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Small Intestine

The small intestine extends from the pyloric end of stomach to ileo-caecal junction. Itconsists of the proximal fixed part, the duodenum, and the lower mobile part which includes the jejunum and ileum. The total length of small Intestine is about 6 meters long.

  1. Duodenum is 'C' shaped, shortest, widest and most fixed part of small intestine. It is 25 cm long. It is devoid of mesentery. Most of the duodenum is retroperitoneal and fixed, except at its two ends where it is suspended by folds of peritoneum, and is therefore mobile. Duodenum lies opposite L 1, L2 and L3 vertebrae.
  2. Duodenum is C-shaped curve which encloses the head of pancreas and is subdivided into four parts:
    1. First part (Superior part): It is 5 cm (2 inches) long. It begins at the pylorus and meets the second part at superior duodenal flexure. This part appears as duodenal capon barium studies.
    2. Second part (Descending part): It is about 7.5 cm (3 inches) long. It is vertical part which begins at superior duodenal flexure and meets the third part at inferior duodenal flexure. The interior of second part of duodenum shows following features:
      1. Major duodenal papilla: It is present 8-10 cm distal to the pylorus. The hepatopancreatic ampulla (joint part of bile duct and pancreatic duct) opens here.
      2. Minor duodenal papilla: It is present 6-8 cm distal to the pylorus. Accessory pancreatic duct opens here
    3. Third part (Horizontal part): It is 10 cm (4 inches) long. It begins at inferior duodenal flexure and passes towards the left in front ofIVC behind superior mesenteric vessels and root of mesentery to meet 4th part of duodenum.
    4. Fourth part: It is 2.5 cm (1 inch) long and runs upward immediately to the left of aorta. It ends at duodenojejunal flexure by joining the jejunum.

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Arterial Supply


The part of duodenum before the opening of bile duct (major duodenal papilla) develops from foregut and therefore is supplied by coeliac trunk through superior pancreaticoduodenal artery, a branch of gastroduodenal artery, which in turn is a branch of common hepatic artery. Part of duodenum distal to opening of bile duct is developed from midgut and therefore is supplied by superior mesenteric artery through inferior pancreatico- duodenal artery. First part of duodenum receives additional supply from right gastric artery, supraduodenal artery (a branch of common hepatic artery, retroduodenal branch of gastroduodenal artery and right gastroepiploic artery.

Jejunum And Ileum

  1. The lower mobile part of small intestine includes jejunum (upper 2/5) and ileum (lower 3/5). Jejunum and ileum are suspended from posterior abdominal wall by the mesentery. They are supplied by superior mesenteric vessels as they are midgut derivatives.




1. Location

Occupies upper and left
parts of the intestinal area

Occupies lower and right parts of the
intestinal area

2. Walls

Thicker and more vascular

Thinner and less vascular

3. Lumen

Wider and often empty

Narrower and often loaded

4. Mesentery

Windows present

Fat less abundant

Arterial arcades, 1 or 2

Vasa recta longer and fewer

No windows

Fat more abundant

Arterial arcades, 3 or 6

Vasa recta shorter and more numerous

5. Circular mucosal folds

Larger and more closely set

Smaller and sparse

6. Villi

Large, thick (leaf-like) and
more abundant

Shorter, thinner (finger like and less abundant)

7. Peyer's patches



Solitary lymphatic


More numerous

  1. Peyer's patches are aggregated lymphoid follicles which are more numerous in ileum and are present along antimesenteric border.
  2. The nervous and villous coat of jejunum is extensive and is thrown into folds, called Valvulae conniventes (plica circulare).

Meckel's diverticulum


Meckel's diverticulum is the persistent proximal part of the vitellointestinal duct which normally disappears during intrauterine life. It follows 'rule of 2':- present in 2% subjects, 2 inches (5 cm) long and is situated 2 feet (60 cm) proximal to Ileocoecal valve. It is attached to antimesenteric border of ileum. Its calibre is equal to that of the ileum. Its apex may be free or attached to umblicus or mesentery by a fibrous band. Vitellointestinal duct possesses all three coats of intestinal wall.

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