Anatomy of the Digestive System

Lecture 1
Oral Cavity (Mouth)
 The mouth extends from the lips to the oropharyngeal isthmus,
through which it communicates with the oral part of the pharynx.
 It is divided into an outer part, the vestibule and an inner part,
the mouth proper.

The Lips
 These are two folds that enclose the mouth opening, and act as a
voluntary sphincter.
 Each lip is covered externally by skin and internally by mucous
membrane that continues into the oral cavity, where it lines the
mouth.
 The core of the lip is filled by the fibers of the orbicularis oris
muscle, loose connective tissue, labial vessels and nerves,
lymphatic vessels, and several labial salivary glands.
 Their ducts open into the vestibule.
 The upper lip is marked at midline by a shallow vertical groove,
the philtrum, which ends at the junction between skin and mucous
membrane in a small prominence, the tubercle.
 When the lips are closed, the fissure between them is called the

oral fissure. The internal surface of each lip is connected to the

corresponding dental arch by a midline fold of mucous
membrane, the labial frenulum.

The Vestibule
 Is a slit-like space.
 Bounded externally by the lips (anteriorly) and the cheek
(laterally); and internally by the upper and lower dental arches
(gums and teeth).
 When the mouth is closed, it communicates posteriorly behind the
third molar tooth with the mouth proper.
 The parotid ducts open into the vestibule opposite 2 nd upper
molar teeth.
 The internal surface of each lip is connected to the corresponding
dental arch by a midline fold of mucous membrane, the labial
frenulum.

1
The Cheeks
 The cheeks form the lateral walls of the vestibule.
 The core of the cheek is principally formed by the buccinators
muscle with a considerable amount of adipose tissue.
 The checks are lined by mucous membrane, and covered by
skin.
 Several small mucous secreting glands, the buccal glands are
situated in the submucosa.
 Four or five of these glands, the molar glands are larger than
the rest, situated external to the buccinators around entry of
parotid duct. Their ducts open into the mouth opposite 3 rd
molar teeth.

The Gingiva (Gum)

 The gengiva is a mucous membrane covers the alveolar process
of the maxillae and mandible, respectively, and is firmly
adherents to their periosteum and to neck of the teeth.
 They extend slightly into each socket to form the gingival
sulcus.

The Teeth
 These are accessory organs fitted in sockets of the alveolar
process of the maxillae (upper teeth) and mandible (lower
teeth).
 Each tooth is composed of three principal regions, crown, neck,
and root.
 The crown is the portion of the tooth that lies above the level of
the gum, and is the only visible part.
 Each tooth has from 1 – 3 roots, embedded in the
corresponding socket of the alveolar process.
 The neck is the constricted portion between the crown and
roots, and situated close to the gum line.
 The crown is covered by the hardest tissue in the body, the
enamel.
 The root is covered by cementum, which is a calcified tissue
rather like bone.
 At the neck region, the enamel and cementum meet.
 The tooth consists of dentin, a vascular calcified connective
tissue that gives the tooth the basic shape and rigidity.

2
 The dentin is perforated by minute canals, the dentinal tubules.
 The dentin surrounds a cavity known as the pulp cavity.
 This cavity lies within the crown, and is filled by the dental
pulp.
 The pulp consists of a loose connective tissue in which nerves,
and blood and lymphatic vessels are embedded.
 The pulp is enclosed with a simple columnar epithelium, which
lies in contact with the inner surface of the dentine.
 The cells of this columnar epithelium are termed odontoblasts.
 These cells present cytoplasmic extensions that occupy the
dentinal tubules.
 Throughout life, the odontoblast cells retain the power to
produce dentin.
 Inferiorly, the pulp cavity becomes continuous with a narrow
canals run through the root(s), the root canals.
 Each one of these canals has an apical foramen at its base,
through which nerves, and blood and lymphatic vessels pass.

The Mouth Proper

 The mouth proper is bounded anterolaterally by the upper and
lower dental arches, and posteriorly by the oropharyngeal
isthmus.
 The roof is formed anteriorly by the hard palate and
posteriorly by the anterior part of the soft palate.
 The floor is formed by the anterior two-thirds of the tongue,
and by the reflection of the mucous membrane from the lower
surface and sides of the tongue to the internal surface of the
gum.
 The frenulum is a prominent median fold of mucous
membrane connects the ventral surface of the tongue to the
floor of the mouth.
 On either side of the frenulum of the tongue, the mucous
membrane of the floor of the mouth presents an elevation, the
sublingual fold, which is produced by the underlying
sublingual gland.
 The sublingual papilla is a small elevation situated on each side
of the frenulum of the tongue.
 It exhibits the opening of submandibular duct. The floor of the
mouth is supported by the genioglossus, geniohyoid, mylohyoid,
and anterior belly of digastrics muscles.

3
The Tongue
 Is a muscular organ covered by a mucous membrane, and is
concerned, with the function of deglutition, taste, and speech.
 Its anterior two-thirds lie in the mouth proper.
 Its posterior one-third of is situated in the oral part of pharynx.
 The root of the tongue is attached to the hyoid bone. A fibrous
septum divides the tongue into right and left half.
 The mucous membrane covering dorsal surface of anterior
two-thirds of tongue is roughened by three types of papillae,
filiform, fungiform, and vallate (lingual papillae).

Filiform papillae
 Are the smallest but the most numerous papillae.
 They are minute conical projections.
 They are present throughout the dorsal surface of the anterior
two-thirds.

