Structure of the Small intestine

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Structure of the Small intestine
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Parts of the small intestine

• The small intestine is split into 3 parts the
  duodenum, jejunum and the ileum.
• There are microscopic finger-like projections
  called villi covering the small intestinal walls
  which increase surface area for absorption.
• Its also contains Intestinal juice (succus
  entericus)

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Structure of the small intestine.

• Duodenum a short section that receives
  secretions from the pancreas and liver via the
  pancreatic and common bile ducts.
• Jejunum considered to be roughly 40 of the
  small gut in man, but closer to 90 in animals.
• Ileum empties into the large intestine
  considered to be about 60 of the intestine in
  man, but veterinary anatomists usually refer to
  it as being only the short terminal section of
  the small intestine.

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The duodenum.
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The duodenum continued

• The duodenum contains
• Mucosal layer made up of villi projections
• Sub mucosa containing connective tissue, glands
  and blood vessels folds under the mucosal layer.
• Muscularis with circular and longitudinal muscle
  layers.
• Serosa made up of viseral peritoneum and
  mesentery.
• Note the folding of the intestinal muscoa into
  structures called plicae circulares which
  increase absorptive surface area.

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Microscopic Duodenum Villi

• The outer edge of the villus is made up of simple
  columnar epithelium with goblet cells
• The lacteal, core of the villus, is lymphatic
  tissue that absorbs digested lipids in the form
  of chylomicrons

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Submucosal Microscopic Detail

• Brunner's glands are only found in the duodenum.
  They secrete mucus.
• There is a very thin layer of smooth muscle cells
  that forms the muscularis mucosa.

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Duodenum Muscularis Microscopic Detail

• Together the circular and longitudinal muscle
  layers work in a coordinated motion to cause the
  peristaltic movement of the GI tract.
• The myenteric plexus of Auerbach located in the
  muscular layer controls the gastrointestional
  motility

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Microscopic View of the Jejunum
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The jejunum continued..

• The jejunum, the middle section of the small
  intestine, is different from the duodenum due to
  lack of Brunner's glands. It is different from
  the ileum because it has less goblet cells and
  generally lacks Peyer's patches.
• The jejunum is slung from the posterior abdominal
  wall by the mesentery of the small intestines
  and, therefore, is extremely mobile.

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Continued again..

• The jejunum is about 2.5m (8ft) long and passes
  imperceptibly into the ileum, which is about 4m
  (12ft) long. this part of the small intestine
  occupies a central position in the abdominal
  cavity, below the liver and the stomach, and
  behind the transverse mesocolon, the transverse
  colon and the greater omentum.

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Villi of the Jejunum Mucosa

• At the base of the many villi of the jejunum are
  simple tubular invaginations or pits that extend
  to the muscularis mucosae.

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Submucosa of the Jejunum

• Note the brightly stained collagen of the
  connective tissue

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Muscularis Externa of the Jejunum

• Consists of smooth muscle

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Ileum Microscopic Cross Section
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Ileum continued..

• The ileum is different from the duodenum and the
  jejunum by having more goblet cells in the mucosa
  and lymph nodules called Peyer's patches.
• Is also slung from the posterior abdominal wall
  by the mesentery of the small intestines and,
  therefore, is extremely mobile

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Definitions

• Mesentery-Those arteries and veins that supply
  the small and large intestines.
• Lacteal-Pertaining to, or containing, chyle as,
  the lacteal vessels