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Enumerate the parts of small intestine.

Small intestine is about 6 m  long and is divided into 3 parts:Parts of small intestine

  • Duodenum
  • Jejunum
  • Ileum

The duodenum is the proximal fixed part  and mostly retroperitoneal. The other  parts, i.e.,  jejunum and ileum are freely mobile and are encosed in peritoneal fold called mesentery.

Jejunum and ileum extend from duodenojejunal flexure to the ileocaecal junction.The upper 2/5th is jejunum and the lower 3/5th is the ileum. However, there is no clear line of demarcation

 What are the differences between jejunum and ileum?

Following are the differences between Jeunum and Ileum:

FeatureJejunumIleum
LocationUsually occupies umbilical regionOccupies hypogastric and pelvic regions
LengthProximal 2/5 th of small intestine except duodenumDistal 3/5 th of small intestine
CaliberWiderNarrower
Wall thicknessThickerThinner
VascularityMore vascularLess vascular
Plicae circulares Closely setWidely separated
Peyer’s patches (aggregated lymphoid follicles)ScantyNumerous

Differences in mesentery
Distribution of fatLessMore
Number of arcadesFebruary 1, 2018April 3, 2018
Vasa rectaLonger and fewerShorter and numerous

jejunum and ileum differences

What is mesentery? Enumerate the structures crossed by the root of mesentery.

Mesentery

mesentery and structures crossed by it

  • Mesentery is a fan shaped fold of peritoneum that suspends jejunum and ileum from the posterior abdominal wall.
  • Its attached margin (to posterior abdominal wall) is called root of the mesentery.
  • The root is approx. 15 cm. long.
  • It extends from the left side of the L2 vertebra to the right sacroiliac joint.

Structures crossed by the root of the mesentery from above downwards are:

  • Third part of duodenum
  • Abdominal aorta
  • Inferior vena cava
  • Right gonadal vessels.
  • Right ureter
  • Right psoas major muscle.

What are the contents of mesentery?

 Following are the contents of mesentery:

  • Coils of jejunum and ileum
  • Jejunal and ileal branches of superior mesenteric artery
  • Mesenteric lymph nodes
  • Intestinal lymph vessels
  • Nerve plexus
  • Extraperitoneal loose connective tissue
  • Fat

 Describe the arterial supply of jejunum and ileum.

Superior mesenteric artery, a branch of abdominal aorta supplies jejunum and ileum.  

  • 12-15 jejunal and ileal arteries arise from the left side of superior mesenteric artery to supply jejunum & ileum..
  • Within the mesentery they branch and anastomose to form arterial arcades from the terminal  arcades vasa recta arise that supply jejunum and ileum.

jejunum and ileum - arteries supplying

Describe in brief the nerve Supply of jejunum and ileum.

Small intestine is supplied by autonomic nervous system.

  • Sympathetic nerve supply: from T10-T11 spinal segments. Are vasomotor.
  • Parasympathetic nerve supply : from vagus nerves. It stimulates peristalsis.

Applied Aspects

Meckel’s diverticulum

  • Is a blind diverticulum from the antimesenteric border of ileum.
  • Is located about two feet from ileocaecal junction.
  • Is a remnant of proximal part of vitellointestinal duct.
  • Is usually 2 inches long.
  • Occurs in 2% of population.
  • It may contain ectopic gastric mucosa or pancreatic tissue.
  • Can be a site of peptic ulcer.
  • May cause intestinal obstruction.
  • When inflamed , symptoms mimic those of appendicitis.

Meckel's diverticulum

Peyer’s patches

Peyer’s patches  are located along the antimesenteric border of the ileum. They may ulcerate in typhoid fever and after recovery these ulcers don’t cause intestinal obstruction like tubercular ulcers.  This is because, the tubercular ulcers are circular and therefore, after recovery they may cause constriction of the lumen of small intestine by fibrous tissue, whereas the typhoid ulcers are longitudinal.

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