Fungiform papillae
 Are larger and less numerous than the preceding papillae.
 They resemble mushroom and are visible as a bright red spots.
 Although they are scattered throughout the dorsum of anterior
two-thirds of tongue, but are especially numerous near sides
and tip of the organ.

Vallate papillae
 Are the largest form.
 They are circular-shaped; vary from 7 – 12 papillae arranged
in the form of a V-shaped row with apex pointing backwards,
immediately in front and parallel with the sulcus terminalis.
 The latter marks the junction of the anterior two-third and the
posterior third of tongue.
 The apex of the sulcus terminalis exhibits a small pit, the
foramen cecum, which is the remains of the upper end of the
thyroglossal duct.
 The mucous membrane covering dorsal surface of posterior
third of tongue is smooth and has a nodular appearance due to
the presence of underlying mass of mucous and serous glands
and aggregations of lymphoid follicles, the lingual tonsil.
 A median fold, the median glossoepiglottic fold connects the
tongue to the epiglottis.

4
 On each side of this fold there is a deep fossa, the epiglottic
vallicula, which is bounded laterally by the lateral
glossoepiglottic fold.
 Each vallate papilla is surrounded by a deep circular sulcus
containing numerous taste buds and serous glands.
 These glands secrete a lipase which perhaps prevents the
formation of a hydrophobic layer over the taste buds that would
prevent their function.
 The fungiform and vallate papillae present taste buds on their
surfaces.
 These buds are specialized onion-shaped structures containing
50 – 100 epithelial cells, most of which are known as the taste
cells.
 These cells are detectors of tastants (substances capable of
eliciting taste).
 The bud rests on the basal lamina.
 At the apical portion of the buds, the taste cells present
microvilli that project through an openings termed the taste
pores.
 Other cells have a supportive function, secreting an amorphous
material that surrounds the microvilli in the taste pore.
 Basal cells are responsible for the replacement of all cell types.
In the human there are at least four types of taste perception,
saltiness, sourness, sweetness, and bitterness.
 The mucous membrane covering inferior surface of tongue is
smooth, and thin.
 It presents scattered mucous and serous glands near sides and
tip of the organ.
 Behind the tip, there is a large mixed gland, the anterior lingual
gland.
 In the median plane, the frenulum of the tongue connects the
inferior surface to floor of mouth cavity.

Extrinsic Muscles of the Tongue

a. Genioglossus
 Fan-shaped, forms the main mass of tongue.
 Arises from the superior genial tubercle (upper mental spine)
of the mandible.
 Inserted into mucous membrane covering the dorsal surface of
tongue (from the tip to the base), and the body of hyoid bone.
Actions:
 The posterior fibers protrude the tongue.

5
 The middle fibers depress central part of tongue to enlarge
mouth cavity.
 The anterior fibers depress and retract tip of tongue.
 Paralysis of the right genioglossus, when you ask the patient to
protrude his tongue the tongue will deviate toward the
paralysed geniglossus.

b. Hyoglossus
 Arises from lateral part of body and greater wing of hyoid
bone.
 Inserted in to posterior half of side of tongue.
Action:
Depresses side of tongue, and assists the genioglossus in the
enlargement of the oral cavity.

c. Styloglossus
 Arises from anterior aspect of lower part of styloid process and
upper part of stylohyoid ligament.
 Inserted into whole length of side of tongue.
Action:
Pulls tongue upwards and backwards.

d. Palatoglossus
 Arises from inferior surface of palatine aponeurosis.
 It descends deep to mucous membrane in front of palatine
tonsil, raises a fold of mucous membrane, the palatoglossal arch
(anterior pillar of fauces).
 Inserted into side of tongue.
Action
 Acts as sphincter at oropharyngeal isthmus, elevates the root of
the tongue and narrows the transverse diameter of the isthmus
by approximating the palatoglossal arches.

The intrinsic muscles of the tongue include superior and inferior

longitudinal; Transverse, and vertical. Their fibers run between
the fibers of genioglossus.

Sensory Supply of Tongue

A.
 The mucous membrane covering anterior two-thirds of tongue
is supplied by lingual branch of the mandibular nerve.

6
 The trigeminal component of this nerve mediates common
sensibility.
 The chorda tympani (branch of facial nerve) component
mediates taste.
B.
The posterior third of tongue is supplied by glossopharyngeal
nerve.

Motor Supply of Tongue

 The palatoglossal muscle is supplied by pharyngeal plexus of
nerves.
 The remaining muscles (intrinsic and extrinsic are innervated
by hypoglossal nerve.
 The mucous membrane of the mouth proper is composed of
stratified squamous epithelium keratinized or nonkeratinized
and lamina propria.
 Keratinized squamous epithelium covers the hard palate and
dorsal surface of anterior two-thirds of tongue.
 The remaining part of the epithelial lining (soft palate, floor of
the mouth, and the dorsal surface of the posterior third and the
inferior surface of the tongue) is of the nonkeratinized type.

7
 Anatomy of the Digestive System
Lecture 2
Salivary Glands
These are cells or organs that discharge a secretion into oral cavity.

A. Major salivary glands

 Lie at some distance from oral mucosa, with which they
communicate through one or more extraglandular ducts.
 In man they comprise: the parotid, submandibular, and
sublingual glands.

B. Minor salivary gland

 Lie in the oral mucosa or submucosa and open directly or
indirectly via many short excretory ducts, on the epithelial
surface of the mucosa.
 They comprise: labial, buccal, and palatal glands, and Ebner's
glands in mucosa of tongue.

