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Digestive Anatomy
By Amanda Neufeld & Sheri Mullen
The digestive system is a complex system
consisting of the oral cavity, pharynx, esophagus,
stomach, small intestine and the large intestine;
also includes the salivary glands, hepatobiliary
apparatus( liver and gallbladder), and pancreas
which includes accessory organs The
development of this system starts at about 6-8
wks after fertilization. This complex system is
responsible for our ability to live. Each part of the
digestive system is important to the bodies over
homeostasis.
The muscle of the digestive system are
mainly smooth muscle in nature, however
they can also consist of skeletal as well.
The mouth and the pharynx are skeletal
and develop from the branchial
mesoderm. The esophagus is part
smooth as well as skeletal, leaving the
rest of the GI tract as smooth muscle
that develops from the surrounding
mesoderm.
The lining of the structures first arises for
the primitive gut tube. This tube consists
of three parts; the forgut, midgut, and
the hindgut.
* forgut : gives rise to the region
from the oral cavity to the proximal
half of the duodenum.
* midgut :gives rise to the region
from the distal half of the
duodenum to the right 2/3rds of the
transverse colon.
* hindgut: gives rise to the region
from the left 1/3 of transverse colon
to the superior portion of the anal
canal.
All the digestive organs arise from
the primitive gut and while
developing they develop next to the
peritoneum cavity. This cavity
consist of two layers the visceral,
and parietal. The parietal layers
surrounds the entire digestive
forgut
midgut
hindgut
Peritoneum
Most of the digestive system organs resides in the abdominal cavity and are contained in the peritoneum. The visceral
peritoneum covers the external surfaces of most digestive organs and is continuous with the parietal peritoneum that
lines the body wall. As the organs develop they invaginate into the visceral peritoneum, others are either partly covered
or lie behind. The organ that have invaginated into the visceral peritoneum have folds or two layers called mesentery
which the blood vessels and nerves pass through. Organs that lie behind the visceral peritoneum are called
retroperitoneal.
Organs inside the visceral
peritoneum.
Retroperitoneal organs
*pancreas
•Stomach
*ascending colon
•Small intestine
*descending colon
•Sigmoid colon
*rectum
•Transverse colon
*aorta
•Jejunum and ileum
visceral
parietal
*duodenum
Histology of alimentary canal
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From the esophagus to the anal canal the
walls of the alimentary canal have the
same four basic layers, or tunics. Each
containing a predominant tissue type that
plays a specific role in the breakdown of
food.
Musclaris Externa: is just deep to
the submucosa and also called
muscularis. This layer is responsible for
segmentation and peristalsis. It typically
has two layers. The inner circular layer
and the outer longitudinal layer of
smooth muscle cells. In several places
along the tract the circular layer
thickens forming sphincters. In between
these two layer there are nerve plexus
called Myeriteric nerve plexus, which
feed the meissner’s nerve plexus.
Submucosa: is just external to the mucosa
It’s made up by connective tissue and contains
blood and lymphatic vessels, lymphoid follicles,
and nerve plexuses. This layer is lax providing
elasticity for mobility. Nerve plexus in this area is
known as Meissner’s plexus (parasympathetic in
nature) And found mainly in the esophagus and
duodenum.
Submucosa
gland
circular
longitudinal
Mucosa: is the inner most
Serosa / Adventitia: This layer is named
depending on whether or not it’s covered by the
visceral peritoneal cavity. ( exp. Esophagus) If it
is covered it is referred to as serosa.
* serosa- areolar connective tissue covered
with mesothelium.
* adventitia- fibrous connective tissue.
layer and goes from the
mouth to the anus. It
functions to secret mucus,
digestive enzymes and
hormones; it helps with the
absorption of end products of
digestion into the blood; and
protects against infectious
disease. The mucosa
contains three sub layers.
* lining epithelium
* lamina propria
* muscularis mucosa
Left
gastric
Common
hepatic
artery
splenic
Celiac axis:
The splanchnic circulation includes the
arteries that branch off the abdominal aorta to
serve the digestive organs.
The arterial supply ( hepatic, splenic, and left
gastric branches of the celiac trunk serves the
spleen liver and stomach.
Abdominal
aorta
Sup. and Inf. mesenteric
Sup. mesenteric
The mesenteric arteries serve both the large and
small intestines.
Inf. mesenteric
Salivary Glands
Secrete saliva into the oral cavity, lubricating, dissolving and
beginning the chemical digestion of food that has been ingested. They arise
from the forgut and receive blood through the celiac axis. They consist of
rounded acini which can be ether mucus and serous secreting. The
epithelium of larger ducts are lined by stratified cuboidal epithelium, and small
ducts are lined by cuboidal epithelium.
