Anatomical Parts of the Anti-Reflux Barrier

Ever wonder how your stomach contents defy gravity and don’t leak out when you hang upside down?

Knowing the anatomical parts of anti-reflux barrier helps explain this phenomenon and leads to a better understanding of why heartburn happens.

In Part I, we discuss the physical structures.

In Part 2, we get into the details of how they all work together forming the high pressure zone (HPZ).

Physical Structure Details
Esophagus An organ in vertebrates which consists of a muscular tube through which food passes from the pharynx (throat) to the stomach. The esophagus is sometimes called the “gullet”
Respiratory Diaphragm A dome-shaped muscle shelf extending across the lower rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity. It is controlled by the phrenic nerve.
Lower esophageal sphincter A small ring of smooth muscle fibers at the junction of the esophagus and stomach (also called cardiac sphincter, gastroesophageal sphincter).
Fundus Upper portion of the stomach.  This rounded part of the upper stomach allows for the accumulation of gases produced by chemical digestion.
Angle of His Angle at which the esophagus enters the stomach. When intact, creates a valve that acts as a functional sphincter which helps prevents stomach acid from traveling back into the esophagus where it can cause GERD.
Gastroesophageal Junction* The term for the junction orifice of the esophagus into the stomach.  At this level, the mucosa of the esophagus transitions into gastric mucosa.
Z-line The squamocolumnar junction where the lining changes from white esophageal squamous tissue to red gastric columnar tissue. The line is irregular hence the name Z (zigzag) line.  The lower esophageal sphincter is located in this area.
Gastroesophageal Flap Valve 3 – 4 cm musculomucosal fold created by the oblique angle at which the esophagus enters the stomach. It opens only for swallowing and closes promptly.  When competent and fully intact, it prevents the reflux of gastric contents up into the esophagus.

Distal Esophageal and Gastroesophageal Anatomy

GERD is a progressive disease with symptoms that start with occasional episodes of heartburn. As the anatomical structures and high pressure zone break down, the frequency and intensity of reflux symptoms increase. Click here to read Part II on how the HPZ is formed and its role in GERD.

*Note to GERD nerds: By calling this region the “Gastroesophageal junction” many clinicians point to the diseased state. The proper anatomical term is “esophagogastric junction” since medical terms should always indicate normal, proximal-to-distal flow.