Parotid Gland
 The largest of the salivary glands, composed almost entirely serous
acini, and it has a very irregular shape.
 It is wedged in the fossa posterior to ramus of the mandible, and
extends from the external acoustic meatus above, to the upper part
of carotid triangle below.
 Medially, it extends to the styloid process (close to side of
pharynx).
 Posteriorly, it overlaps sternocleidomastoid.
 Anteriorly, it extends forwards over masseter for a variable
distance; a portion of this part is often detached from the rest, the
accessory parotid gland.
 Part of the cervical fascia in which the gland is embedded is
thickened to form the stylomandibular ligament, which extends
from styloid process to posterior border of ramus of mandible, and
separates the parotid gland from the submandibular gland.

Surfaces of the Gland

1. Lateral (superficial) surface

8
 Is covered by skin and fascia, which contains superficial parotid
lymph nodes.

2. Anteromedial surface
 Is grooved by the posterior border of the ramus of the mandible
and extends anteriorly over the masseter and medially to the T.M
(temporomandibular) joint.
 The branches of the facial nerve emerge from the anterior border
of this surface.

3. Posteromedial surface
Is molded to the mastoid process, sternocleidomastoid, posterior belly
of digastric, and styloid process and styloid apparatus.

4. Superior surface
Is in contact with the cartilaginous part of external acoustic meatus.

5. Apex of the gland: Overlaps the carotid triangle.

Parotid duct
 Is a thick walled tube about 5 cm long.
 It appears at the anterior border of the gland.
 It crosses the masseter as far as the anterior border of this
muscle, where it turns inwards, and pierces the buccinator.
 It then opens into the vestibule of the mouth on a small papilla
opposite the 2nd upper molar tooth.

Structure within Parotid Gland

a. The external carotid artery:
 Lies deeper than other.
 It divides within the substance of the gland into superficial
temporal and maxillary arteries.
b. The retromandibular vein:
 Lies superficial to external carotid artery.
 Formed by the union of maxillary and superficial temporal veins.
c. The facial nerve:
 On a still more superficial plane the facial nerve traversed the
gland.
 Within the glands, the nerve divides into its five terminal
branches, which leave the gland at its anterior border.

9
 Submandibular Gland
It is a mixed mucous and serous in type, consists of a large superficial
part and a small deep part, which are continuous with one another
round the posterior border of the mylohyoid.

Superficial part
Lies in the digastric triangle:
Relations
Anterior relations: Anterior belly of digastric muscle.
Posterior relations: Posterior belly of digastric and stylohyoid
muscles, and parotid gland.
Medial relations: Mylohyoid and hyoglossus muscles, and lingual and
hypoglossal nerves.
Lateral relations: It is in contact with the submandibular fossa on
the medial aspect of the mandible.
Inferolateral relations:
 It is covered by investing layer of deep cervical fascia, platysma

muscle, and skin.

 It is crossed by facial vein and cervical branch of facial nerve.
Also the submandibular lymph nodes.

Deep part
 Extends forwards as far as the posterior end of the sublingual
gland, between mylohyoid (below and laterally), and hyoglossus
and styloglossus (medially).
 It is related above to Lingual nerve, and below to hypoglossal
nerve.

Submandibular duct
 Is about 5 cm long, emerges from the middle of the medial
surface of the deep part of the gland.
 It runs forwards between the sublingual gland and the
genioglossus.
 Opens into floor of mouth on the sublingual papilla, which is
situated at the side of the frenulum of tongue.

Sublingual Gland
 Is the smallest of the salivary glands.
 It is mixed mucous and serous in type, the former predominating.
 It is almond-shaped, situated beneath the mucous membrane of
the floor of mouth, close to the midline.

10
Relations
Above: to mucous membrane of mouth. The latter is elevated by the
gland to form the sublingual fold.
Below: to mylohyoid muscle.
Medially: to genioglossus, lingual nerve, and submandibular duct.
Laterally: to sublingual fossa of mandible.
Anteriorly: to the gland of opposite side.
Posteriorly: to deep part of submandibular gland.

Sublingual ducts
 They are 8 – 20 in number.
 Most open separately on the sublingual fold.
 Few may open directly into the submandibular duct.

Histology of Salivary Glands

 The three major salivary glands (parotid, submandibular, and
sublingual), each is surrounded by a fibrous capsule rich in
collagen fibers.
 Each salivary gland secrete saliva, which is a complex fluid that
has digestive lubricating, and protective function.
 The parenchyma of the salivary glands consists of a secretory
portions and branching duct system arranged in lobules.
 These ducts conduct saliva secreted by the secretory portion into
the oral cavity.
 Each gland consists of Lobules, separated from each other by
connective tissue septa originating from the fibrous capsule.
 The secretory portions contain serous and/or mucous cells.
 In human submandibular and sublingual glands, the secretory
portion of the glands contains serous and mucous cells.
 The serous cells form acini; whereas the mucous cells form
tubules.
 The end of these tubules is cupped by serous cells, which
constitute the serous demilunes.
 In addition to the secretory cells, the secretory portion contains
myoepithelial cells.
 The latter cells are found between the basal lamina and the basal
surface of the secretory cells, thus they surround the secretory
portions.

