Diaphragm
Say it: DY-uh-fram
In anatomy, the diaphragm is the dome-shaped sheet of muscle and tendon dividing the chest from the abdomen, and the main muscle of breathing.
Definition
What is the diaphragm?
The diaphragm closes off the bottom of the chest cavity and arches over the abdominal organs below it. It is shaped like a double dome, the right side sitting slightly higher because the liver lies beneath it. Its muscle fibers arise from the lower ribs, the tip of the sternum and the lumbar vertebrae and converge on a flat central tendon, to which the sac around the heart is fused. Three main openings let structures pass between chest and abdomen: one for the inferior vena cava, one for the esophagus and vagus nerves, and one for the aorta and thoracic duct.
When the diaphragm contracts, it flattens and descends, enlarging the chest so that air is drawn into the lungs; when it relaxes, the elastic lungs recoil and air flows out, so quiet breathing out needs no effort. Holding it contracted while tightening the abdominal wall raises pressure in the abdomen, which helps in coughing, defecation and childbirth. Each half is driven by a phrenic nerve, formed from spinal nerves C3 to C5 in the neck.
That high nerve origin is why a spinal cord injury above C3 can stop breathing. In a hiatal hernia, part of the stomach slides up through the esophageal opening, and hiccups are sudden, involuntary spasms of the diaphragm.
Word parts
Where does the word “diaphragm” come from?
- dia-
- across, throughGreek dia
- -phragm
- fence, partitionGreek phragma, from phrassein (to enclose)
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Terms that go with it
- Tidal volumeTidal volume is the amount of air that moves into or out of the lungs in one normal, relaxed breath, about 500 mL in a healthy adult.
- Gas exchangeGas exchange is the movement of oxygen into the blood and carbon dioxide out of it by diffusion across thin membranes, mainly in the lungs and tissues.
- HerniaA hernia is a bulge of an organ or tissue, often fat or a loop of bowel, through a weak spot in the wall that normally holds it in place.
- EsophagusThe esophagus is the muscular tube, about 25 centimeters long, that carries swallowed food and liquid from the pharynx down to the stomach.
- Spinal cordThe spinal cord is the column of nerve tissue in the vertebral canal that relays signals between the brain and the body and runs many reflexes.
- Skeletal muscleSkeletal muscle is the striated, voluntary muscle tissue attached to bones by tendons that moves the body, holds posture and produces heat.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Anatomy and Physiology 2e, 11.4 Axial Muscles of the Abdominal Wall and Thorax
- TeachMeAnatomy: The Diaphragm
- NCBI MeSH: Diaphragm
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