Diaphragm and Respiratory System Quiz

Diaphragm and Respiratory System

• The diaphragm is the main muscle of inspiration, and it is responsible for sucking down the lung bases and not disturbing the mediastinum.
• During tranquil inspiration, the diaphragm's contraction only descends the domes, and in deeper breaths, further descent of the domes can depress the central tendon from T8 to T9 level.
• Maximum inspiration involves further contraction of the muscle, which everts the ribs of the costal margin in a 'bucket handle'-like movement with widening of the subcostal angle.
• The diaphragm is used also in abdominal straining, and its contraction is accompanied by closure of the glottis and subsequent release of trapped air to produce the characteristic sound of a hiccup.
• Expiration is a passive process, where the diaphragm is relaxed, and its fibres are elongated by pressure from below.

Thoracic Movements and Respiration

• The external intercostals are most active in inspiration, and the internal intercostals are more important for expiration and stiffening of the chest wall.
• Elastic recoil of the lungs assisted by contraction of the muscles of the abdominal wall makes the relaxed diaphragm regain its domed form during expiration.
• Other muscles, such as scalene muscles, sternocleidomastoid, quadratus lumborum, erector spinae, and pectoralis major, contribute to chest expansion during maximal inspiratory efforts.

Development of the Diaphragm

• The diaphragm develops from four sources: septum transversum, third, fourth, and fifth cervical myotomes, pleuroperitoneal membranes, and oesophageal mesentery.
• Failure of pleuroperitoneal membrane development is the most common cause of congenital diaphragmatic hernia.

Diaphragmatic Hernia

• The most common acquired variety of diaphragmatic hernia is the sliding type of hiatus hernia, where the oesophagogastric junction rises up into the thorax, encouraging gastro-oesophageal reflux.
• The paraoesophageal (rolling) type is rarer, where the oesophagogastric junction remains in the abdomen, but a pouch of peritoneum containing a part of the stomach projects upwards alongside the oesophagus, compressing the lower oesophagus and compromising the blood supply of the herniated stomach.

Test your knowledge of the diaphragm's role in the respiratory system, including its muscle contraction and effect on lung bases and mediastinum.