Myoepithelial cells

11
 Are found between the basal lamina and the basal surface of the
secretory cells, thus they surround the secretory portions, usually
2 – 3 cells per secretory unit.
 They are well developed and branched, and are frequently known
as basket cells.
 In the intercalated ducts they lie parallel to the length of the duct.
 Their shapes in these ducts are spindle and present the
characteristics of smooth muscle cells, including contractily.
 In addition to the acceleration of the evacuation of the saliva,
myoepithelial cells play an important function in prevention of
end piece distention during secretion due to the increase in
intraluminal pressure.
 The secretory portions empty into short intercalated ducts.
 These ducts are lined by cuboidal epithelial cells, which have the
ability to divide and differentiate into secretory or ductal cells.
 Many of these intercalated ducts join to form striated ducts.
 Intercalated ducts and striated ducts are also known as
intralobular ducts since they are located within the lobule.
 Striated ducts drain into interlobular or excretory ducts located
within the connective tissue septa separating lobules.
 Proximally, the interlobular ducts are lined by stratified cuboidal
epithelium, but more distally the epithelial lining is converted into
stratified columnar epithelium containing few mucous secretory
cells.
 The main duct of each salivary gland opens into the oral cavity,
and is lined by nonkeratinized stratified squamous epithelium.

Parotid Gland
 It is a branched acinar gland.
 Its excretory portion is composed exclusively of serous cells.
 Serous cells contain secretory granules that are rich in protein
and have a high amylase activity.
 This activity is responsible for hydrolysis of most of the ingested
carbohydrates.
 The digestion begins in the mouth and continues for a short time
in the stomach, before the gastric juice acidifies the food and thus
decreases amylase activity considerably.
 As in other large salivary glands, the connective tissue contains
many plasma cells and lymphocytes.
 The plasma cells secrete IgA, which form a complex with a
secretory component synthesized by the serous acinar,
intercalated duct, and striated duct cells.

12
  The IgA rich secretory complex release into the saliva is resistant
to enzymatic digestion and constitutes an immunological defense
mechanism against pathogens in the oral cavity.

Submandibular Gland
 It is a branched tubuloacinar gland.
 Its secretory portion contains both mucous and serous cells.
 The serous cells are the main component of this gland.
 Serous cells are responsible for the weak amylolytic activity

present in this gland and its saliva. Mucous cells contain

glycoproteins (most of which are called mucins) important for the
moistening and lubricating functions of the saliva.
 Mucous cells are most often organized as tubules.
 The cells that form the serous demilunes in the submandibular
gland secrete the lysozyme, whose main activity is to hydrolyze the
walls of certain bacteria.
 Some acinar and intercalated duct cells in large salivary glands
also secrete lactoferrin, which binds iron, a nutrient necessary for
bacterial growth.

Sublingual Gland
 Like the submandibular gland, it is a branched tubuloacinar
gland formed of serous and mucous cells.
 Mucous cells predominate in this gland.
 As in the submandibular gland, cells that form the serous
demlunes in this gland secrete lysozyme.

13
 Anatomy of the Digestive System
Lecture 3
The Palate
1. The Hard Palate
 Forms the anterior part of roof of mouth.
 Bounded in front and laterally by the upper dental arch (gum
and teeth).
 Its anterior two-thirds are formed by the palatine processes of
maxilla bones.
 Its posterior third is formed by the horizontal plates of the
palatine bones.
 These bones are separated by a cruciform suture made up of
the intermaxillary, interpalatine, and palatomaxillary sutures.

The Soft Palate

 Forms the posterior part of roof of mouth.
 Projects backwards and downwards from the posterior part of
hard palate.
 It consists of an aponeurosis, the palatine aponeurosis, to which
four paired of muscles are attached.
 However, much of the mass of soft palate is formed by mucous
and serous glands.
 The upper and lower surface of the mass of soft palate is
covered by mucous membrane.

Tensor Veli Palatini

 The palatine aponeurosis is formed by the tensor vili palatini.
 The muscles attached to the aponeurosis include the 3 extrinsic
muscles (levator veli palatine, palatoglossus, and palatopha-
ryngeus).
 It then spreads out horizontally to meet the opposite tendon in
the midline to form the palatal aponeurosis.
 The anterior border of the palatine aponeurosis is attached to
the hard palate close to posterior border.
 Anteriorly, the posterolateral borders of the aponeurosis fuse
with the wall of pharynx.

14
 Posteriorly, they are free, and meet in the midline at the uvula.
 The latter hangs free above the posterior third of the tongue.

Actions
 Acting on both sides, they tighten the palatine aponeurosis, so
that other muscles can alter the position of the soft palate.
 Also, it opens the austachian tube to equalize air pressure
between nasal cavity and middle ear.

Levator veli palatine:

 Cylindrical muscle lies medial to tensor veli palatine and
austachian tube.
 It arises from inferior surface of petrous part of temporal bone,
just in front of the external opening of the carotid canal, and
from medial wall of cartilaginous part of austachian tube.
 Fibers of the right and left muscles pass forward, downward
and medially to upper surface of palatine aponeurosis, forming
a V-shaped sling.
Actions
 Bilateral contraction of the levator veli palatine, pulls the soft
palate upwards and backwards, shut off the nasal part of the
pharynx from the oral part.
 Also, opens the austachian tube, and permits equalization of air
pressure between nasal cavity and middle ear.

Palatoglossus
 Arises from the inferior surface of palatine aponeurosis.
 It descends in front of tonsil, raises a fold of mucous
membrane, the palatoglossal fold (anterior pillar of fauces).
 Inserted into side of tongue.
 This muscle acts as sphincter at the oropharyngeal isthmus.
Actions
It elevates the root of the tongue and narrows the transverse
diameter of the isthmus by approximating the palatoglossal
arches.

