The word diaphragm literally means, dia that is across, and phragm means wall It is a muscular fibrous partition separating the abdominal and thoracic cavities. It is connected to the spine and the lumbar vertebrae.
The diaphragm, a skeletal muscle, is very useful in breathing and thus in maintaining our life on a minute to minute basis. Our normal quiet breathing is achieved almost entirely with the help of diaphragm.
Contraction of the diaphragm muscle makes the chest or thoracic cavity longer, and when its associated intercostals (between ribs) muscles contract, the chest widens. All these actions result into inspiration. When the diaphragm and external intercostal muscles relax expiration takes place. We breathe about 12 -14 times a minute. When exercising the breathing rate increases to about 40 times a minute. In heavy breathing additional muscles like, the abdominal muscles are brought into play and they push diaphragm further upwards or downwards to take in or push out a greater volume of air.
If the diaphragm is fatigued due to accumulation of lactic acid, we feel breathless.
The diaphragm is also important in performing such actions as blowing out the air, laughing, singing, whistling, crying, yawning, coughing, sneezing, vomiting, defecating, urinating, and in parturition i.e. in delivering a baby or giving birth.
There are three major openings in diaphragm to allow the esophagus, aorta and the vena cava to pass through.
Only mammals have the diaphragm. No other vertebrates like the fish, amphibia, reptiles or birds possess a diaphragm. Naturally their torso that is the trunk has a single undivided body cavity. They do not have separate thoracic and abdominal cavities.
Earthworms have septa i.e. partitions between their segments, especially those septa before the dark brown band, the clitellum, are without any perforations and cut off their coelom - the body cavity into distinct compartments, something which the diaphragm does for us. The earthworms can contract their body wall muscles and the body fluid trapped between non-perforated septa gives the anterior part of their body stiffness. Such stiff front portion of body helps them to burrow in the soft soil. If these septa were absent or had perforations the limp earthworms would never be able to penetrate in the soil and would perhaps have become extinct without the protective burrows.
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