Duodenum & Mesentery

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DUODENUM

  • It is proximal dilated and fixed part of the small intestine.
  • It shows a C-shaped curve which encloses head of the pancreas.
  • It is divided into 4 parts.
    • First (upper) part – 5cm
    • Second (vertical) part – 8-10cm
    • Third (horizontal) part – 10cm
    • Fourth (ascending) part – 2.5cm

 

RELATIONS

First  Part :-

  • It extends from pylorus to superior duodenal flexure.
  • It is directed upwards, backwards to the right.
  • It is the most movable part of duodenum.

In front –

  • Quadrate lobe of liver
  • Neck & body of gall bladder

Behind –

  • Portal vein, bile duct, gastroduodenal artery
  • Inferior vena cava

Above –

  • Lesser omentum
  • Floor of epiploic foramen
  • Hepatic artery

Below –

  • Head & neck of pancreas
  • Greater omentum

Second  Part :-

  • It extends from superior duodenal flexure to right inferior duodenal flexure.
  • It lies against L1-L3 vertebrae.

In front –

  • Transverse colon
  • Right lobe of liver
  • Fundus & body of gall bladder
  • Coils of jejunum

Behind –

  • Right kidney
  • Right renal vessels
  • Pelvis of right ureter
  • Right psoas major
  • Inferior vana cava
  • Right supra-renal gland

Laterally –

  • Right colic flexure

Medially –

  • Head of pancreas
  • Pancreatico-duodenal vessels
  • Bile duct
  • Main pancreatic duct

Interior –

Circular folds (Plica circularis)- 

  • They are permanent mucosal folds

Major duodenal papilla-

  • It’s a conical projection on the posteromedial wall
  • Lies 8-10 cm distal to pylorus
  • Its summit receives common opening of bile duct & pancreatic duct

Minor duodenal papilla-

  • It’s a conical projection
  • Lies 2 cm above the major papilla
  • Its summit receives opening of accessory pancreatic duct

Plica semicircularis- 

  • It’s a mucosal arch above the major papilla.

Plica longitudinalis- 

  • It’s a vertical mucosal fold extends downwards from major papilla.

Third  Part :-

  • It extends from right inferior duodenal flexure to left inferior duodenal flexure.
  • It lies opposite L3 vertebra.

In front –

  • Superior mesenteric vessels
  • Root of mesentery

Behind –

  • Right psoas major
  • Right ureter
  • Inferior vena cava
  • Right gonadal vessels
  • Abdominal aorta
  • Inferior mesenteric artery

Above –

  • Head of pancreas
  • Inferior pancreatico-duodenal vessels

Below –

  • Coils of jejunum

Fourth  Part :-

  • It lies left to L2 vertebra.

  • It extends from left inferior duodenal flexure to duodeno-jejunal flexure.
  • Duodeno-jejunal flexure is kept in position by suspensory muscle of duodenum.
Suspensory muscle of duodenum (ligament of Treitz) –
  • It is a fibro-muscular band.
  • Arises from the right crus of diaphragm close to the oesophageal opening.
  • The band is attached to the postero-superior surface of duodeno-jejunal flexure.
  • Upper third of the band consists of striated muscle.
  • Middle third consists of elastic tissue.
  • Lower third consists of unstriped muscle.

In front –

  • Transverse colon & mesocolon
  • Stomach separated by lesser sac

Behind –

  • Left crus of diaphragm
  • Left psoas major
  • Left sympathetic trunk
  • Left renal vessels
  • Left gonadal vessels
  • Left supra-renal vein
  • Inferior mesenteric vein

Right side –

  • Uncinate process of pancreas

Left side –

  • Left kidney & Ureter

Above –

  • Body of pancreas

ARTERIAL  SUPPLY

First  Part :-

  • Supra-duodenal branch of gastroduodenal artery
  • Retro-duodenal branch of gastro-duodenal artery
  • Infra-duodenal branch of right gastro-epiploic artery

Second,  Third  &  Fourth  Parts :-

  • 2 rows of vasa recta from ventral & dorsal anastomoses of superior & inferior Pancreatico-duodenal arteries.