Palatopharyngeus
 Arises by two heads, anterior and posterior.
 The anterior head arises from posterior border of hard palate
and anterior part of upper surface of palatine aponeurosis.

15
 The posterior head is attached further back on upper surface
of the aponeurosis.
 Both heads arch downwards over lateral edge of aponeurosis,
join and form a muscle that passes downwards beneath mucous
membrane of lateral wall of pharynx, raises the
palatopharyngeal fold (posterior pillar of fauces) behind tonsil.
Actions
Acts with the stylopharyngeus and sulpingopharyngeus, to elevate
the pharynx and larynx during swallowing so that the pharynx
becomes shorter.

Musculus Uvulae
 Its contraction shortens the uvula.
 Nerve Supply
 The tensor veli palatini muscle is supplied by mandibular
nerve. The remaining four muscles of soft palate are innervated
by pharyngeal plexus of nerves.

The Pharynx
 Is a funnel shaped fibromuscular tube, about 12 – 14 cm long.
 Extends from base of skull to the level of C6 vertebra (cricoid
cartilage), where it becomes continuous with the esophagus.
 Its anterior wall is largely deficient, through which it
communicates with nasal and oral cavities, and with larynx.
 On account of these communications, it is divided into three
parts.

Nasal Part (Nasopharynx)

 Lies behind the nasal cavity, and extends from base of skull to
upper surface of soft palate, at the level of C1 vertebra.
 It communicates anteriorly with the nasal cavity through the
posterior nasal openings (choanae).
 Inferiorly, it becomes continuous with the oropharynx behind
the soft palate through the pharyngeal isthmus. The pharyngeal
opening of auditory tube lies on lateral wall, through which the
pharynx communicates with the middle ear (tympanic cavity).
 It is guarded above and behind by a prominent rounded ridge,
the tubal ridge, formed by the underlying proximal end of the
cartilagenous part of auditory tube.
 Here, the mucous membrane contains lymphatic tissue known
as the tubal tonsil.

16
 The tubal ridge is in the shape of an inverted J, the long limb
lying posteriorly and being continued downwards as
salpingopharyngeal fold, produced by the underlying
salpingopharyngeus muscle.
 Behind the tubal elevation, there is a narrow vertical gutter,
the pharyngeal recess.
 The roof forms a continuous slope with the posterior wall.
 Here lies a collection of lymphoid tissue, prominent only in
children, the pharyngeal tonsil.
 When enlarged the nodules are commonly known as the
adenoid, which sometime may cause complete obstruction of
the tube.

Oral Part (Oropharynx)

 Lies behind mouth cavity, and extends from the lower surface
of the soft palate to the upper border of the epiglottis.
 Anteriorly, it communicates with mouth cavity through
oropharyngeal isthmus.
 Superiorly, it is continuous with nasal part and inferiorly with
laryngeal part.
 The lateral walls on each side have the palatoglossal and
palatopharyngeal arches (pillars of fauces), formed by the
underlying corresponding muscles.
 The two folds are separated by a triangular recess, the tonsillar
sinus or fossa, which is occupied by palatine tonsil.
 The palatoglossal arches form the boundary between pharynx
and oral cavity.
 The posterior wall is on a level with body of C2 vertebra and
upper half of body of C3.
 The palatine tonsil is a large collection of lymphoid tissue
which projects into oropharynx from tonsillar fossa.
 The lateral surface is covered by fibrous tissue which forms the
tonsillar hemicapsule.
 A peritonsillar abcess occurs outside the capsule.
 The superior constrictor muscle separates this surface from the
facial artery.

Laryngeal Part (Laryngopharynx)

 Lies behind larynx, and extends from upper border of
epiglottis to level of cricoids cartilage (C6 vertebra).
 The upper part of the anterior wall presents the laryngeal inlet,
through which laryngopharynx communicates with larynx.

17
 Below laryngeal opening, the anterior wall is formed by
mucous membrane covering posterior surfaces of arytenoids
and cricoids cartilages.
 The piriform fossa, are small recesses, one on each side of
laryngeal inlet.

The Wall of the Pharynx is formed from without inward by:

1. Buccopharyngeal Fascia:
This layer contains a plexus of nerves (pharyngeal plexus) that
supplies the pharyngeal muscles and extensive pharyngeal
venous plexus.

2. Muscular Coat:
 Consists of three circular muscles, the constrictor muscles:
superior middle and inferior constrictors, and three
longitudinal muscles: stylopharyngeus, palatopharyngeus, and
salpingopharyngeus muscles.
 The constrictors overlap posteriorly, being telescoped into each
other like three stacked cusps.
 The constrictors, however does not extend up to base of skull,
and the gap between the upper border of the superior
constrictor and the base of the skull is filled by tensor veli
palatini and levator veli palatini, and closed by a rigid
membrane, the pharyngobasilar fascia.

Superior constrictor
 Anteriorly, arises from lower part of posterior border of
medial pterygoid plate down to tip of pterygoid hamulus, and
from pterygomandibular raphe, which extends from the
hamulus to mandible just above posterior end of mylohyoid
line.
 From this wide origin the muscle sweeps backwards around the
pharynx, its fibers diverging to meet their opposite fellows in
the midline, being inserted into pharyngeal tubercle of occipital
bone and the median pharyngeal raphe.

Middle Constrictor
 Arises anteriorly from greater and lesser horns of the hyoid
bone, and the lower part of the stylohyoid ligament.
 Inserted into whole length of median pharyngeal raphe.

