The document provides a comprehensive overview of the duodenum, covering its anatomy, histology, blood supply, innervation, physiological functions, and common conditions. It describes the duodenum's location in the abdominal cavity, its structure divided into four parts, and its role in digestion, hormone secretion, and nutrient absorption. Additionally, it addresses various conditions affecting the duodenum, such as ulcers, inflammation, and cancer.

1. Duodenum
Prepared by
Dr.Ismael I. Surchi

2. Objectives
Anatomy and Physiological of duodenum.
Histology of duodenum.
Blood supply and lymphatic drainage of
duodenum.
Neurological innervation of the duodenum.
Physiological functions of the duodenum.
Common conditions of duodenum.

3.  The duodenum It is the initial
portion of the small intestine,
connecting the distal end (i.e.
the latter part) of the stomach
to the proximal end (i.e. the
upper part) of the jejunum.
 It receives partially digested
food (chyme) with high acidity
from the stomach, and
involves in neutralizing the
acidity of the food and
propelling it through the rest of
the small intestine for further
digestion and absorption.

4. Location
 In humans, it is located in the upper
part of the abdominal cavity, slightly
more towards the right side from
the midline.
 It is a C-shaped hollow tube that
extends from L1 to L3 vertebral
levels, in a curve around the head
of the pancreas.
 Its surface marking is roughly at the
midpoint between the suprasternal
notch and the pubic symphysis.
 It begins at the gastroduodenal
junction and ends at the
duodenojejunal junction.

5.  For description, the duodenum
is divided into four parts:
 first, second, third, and fourth.
These parts may also be called
as superior, descending,
horizontal, and ascending parts
respectively.
 The average length of each of
these parts 5 cm, 7.5 cm, 10
cm, and 2.5 cm).

6. Parts of duodenum
The first part of the duodenum begins at the pylorus and
runs upward and backward on the transpyloric plane at
the level of the 1st lumbar vertebra.
Relations:
Anteriorly: The quadrate lobe of the liver and the
gallbladder.
Posteriorly: The lesser sac (first inch only), the
gastroduodenal artery, the bile duct and the portal vein,
and the inferior vena cava.
Superiorly: The entrance into the lesser sac (the
epiploic foramen) • Inferiorly: The head of the pancreas

7. The second part of the duodenum runs vertically
downward in front of the hilum of the right kidney on
the right side of the 2nd and 3rd lumbar vertebrae.
Relations
Anteriorly: The fundus of the gallbladder and the right
lobe of the liver, the transverse colon, and the coils of
the small intestine .
Posteriorly: The hilum of the right kidney and the right
ureter.
Laterally: The ascending colon, the right colic flexure,
and the right lobe of the liver.
Medially: The head of the pancreas, the bile duct, and
themain pancreatic duct .

8. Third Part Of Duodenum
Runs horizontally to the left on the subcostal plane,
passing in front of the vertebral column and following
the lower margin of the head of the pancreas.
• Relations:
• Anteriorly: The root of the mesentery of the small
intestine, the superior mesenteric vessels contained
within it, and coils of jejunum.
Posteriorly: The right ureter, the right psoas muscle,
the inferior vena cava, and the aorta.
Superiorly: The head of the pancreas.
Inferiorly: Coils of jejunum

9. Fourth Part Of Duodenum
Runs upward and to the left to the duodenojejunal
flexure. The flexure is held in position by a
peritoneal fold, the ligament of Treitz, which is
attached to the right crus of the diaphragm.
Relations:
Anteriorly: The beginning of the root of the
mesentery and coils of jejunum.
Posteriorly: The left margin of the aorta and the
medial border of the left psoas muscle .

10. HISTOLOGY
 Histologically the duodenum is
similar to all the other hollow organs
of the gastrointestinal tract: mucosa,
submucosa and muscularis.
 The mucosa consists of simple
columnar epithelium (lamina
epithelialis), a connective
tissue layer (lamina propria) and
a smooth muscle layer (lamina
muscularis). The intestinal epithelial
cells (enterocytes) are overlaid by a
layer of glycoproteins and mucin.
 The submucosa comprises loose
connective tissue, numerous blood
vessels and the Meissner's plexus.
 The muscularis consists of an inner
circular and an outer
longitudinal musculature between
which the Auerbach’s plexus lies.

12.  The mucosa forms fingerlike projections called villi that extend into the
intestinal lumen. These are epithelial folds lined by two types of cells,
enterocytes and goblet cells.
 Enterocytes are simple columnar cells with basal elongated nuclei and
an apical brush border.
 The brush border is the microscopic representation of small protrusions
of the cell membrane, microvilli, which greatly increase the surface area
of the cell enhancing absorptive capacity.
 The mucous membrane of the duodenum is thick in the first part of the
duodenum, it is smooth in the remainder of the duodenum, it is thrown
into numerous circular folds called the plicae circulares.
 At the site where the bile duct and the main pancreatic duct pierce the
medial wall of the second part is a small, rounded elevation called the
major duodenal papilla .
 The accessory pancreatic duct, if present, opens into the duodenum on
a smaller papilla about 0.75 in. (1.9 cm) above the major duodenal
papilla.

