Diaphragm - The Respiratory Muscle Mechanism
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Diaphragm : The Respiratory Muscle

Dr.Surya Rao Poodipeddi profile Authored by Dr.Surya Rao Poodipeddi on 13 May 2014 - 16:05.

Human diaphragm, is very big in size, and is the primary muscle responsible for respiration. It has two domes one slightly at a higher level than the other .The Esophagus (food pipe) and the great vessels of the human body pass through the diaphragm from above downwards.

Diaphragm structure and role: Connected to the abdominal wall, are the lumbar vertebrae, the lower ribs, the sternum (breast bone) and the layer of the heart called pericardium (by tendinous tissue), this thin muscle creates a partition between the chest and abdominal cavities. Both the domes of the diaphragm adopt a flattened arrangement when the muscle contracts. This flattening creates a vacuum in the chest cavity and a pressure in the abdominal cavity.

The expanding lungs fill the vacuum so created in the chest cavity along with the air inhaled. The pressure so created in the abdominal cavity is of immense help in the expulsion of a fetus in a pregnant mother during labor. The pressure also helps in pushing the fecal matter in the intestines making it easy for expulsion. When the diaphragm relaxes to its domed structure the air is pushed out (exhaled) and the lungs start contracting.

It is essential to know the basics of the mechanics of respiration in order to understand the role of diaphragm in the act of respiration.

Respiration mechanism: Even when we are asleep the basic rhythm of respiration is carried on through nerve cells in the respiratory center of the brain. From this center in the brain, messages are sent to the concerned muscles, namely the intercostal muscles (muscles between the ribs) and the diaphragm which stimulate them to perform the act of respiration. The amount of carbon dioxide in the blood changes in tune with the activities we perform like a sedentary state, walking, running, and during sleep. 

Some of the large arteries have receptors, which can detect any change in the amount of carbon dioxide and send instructions to the brain, which acts accordingly. Nerve cells in the arteries and respiratory center in the brain are very sensitive to any changes in the blood levels of carbon dioxide. Even a slight increase in the blood levels of carbon dioxide leads to increased breathing to restore normal levels.

To put it in a simple equation, let us suppose that the carbon dioxide levels in the blood are normal. Any increased activity will increase the carbon dioxide levels in the blood. The receptors in the blood vessels detect this increase and send messages to the brain. The brain at once sends messages to the concerned muscles of respiration to act rigorously.  And the breathing rate increases sufficient enough to expel the gas into the lungs, which exhales it out thereby restoring normal levels in the blood. The cycle continues. The mechanism fails only when the offending gas increases in levels beyond the capacity of the respiratory center to correct the increase. This is when other life saving measures takes over.

During sleep it is only the diaphragm, which plays an important role in maintaining normal rhythms of respiration. The diaphragm has rich blood supply through the phrenic arteries and the phrenic nerve maintains the nerve supply.

The mechanism of respiratory control, which involves simply taking oxygen-rich air into the lungs and expelling waste carbon dioxide, is called external respiration. The diaphragm accomplishes a large percentage of this act. However, gaseous exchange involving release of oxygen to the lungs and expulsion of waste material in the form of carbon dioxide, takes place in the alveoli of the lungs.

When the diaphragm and other muscles of respiration get fatigued, lactic acid accumulates leading to a feeling of breathlessness.

Besides respiration the diaphragm also comes into picture to provide extra power in most of the expulsive activities like laughing, crying, coughing, sneezing, vomiting, childbirth, defecating. and urinating.

Spasmodic contractions of the diaphragm result in hiccups. The diaphragm is subject to developmental defects, hernia, and injury.

Hiccupa is a characteristic sharp sound resulting from involuntary spasmodic contractions of the diaphragm followed by a sharp intake of air which abruptly stops due to involuntary closing of the glottis (the opening between the vocal cords). It is believed that hiccup is due to stimulation of nerve pathways. In most cases they are transient and self-limiting. In extreme cases surgical intervention might become necessary.

Herniation of the stomach through the diaphragm is not uncommon and needs the attention of a surgeon.


*Disclaimer: This is not medical advice. The content is for educational purposes only. Please contact your doctor for any health care issues.