CGRN Exam

The section moves from the wall of the gut to the luminal organs, then to the accessory organs, blood supply and nerves, and finally to digestion, hormones, the microbiome and age-related change. Read it with a scope image in mind, because the exam rewards nurses who can link a landmark to a finding, a finding to a pathophysiologic mechanism, and a mechanism to a nursing action.

This chapter reviews the layered structure shared by the entire tube, then follows the path of a swallowed bolus from the mouth through the esophagus, with the endoscopic distances that orient every upper endoscopy.

From the lumen outward, the GI tract has four layers. The mucosa contains the epithelium, the lamina propria (loose connective tissue with immune cells and capillaries) and the muscularis mucosae. The submucosa holds larger vessels, lymphatics and the submucosal (Meissner) plexus. The muscularis propria has an inner circular and an outer longitudinal layer with the myenteric (Auerbach) plexus between them. The outermost layer is the serosa in intraperitoneal segments, or adventitia where the organ is retroperitoneal or in the chest, as with the esophagus.

Depth of invasion defines cancer staging, which EUS images as alternating bright and dark bands. A lesion confined to the mucosa or superficial submucosa may be removed endoscopically by EMR or ESD, while deeper invasion usually means surgery. Lift injection during EMR works by expanding the submucosa; a polyp that will not lift ("non-lifting sign") suggests invasion or scarring. Perforation means a breach through the muscularis propria and serosa. Because the esophagus lacks a serosa, esophageal cancers spread early and esophageal perforations leak directly into the mediastinum.

Digestion begins in the mouth. Chewing increases surface area, and saliva from the parotid, submandibular and sublingual glands adds salivary amylase (starch digestion begins here), lingual lipase, mucus and bicarbonate. The pharynx is a shared pathway for air and food. During a swallow, the soft palate rises to close the nasopharynx, the larynx elevates, the epiglottis tilts to cover the airway and the vocal cords close. This protective sequence is blunted by sedation and by topical pharyngeal anesthetic spray, which is why aspiration risk rises during and after upper endoscopy and why patients are kept NPO until the gag reflex and swallowing return per facility policy.

The upper esophageal sphincter (UES), formed mainly by the cricopharyngeus muscle, is a band of skeletal muscle that stays closed at rest to prevent air entering the esophagus and reflux of contents into the pharynx. It relaxes briefly with each swallow. The UES is the narrowest point that the endoscope must pass, and it is the most common site of iatrogenic perforation during intubation, especially when a Zenker diverticulum is present just above it.

The lower esophageal sphincter (LES) is a zone of tonically contracted smooth muscle at the gastroesophageal (GE) junction, reinforced externally by the crural diaphragm. It relaxes with swallowing to admit the bolus into the stomach and otherwise resists reflux. LES pressure falls with fatty meals, chocolate, peppermint, alcohol, nicotine, caffeine, pregnancy (progesterone) and drugs such as calcium channel blockers, nitrates and anticholinergics. Failure of the LES to relax is the defining physiology of achalasia; low LES pressure and transient LES relaxations underlie GERD.

Endoscopists record distances from the incisors (the upper front teeth) because the insertion tube is marked in centimeters. These approximate adult measurements help the nurse follow the procedure and verify documentation.

The esophagus is about 25 cm long and lined by pale pink squamous epithelium. The Z-line (squamocolumnar junction) is the irregular boundary where pale squamous mucosa meets the redder, salmon-colored columnar mucosa of the stomach. Normally the Z-line sits at or very near the top of the gastric folds. Salmon-colored mucosa extending at least 1 cm above the top of the gastric folds raises suspicion for Barrett esophagus, which requires biopsy confirmation of intestinal metaplasia. If the diaphragmatic pinch lies 2 cm or more below the GE junction, a hiatal hernia is present.

The upper third of the esophagus is skeletal muscle, the middle third is mixed, and the lower third is smooth muscle. This explains why scleroderma, a smooth muscle disease, weakens peristalsis and LES tone in the distal esophagus, while myasthenia gravis affects the proximal swallow.

• The GI wall has four layers: mucosa, submucosa, muscularis propria and serosa or adventitia; depth of a lesion guides endoscopic versus surgical treatment.
• The esophagus has no serosa, so perforation and tumor spread reach the mediastinum quickly.
• The UES sits about 15 cm from the incisors and is the narrowest point for scope passage; the GE junction sits about 38 to 40 cm.
• The Z-line marks the squamocolumnar junction; columnar mucosa at least 1 cm above the gastric folds prompts biopsy for Barrett esophagus.
• Sedation and topical spray blunt protective swallowing reflexes, so aspiration precautions continue until swallowing returns.