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What is a Hemidiaphragm?

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  • Written By: Shelby Miller
  • Edited By: W. Everett
  • Last Modified Date: 19 November 2016
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A hemidiaphragm is the right or left half of the diaphragm, the muscle bisecting the torso that separates the thoracic cavity, which houses the heart and lungs, from the abdominal cavity, which contains the stomach, intestines, and other organs of digestion and waste removal. As this muscle is shaped like an umbrella, hemi refers to one semicircular half. When it contacts, it facilitates breathing by pulling downward and allowing the lungs to expand, making inhalation possible. The right hemidiaphragm may be stronger than the left, which is more susceptible to injury like muscle rupture.

Like a domed ceiling to the abdominal cavity, the two hemidiaphragm halves fill the bottom of the ribcage, continuously attaching to several structures. Where the two halves meet at the topmost point, the diaphragm attaches to the xiphoid process of the sternum, which is the lowest point on the breastbone in the center of the chest. It has additional attachments on the lower six ribs along their inside surfaces and in the lower spine on the lumbar vertebrae. Here it affixes to the spine as well as the lumbocostal arches. Found immediately to either side of the spine, each lumbocostal arch is a fibrous rim encircling a hole through which the psoas major muscle passes.

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The diaphragm is punctured at several points along its middle where structures such as the spine and esophagus pass through it, with the right and left hemidiaphragm lying to either side. Still, they function as a unit, contracting and expanding each time a breath is taken. During inhalation, the diaphragm contracts, pulling away from the thoracic cavity. The suction created by this contraction allows the lungs to fill with air, expanding in the thoracic cavity, whereas during exhalation the lungs deflate, the diaphragm relaxes, and the abdominals contract, pushing the air out.

Contractions of the diaphragm also place pressure on the abdominal cavity, and therefore this muscle also functions to enable vomiting, urination, and defecation. Due to the amount of pressure it can create, however, excessive straining by this muscle can lead to such injuries as a hernia or muscle rupture, in which the muscle tears away from a bone or other structure to which it attaches. These injuries are more likely to occur in the left hemidiaphragm than in the right, which has the protection of the liver and which has been shown to be stronger, likely as a result of the way the muscle fuses in utero.

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lighth0se33
Post 4

I would never have thought that the diaphragm had anything to do with defecation. It's so far away from the lower intestines!

I always wondered what muscle was responsible for allowing us to push out feces, though. I figured it must be some muscle in the intestines.

Now that I think about it, I usually take a deep breath before defecating. So, the diaphragm is contracted and applying pressure to the organs and intestines below it.

Really, I feel like everything inside of my abdomen that can possibly push is applying force to help me defecate. The diaphragm is probably at the top of the chain, but it has some help.

wavy58
Post 3

@seag47 – The diaphragm is crucial to professional singers, and they need both halves of it in order to do their job. I have a friend who was an excellent rock singer, but once she injured her left hemidiaphragm, her career ended.

She was in a car accident, and various parts of her abdomen received a direct blow. She had to be placed on a ventilator and carried on an ambulance to ICU.

At the hospital, the doctor discovered that her left hemidiaphragm had pulled away from its supporting structure. She had to have surgery, and it took so long for her to recover that she had to find another line of work to support herself.

Perdido
Post 2

This description of a hemidiaphragm reminds me of a jellyfish. Their umbrella shaped bell contracts so that they can push themselves upward, like the diaphragm contracts so that our lungs can rise with air. When the jellyfish bell relaxes, they sink a little and float along, like our lungs deflate when we exhale.

One major difference would be that no side of the jellyfish is weaker. They don't fuse into things for support like the hemidiaphragms do, so they function more like one unit on equal terms with its parts.

seag47
Post 1

I didn't even know what a diaphragm was until I started taking singing lessons. Then, I learned the role that it plays in singing.

Everyone had been telling me that I had a great voice, but it was too quiet and soft. I didn't know how to make it any louder.

My vocal teacher told me to sing from my diaphragm. She pointed out where it was, but I still couldn't quite understand how to do this.

So, she told me to sing a note. As I sung, she abruptly pushed on my diaphragm with her fist. Suddenly, the note became louder.

I learned to use air to put more force behind my voice, rather than strain my vocal cords. If it hadn't been for this punch in the diaphragm, I might have never learned how to sing properly.

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