VENOUS  DRAINAGE

  • Veins correspond to the arteries.
  • They drain into Superior mesenteric vein & Portal vein.

LYMPHATIC  DRAINAGE

lymph vessels drain into Pancreatico-duodenal lymph nodes 

which drain into Coeliac & Superior mesenteric groups of Pre-aortic lymph nodes

NERVE  SUPPLY

Sympathetic Supply :-

  • From coeliac & superior mesenteric plexuses from T6 – T9 spinal cord segments

Parasympathetic Supply :-

  • From both vagus nerves

DEVELOPMENT

  • Mucous membrane of above the ampulla of Vater, develops from endoderm of fore gut.
  • Mucous membrane below the ampulla develops from endoderm of midgut.
  • Musculature and other tissues develop from the splanchnic layer of lateral plate mesoderm.

APPLIED  ANATOMY

Peptic  Ulcer :-

  • First part of duodenum is vulnerable to form peptic ulcer as it is supplied by end arteries.
  • It may produce severe haemorrhage due to the involvement of gastro-duodenal artery.

Obstructive  Jaundice :-

  • It can be produced by impacted bile stone on the summit of major duodenal papilla in the interior of second part of duodenum.

Duodenal  Obstruction :-

  • Second part of duodenum can be obstructed by malignant growth of annular pancreatic head.

Duodenal  Rupture :-

  • Third part of duodenum is most vulnerable to external injury.
  • It may be compressed between the vertebral column & anterior abdominal wall.

Internal  Hernia :-

  • Fourth part of duodenum is related to few peritoneal duodenal recesses.
  • They are- superior, inferior, retro-duodenal & para-duodenal recesses.
  • They are bounded by duodenal folds which are formed by the course of inferior mesenteric vein.
  • A loop of small gut may herniate into any of the recesses producing internal hernia & internal obstruction.

MESENTERY

  • It is a broad fan-shaped fold of peritoneum.
  • It suspends jejunum and ileum from posterior abdominal wall.
  • It conveys nutrition and innervation to the small gut.
  • It is about 15 - 20 cm in breadth.

LAYERS  OF  MESENTERY

  • Mesentery consists of 2 layers - right & left - derived from greater sac.

Right  Layer –

  • It covers the front & sides of the ascending colon forming right para-colic gutter.
  • Above it covers inferior surface of the body of pancreas & continuous with the lower layer of transverse mesocolon.

Left  Layer –

  • Left layer covers front & sides of descending coon forming left para-colic gutter.
  • Below it enters the pelvic cavity & reflects to enclose the sigmoid colon forming sigmoid mesocolon.

BORDERS  OF  MESENTERY

  • Mesentery presents 2 borders- vertebral border or root & intestinal or free border.

Root :-

  • It is 15 cm long
  • It extends from the left side of L2 vertebra at duodeno-jejunal flexure to right sacro-iliac joint at ileo-caecal junction.

Structures crossed by the root – (from above downwards)
  • Third part of duodenum
  • Abdominal aorta
  • Inferior vena cava
  • Right gonadal vessels
  • Right ureter
  • Right psoas major
  • Right genito-femoral nerve
  • Right sacro-iliac joint

Free  Border :-

  • It is a frilled border
  • It is about 20 feet long
  • It encloses the jejunum and ileum

CONTENTS  OF  MESENTERY

  • Jejunum & ileum
  • Jejunal & ileal branches of superior mesenteric vessels
  • Intestinal lymphatics known as lacteals & mesenteric lymph nodes
  • Loose areolar tissue & plexus of nerves around the blood vessels
  • Fat – 
    • It is confined along the root of jejunal mesentery presents translucent windows between the blood vessels.
    • In ileum the fat spreads throughout the breadth of mesentery & windows are usually not observed.
  • Occasional contents – suspensory muscle of duodenum, accessory suprarenal tissue, tip of vermiform appendix.

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