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    From Digestive System

    Internal Anal Sphincter
    Involuntary muscle around anal canal.
    Quadrate Lobe
    Small lobe located between gallbladder and round ligament.
    Rugae of Stomach
    Internal folds allowing expansion of the stomach.
    Mesocolon
    Peritoneal fold attaching colon to posterior wall.
    Mesentery
    Fold of peritoneum anchoring intestines.
    Right Lobe
    Larger functional lobe of the liver.
    Sigmoid Colon
    S-shaped final segment of the colon.
    Gallbladder
    Stores and concentrates bile.
    Transverse Colon
    Horizontal part of the colon.
    Gingiva
    Gums; soft tissue covering the bones of the jaw.
    Neck of Pancreas
    Short section between head and body.
    Stomach
    Muscular sac that begins digestion of protein.
    Accessory Pancreatic Duct
    Secondary duct emptying into duodenum.
    Pyloric Sphincter
    Regulates passage of chyme from stomach to duodenum.
    Duodenal Bulb
    Initial section of duodenum closest to the stomach.
    Epiploic Appendages
    Fat-filled pouches attached to colon.
    Lingual Frenulum
    Fold of mucous membrane anchoring the tongue to the floor of the mouth.
    Soft Palate
    Muscular posterior part of the roof of the mouth.
    Anus
    Opening through which feces are expelled.
    Left Lobe
    Smaller lobe of the liver.
    Pancreas
    Gland with both endocrine and exocrine functions.
    Anal Canal
    Terminal part of the large intestine.
    Submandibular Glands
    Salivary glands beneath the mandible.
    Minor Duodenal Papilla
    Opening for accessory pancreatic duct.
    Rectum
    Straight section of the colon leading to anus.

    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? Your gut contains millions of neurons and is often referred to as the "second brain."