Gardnerella vaginalis

Gardnerella Vaginalis

Definition Gardnerella vaginalis is the name of a micro-aerophilic coccobacillus found in the vaginal flora. Gardnerella vaginalis does not cause bacterial vaginosis (vaginal infection) unless...
Acetic Acid

Acetic Acid

Definition Acetic acid is a mildly corrosive monocarboxylic acid. Otherwise known as ethanoic acid, methanecarboxylic acid, hydrogen acetate or ethylic acid, this organic compound is...
Amino Acids

Amino Acids

Definition Amino acids are the building blocks of polypeptides and proteins and play important roles in metabolic pathway, gene expression, and cell signal transduction regulation....
BCAA supplements: a muscle myth?

Branched Chain Amino Acids

Definition The branched-chain amino acids or BCAAs, leucine, isoleucine, and valine are three of the nine nutritionally essential amino acids. These three ingredients form a...
Sulfuric acid

Sulfuric Acid

Definition Sulfuric acid (sulphuric acid) is a corrosive mineral acid with an oily, glassy appearance that gave it its earlier name of oil of vitriol....
Bile salt action in the gut

Bile Salts

Definition Bile salts are found in bile, a secretion produced by liver cells to aid digestion. Although bile is 95% water, bile salts are its...
The salivary glands

Submandibular Gland

Definition Submandibular glands are the second-largest salivary gland type, producing around 65% of our saliva when unstimulated (at rest). Located under the jaw, the exocrine...
Metaphase I

Metaphase I

Definition The first metaphase of meisosis I encompasses the alignment of paired chromosomes along the center (metaphase plate) of a cell, ensuring that two complete...
Prophase II

Prophase II

Definition During prophase II of meiosis II, four important steps occur. These are the condensing of chromatin into chromosomes, disintegration of the nuclear envelope, migration...


Definition Aldosterone (C21H28O5) is a mineralocorticoid hormone compound secreted by the adrenal gland cortex. It is part of the renin angiotensin aldosterone system or RAAS...


Esophagus Definition

The esophagus (a.k.a. oesophagus, food pipe, and gullet) is a long, hollow organ which transports food from the mouth to the digestive system. Typically, the esophagus travels directly from the mouth to the digestive tract. Some animals do not have a specialized stomach region, and the esophagus dumps directly into the intestines. In higher animals, the esophagus carries food through the thoracic cavity to the stomach. In animals with lungs, the esophagus and the larynx are separated after the pharynx, which exists near the back of the throat. In the diagram below of the human digestive system, the esophagus is highlighted.

Tractus intestinalis esophagus

The esophagus is formed from several layers of cells originally derived from the endoderm, or innermost cell layers of the embryo. The innermost cells develop into a mucosa, or lining which separates the body from the food being digested inside. On top of that is the submucosa, which contains connective tissues allowing the attachment of various muscles, veins, nerves, and other connective tissues. The overall structure of the esophagus can be seen below.

Layers of the GI Tract

The esophagus is controlled by a number of nerves, which control both peristalsis and supply signals back to the brain about food in the esophagus. The vagus nerve controls peristalsis, or the squeezing contraction of the digestive tract. The sympathetic trunk is a series of nerves which send signals back from the esophagus to the brain, and help control the periodic contractions of the esophagus and other parts of the digestive tract.

Function of the Esophagus

The esophagus is an important connection to the digestive system through the thoracic cavity, which protects the heart and lungs. The esophagus carries food through this cavity, keeping it separate and moving it through with muscular contractions. Two sphincters on either side of the esophagus separate food into small units known as a bolus. The size and complexity of the esophagus varies by species.

  • Larynx – The start of the tube leading to the trachea and lungs, which houses the vocal cords in some animals.
  • Pharynx – The specialized region of the throat in which the esophagus and larynx connect.
  • Trachea – Below the larynx, which leads into the bronchi of the lungs.
  • Peristalsis – The muscular contractions which move food through the digestive system by systematically contract the smooth muscle surrounding the digestive tract.


1. Art and science often intersect in society. In many stories and artistic works, a human gets swallowed by an animal, and must pass through their digestive tract, arriving safely on the other side. While this is hardly possible, it is certainly more feasible with some animals than others. Which of these animals has an esophagus which makes this a more feasible story?
A. Snake
B. Whale
C. Shark

Answer to Question #1
A is correct. Snakes, like other reptiles, swallow their food whole. This means that their esophagus must be able to expand to many times its size to be able to accommodate the large meals that the snakes intake. Sharks use a much different method to eat food. Their many rows of teeth serve as a large serrated knife, and they rip their head back and forth to remove large chunks of flesh. Whales are either baleen whales, which filter very small meals from the water, or toothed whales which use sharp teeth to catch bite-size prey or tear apart larger prey. In both B and C, a human could not even survive a trip through the mouth, let alone esophagus. Some snakes are known to grow large enough to eat a human, which at least makes the swallowing a person whole part of the story feasible.