18
 The upper fibers ascends and overlaps superior constrictor, the
middle fibers pass transversely, and the lower fibers descend
deep to inferior constrictor as far as inferior end of pharynx.
 Laterally, there is a gap between superior and middle
constrictors, through which stylopharyngeus enters pharynx.

Inferior Constrictor
It is divided into two parts.

Thyopharyngeus part: Arises from oblique line of thyroid

cartilage.
Cricopharyngeus part:
 Is rounded, and extends around the pharynx from one side of
the cricoids arch to the other.
 The lowest fibers pass transversely backwards, whereas the
upper fibers ascend obliquely to be inserted into median

pharyngeal raphe.
 Anteriorly, the triangular gap between origins of middle and
inferior constrictors is closed by thyrohyoid membrane.
 The membrane is pierced in this area by internal laryngeal
nerve and superior laryngeal vessels.

Stylopharyngeus
 Long slender muscle arises from styloid process.
 The muscle passes obliquely downwards and forwards along
side of pharynx, passes through interval between superior and
middle constrictors, and joins palatopharyngeus to be inserted
into posterior border of thyroid cartilage.

Sulpingoharyngeus
 Arises from inferior part of cartilaginous part of auditory tube.
 It passes downwards and blends with the palatopharyngeus.

Palatopharyngeus (Discussed before)

Nerve supply
With the exception of stylopharyngeus and cricopharyngeus
which are supplied by glossopharyngeal nerve and external
laryngeal nerves, respectively, all other muscles of pharynx are
supplied by pharyngeal plexus of nerves.

19
Actions:
 The successive contraction of constrictor muscles propels bolus
of food down into esophagus.
 The longitudinal muscles elevate the pharynx and larynx
during swallowing.
 The lower fibers of the inferior constrictor (cricopharyngeus)
are believed to exert a sphincteric effect on the lower end of
pharynx, preventing the entry of air into esophagus between
the acts of swallowing.

3. Pharyngobasilar Fascia:
 Superiorly, attached to the base of skull.
 It holds the nasopharynx permanently open for breathing.

4. Mucous Coat:
 Consists of a dense connective tissue containing a network of
elastic fibers, which is covered with an epithelium.
 In the nasopharynx, the epithelium is pseudostratified
columnar and ciliated.
 In the oropharynx and laryngopharynx it is of the stratified
squamous type.

Esophagus
 The esophagus is a muscular tube, about 25 cm long.
 Extends from pharynx to stomach.
 Conducts food from pharynx into stomach.
 Begins at lower border of cricoids cartilage (at level of body of
C6 vertebra).
 Passes through diaphragm at level of body of T10 vertebra.
 Ends in abdomen at level of body of T11 vertebra, where it
joins the cardiac orifice of stomach.
 At its commencement it is median, but it inclines slightly to left
side as far as root of neck.
 Gradually pass again to median plane, at level of T5 vertebra.
 Again at level of T7 vertebra, deviates to the left and then turns
anteriorly to the esophageal opening in diaphragm.

The course of the esophagus can be divided into three parts:

Cervical Part
 Lies between trachea and prevertebral fascia overlying the
anterior longitudinal ligament and longus coli muscles.

20
 The recurrent laryngeal nerves ascend, one on each side, in the
groove between trachea and esophagus.
 On right, it is in contact with thyroid gland and, at the root of
neck, with cervical pleura.
 On left, with thyroid gland, but the subclavian artery and
thoracic duct separate it from the pleura.

 In addition, the esophagus is related on each side to carotid

sheath.

Thoracic Part
 At first passes through superior mediastinum and then through
posterior mediastinum.
Anterior relations
 From above downwards: Trachea, right pulmonary artery, left
principal bronchus, pericardium (separates esophagus from
left atrium), and diaphragm.
Posterior relations
 longus coli, thoracic vertebra, thoracic duct, azygos vein,
terminal parts of hemiazygos and accessory hemiazygos veins,
right posterior intercostals arteries, and inferiorly, close to
diaphragm, the descending thoracic aorta.
Right relations
Mediastinal pleura and the arch of the azygos vein.
Left relations
 In the superior mediastinum, it is related to the aortic arch, the
left subclavian artery, the thoracic duct, and mediastinal
pleura. The left recurrent laryngeal nerve ascends in the
groove between esophagus and trachea.
 In the posterior mediastinum, it is related to descending
thoracic aorta and mediastinal pleura.

Abdominal Part
 Lies in the esophageal groove on the posterior surface of the
left lobe of liver.

Arterial supply of esophagus

 Upper third by inferior thyroid artery.
 Middle third by esophageal branches of descending thoracic
aorta.
 Lower third by esophageal branches of left gastric artery.

Venous drainage of esophagus

21
 From upper third into inferior thyroid veins.
 From middle third into azygos veins.
 From lower third into left gastric vein, a tributary of portal
vein.

Anatomy of the Digestive System

Lecture 4
Peritoneum
 Is a thin serous membrane.
 Lines the greater part of the wall of abdominopelvic cavity, the
parietal peritoneum.
 Reflected from abdominal wall over the contained viscera, the
visceral peritoneum.
 It must be realized that the parietal and visceral layer form a
continuous sheet and the potential space, not actual between

them is called the peritoneal cavity. The peritoneal cavity

contains only a few milliliters of tissue fluid, which lubricates
the surfaces of viscera so they can glide over one another.
 The peritoneal cavity can be subdivided into a main part, the
greater sac, and a diverticulum of it, the lesser sac (omental
bursa), which is situated behind the stomach.
 The Two cavities communicate with each other via the epiploic
(omental) foramen.
 In the male the peritoneal cavity is a closed sac.
 In the female, the lateral ends of the uterine tubes connects the
peritoneal cavity in the region of the ovary with the cavity of
uterus.

