The diaphragm, placed beneath the lungs, is a respiratory muscle that aids in the breathing process. It is a big, dome-shaped muscle in the body that acts as the primary inspiratory muscle. It contracts involuntarily in a continuous and rhythmic fashion. The diaphragm begins to contract during inhalation and the chest cavity expands. This contraction produces a vacuum that draws air into the lungs. Exhalation causes the diaphragm to relax and revert to its dome-like form, forcing air out from the lungs.
Table of Contents
- Respiratory Muscles
- Diaphragm – Structure
- Structures Passing through the Diaphragm
- Functions
- Disorders of Diaphragm
- Frequently Asked Questions
Respiratory Muscles
The diaphragm is a major dome-shaped respiratory muscle. The respiratory muscles contribute to exhalation and inhalation by aiding in the contraction and expansion of the thoracic cavity.
Muscles involved in inspiratory movements are known as inspiratory muscles.
- Primary muscles for inspiration are the external intercostal muscles and diaphragm.
- Accessory inspiratory muscles include scalene, sternocleidomastoid, pectorals and serratus anterior of the scapulae.
Likewise, muscles involved in expiration are termed expiratory muscles.
- Primary muscles involved in expiration are the internal intercostal muscles.
- Accessory expiratory muscles include the abdominal muscles.
Where is the diaphragm located in the human body?
The diaphragm is present beneath the lungs in the trunk region. It is a musculotendinous sheet that separates thoracic and abdominal cavities. Here, let us discuss more about the structure of the diaphragm with functions.
Diaphragm – Structure
The diaphragm is a musculotendinous sheet that defines the superior border of the posterior abdominal area. It divides abdominal and thoracic cavities. Thus there are two surfaces to the diaphragm – thoracic and abdominal. The thoracic diaphragm touches the pericardium and pleura, which are serous layers of the heart and lungs. Whereas the liver, spleen and stomach are all in direct contact with the abdominal diaphragm.
The musculotendinous diaphragm has 3 muscular parts – lumbar, sternal and costal. The diaphragm comprises a core tendinous portion (central tendon) into which the circularly organised muscle fibres join. The diaphragm is attached to the lumbar vertebrae via tendinous bands named crura.
Domes
Because of the liver, the diaphragm is structured as 2 domes – right and left. The right dome is somewhat higher than the left one. The pericardium gently depresses the diaphragm, causing depression between both the two domes.
Attachments – Diaphragm is peripherally attached to:
- Xiphoid process of the sternum
- Costal margin of the thoracic wall
- Ends of ribs 11 and 12
- Vertebrae of the lumbar region
- Ligaments that span across the posterior abdominal wall
Structures Passing through the Diaphragm
Many structures like the aorta and thoracic duct pass between the abdomen and thorax. The diaphragm’s function is to create a pathway for structures from the thoracic to the abdominal region for respiration. It contains numerous openings on its surface for that purpose. The three openings associated with the diaphragm are:
Aorta – The aorta passes posterior to the diaphragm and anterior to the vertebral bodies at the lower level of vertebra T12 between the two crura of the diaphragm.
Esophageal opening – At vertebra T10, close to the left of the aortic hiatus, the oesophagus passes through the muscles of the right crus of the diaphragm.
Caval opening – This is the third large opening in the diaphragm through which the inferior vena cava passes from the abdominal cavity to the thoracic cavity at approximately vertebra T8 in the central tendinous part of the diaphragm.
Also the left phrenic nerve (C3 to C5) goes through the muscular section of the diaphragm precisely anterior to the central tendon on the left side. Additional structures also pass from the thoracic cavity to the abdominal cavity through small openings in or just outside the diaphragm.
Functions
The diaphragm plays a vital role in the breathing process. Apart from that, it also aids in bowel movement, urination, childbirth and while lifting heavy objects.
The movement of the diaphragm expands the vertical diameter of the thoracic cage. Normally, the diaphragm is dome-shaped before inspiration, with the convexity facing upwards. Muscle fibres are shortened during inspiration due to contraction. However, the middle tendinous section is dragged downward, flattening the diaphragm. The diaphragm flattening raises the vertical diameter of the chest cavity. This eventually decreases the intrapulmonary pressure and the air is drawn inside the lungs.
Likewise, when the diaphragm relaxes, the opposite happens. The vertical diameter of the chest cavity decreases and the intrapulmonary pressure increases. Thus air is exhaled out.
See more: Mechanism of Breathing
Disorders of Diaphragm
There are several clinical conditions associated with the diaphragm. Anatomical defects or traumatic injuries can affect its functioning. Repeated involuntary contraction of the diaphragm causes hiccups. This happens due to irritation while drinking or eating. There are also certain disorders associated with the diaphragm.
Diaphragmatic Hernias – This can be either acquired or congenital. These are caused by abnormalities in the foetal diaphragm during early embryogenesis. Abdominal organs may protrude into the thoracic cavity and disturb lung development, creating issues with lung development and function. It can also develop as a consequence of blunt force trauma, such as a car accident or a hard fall.
Hiatal Hernia – It is the protrusion of the lower oesophagus into the chest cavity. A loose diaphragm allows the stomach fundus to herniate into the posterior mediastinum. This usually results in acid reflux symptoms. Ulceration may also happen, leading to bleeding and anaemia.
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