The oesophagus is a muscular tube approximately 25 cm long; it is designed to transport the bolus of food from the mouth to the stomach with the assistance of the mucus that it produces. The oesophagus passes in front of the vertebral column in the chest and through the diaphragm. It is positioned behind the left lobe of the liver and enters the stomach at the cardia. The oesophagus is made up of four layers, as is the rest of the digestive tract:
1. Mucosa: epithelium lined with squamous cells
2. Submucosa: contains blood vessels and nerves
3. Muscular: contains an inner ring of smooth muscle
4. Fibrous: dense connective tissue of longitudinal folds that contain the stratified squamous epithelium.
The food bolus passes into the oesophagus by the action of swallowing and then by peristalsis. It is possible to eat and drink at the same time and in a variety of positions from sitting, standing, lying down and huddled up in a crouched sitting position, all without choking as a result of the vagus nerve stimulating peristalsis. The vagus nerve is the tenth cranial nerve and is responsible for gut stimulation. The bolus of food has to pass over the larynx where it shares a common opening with the oesophagus. This is achieved by the tongue closing the back of the mouth, the nasal passage being blocked by the soft palate and the epiglottis covering the larynx as the bolus is swallowed. When this process fails we say that 'food has gone down the wrong way' and a cough reflex brings the food back. The swallowing reflex may be lost in anyone who has had a cardiovascular accident or is unconscious.
The food bolus takes between 4 and 8 seconds to travel into the stomach; liquid is much faster. The bolus continues along the oesophagus until it reaches the stomach via the cardiac sphincter.
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