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    Related Topics

    From Digestive System

    Left Lobe
    Smaller lobe of the liver.
    Cheeks
    Lateral walls of the oral cavity composed of muscle and fat.
    External Anal Sphincter
    Voluntary muscle around anus.
    Mesentery
    Fold of peritoneum anchoring intestines.
    Rugae of Stomach
    Internal folds allowing expansion of the stomach.
    Upper Esophageal Sphincter
    Muscle ring that controls entry into the esophagus.
    Lesser Omentum
    Connects stomach and liver.
    Nasopharynx
    Superior region of pharynx behind the nasal cavity.
    Splenic Flexure
    Bend between transverse and descending colon.
    Teeth
    Structures in the jaws for mechanical breakdown of food.
    Gingiva
    Gums; soft tissue covering the bones of the jaw.
    Epiploic Appendages
    Fat-filled pouches attached to colon.
    Gallbladder
    Stores and concentrates bile.
    Palatine Tonsils
    Lymphatic tissues on either side of the oropharynx.
    Major Duodenal Papilla
    Opening for bile and pancreatic ducts into duodenum.
    Oral Cavity
    Entry point of the digestive system; includes teeth, tongue, and salivary openings.
    Ileum
    Final and longest portion of the small intestine.
    Hard Palate
    Bony anterior portion of the roof of the mouth.
    Anus
    Opening through which feces are expelled.
    Body of Pancreas
    Central elongated portion of pancreas.
    Sigmoid Colon
    S-shaped final segment of the colon.
    Liver
    Largest gland in the body with roles in metabolism and bile production.
    Caudate Lobe
    Lobe of liver near inferior vena cava.
    Rectum
    Straight section of the colon leading to anus.
    Duodenal Bulb
    Initial section of duodenum closest to the stomach.

    Lower Esophageal Sphincter

    Reviewed by our medical team

    Muscle at the junction of esophagus and stomach.

    Overview

    The lower esophageal sphincter (LES), also known as the gastroesophageal sphincter, is a critical muscular structure that marks the junction between the esophagus and the stomach. It plays a central role in the digestive system by acting as a one-way valve that prevents the reflux of acidic gastric contents back into the esophagus. Although not a distinct anatomical sphincter, it functions as a high-pressure zone essential for maintaining esophageal integrity.

    Location

    The LES is located in the distal portion of the esophagus, at the level of the esophageal hiatus of the diaphragm. Specifically, it:

    • Is situated just above the cardia of the stomach

    • Lies at the approximate level of the 10th or 11th thoracic vertebra (T10–T11)

    • Is partially supported by the diaphragmatic crura, which aid in sphincter competence

    Its position makes it susceptible to pressure changes from both the thoracic and abdominal cavities.

    Structure

    The LES is a physiological, not an anatomical sphincter, composed of:

    • Circular smooth muscle fibers: Located within the distal 2–4 cm of the esophageal wall

    • Intrinsic tone: Maintained by myogenic and neurogenic mechanisms, generating a resting pressure of 10–30 mmHg

    • External support: From the right crus of the diaphragm, which augments LES function during inspiration and increased intra-abdominal pressure

    • Innervation: Regulated by the enteric nervous system and modulated by parasympathetic fibers of the vagus nerve

    The LES relaxes reflexively in response to swallowing and remains tonically contracted at rest.

    Function

    The primary function of the lower esophageal sphincter is to:

    • Prevent gastroesophageal reflux: Acts as a barrier to the backward flow of acidic gastric contents into the esophagus

    • Permit passage of food: Relaxes transiently to allow swallowed food and liquids to enter the stomach

    The LES also works in conjunction with the esophageal peristaltic wave to ensure proper timing and coordination of food entry.

    Physiological Role(s)

    The LES plays vital roles in maintaining digestive homeostasis:

    • Maintains acid gradient: Prevents esophageal mucosal damage by maintaining a sharp pH contrast between the esophagus and stomach

    • Prevents air entry: Prevents excessive air from entering the stomach during respiration and swallowing

    • Reflex regulation: LES tone is modulated by complex reflexes involving the brainstem, vagus nerve, and enteric nervous system

    • Coordinates with diaphragmatic crura: Acts synergistically with diaphragmatic contractions to provide an additional mechanical barrier against reflux

    Clinical Significance

    Dysfunction of the LES is associated with several common and serious medical conditions:

    • Gastroesophageal reflux disease (GERD): Caused by a hypotensive or incompetent LES, leading to reflux of stomach acid into the esophagus

    • Hiatal hernia: The LES may become displaced into the thoracic cavity, impairing its function and contributing to reflux

    • Achalasia: A neurogenic disorder where the LES fails to relax properly, leading to esophageal outflow obstruction and dysphagia

    • Esophagitis: Chronic exposure of the esophagus to gastric acid can lead to inflammation, ulceration, and even Barrett’s esophagus

    • Surgical considerations: Procedures like Nissen fundoplication aim to reinforce the LES in patients with severe reflux or hernia

    • Manometry testing: Esophageal manometry is used to measure LES pressure and coordination for diagnostic evaluation of motility disorders

    Understanding LES function is crucial for diagnosing and managing upper gastrointestinal diseases, and it is a major target in both pharmacologic and surgical treatments for reflux-related disorders.

    Did you know? The stomach lining secretes mucus to protect itself from the strong acids it produces to digest food.