Parotid
Sublingual
Submandibular
Parotid: Is serous gland containing serous acini.
Anterior to the tragus of the ear and covered by thick
fascia.
Submandibular:
both serous and mucus secreting
glands. Lies in the mandibular fossa, ducts opening on
the floor of the mouth.
Sublingual: mainly mucus secreting. They are
Ant. and sup. to the submandibular gland opening
through multiple ducts on the floor of the mouth.
Pancreas: contains acini darkly staining, and ducts
from the exocrine portion. The endocrine portion
contains the islets of langerhans which show up as
a cluster of cells, surrounded by lots of capillaries
and blood vessels.
Pancreas
Portal triad
Liver: Is made up of hepatocytes arranged as
plates around the central vein. The hepatocytes
receive nutrients and oxygen through the sinusoids,
in which the hepatic arterial and portal veins drain.
Both the sinusoid and bile canaculi lie in between
each hepatocyte. – portal triad consists of a branch
of the hepatic artery, and portal vein, also including
a bile ductule.
Liver
Pharynx and Esophagus
Through progression of coordinated contraction and relaxation (peristalsis) food
is propelled down to the stomach.
Pharynx
Esophagus
The muscular layer is skeletal and
Is contained mainly in the thoracic
Consists of an inner longitudinal and
but passes through the diaphragm
outer circular.
Into the abdomen.
pharynx
esophagus
Gastro-esophageal or cardio-esophageal junction guarded by the physiological
sphincter. (smooth muscle)
STOMACH
STOMACH
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Lies in left hypochondriac, epigastric & umbilical region.
Cardia- surrounds the superior opening of the stomach
Fundus- The rounded portion superior and to the left of the cardia
Body- inferior to the fundus . Large central portion on the stomach
Pylorus-communicates with the duodenum via the pyloric sphincter. Has two parts.
Pyloric antrum connects to the body of the stomach. Pyloric canal leads into the
duodenum.
Lesser curvature-concave medial border.
Greater curvature-convex lateral border.
Parietal & chief cells of stomach
Liver, Gallbladder & Bile duct
Histology of the liver and gallbladder
The lobes of the liver are made up of many functional units called Lobules. A lobule is
typically a six-sided structure that consists of specialized epithelial cells, called
hepatocytes , arranged in irregular, branching, interconnected plates around a
central vein. Instead of capillaries, the liver has larger, endothelium-lined spaces
called sinusoids, through which blood passes. Also present in the sinusoids are fixed
phagocytes called stellate reticuloendothelial (KUPFFER) cells, which destroy
worn-out white and red blood cells, bacteria, and other foreign matter in the venous
blood draining from the gastrointestinal tract.
Bile, which is secreted by hepatocytes, enters Bile canaliculi, which are narrow
intercellular canals that empty into small bile ductules. The ductules pass bile into
bile ducts at the periphery of the lobules. The bile ducts merge and eventually form
the larger right and left hepatic ducts, which unite and exit the liver as the
common hepatic duct. Farther on the common hepatic duct joins the cystic duct
from the gallbladder to form the common bile duct.
Liver cells (hepatocytes)
Portal triad
Hepatic artery, branch of the portal vein and
a bile ductule
Pancreas
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Is both and exocrine and
endocrine gland
It is retroperitoneal
Head, uncinate process, body and
tail
Head lies in the C of the
duodenum.
Tail is related to the spleen
Large pancreatic duct runs
through the length of the gland
and usually joins the bile duct to
drain into the duodenum at the
major duodenal papilla
Minor or accessory duct may also
be seen
SMALL INTESTINES
DUODENUM- The shortest region, is retroperitoneal and C shaped. It
starts at the pyloric sphincter of the stomach and extends about
25cm (10 in.) until it merges with the jejunum.
Jejunum- is about 1 m (3 ft) long and extends to the ileum. Possess
mesentery.
Ileum-Longest region of the small intestine. It measures about 2 m (6
ft) and joins at the large intestine at the ileocecal sphincter. Possess
mesentery.
Major function is to absorb nutrients
SMALL INTESTINES
epithelium is thrown into evaginations called villi which increase surface area for
absorption and also secrete a few enzymes to complete digestion
LARGE INTESTINES
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The overall function of the large intestine is the
completion of absorption of water , and production of
certain vitamins, the formation of feces, and the
expulsion of feces from the body.
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Extends from the ileocecal valve to the anal opening.
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Is about 1.5 m long in a cadaver
The large intestine has numerous goblet cells
which secrete mucus and serves as a lubricant.
Also seen in the large intestine are numerous
lymph follicles, because of the bacterial flora that
are present.