A) Peritoneal Folds of Anterior Abdominal Wall

Six folds are reflected from the parietal peritoneum lining the
posterior surface of the anterior abdominal wall, one above and
five below the umbilicus.

1. Fold above the umbilicus:

Falciform ligament:
 Is a sickle-shaped fold of parietal peritoneum connecting
anterior surface of liver to supraumblical part of anterior
abdominal wall and inferior surface of the diaphragm.

22
 Its concave, free inferior border contains a fibrous cord, the
ligamentum teres (the obliterated remains of the umblical vein),
which extends from the umbilicus to the inferior surface of the
liver.
 The falciform ligament divides the liver into two lobes, right
and left.
 At the superior surface of the liver, the right and left layers of
falciform ligament diverge from each.
 The right layer passes transversely to the right forming the
anterior layer of the coronary ligament of the liver.
 The left layer passes to the left to form the anterior layer of the
left triangular ligament.
 The visceral peritoneum forms the posterior layer of the
coronary ligament and the posterior layer of the left triangular
ligament.
 Between the two layers of the coronary ligament there is a
large triangular area on the back of the right lobe of the liver
devoid of peritoneal covering, the bare area of liver, where it is
directly in contact with diaphragm without intervention of
peritoneum.
 The anterior and posterior layers of the coronary ligament
approach each other and ultimately fused to form the right
triangular ligament.
 The right and left triangular ligaments connect the liver to the
diaphragm.

2. Folds below umblicus:

 Below umbilicus the peritoneum of anterior abdominal wall
presents five folds:
 Centrally is the median umblical fold, containing the median
umblical ligament (the obliterated remains of urachus), which
extends from apex of bladder to umbilicus.
 On each side of median umblical ligament are two folds:
 The more medial, the medial umblical folds containing the
medial umblical ligament (the obliterated remains of the
umblical artery).
 The more lateral, the lateral umblical folds containing the
inferior epigastric artery.

B) Peritoneal Folds of Posterior Abdominal Wall

a. Mesentery of small intestine:

23
 It is a broad, fan-shaped peritoneal fold connecting coils of
jejunum and ileum to posterior abdominal wall.
 The border attached to posterior wall of abdomen is called the
root of the mesentery, which is about 15 cm long, and extends
obliquely downwards and to the right from duodenjejunal
flexure to the upper part of right sacroiliac joint. The intestinal
border of mesentery is about 6 m long and is thrown into
numerous pleats.
 At this border the two layers of the peritoneum separate to
enclose the gut, forming its visceral layer.

b. Transverse mesocolon:
 It is a broad peritoneal fold that connects the transverse colon
to posterior abdominal wall.
 Its two layers pass from anterior aspect of head and body of
pancreas to posterior surface of transverse colon, where they
separate to enclose that part of the colon.
 Between the two layers of the transverse mesocolon are the
blood vessels, nerves and lymphatics of the transverse colon.

c. Sigmoid mesocolon:
 This fold connects the sigmoid colon to pelvic wall.
 The line of attachment to pelvic wall has the form of an inverted
V, the apex of which lies near the division of the left common
iliac artery.
 The left limb descends medial to the left psoas major muscle.
 The right limb descends into the pelvis and ends in the medial
plane.
 The sigmoid and superior rectal vessels pass between the two
layers of the sigmoid colon.

d. Mesoappendix:
 It is a triangular peritoneal fold around the vermiform
appendix.
 It is attached to the back of lower end of the mesentery, close to
ileocaecal junction.
 Usually, it extends to tip of the appendix.
 The blood vessels, nerves and lymph vessels of the vermiform
appendix, together with a lymph nodes lie between its two
layers.

Lesser Omentum

24
 Constitute the two layers of peritoneum that descends from the
fissure for ligamentum venosum and porta hepatis to the lesser
curvature of stomach, and proximal 2 cm of duodenum.
 Between the liver and the 1st 2 cm of duodenum, the omentum
presents a free right border, which forms the anterior boundary
of the epiploic foramen.
 This free border contains between its two peritoneal layers the
portal vein, hepatic artery and bile duct.

Greater Omentum
 It is the largest peritoneal fold, and consists of a double sheet of
peritoneum, folded on itself to form four layers.
 The anterior two layers descend from greater curvature of
stomach and first 2 cm of duodenum, pass downwards in front
of loops of small intestine for a variable distance, and then they
turns round and ascend up to the transverse colon where they

loosely blend with the peritoneum on The greater is a storage

house for fat.
 In addition, the greater omentum contains numerous fixed
macrophages, which can be mobilized as free macrophages.
 These cells may accumulate in places into dense, oval or round
patches, visible to the necked eye as 'milky spots‘ on the
omentum.
 The anterior surfaces of the transverse colon and mesocolon.

Peritoneal Compartments
 The peritoneal cavity can be divided into three compartments,
supracolic, infracolic, and pelvic.
 The dividing line between the supracolic and infracolic
compartments is the attachment of the transverse mesocolon to
the posterior abdominal wall.
 The attachments of the liver to the diaphragm and
supraumblical part of the anterior wall of the abdomen define
the subdivision of the supracolic compartment.
 To the right and left of the falciform ligament are the right and
left subphrenic spaces.
 Behind the right lobe of the liver and in front of the right
kidney is the right subhepatic space.
 Below the transverse mesocolon, the infracolic compartment is
subdivided into right and left infracolic spaces, by the
attachment of the root of the mesentery of small intestine.

