DIGESTIVE SYSTEM
ASSIS PROF / REDHWAN AHMED ALSHAMARI
The digestive system is concerned with the
uptake, digestion, absorption and excretion
of non-digested food. The digestion is the
breakdown of food into small molecules
which are then absorbed into the body.
A. Anatomy of the Digestive System
• 1. Digestive tract: also called
alimentary tract
• 2. GI tract: technically refers to
stomach and intestines
• 3. Accessory organs
• 4. Regions
– Mouth or oral cavity with salivary
glands and tonsils
– Pharynx (throat
– Esophagus
– Stomach
– Small intestine (duodenum, ileum,
jejunum)
– Large intestine including cecum,
colon, rectum
– anal canal with mucous glands
– Anus
ORAL cavity
•The oral cavity is the first portion of
the digestive tube.
•It extends from the lips and opens
posteriorly in the oropharynx.
•Vestibule
•Oral cavity proper
Tongue
It is a highly mobile muscular organ
which is formed of striated muscle fibers
and covered by mucous membrane.
•The mucous membrane on the
dorsum of the tongue is rough, and it is
covered with small projections called
lingual papillae. Some of the papillae
contain taste buds. There is “V”-shaped
sulcus (sulcus terminalis) which
separates the anterior ⅔ and posterior ⅓
of the tongue. Lymphatic follicles lie
posterior to this and called "lingual tonsils"
.
•The tongue helps in deglutition, taste
and speech.
Teeth

•Deciduous (milky teeth):
they are 20 teeth (4 incisors
& 2 canines & 4 molars).
The 1st tooth to erupt is the
central incisor (6th month).
•Permanent teeth: they are 32
teeth (4 incisors & 2 canines &
4 premolars & 6 molars). The
1st to erupt is the 1st molar.
The last to erupt is the 3rd
molar (wisdom tooth).
The pharynx




It is a common pathway for
digestive and respiratory systems.
•It is musculo-membranous tube
that lies behind the nose, mouth
and larynx.
•It is about 12 cm in length and
extends from the base of skull
down to the 6th cervical vertebra,
where it continues as oesophagus.
•Its wall is formed muscle coat
lined by mucosa. The muscle coat
is formed of 3 constrictor muscles.
OESOPHAGES
It is a muscular tube about 25 cm long.
 •It begins as the continuation of the
lower end of pharynx (level ofC6 ).
 •It passes in the neck, then in the thorax
through the mediastinum & then
through the diaphragm to end in the
stomach.
 •Most of its course is in the middle line
but deviates to the left at the level of
T7vertebra where it passes in front of
descending aorta till it passes through
opening of the diaphragm at level of
T10.
 •Through its course, it is related:
•Posteriorly to the cervical and thoracic
vertebrae, while
•Anteriorly it descends behind the
trachea and heart respectively.

The stomach
•It lies in the upper
part of the abdominal
cavity, in the
epigastrium and left
hypochondrium.
•It is commonly Jshaped that has:

•2orifices

•2curvatures

•2 surfaces

•2 portions
The Small Intestine
•It is 6 meters long and takes the
shape of coiled loops that fill most of
the abdominal cavity.
 •It consists of 3 divisions:

•Duodenum:
 •It is the shortest and widest of the
small intestine (about 25 cm in
length).
 •It is “C” shaped and is formed of 4
parts.
 •It is firmly attached to the posterior
abdominal wall and not mobile.
 •The head of pancreas lies in the “C”
shaped concavity.
 •The bile duct and main pancreatic
duct unit together and open in the
middle of the 2nd part.

