The Esophagus and Stomach

What is the basic function of the esophagus?

To transport the bolus of food from the pharynx to the stomach.

How long is the esophagus and what is its structure?

25 cm (10 in); a closed lumen that opens only to transport bolus and closes immediately after.

What is the esophageal hiatus?

Hole in the diaphragm through which the esophagus passes.

What is the cardiac/lower esophageal sphincter (LES)?

A circular smooth muscle valve at the end of the esophagus that prevents stomach acid from entering the esophagus.

What does GERD stand for and what causes it?

Gastroesophageal Reflux Disease; caused by a malfunctioning LES that allows stomach acid to erode the esophagus.

What are the short- and long-term effects of GERD?

Short-term: pain and discomfort; Long-term: tissue changes that can lead to esophageal cancer.

What is the epithelium lining of the esophageal mucosa?

Non-cornified stratified squamous epithelium.

What occurs at the gastro-esophageal junction?

Epithelial transition from stratified squamous to simple columnar.

What does the esophageal submucosa contain and do?

Mucus glands that secrete mucus to lubricate the bolus.

Describe the muscle composition of the esophageal muscularis externa.

Starts with skeletal muscle and transitions to smooth muscle by the lower third.

What forms the LES?

A thickened inner circular smooth muscle layer.

What is the adventitia of the esophagus?

Outer layer of dense connective tissue.

Describe the voluntary step of swallowing.

The tongue pushes bolus into the pharynx, activating pressure receptors.

Describe the involuntary steps of swallowing.

Pharynx muscles close the epiglottis and produce peristalsis; the esophagus propels the bolus to the stomach.

What are the four basic functions of the stomach?

Storage, protection, limited digestion, and mixing food into chyme.

Where is the stomach located?

Left upper quadrant of the abdominal cavity, inferior to the diaphragm.

What are the two sphincters associated with the stomach?

Cardiac sphincter (entry) and pyloric sphincter (exit).

Name the four anatomical regions of the stomach.

Cardia, Fundus, Body, Pylorus.

What is the fundus of the stomach?

A dome-shaped region that serves as extra storage.

What is the pylorus?

Funnel-shaped distal end of the stomach that leads to the pyloric sphincter.

What are the lesser and greater curvatures?

Lesser: concave left side; Greater: convex right side of the stomach.

What is the lesser omentum?

Sheet of mesenteries between the liver and the lesser curvature; contains adipose tissue.

What is the greater omentum?

Large fatty mesenteric sheet hanging from the greater curvature and covering intestines.

What are rugae?

Folds of mucosa in the empty stomach that allow for expansion.

What are gastric pits and gastric glands?

shallow invaginations; tubular structures branching from pits.

What kind of epithelium lines the stomach mucosa?

Simple columnar epithelium with specialized secretory cells.

What do mucus (neck) cells do?

Secrete alkaline mucus to coat and protect the stomach lining.

What causes peptic ulcers?

Erosion of the mucosal lining, most commonly by Helicobacter pylori infection.

What do parietal cells secrete?

HCl (hydrochloric acid) and intrinsic factor.

What is the role of HCl in the stomach?

Produces a pH of 1–2, denatures proteins, and kills microbes.

What is the role of intrinsic factor?

Allows absorption of vitamin B12 later in the digestive tract.

What do chief cells produce?

Pepsinogen (inactive form of pepsin) and gastric lipase.

How is pepsin formed and what is its function?

Pepsinogen is activated by HCl into pepsin; pepsin digests proteins into polypeptides.

What is the equation for protein digestion by pepsin?

Protein + Pepsin ↔ Smaller polypeptides + Pepsin

How much protein does pepsin digest?

Approximately 10% of consumed protein.

What does gastric lipase do?

Breaks triglycerides into fatty acids and monoglycerides.

Why is gastric lipase digestion inefficient?

Only digests ~5% of triglycerides due to low surface area of lipid droplets.

What hormone do G-cells (enteroendocrine cells) secrete?

Gastrin.

What is the function of gastrin?

Stimulates acid secretion by parietal cells.

Describe the three layers of the stomach’s muscularis externa.

Inner oblique, middle circular, and outer longitudinal smooth muscle layers.

What is the function of the muscularis externa in the stomach?

Produces peristaltic and segmental contractions for mixing and propulsion.

Describe the steps of stomach acid production in parietal cells.

Stimulated by ACh, histamine, or gastrin → H+/K+ ATPase pumps H+ into the lumen.

What enzyme helps generate H+ inside parietal cells?

Carbonic anhydrase.

What happens to the bicarbonate (HCO3–) in parietal cells?

Exchanged for Cl– via Cl–/HCO3– exchanger and enters bloodstream.

How is HCl formed in the stomach lumen?

Cl– is secreted into the lumen where it combines with H+ to form HCl.