This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
Foreign bodies may become impacted at any part of its course; this is particularly the case if they are hard and rough with irregular outlines. If they are smooth and soft and more or less rounded they are apt to lodge at the constricted parts of the tube. These points are, as already stated, at its commencement, where it crosses the aorta and left bronchus, and where it passes through the diaphragm. The upper constriction is 1.5 cm. (or -3/5 in.) in diameter, and is least distensible. It will dilate to the width of 2 cm., and thus will allow a body of about 3/4 inch diameter to pass. The two lower constrictions are more distensible and a body that passes the oesophagus can usually pass the ileocaecal valve, so that the upper end of the oesophagus acts as a gauge to prevent the entrance of substances too large for the rest of the alimentary tract. The bodies which become lodged are usually those which have been pushed down beyond the opening of the oesophagus by the contraction of the muscles of the pharynx, and then on account of their irregular form become caught by the contraction of the tube below. With the head moderately extended, the first constriction will be 15 cm. (6 in.) from the teeth. A foreign body at this point will be opposite the cricoid cartilage at the level of the sixth cervical vertebra.
Pig. 22.?. - The oesophagus. From a plaster cast.
The second constriction is opposite the middle of the first piece of the sternum. This is 7 cm. (2 3/4 in. ) below the cricoid cartilage. Therefore a foreign body lodged just above it would be just below the top of the sternum.
The third constriction is 15 cm. (6 in.) below the second, or 37 cm. (14 4/5 in.) from the teeth, and is accessible from the stomach. This third constriction is more distensible than the two above it. Maurice H. Richardson was able, after introducing the hand into the stomach, to put two fingers into the cardiac opening from below, and so dislodge some impacted false teeth.
Foreign bodies are dangerous on account of the ulceration into the various organs which they cause and also on account of pressure. Pressure on the left bronchus and trachea has caused suffocation.
Ulceration may cause fatal hemorrhage by involving the carotid arteries, more likely the left, the inferior thyroids, the innominate, and even the aorta itself lower down. Low down in the chest the pericardium is in front of the oesophagus, and has been perforated. On the left side above and the right side below, the pleurae have been perforated and the lungs involved. Abscesses may occur from the ulcerative process and they are particularly dangerous, as the distance between the upper portion of the sternum and anterior portion of the bodies of the vertebrae is so small that compression of the air-passages and suffocation is readily produced.