Jejunum andIleum
form the free part of the small intestine
and are freely mobile. They are attached
to the posterior abdominal wall by
means of mesentery.
•The jejunum extends from the
duodenum and forms the first two fifths
while the ileum forms the next three
fifths.
•The jejunum has wider diameter than
the ileum. The ileum ends by opening
into the medial aspect of the cecum. A
muscular sphincter (ileocecal valve) is
present at this opening.
The Large Intestine (colon)



•It is about 1.5 meters
in length.
It extends from the
end of the ileum to the
anus.
•It is larger in diameter
than the SMALL bowel
The large intestine is divided into
following parts:
•Cecum is a blind pouch which
hangs down at the junction of the
ileum and the colon. The Ileocecal
valve lies at its medial aspect and
prevents the return of the faeces
from the cecum into the small
intestine. The appendix arises from
the cecum about 2.5 cm below the
ileocecal valve.
•Ascending Colon extends from
the cecum to the under surface of
the liver where it turns to the left.
This bend is called right colic
(hepatic) flexure.
Transverse Colon crosses the upper part of
abdominal cavity from right to left and then
curves sharply downwards under the lower end
of the spleen forming the left colic (splenic)
flexure.
•D escending Colon extends from the splenic
flexure to the brim of the pelvis, where it turns
towards the midline to become the sigmoid colon.
•S igmoid Colon extends from the descending
colon at the level of pelvic brim to the rectum. It
is “S” shaped.
•Rectum extends from the sigmoid colon to the
anal canal. It descends along the sacrum to the
tip of coccyx. Its lower part shows dilatation
called "ampulla of rectum".
•Anal Canal is the terminal portion of the large
intestine. It extends from the rectum to the anus
and is about 4 cm in length. In the anal canal the
circular muscle fibres are thickened to form
internal anal sphincter. The external anal
sphincter is composed of skeletal muscle,
therefore under voluntary control.

The large intestine has the following
features :




•Appendices epiploicae : are small peritoneal sacs filled with fat
scattered on the wall of large intestine (except on cecum &
appendix & rectum).
•Taenia coli: the outer longitudinal muscle coat of large intestine
is arranged in 3 longitudinal bands begin that at the base of
appendix (they are absent in the appendix & rectum).
•Sacculations: the length of taenia coli is shorter than the true
length of large intestine puckering of the wall.
The Salivary Glands
The parotid gland:
It is the largest salivary gland,
which lies below and in front of
the ears, between the mastoid
processes of temporal bone and
the ramus of mandible.
It is a wedge-shaped with its
base directed upwards and apex
directed downwards.
The parotid duct passes
through the buccinator muscle
and opens into the vestibule of
the mouth opposite the upper
second molar tooth.
Its secretion is principally
watery.

The submandibular
gland:
It lies in contact with
the inner surface of the
mandible and the ducts.
 It opens into the floor
of the mouth beside the
frenulum of the tongue,
behind the lower
incisors.
 Its secretion is both
watery and mucous.

The sublinigual gland:



It the smallest salivary gland,
which lies beneath the
mucous membrane of the
floor of the mouth.
It opens by several minute
ducts into the floor of the
mouth.
Its secretion is principally
mucous in nature.
The Liver
•It is the largest organ of the body
weighing about 1.4 kg in an adult.
 •It is located in the upper part of the
abdominal cavity, mainly in the right
hypochondrium and epigastrium.

•It is a wedge-shaped which has:
 •Smooth convex anterior, superior,
posterior and right lateral surfaces.
Collectively called diaphragmatic
surface of the liver, as they are
related to the diaphragm, which
separates it from right pleura and
lung, pericardium, left pleura and
lung.
 •Inferior surface, which is concave
and shows impressions of the
underlying organs.

