1. Dr. Kamal Motawei H.I.M.T. Introduction to Anatomy (ANAT 215)
The Gastrointestinal (Digestive) System
The digestive system is formed of the gastrointestinal tract (GIT) and the adjuvant
glands.
The GIT has reservoir, digestive, absorptive and excretory functions.
The glands provide the GIT with digestive secretions. Also, they may have extra-
digestive functions.
A. The Gastrointestinal Tract (GIT)
(Alimentary canal)
The GIT starts at the mouth and ends at the anus. It consists of the following parts:
mouth, pharynx, esophagus, stomach, small intestine and large intestine.
The abdominal part of the GIT (starting from the stomach down to the upper part of
the rectum) is covered with a serous sac called peritoneum. The peritoneum
prevents friction.
General Plan of the microscopic anatomy of the alimentary canal:
The wall of GIT is formed of four layers
l. Mucosa (innermost)
 (a) Formed of epithelium, lamina propria and smooth muscle muscularis mucosae.
 (b) The epithelium in most places takes a glandular form, with simple tubular glands and a
secreting surface epithelium.
 (c) Some parts have discrete compound glands lying in the mucosa.
 (d) Single lymphoid nodules can occur anywhere.
2. Submucosa
 (a) Formed of fairly dense CT, with blood and lymphatic vessels, and having a plexus of
unmyelinated autonomic nerve fibres - Meissner's submucosal plexus.
 (b) Glands are present in a few places.
3. Muscularis externa
 (a) Two or more helical layers of smooth muscle: the inner, tight 'circular'; the outer, loosely
coiled 'longitudinal'.
 (b) Served by a nerve fibre plexus - Auerbach's myenteric plexus, whose parasympathetic
ganglion cells lie between the muscle layers.
 (c) Circular coat is more developed at sphincters and valves.
4. Serosa or adventitia/fibrosa (outermost)
 (a) Loose CT, with collagen and elastic fibres, nerves and vessels.
 (b) The serosa has a smooth mesothelial covering.
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2. Dr. Kamal Motawei H.I.M.T. Introduction to Anatomy (ANAT 215)
Blood Supply of the GIT:
A) Arterial Blood Supply:
Most of the GIT is supplied by three branches from the abdominal aorta:
1. Coeliac artery: to the FOREGUT (abdominal esophagus, stomach and upper half
of the duodenum)
2. Superior mesenteric artery: to the MIDGUT (lower half of the duodenum,
jejunum, ileum, cecum, appendix, ascending colon, right two thirds of the
transverse colon).
3. Inferior mesenteric artery: to the HINDGUT (left one third of the transverse
colon, descending colon, pelvic colon, rectum and upper half of the anal canal).
B) Venous Drainage of GIT (Portal Vein):
All the veins from the foregut, midgut and hindgut are collected into one vein called
the portal vein. The portal vein divides into two branches before entering the liver
where it divides into smaller branches then capillaries. The portal vein transmits
absorbed food to the liver.
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3. Dr. Kamal Motawei H.I.M.T. Introduction to Anatomy (ANAT 215)
1. The Mouth:
The mouth cavity contains the teeth and tongue.
The salivary glands discharge their secretions in
the mouth cavity.
Posteriorly, The mouth opens into the
oropharynx.
The roof of the mouth is formed of the hard and
soft palates.
The soft palate has a midline projection at its
posterior end called uvula. The soft palate
acts as a valve to prevent the food entering
the nasopharynx during deglutition.
The tongue is a muscular organ that move the
food from side to side during mastication and finally to the oropharynx during
swallowing. It is covered with mucous membrane containing taste buds concerned
with taste sensation. The undersurface of the tongue is connected to the floor of the
mouth by a fold of mucous membrane called frenulum.
2. The Pharynx :
Only its lower two divisions are considered parts of the digestive system:
1. The Oropharynx:
Its lateral walls show the palatine tonsils lying in-between double folds of mucous
membrane.
2. The Hypopharynx (Laryngopharynx):
Its posterior wall is adherent to the larynx (below the level of the inlet of the
larynx). It is continuous below with the esophagus.
3. The Esophagus:
It is a muscular tube lined with mucous membrane. It is 25 cm long.
It passes in the neck, thorax, and abdomen. It terminates in the cardiac end of the
stomach.
It lies in front of the vertebral column and behind the trachea, heart and diaphragm,
successively.
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4. Dr. Kamal Motawei H.I.M.T. Introduction to Anatomy (ANAT 215)
The function of the esophagus is to conduct food from the pharynx into the stomach.
It has three sites of constriction:
1) at its beginning
2) at its middle: where it is crossed by the left bronchus and arch of the aorta.
3) close to its end: where it crosses the diaphragm.
4. The stomach:
The stomach is the most dilated part of the GIT.
It lies in the upper left part of the abdomen and extends down to the umbilical region
(or even the hypogastric region).
Its capacity is very variable (average 1500cc in adults).
Cardiac orifice: Where the esophagus enters the stomach.
2 orifices
Pyloric orifice: Where the stomach joins the duodenum.
It is surrounded by thick pyloric sphincter.
Related to the diaphragm, left lobe of liver and
Anterior surface:
2 surfaces anterior abdominal wall.
Related to the stomach bed (the spleen,
Posterior surface
pancreas, left kidney, left suprarenal)
Lesser curvature: Forms the right border.
2 curvatures Forms the left border. It is longer than the
Greater curvature:
lesser curvature.
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5. Dr. Kamal Motawei H.I.M.T. Introduction to Anatomy (ANAT 215)
5. Small Intestine :
It is divided into three regions: the duodenum, the jejunum, and the ileum.
