Anatomía - Duodeno (Relaciones, Porciones, Vasos y Nervios)

Duodenum: Anatomy and Functions

Introduction to the Duodenum

• The term "duodenum" is derived from Latin, meaning "twelve fingers," referring to its length of approximately 25 centimeters.

• It is the first portion of the small intestine where bile and pancreatic juices are secreted to aid in fat digestion.

Anatomical Position and Structure

• The duodenum is primarily retroperitoneal, except for its first portion, which is intraperitoneal. This positioning affects its mobility and relationships with surrounding organs.

• It occupies both the supramesocolic and inframesocolic compartments, with significant connections to adjacent structures like the liver and pancreas.

Fixation Mechanisms

• The first part of the duodenum connects to the liver via the lesser omentum (gastrohepatic ligament), while other portions are fixed by their retroperitoneal position against the posterior abdominal wall.

• The suspensory ligament of Treitz provides additional fixation at the junction between the duodenum and jejunum.

Segmentation of the Duodenum

• The duodenum consists of four segments:

• First Portion: Begins at the pylorus, measuring about 5 cm; known as bulbus duodenalis. It curves outward towards the right side near gallbladder neck.

• Second Portion: Descending segment measuring 7–10 cm that runs vertically downwards from L1 to L3/L4 vertebrae.

• Third Portion: Horizontal segment that wraps around pancreatic head; contains mesenteric vessels passing through it.

• Fourth Portion: Ascending segment extending from L3/L4 up to L2, measuring between 2.5–5 cm in length before connecting with jejunum at flexure duodenojejunalis.

Relationships with Surrounding Structures

• In its first portion, important anatomical relations include coverage by liver's quadrate lobe and gallbladder anteriorly, while posteriorly lie critical vessels such as gastroduodenal artery and portal vein—important considerations during surgical procedures.

• A notable anatomical feature is a triangle formed by these vessels called "interporto triangle," crucial for understanding vascular relationships in this region.

Duodenum Anatomy and Relationships

Second Portion of the Duodenum

• The second portion, known as the descending duodenum, is closely related to the pancreas and is covered anteriorly by the liver, gallbladder, and hepatic flexure of the colon.

• It has posterior relations with renal pedicle structures including renal artery, vein, and pelvis; separated by retro-duodenal fascia.

• This section is significant as it receives both the common bile duct and main pancreatic duct at a junction called Vater's ampulla.

• The accessory pancreatic duct (Santorini's duct) also drains into this area above the main ducts.

Third Portion of the Duodenum

• The third portion is horizontal in orientation and crosses over superior mesenteric vessels which can create a vascular clamp effect known as Wilkie's syndrome if angulation is less than 65 degrees.

• Compression from these vessels can lead to digestive tract issues or renal problems due to venous return obstruction.

• Posteriorly, it relates to both aorta and inferior vena cava while being in contact with intestinal loops below.

Fourth Portion of the Duodenum

• Extending towards the duodenojejunal flexure (angle of Treitz), this portion connects with transverse colon and mesocolon structures.

• It interacts with left kidney structures and ovarian/testicular vessels that cross over to the right side.

• Notably associated with vascular arches formed by left colic artery and inferior mesenteric vein leading to duodenal recesses.

Flexura Duodeni (Angle of Treitz)

• This angle marks a critical transition between upper and lower gastrointestinal tracts; important for clinical assessments regarding gastrointestinal bleeding sources.

• Contains suspensory muscle (ligament of Treitz), connecting from this angle to diaphragm’s left crus; plays a role in maintaining duodenal position.

Recesses Duodenales

• Presence of small diverticula known as duodenal recesses influenced by surrounding vasculature; primarily noted are three or four major recesses rather than six mentioned in literature.

Anatomy of the Duodenum

Overview of the Duodenum's Structure

• The fourth portion of the duodenum is not defined by a small fold known as the superior duodenal fold, which extends from this section to the transverse colon. It contains the mesenteric vein.

• The inferior duodenal recess is located slightly lower than the fourth portion and also extends towards the mesocolon, present in 75% of cases without any vessels inside.

• The arterial recess for duodenal structures is formed by the left colic artery and is situated between other recesses, highlighting its anatomical significance during surgical procedures.

• Understanding these recesses is crucial in surgery due to their potential to trap intestinal contents, leading to internal hernias that can strangulate intestines.

Anatomical Composition of the Duodenum

• The duodenum consists of four layers: serosa, muscularis, submucosa, and mucosa. The muscular layer and mucosa are particularly important for function.

• Muscular structure includes superficial longitudinal fibers and deeper circular fibers; while submucosal connective tissue houses glands essential for digestion.

• Macroscopically, the inner surface appears velvety due to intestinal villi and has irregularities from circular folds known as valvulae conniventes or circular folds.

Mucosal Features and Duct Openings

• Notably smooth in its first portion where ulcers commonly occur; however, subsequent portions feature significant folds that enhance nutrient absorption.

• Accessory pancreatic ducts (Santorini's duct) and common bile duct openings are found in the second portion of the duodenum, marked by papillae indicating their entry points into this segment.

• Key papillae include minor (lesser papilla - Santorini’s duct) and major (greater papilla - Vater’s ampulla), which serve as critical junction points for digestive secretions.

Vascular Supply to the Duodenum

• Blood supply originates from two main sources: common hepatic artery via gastroduodenal artery or superior mesenteric artery stemming from celiac trunk branches.

• Gastroduodenal artery supplies blood behind the first part of the duodenum with branches like supraduodenal arteries feeding this area specifically.

• Descending vertically behind it are pancreaticoduodenal arteries bifurcating into anterior-superior and posterior-superior branches vital for nourishment.

Venous Drainage Mechanisms

• Venous drainage mirrors arterial pathways forming anastomoses resembling arterial arches previously mentioned; ensuring efficient blood return post-nutrient absorption.

Innervation and Venous Drainage of the Duodenum

Venous Drainage

• The duodenum is drained by three specific veins, which are crucial for its venous drainage system.

Nervous System Involvement

• Innervation of the duodenum involves both sympathetic and parasympathetic nerves, originating from the vagus nerve as well as celiac ganglia and the superior mesenteric plexus.

Effects of Parasympathetic and Sympathetic Innervation

• Parasympathetic innervation stimulates gastrointestinal motility and secretion activity, enhancing digestive processes.

• Conversely, sympathetic innervation inhibits or slows down the movement within the digestive tract, counteracting parasympathetic effects.

Conclusion