The liver has:
 •Two main lobes: are theright and theleft ,
separated by the falciform ligament.
 •Two small lobes: quadrate and caudate
lobes. Anatomically, these 2 lobes belong
to the right lobe. While physiologically,
they are part of left lobe as they are
supplied by left branch of hepatic artery
and portal vein.
 •The liver is almost entirely covered with
peritoneum except posteriorly. That area
is calledbare area . The right and left
triangular ligaments are thickenings of
the peritoneum which help to keep liver in
place.
 •The liver has double blood supply from
hepatic artery (provides 30%) and portal
vein (provides 70%).
 •The liver is drained by 3 hepatic veins
which end in the inferior vena cava.
Porta hepatis
•
 It is the hilum of the liver which lies




between the caudate and quadrate lobes.
•It gives passage to the following
structures:
•Hepatic ducts : one duct emerges from
each lobe. They are anterior in position.
•Hepatic artery : is intermediate in
position, which divides into right and left
branches; each one enters the
corresponding lobe of the liver.
•Portal vein : posterior in position. It
enters the liver and divides right and left
branches; each one enters the
corresponding lobe of the liver.
Biliary system
: is formed of the following:
•Gall Bladder:
•It is a pear-shaped sac with an average capacity of 40
to 50 ml.
•It is located in gall bladder fossa on the under surface
of the liver.
•It is formed of fundus, body and neck.
•Its neck is continuous with the cystic duct. This duct is
about 4 cm in length and contains spiral valve.
•Right hepatic duct and left hepatic ducts:
•They are coming from the right and left lobes of the
liver and unite to form common hepatic duct just below
the porta hepatis.
•Common hepatic duct:
•It is joined by cystic duct of the gallbladder at acute
angle to from common bile duct.
•Common bile duct:
•It is about 10 cm in length.
•It descends behind the head of the pancreas, where it
joins the main pancreatic duct, forming a dilatation
called "hepatopancreatic ampulla" that opens into the
2nd part of the duodenum.
•This opening is guarded by a valve (sphincter of Oddi).
The Pancreas
•It
is elongated gland that lies across the
posterior abdominal wall at the level of 2nd
lumbar vertebra.
•It is not mobile as it is retro-peritoneal.
•It has the following parts from right to left:
•Head:
•It is the broad right end which is enclosed
within the “C” shaped curve of the duodenum.
•It sends a downward process called
uncinate process.
•Neck:
•It is the junction between the head and body.
It is related to the beginning of the portal vein
as a result of union between the splenic and
superior mesenteric veins.
•Body :is triangular in cross section with:
•anterior surface : lies behind the lesser
sac.
•inferior surface : is related to small
intestine.
•Tail :the left narrow end which reach the
visceral surface of spleen.
Ducts of pancreas:
•Main pancreatic duct : extends through the
whole length of pancreas to unite with the
common bile duct forming the hepatopancreatic ampulla which in the 2nd part of
duodenum
.
•Accessory pancreatic duct : starts in the
uncinate process & ascends in front of the main
pancreatic duct and opens in the 2nd part of
duodenum (1 inch proximal to the main
pancreatic duct).
•NB: the main and accessory ducts may
communicate.
•The pancreas is both an exocrine and an
endocrine gland:
•The exocrine portion secretes pancreatic juice.
•The endocrine portion consists of irregular
clumps of cells calledIslets of Langerhans .
These have two types of cells which secrete
insulin (produced by beta cells) and glucagon
(produced by alpha cells) hormones.
Arterial supply
•Arterial supply : by 3 single arteries
which arise from the front of the
abdominal aorta:
•Coeliac trunk: supplies the foregut (lower
part of oesophagus, stomach, upper half of
the second part of duodenum, liver, pancreas
and spleen) through 3 branches: common
hepatic, left gastric and splenic arteries.
•Superior mesenteric artery : supplies the
midgut (lower half of the second part of
duodenum, jejunum, ileum, cecum,
ascending colon, right ⅔ of transverse colon).
•Inferior mesenteric artery : supplies the
hindgut (left ⅓ of transverse colon,
descending colon, pelvic colon, rectum upper
half of anal canal).
Venous drainage
:by tributaries corresponding to
the branches of arteries, which
ultimately drained into the portal
vein.
This vein is formed by the union
of superior mesenteric vein and
the splenic vein behind the neck
of the pancreas then, it goes to
the liver.
•From the liver 2 hepatic veins
drain into the inferior vena cava.