Logo

    Related Topics

    From Digestive System

    Lesser Omentum
    Connects stomach and liver.
    Anus
    Opening through which feces are expelled.
    Lingual Frenulum
    Fold of mucous membrane anchoring the tongue to the floor of the mouth.
    Quadrate Lobe
    Small lobe located between gallbladder and round ligament.
    Esophagus
    Muscular tube conveying food from the pharynx to the stomach.
    Soft Palate
    Muscular posterior part of the roof of the mouth.
    Oral Cavity
    Entry point of the digestive system; includes teeth, tongue, and salivary openings.
    Major Duodenal Papilla
    Opening for bile and pancreatic ducts into duodenum.
    Oropharynx
    Middle region of the pharynx behind the oral cavity.
    Parotid Glands
    Largest salivary glands located near the ear.
    Lips
    Fleshy borders of the mouth that aid in speech and food intake.
    Mesentery
    Fold of peritoneum anchoring intestines.
    Nasopharynx
    Superior region of pharynx behind the nasal cavity.
    Cystic Duct
    Connects gallbladder to common bile duct.
    Splenic Flexure
    Bend between transverse and descending colon.
    Peritoneum
    Serous membrane lining the abdominal cavity.
    Sigmoid Colon
    S-shaped final segment of the colon.
    Body
    Main central region of the stomach.
    Descending Colon
    Vertical segment of the colon on the left side.
    Caudate Lobe
    Lobe of liver near inferior vena cava.
    Cardia
    Upper opening of the stomach.
    Rectum
    Straight section of the colon leading to anus.
    Main Pancreatic Duct
    Primary duct draining pancreatic juices.
    Sublingual Glands
    Salivary glands beneath the tongue.
    Hard Palate
    Bony anterior portion of the roof of the mouth.

    Jejunum

    Reviewed by our medical team

    Second portion of the small intestine.

    Overview

    The jejunum is the middle segment of the small intestine, positioned between the duodenum and the ileum. It is a major site for nutrient absorption, including carbohydrates, amino acids, and vitamins. Characterized by prominent mucosal folds and rich vascular supply, the jejunum plays a vital role in digestion and absorption during the post-gastric phase of food processing.

    Location

    The jejunum occupies the upper left quadrant and central part of the abdomen. It:

    • Begins at the duodenojejunal flexure, located to the left of the second lumbar vertebra (L2), where the duodenum transitions into the jejunum

    • Is suspended by the mesentery, allowing mobility within the abdominal cavity

    • Gradually transitions into the ileum without a clear anatomical landmark

    The first 40% of the intraperitoneal small intestine after the duodenum is considered the jejunum.

    Structure

    The jejunum has distinct structural features that differentiate it from the duodenum and ileum:

    • Mucosa: Lined with simple columnar epithelium with microvilli; contains numerous plicae circulares (circular folds) for increased surface area

    • Villi: Long, finger-like projections that maximize absorptive efficiency

    • Submucosa: Contains blood vessels, nerves, and connective tissue, but lacks the Brunner’s glands of the duodenum and Peyer’s patches of the ileum

    • Muscularis externa: Two layers of smooth muscle: inner circular and outer longitudinal, enabling peristalsis and segmentation

    • Serosa: Covered by visceral peritoneum and suspended by the mesentery, which contains arterial arcades and long vasa recta

    Function

    The primary functions of the jejunum include:

    • Absorption of nutrients: Most of the digested carbohydrates, proteins, and water-soluble vitamins are absorbed here

    • Enzymatic digestion: Brush-border enzymes aid in the final breakdown of disaccharides and peptides

    • Fluid absorption: Absorbs water and electrolytes as chyme moves through the lumen

    Physiological Role(s)

    The jejunum plays a central role in gastrointestinal physiology:

    • Maximized surface area: Due to extensive villi and plicae circulares, the jejunum has a large surface area optimized for absorption

    • Transport mechanisms: Active transport (e.g., sodium-glucose cotransporters) and passive diffusion facilitate nutrient uptake

    • pH regulation: The jejunal environment is slightly alkaline (pH 7–8), ideal for enzymatic activity from pancreatic secretions

    • Hormonal signaling: Interacts with hormones like cholecystokinin (CCK) and secretin to coordinate digestive processes

    Clinical Significance

    Several medical conditions and procedures are associated with the jejunum:

    • Malabsorption syndromes: Disorders like celiac disease can cause villous atrophy, reducing the jejunum’s ability to absorb nutrients

    • Short bowel syndrome: Surgical resection of a large portion of the jejunum can severely impair nutrient and fluid absorption

    • Jejunal atresia: A congenital condition where a portion of the jejunum is absent or narrowed, often presenting with bilious vomiting in neonates

    • Peptic ulcers: Though rare in the jejunum, ulcers may occur in the setting of Zollinger-Ellison syndrome or ectopic gastric mucosa

    • Jejunal diverticulosis: Outpouchings of the jejunal wall can lead to stasis, inflammation, or perforation

    • Feeding access: A jejunostomy tube may be placed surgically for enteral nutrition in patients unable to use the upper GI tract

    The jejunum can be assessed using imaging (e.g., CT enterography), endoscopy, or biopsy, especially in cases of suspected malabsorption or chronic diarrhea.

    Did you know? The large intestine absorbs water, and the remaining material is turned into waste for elimination.