25
Paracolic Gutter
These gutters lie on lateral and medial sides of ascending and
descending colons, respectively.

Intraperitoneal Organs
An organ is said to be intraperitoneal when it is almost totally
covered with visceral peritoneum. The stomach, jejunum, ileum,
transverse colon, sigmoid colon, and spleen are good examples of
intraperitoneal organs.

Retroperitoneal Organs
Retroperitoneal organs lie behind the peritoneum and are only
partially covered with visceral peritoneum. The pancreas,
ascending and descending colons, kidneys, and ureters are
examples of retroperitoneal organs.

Nerve Supply of the Peritoneum

1. The parietal peritoneum:
 Is sensitive to pain, temperature, touch, and pressure.
 The parietal peritoneum lining the central part of diaphragm is
supplied by the phrenic nerve (C4) --- hence referred pain from
this area to tip of shoulder.
 The peritoneum lining the peripheral part of diaphragm is
supplied by the lower six intercostals nerves. The remainder of
the parietal peritoneum is supplied by the lower six intercostals
and L1 nerves.
 In the pelvis the obturator nerve is the chief source of supply.

2. The visceral peritoneum:

 Is sensitive only to stretch and tearing and is not sensitive to
touch, pressure, or temperature.
 It is innervated by afferent nerves which travel with the
autonomic supply to the viscera.
 Overdistension of a viscus leads to the sensation of pain.

26
 Anatomy of the Digestive System
Lecture 5
Stomach
 Is the most dilated part of the gastrointestinal tract, interposed
between end of esophagus and beginning of duodenum.
 It lies in epigastric, umblical, and left hypochondriac regions of
abdomen.
 Its main functions is storage of food mixed the food with gastric
secretion to form a semifluid chyme, and the controlled the rate
of delivery of chyme to the small intestine.
 It is roughly J-shaped and has two openings, two borders, and
two surfaces

Cardiac orifice
 Is the opening by which esophagus communicates with
stomach.
 Lies on the left of median plane, behind the 7th left costal
cartilage 2.5 cm from its junction with the sternum (at the level
of T11 vertebra).

Pyloric orifice
 Is the opening by which stomach communicates with
duodenum.
 Lies about 1.2 cm to the right of median plane near the level of
lower border of L1 vertebra (transpyloric plane), when the body
is in the supine position.

Right border (lesser curvature)

 Continuous with right border of esophagus.
 The angular incisure is a notch on this border, nearer pylorus
than esophagus.

Left border (greater curvature)

27
Joins the left border of esophagus at an acute angle, the cardiac
notch.

Anterior surface
Is related to anterior abdominal wall, left costal margin, left
pleura and lung, diaphragm, and left lobe of liver.

Posterior surface
Is related to stomach bed (lesser sac, diaphragm, spleen, left
suprarenal gland, upper part of left kidney, splenic artery, body of
pancreas, transverse mesocolon, and transverse colon).

The stomach is divided into three parts: fundus, body and pylorus.
Fundus
 Is dome-shaped and projects upwards and to the left of
cardiac orifice.
 It is usually filled with swallowed air.
Body
Is the largest part of stomach, extends from cardiac orifice to level
of angular incisure.

Pyloric part
 Extends from body to pyloric orifice.
 It is subdivided into three regions: The pyloric antrum, pyloric
canal, and pylorus.
a. The pyloric antrum: Is the dilated proximal portion of pylorus.
b. The pyloric canal: Is the narrow, cylindrical portion, 2 – 3 cm
long, which continues distally with pylorus.
c. The pylorus: Is the thickened portion of the stomach that unites
it to duodenum. The thickening is due to an increase in the
amount of circular muscle to form the pyloric sphincter, which
is concerned with controlling the rate of discharge of stomach
contents into duodenum.

 When the stomach is empty, the mucosa lies in large folds,

called rugae.
 The stomach is completely enclosed by visceral peritoneum,
which leaves the lesser curvature as the lesser omentum and

Arterial Supply:
The arterial supply of stomach arises from celiac trunk.

28
a. Right and left gastric arteries: Are branches of hepatic and
celiac arteries, respectively. They form an anastomosing arch
along lesser curvature.
b. Right and left gastroepiploic arteries: Are branches of
gastroduodenal and splenic arteries, respectively. They form a
similar arch along the greater curvature.
c. Short gastric arteries: Branches of the splenic artery. They
supply the fundus.
Venous Drainage
 Veins from stomach drain into portal circulation.
 The right and left gastric veins drain directly into portal vein.
 The right gastroepiploic vein joins the superior mesenteric
vein. The left gastroepiploic and short gastric veins join the
splenic vein.

Lymph Drainage
 Lymphatic vessels from stomach drain into scattered lymph
nodes lie along the arteries supplying the four quarters of the
stomach (right and left gastric; and right and left
gastroepiploic arteries),.
 Efferent vessels from these nodes pass to the coeliac nodes.
 Few lymph vessels pass to retropancreatic nodes.

Nerve Supply:
The stomach is supply by sympathetic and parasympathetic fibers
(vagi) via the celiac plexus.

Notice
1. Since the pancreas lies behind the stomach, acute pancreatitis
is frequently diagnosed as gastritis.
2. An ulcer in the posterior wall of stomach may penetrate the
wall and erode the splenic artery, causing a sever hemorrhage.

29
30