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    Related Topics

    From Digestive System

    Pylorus
    Distal part of stomach leading to duodenum.
    Fundus
    Upper curved portion of the stomach.
    Parotid Glands
    Largest salivary glands located near the ear.
    Abdomen
    The abdomen is the body region between the chest and pelvis housing vital digestive, metabolic, and excretory organs, protected by muscular and peritoneal layers.
    Esophagus
    Muscular tube conveying food from the pharynx to the stomach.
    Lesser Omentum
    Connects stomach and liver.
    Sublingual Glands
    Salivary glands beneath the tongue.
    Transverse Colon
    Horizontal part of the colon.
    External Anal Sphincter
    Voluntary muscle around anus.
    Greater Omentum
    Fatty fold of peritoneum covering intestines.
    Anus
    Opening through which feces are expelled.
    Common Bile Duct
    Conveys bile from liver and gallbladder to duodenum.
    Oral Cavity
    Entry point of the digestive system; includes teeth, tongue, and salivary openings.
    Rectum
    Straight section of the colon leading to anus.
    Cardia
    Upper opening of the stomach.
    Common Hepatic Duct
    Carries bile from liver to bile duct.
    Mesentery
    Fold of peritoneum anchoring intestines.
    Major Duodenal Papilla
    Opening for bile and pancreatic ducts into duodenum.
    Cystic Duct
    Connects gallbladder to common bile duct.
    Anal Canal
    Terminal part of the large intestine.
    Lips
    Fleshy borders of the mouth that aid in speech and food intake.
    Body of Pancreas
    Central elongated portion of pancreas.
    Uvula
    Dangling soft tissue at the back of the soft palate.
    Descending Colon
    Vertical segment of the colon on the left side.
    Tongue
    Muscular organ aiding in taste, speech, and food manipulation.

    Duodenum

    Reviewed by our medical team

    First portion of the small intestine.

    Overview

    The duodenum is the first and shortest section of the small intestine, playing a critical role in the initial phase of digestion following gastric emptying. It receives chyme from the stomach and secretions from the pancreas, liver, and gallbladder, creating an optimal environment for enzymatic breakdown and nutrient absorption. Despite its small size, the duodenum is essential in regulating digestive processes and coordinating gastrointestinal function.

    Location

    The duodenum is located in the epigastric and umbilical regions of the abdomen. It:

    • Extends from the pylorus of the stomach to the duodenojejunal flexure

    • Forms a C-shaped curve around the head of the pancreas

    • Lies primarily in a retroperitoneal position, except for the proximal portion (the duodenal bulb), which is intraperitoneal

    It is closely related to important vascular and ductal structures including the common bile duct, pancreatic duct, superior mesenteric artery and vein, and portal vein.

    Structure

    The duodenum measures approximately 20–25 cm in length and is divided into four parts:

    1. First part (superior): Also called the duodenal bulb, it is intraperitoneal and connects to the pylorus

    2. Second part (descending): Receives the common bile duct and pancreatic duct at the major duodenal papilla

    3. Third part (horizontal): Crosses the midline, posterior to the superior mesenteric vessels

    4. Fourth part (ascending): Ascends to join the jejunum at the duodenojejunal flexure, supported by the ligament of Treitz

    Histologically, it has four main layers:

    • Mucosa: Contains villi, microvilli, goblet cells, and specialized Brunner’s glands in the submucosa for mucus secretion

    • Submucosa: Rich in lymphatics and Brunner’s glands

    • Muscularis externa: Two smooth muscle layers that produce peristalsis

    • Serosa/adventitia: Depending on its position, the outer layer varies

    Function

    The duodenum serves multiple vital functions:

    • Neutralizes gastric acid: Bicarbonate-rich mucus from Brunner’s glands buffers incoming chyme

    • Receives digestive enzymes: Accepts pancreatic juice (with enzymes) and bile for chemical digestion

    • Mixes and regulates chyme: Coordinates contractions and hormone release to regulate gastric emptying and motility

    • Initiates absorption: Begins absorption of iron, calcium, and some vitamins

    Physiological Role(s)

    The duodenum contributes to overall digestive physiology in several ways:

    • Hormonal signaling: Releases secretin and cholecystokinin (CCK) in response to acidic or fatty chyme, stimulating the pancreas and gallbladder

    • pH regulation: Maintains optimal pH (6–7.5) for enzymatic activity by neutralizing acidic contents

    • Gatekeeper role: Modulates pyloric opening to control the rate of gastric emptying

    • Immune function: Contains lymphoid tissue contributing to mucosal immunity

    Clinical Significance

    The duodenum is associated with several common and important clinical conditions:

    • Duodenal ulcers: Most often affect the duodenal bulb and are linked to Helicobacter pylori infection or NSAID use; may cause pain, bleeding, or perforation

    • Duodenitis: Inflammation due to infection, acid, or autoimmune conditions

    • Obstruction: Can occur from congenital anomalies (e.g., duodenal atresia), masses, or external compression (e.g., superior mesenteric artery syndrome)

    • Malabsorption syndromes: Damage to duodenal mucosa (e.g., in celiac disease) affects absorption of key nutrients like iron and folate

    • Carcinoma or adenomas: Though rare, duodenal tumors can obstruct bile or pancreatic flow and cause weight loss, vomiting, or jaundice

    • Diagnostic tools: Upper endoscopy, barium studies, CT scans, and capsule endoscopy are used to examine duodenal disorders

    Due to its anatomical complexity and functional importance, the duodenum plays a central role in digestive health and disease.

    Did you know? The body absorbs over 90% of the nutrients from the food you eat in the small intestine.