmus fauces.
Tonsillar fossa.
Ⅳ. The Palatine Tonsils
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The palatine tonsils,
which are
composed mainly
of lymphoid tissue,
are located in the
tonsillar fossae.
Ⅴ. The Teeth (Dentes)
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Two sets of teeth in man: Deciduous
(milk) and permanent.
Basic shape: all teeth have a similar
basic structure
Crown: projecting above the gum
Root (or roots): in the jaw and a
narrowed part
Neck: between the crown and the
root
Structure:
Dentine: the bulk of the tooth consists
of dentine.
Enamel: over the dentine of the crown
is the enamel.
Cement: round the dentine of the root
is the cement.
Periodontal membrane: attaches the
root of the tooth to its socket.
Cavum dentis (dental cavity) and
dental pulp: there is a small opening
called the apical foramen at the apex
of the root through which vessels
and nerves pass to and form the
dental pulp. The cavum dentis, (or
dental cavity) within a tooth, is
divided into the cavity of the crown
and a root canal, both filled with
dental pulp.
Dental arrangement:
Deciduous teeth: 20 in number. 5 in each
quadrant.
They are, from the midline in front passing
laterally and backwards,
2 incisors, 1 canine and 2 molars.
Permanent teeth: 32 in number, 8 in each
quadrant.
They are, from the midline in front and
going backwards, 2 incisors, 1 canine, 2
premolars, and 3 molars. The third molars
are also called wisdom teeth. Sometimes
the third molars do not erupt.
Dental functions:
In general the incisors and canine are
for cutting and the premolars and
molars for masticating.
The periodontal structure: the sockets
and the gums (gingivae) together
with the periodontal membrane are
usually called the periodontal
structure.
Ⅵ. The Tongue (Lingua)
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The tongue forms the floor of the mouth.
It is composed of interwoven bundles of
skeletal muscles covered with mucous
membrane.
The shape of tongue:
The tongue has a root, an apex, a dorsum
and an inferior surface.
The dorsum: has a V-shaped groove called
the terminal sulcus. It serves as the
boundary between the oral part (or
anterior 2/3) , and pharyngeal part (or
posterior 1/3) of the tongue.
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Papillae:
The mucous membrane that covers
the dorsum of the tongue is modified
by the presence of numerous small
projections called papillae.
There are three types of papillae on
the tongue.
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Vallate papillae: They are about 1～
2mm in diameter and form a row in
each side just in front of and parallel
to the terminal sulcus. Each papilla is
a flat-topped elevation of mucous
membrane and surrounded by a
deep groove. In the walls of the
groove are studded with taste buds.
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Fungiform papillae: They are found
chiefly on the sides and tip of the
tongue and appeared as red spots.
These papillae also have taste buds.
Filiform papillae: They are conical in
shape and are found over the
dorsum of the front part of the
tongue. These papillae have no taste
buds.
The mucous membrane of the
inferior surface of the tongue:
Frenulum of tongue is a vertical fold of
mucous membrane in the midline
between the tongue and the floor of
the mouth.
Sublingual caruncle
Sublingual fold
Lingual muscles:
Including two types of muscles
The extrinsic muscles of the tongue connect
the tongue to the base of the skull above
and behind, to the hyoid bone below, to
the jaw below and in front and to the soft
palate above. The extrinsic muscles of the
tongue are three on each side:
hyoglossus,
styloglossus,
genioglossus.
The intrinsic muscles are originate and
insert in the tongue. Their fibers run
in various directions and modify the
shape of the tongue in many
different ways.
Action of tongue: the tongue can be
raised, depressed, protruded and
retraceted by these muscles.
Ⅶ. The Salivary Glands
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About 1000 to 2000 ml of saliva is
secreted daily into the mouth.
There are three pairs of the major salivary
glands whose ducts open into the mouth.
There are also much minor salivary glands
in the lips, cheeks, tongue and palate.
The major salivary glands comprise three
large paired masses- the parotid,
submandibular and sublingual glands.
Ⅰ). The Parotid Gland
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The largest pair.
Shape: an inverted, flattened, three sided
pyramid.
Location: It lies below the external acoustic
meatus, between the mandible and the
sternocleidomastoid.
Parotid duct: each parotid gland has a duct
(parotid duct) that passes forwards across the
masseter muscle and then turns inwards. It
pierces the buccinator and opens upon a small
papilla on the oral surface of the cheek opposite
the crown of the second upper molar tooth.
Ⅱ). The Submandibular Gland
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Shape: it is irregular in form and about
the size of a chestnut.
Location: it lies in the upper part of the
neck under the skin below the floor of the
mouth and deep to the body of the
mandible.
Submandibular duct: is about 5 cm long,
opens on the sublingual caruncle at the
side of the frenulum of the tongue.
Ⅲ). The Sublingual Gland
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Shape: narrow, flattened, shaped
somewhat like an almond.
Location: it is located on the floor of the
mouth within a fold of mucous membrane.
Sublingual duct: each sublingual gland has
several small ducts that open onto the
floor of the mouth on the summit of the
sublingual fold; and, occasionally a few
open into the duct of the submandibular
gland.