Duodenum & Mesentery

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.