13.  The other cell type is mucus secreting goblet cells that can be
recognized by the presence of an apical mucous cup. The core of the
villus is part of the lamina propria. The most numerous cells in the
lamina propria are immune cells, most of which are lymphocytes.
Because villi are the site of absorption of nutrition they have a rich
blood supply, each villus is supplied by central arterioles and drained
by central venules and a central lymph vessel.
 Underlying the villi are the intestinal glands, also called the crypts of
Lieberkühn. These glands are lined with numerous relatively
undifferentiated columnar cells that usually undergo two rounds of
mitosis before differentiating into either absorptive cells or goblet cells.
Enterocytes, goblet cells, paneth cells that secrete antibacterial
enzymes (recognized by eosinophilic granules in their apical
cytoplasm) and enteroendocrine cells also line the crypt. A thin layer of
smooth muscle marks the end of the mucosa, the muscularis mucosae.
 In the submucosa numerous pale stained glands are present, namely
the Brunner’s glands. These are branched tubular or alveo-tubular
glands lined with columnar secretory epithelium. Brunner’s glands
secrete large amounts of alkaline mucous that neutralize the acidic
contents from the stomach.

14. Blood Supply and Lymphatics
 The blood supply of the C-shaped duodenum is shared with the head
of the pancreas.
 The proximal segment of the duodenum is supplied by the
gastroduodenal artery and its branches which include the superior
pancreaticoduodenal artery.
 The distal segment of the duodenum is supplied by the superior
mesenteric artery and the inferior pancreaticoduodenal artery.
 The venous drainage follows the arteries and ultimately drains into the
portal system.

15. Lymphatic drainage
 The duodenum also has
lymphatic vessels which drain
into the pancreaticoduodenal
lymph nodes located along the
pancreaticoduodenal vessels
and the superior mesenteric
lymph nodes.
 Efferent vessels of these
nodes drain into coeliac and
sup.mesen.group of pre aortic
lymph nodes.
 Some vesseles drain into
hepatic nodes directly.

16. Innervation

17. Innervation
 Duodenum receives both sympathetic and parasympathetic
nerves from the celiac and superior mesenteric plexuses.
 The nerves of the duodenum travel throughout the
submucosal layer of the duodenum.
 The duodenum is richly innervated by the parasympathetic
nervous system which includes branches of the anterior and
posterior vagus trunks.
 These parasympathetic nerves pass through the celiac
plexuses and follow the celiac trunk toward the duodenum.
The nerves then synapse in ganglia in the gut plexuses in the
duodenum and reach their final targets through short
postsynaptic fibers.
 The sympathetic nerves are branches of the celiac plexus
which originate from T5 through T9. These sympathetic
nerves pass through the sympathetic chain and travel
through the greater splanchnic nerve and synapse in the
celiac ganglia. The postsynaptic sympathetic follow the
branches of the celiac trunk toward the duodenum.

18. Physiological function
 duodenum manifests three fundamental physiological phenomena:
motility, secretion, and absorption.
 The duodenum receives chyme (partially digested food mixed with
acid, mucus and pepsin) from the stomach, and acts as an
intermediate for the further digestion and motility of this food.
 The endocrine cells found in the duodenal epithelium secrete the
hormones secretin and cholecystokinin (CCK) in response to the
acids and fats present in chyme. These hormones act locally on the
pyloric sphincter of the stomach, and thereby regulate the movement
of food out of the pylorus (i.e. regulate gastric emptying).
 Secretin stimulates the release of bicarbonate and mucus from the
duodenal epithelium, and hence helps bring the high acidity (or very
low pH) of chyme back to normal, making it easier to be digested
further. These hormones also stimulate the secretion of bile from the
liver and gallbladder, and the secretion of digestive enzymes such as
trypsin, lipase and amylase from the pancreas.

19.  These secretions are received by the duodenum via the main and
accessory pancreatic ducts, and the food is mixed with these
secretions and prepared for further chemical digestion.
 Bile and the digestive enzymes initiate and continue the chemical
digestion of food inside the duodenum by breaking down all nutrient
macro-molecules into their simpler monomeric forms.
 The duodenum is the main part where calcium and iron absorption
takes place in the small intestine.
 The muscle layers of the duodenum contract and relax in a regulated
manner by way of peristalsis and segmentation movements to transfer
the food in an orderly way to the rest of the small intestine where
further digestion and absorption takes place.

20. Common conditions of duodenum.
Duodenal ulcers are breaks in the mucosa that reach down to
the level of the muscularis mucosa. In the duodenum, ulcers occur
most commonly in its first part. Duodenal ulcers are more common
than gastric ulcers, and are mostly caused by the action of the
bacterium Helicobacter pylori, or due to long term NSAID use.
 Other less common causes include autoimmune conditions,
Crohn’s disease, bile reflux, some viral infections, ingestion of
corrosive substances, excessive cigarette smoking etc
 These ulcers may heal with scar formation, or may cause further
complications such as bleeding, perforation, or gastric outlet
obstruction (due to edema surrounding the inflamed ulcer).

21. Duodenitis means inflammation of the duodenum, which can be
either acute (short-term) or chronic (long-term). It can be caused by
various reasons, and the most common ones are – infection with
Helicobacter pylori, and long term NSAID use.
Duodenal obstruction is usually caused by cancers, the most
common cause being pancreatic cancer. Metastatic deposits from
other cancers such as gastric or colorectal cancer may also cause
duodenal obstruction. Primary duodenal cancer is a less common
cause when compared with the aforementioned causes.
Duodenal cancers are less common when compared to other
gastrointestinal cancers such as gastric cancer and colorectal
cancer. However, it is the most common site for cancers occurring
in the small intestine. The condition named familial adenomatous
polyposis (FAP) is an important risk factor for duodenal cancer.

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