Jejunum - Anatomy & Physiology

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Structure

Jejunum(Dog) - Copywright RVC 2008

• The jejunum is the longest part of the small intestine.
• It is highly coiled and occupies the ventral part of the abdominal cavity, filling those parts that are not occupied by other viscera. This produces species variation (see comparative aspects).
• It lies on the abdominal floor, separated from the parietal peritoneum by the greater omentum.
• It is suspended by the mesentry (mesojejunum). This conveys the blood vessels and nerves and houses lymph nodes.
  • The mesentry converges to its root. This is where the cranial mesenteric artery branches off from the aorta.

Function

• Has digestive and absorptive functions.

Vasculature

• The cranial mesenteric artery, a branch of the abdominal aorta, supplies blood to the jejunum, ileum, caecum, ascending colon and part of the transverse colon.
• It branches greatly within the mesenty of the jejunum.
  • There are many anastomoses within the mesentry, which ensure that the intestine can survive even if a major division of the cranial mesenteric is damaged.
• The cranial mesenteric vein drains blood from the jejunum and enters the portal vein.
  • It is rich in the products of digestion following a meal.
  • The portal vein enters the liver.

Species Differences

• The position of the jejunum is variable between species as it lies in that part of the abdomen not occupied by other viscera.

Canine

• Jejunum lies roughly symmetrically about the midline. It contacts the liver, stomach and spleen cranially and urinary bladder ventrally.

Horse

• The coils of jejunum are confined to the left dorsal part of the abdomen.
  • It is restricted to this position by the large caecum on the right, and ascending colon ventrally on both sides.

Ruminant

• It is pushed entirely to the right side of the abdomen by the rumen which is on the left.
  • Coils of the jejunum usually lie within the supraomental recess; although this can vary between individuals depending on fullness of the rumen and size of the uterus.

Pig

• Jejunumo lies in the caudoventral aspect of the abdominal cavity, mainly to the right of the midline.
  • This is due to the presence of the ascending colon on the left.