The duodenum:
It is a 25cm long, C-shaped tube.
It embraces the head of the pancreas in its concavity.
It is plastered to the posterior abdominal wall by the peritoneum.
At its middle, it receives the common bile duct from the liver and the pancreatic ducts
from the pancreas.
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6. Dr. Kamal Motawei H.I.M.T. Introduction to Anatomy (ANAT 215)
Jejunum and Ileum :
The jejunum and ileum measure about 6m long, the upper two-fifths of this length
being the jejunum. The ileum ends at the ileocecal junction, which is guarded
by a valve (ileocecal valve).
6. Large Intestine:
The function of the large intestine is the absorption of water and electrolytes and the
storage of undigested material until it can be expelled from the body as feces (stool).
The large intestine is divided into the cecum, the vermiform appendix, the ascending
colon, the transverse colon, the descending colon, the sigmoid colon, the rectum and
anal canal.
The cecum:
It is the dilated part of the large intestine that lies below the junction of the ileum with
large intestine.
It is situated in the right iliac fossa.
The appendix is attached to the dorsomedial aspect of the cecum.
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7. Dr. Kamal Motawei H.I.M.T. Introduction to Anatomy (ANAT 215)
The vermiform appendix:
It is a narrow caliper blind tube that is attached to the dorsomedial aspect of the
cecum.
It varies in length from 8 to13cm.
Its caliper decreases with advance in age (wider in early childhood, narrower in
middle age, and obliterated in old age). So, occlusion of the lumen and hence
inflammation of the appendix usually occurs in middle age but rarely occurs in
extremes of age.
The ascending colon:
It lies on the right side of the abdomen.
The transverse colon:
It extends across the abdomen.
The descending colon:
It lies in the left side of the abdomen.
The Sigmoid colon:
It lies partly in the pelvis
The Rectum:
It lies in the pelvis in front of the sacrum.
The anal canal:
It is the terminal part of the large intestine.
It is 4cm long
It is directed backwards and downwards.
It is surrounded with tow sphincters: external voluntary sphincter and internal non-
voluntary sphincter.
It ends at the anus.
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8. Dr. Kamal Motawei H.I.M.T. Introduction to Anatomy (ANAT 215)
B. The Glands of the Alimentary System
1. Salivary Glands:
There are three pairs of salivary glands: the parotid, submandibular, and sublingual
glands. Their secretions moist the mouth, facilitate mastication & deglutition and
digest starch.
The parotid gland:
It lies below the ear in the
interval between the ramus of
the mandible and the
sternomastoid muscle. So, in
mumps (viral infection of the
parotid) there is a swelling
around the lower part of the
ear that rises the ear up.
The opening of its duct lies in
the inner aspect of the check
opposite the upper 2nd molar tooth.
The facial nerve passes through the parotid gland in its way to the face.
The submandibular gland:
It lies below the lower margin of the body of the mandible. Its duct opens close to the
frenulum of the tongue.
The sublingual gland:
It lies undercover of the mucous membrane of the floor of the mouth. It opens into
mouth with about 20 small ducts.
2. The liver:
It is the largest gland in the body (average
weight 1800gm). It lies in the upper part of the
abdominal cavity (mainly to the right side). It
is held in position by the attachment of the
hepatic veins to the inferior vena cava
(vascular attachment); the fibrous and
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9. Dr. Kamal Motawei H.I.M.T. Introduction to Anatomy (ANAT 215)
peritoneal ligaments of the liver and the muscle tone of the anterior abdominal wall
play minor role in its support.
It is covered with the costal wall (Normally it is not palpable below the costal margin).
It is formed of two lobes (large right lobe and smaller left lobe).
It is concerned with metabolism of absorbed carbohydrates and proteins,
detoxicating function, and production of bile.
It receives the portal vein that carries all the venous blood from most of the GIT (from
abdominal part of the esophagus to the upper half of the anal canal). The portal
blood carries the absorbed food to the liver to be metabolized.
The portahepatis (hilum of the liver):
1) hepatic artery
2) hepatic ducts
3) portal vein
The Extrahepatic Biliary Apparatus:
It is the duct system of the liver.
It conveys bile from the liver to the
duodenum.
It consists of (1) the right and left
hepatic ducts, (2) the common hepatic
duct, (3) the common bile duct, (4) the
gall bladder, and (5) the cystic duct.
The liver excretes bile at a constant
rate of 40 ml per hour. The bile gets
out the liver via two hepatic ducts (one
from each lobe). These 2 ducts unite to
form common hepatic duct that joins
the cystic duct to form the common bile
duct. The cystic duct transmits bile to
and from the gall bladder. Finally, The
common bile duct opens in the middle of the second part of the duodenum
transmitting bile to the GIT.
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10. Dr. Kamal Motawei H.I.M.T. Introduction to Anatomy (ANAT 215)
The gall bladder has the following functions: It (1) concentrates bile, (2) stores bile, (3)
selectively absorbs bile salts, keeping the bile acids, (4) excretes cholesterol, and (5)
secretes mucous.
The Pancreas:
It is a soft organ that lies on the on
the posterior abdominal wall. It is
divided into head, neck, body and
tail. The head lies in the concavity of
the duodenum, the body lies behind
the stomach, the tail lies in the hilum
of the spleen.
The pancreas is a mixed (exocrine
and endocrine) gland. The exocrine
portion secretes pancreatic juice
(containing digestive enzymes) that
passes through the pancreatic duct to
the 2nd part of the duodenum. The
endocrine portion (the islets of
Langerhans) produces the hormones
insulin and glucagon that play a key
role in carbohydrate metabolism.
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