2. part of the gastrointestinal tract divided into duodenum/jejunum/ileum
By Sarah
duodenum
jejunum
ileum
3. The duodenum
• C shaped
• Retroperitoneal except for its beginning which is intraperitoneal
• shortest part (10 inches in length)
• most chemical digestion by enzymes happens here
• first section divided into 4 parts
By Sarah
Superior part (first) Descending part (second) Inferior part (third) Ascending part (fourth)
• L1
• Connected to liver by
hepatoduodenal ligament
• Most common site of
duodenal ulceration
• Retroperitoneal except first
3cm
• L1-L3
• Curves inferiorly around the
head of pancreas
• Has the major duodenal
papilla (opening at which bile
and pancreatic secretions to
enter from the ampulla of
Vater (hepatopancreatic
ampulla).
• L3
• Travels laterally to the left
crossing over the inferior
vena cava and aorta
• L3-L2
• Joins the jejunum at the
duodenojejunal flexure
4. The jejunum
• middle section located in the upper left of infracolic compartment
• wide & thick
• Deep red
• mucous membrane has plicae circulares (valves of Kerckring)
• absorption of proteins & carbohydrates
• inner surface is covered in villi (The villi in the jejunum are much longer than in the duodenum or ileum.)
• epithelial cells which line these villi each possess up to 3000 microvilli.
• The transport of nutrients across epithelial cells through the jejunum includes the
passive transport of some carbohydrates and the active transport of amino acids,
small peptides, vitamins, and most glucose.
By Sarah
5. The ileum
• last section located in the lower right of infracolic compartment
• narrow & thin
• Pale pink
• mucous membrane has lymphatic nodules called
By Sarah
6. Tell the difference between the jejunum and ileum
jejunum ileum
Location Upper left quadrant Lower right quadrant
Color Deep red Pale pink
Pattern of vessels Less arcades-Long vasa recta More arcades-Short vasa recta
Mucous membrane Plicae circularis Peyer’s patches
Wall thickness Thick wall Thin wall
By Sarah
7. Characteristic features that help to increase the absorption:
• Length (4-6m)
• Plicae circulares or Valves of Kerckring
• Villi & microvilli (brush border)
microvillivilli
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8. Layers of small intestines
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serosa
Muscularis externa
submucosamucosa
Epithelium
Lamina propria
Muscularis mucosae
9. The small intestine develops from the midgut of the primitive gut tube except
for the upper part of the duodenum.
Molecular regulation: specifies the small intestine.
The upper part of the duodenum → foregut
The lower part of the duodenum, jejunum, ileum → midgut
Meckel’s diverticulum → remnant of the yolk stalk (vitelline duct)
By Sarah
