What Is the Diaphragm and What is its Function?

What is the anatomy of the diaphragm, what is its function, and what are some medical conditions that may affect this muscle?

The diaphragm is a parachute-shaped muscle that separates the chest from the abdomen. It represents the floor of the thoracic cavity and the ceiling of the abdominal cavity.

There are 3 openings (holes) through the diaphragm:

• The esophageal opening: Through which the esophagus passes.
• The aortic opening: Through which the aorta, thoracic duct, and azygous vein pass.
• The caval opening: Through which the inferior vena cava (the large blood vessel returning blood from the legs and lower body to the heart) travels.

The diaphragm can be seen as being divided into two halves, or “hemi-diaphragms.” (Hemi is a word that in translation means half.) Each side of the diaphragm is supplied by a nerve (the left phrenic nerve and the right phrenic nerve) which control the muscle. The phrenic nerves begin in the cervical plexus (nerves exiting the spinal cord in the neck) which carries nerves that begin in the C3 to C5 nerve roots (nerves arising near the neck by the 3^rd through 5^th cervical vertebrae.)

The diaphragm plays an integral role in breathing (respiration.) When the diaphragm contracts and flattens, it decreases pressure in the thoracic cavity, creating a vacuum which air then enters. When the diaphragm relaxes, air is released.  

Most of the time the diaphragm contracts in an involuntary manner, which is the reason we continue to breathe when we sleep, but it can be contracted voluntarily as well. The muscle is used not only in inhalation and forced exhalation, but in coughing, sneezing, vomiting, urinating, defecating (passing a bowel movement), and childbirth.

Diaphragmatic breathing is a technique that is used to strengthen the diaphragm, allowing more air to enter and exit the lungs without tiring the chest muscles.

There are several medical conditions which may be related to the diaphragm or abnormalities of the diaphragm. Some of these include:

Hiccups: When the diaphragm is irritated, such as when drinking carbonated soda, it can contract involuntarily resulting in what we know as hiccups. The sound of hiccups is caused when air is exhaled at the same time that the diaphragm contracts.

Hiatal Hernia: When the diaphragm is weakened in the region through which the esophagus passes through the diaphragm, this is called a hiatal hernia. A hiatal hernia allows the lower esophagus and sometimes the stomach to pass from the abdominal cavity into the chest cavity. This, in turn, can result in gastroesophageal reflux disease (GERD) leading to heartburn and indigestion.

Congenital Diaphragmatic Hernia: In roughly 1 in 2000 births, either one side or the whole diaphragm fails to develop. When this happens, the contents of the abdominal cavity enter the chest cavity, often resulting in the incomplete development of the lungs (pulmonary hypoplasia.) In recent years major strides have been made in supporting babies with a diaphragmatic hernia, including surgeries in which an artificial diaphragm which can expand with growth may be constructed.

Paralysis of the Diaphragm: The diaphragm may be paralyzed either partially or completely due to damage to the nerves supplying the diaphragm. These nerves can be damaged in several ways:

• From compression due to a tumor pressing on the phrenic nerve in the chest (such as with lung cancer) or near the cervical spine or brainstem.
• From trauma to the chest cavity or anywhere along the distribution of the nerve. 
• From neurological conditions such as diabetic neuropathy, Guillain-Barre syndrome, and muscular dystrophy. 

When only one side of the diaphragm is paralyzed, it moved in the opposite way of what would be expected, moving up during inspiration and down during exhalation.  This can result in shortness of breath, especially when lying down, among other symptoms.

Sometimes part of the diaphragm is removed surgically.  This procedure may be done for people having surgery for mesothelioma—a cancer of the lung linings (the pleura)—which can spread to and involve the diaphragm.

The anatomy is a muscle which separates the chest cavity from the abdominal cavity and plays an important part in respiration. Many people are familiar with contraction of the diaphragm with hiccups, but dysfunction of this muscle can cause serious problems. Paralysis of the diaphragm can result in the loss of the vacuum which pulls air into the lungs during inhalation. It is this paralysis of the diaphragm which is often feared with Guillain-Barre syndrome today, and poliomyelitis in the past. 

When a hernia (weakness) occurs in the diaphragm, abdominal contents such as the lower esophagus and stomach can pass through to the chest cavity resulting in acid reflux and the complications of acid reflux. Surgery to repair a hiatal hernia is not uncommonly needed to fix the problem.