Download Letter D – The Diaphragm

Letter D – The Diaphragm
The diaphragm is a dome-shaped sheet of skeletal muscle which
separates the floor of the thoracic cavity containing the heart, lungs and
ribs, from the roof of the abdominal cavity. The diaphragm consists of a
central tendon from which the muscle fibres fan out and down,
attaching to the spine, ribs and sternum. Also known as the thoracic
diaphragm it is the main muscle of respiration along with the external
and internal intercostals.
There are openings in the diaphragm for the esophagus, the phrenic
nerve (which controls the movements of the diaphragm to produce
breathing), and the aorta and vena cava blood vessels, which lead to and
from the heart.
When air is drawn into the lungs, the muscles in the diaphragm contract and pull the central tendon
down. This enlarges the thoracic cavity, decreasing the pressure here and increasing the pressure in
the abdominal cavity. This reduction in pressure in the lungs means that the atmospheric pressure is
now higher outside, thus allowing air to pass into the lungs.
When the diaphragm relaxes, air is exhaled as a result of elastic recoil of the lungs and the tissues
lining the thoracic cavity. The pressure in the lungs is now higher than the atmospheric pressure and
air now moves out. Assisting this function with muscular effort (called forced exhalation) involves
the internal intercostal muscles to be used in conjunction with the abdominal muscles. An example
of this might be when singing or playing a wind instrument.
During the process of breathing, the diaphragm contracts to add volume to the thoracic cavity and
this phenomenon occurs in 2 diverse varieties of respiration. The first is known as abdominal
respiration, where the thoracic cavity stretches downwards. This is often called belly breathing. The
2nd kind of respiration is referred to as thoracic respiration and enables the thoracic cavity to extend
upwards.
The diaphragm is also involved in non-respiratory functions, helping to expel vomit, feces, and urine
from the body by increasing intra-abdominal pressure, and preventing acid reflux by exerting
pressure on the esophagus as it passes through the esophageal hiatus.
So as you can see the diaphragm is the most important muscle of respiration and this all happens
automatically without us having to think about the process at all!