diafragm

Diafragm, often called the diaphragm in English, is the dome-shaped muscular partition that separates the thoracic and abdominal cavities. The spelling diafragm is used in several languages and in some texts. It is the primary muscle driving respiration in mammals, enabling inhalation by increasing thoracic volume.

Anatomy: It consists of a central tendinous portion (the central tendon) and peripheral muscular parts that attach to the xiphoid process, the lower six costal cartilages, and the lumbar vertebrae via the right and left crura. It forms three hiatuses: caval (IVC), esophageal, and aortic, through which vessels and structures pass. The phrenic nerves (C3–C5) provide motor innervation, with sensory fibers from the central portion via the phrenic nerves and from the peripheral portions via lower intercostal nerves.

Function: Contraction flattens the diaphragm, expanding the thoracic cavity and drawing air into the lungs; relaxation allows passive expiration. It also increases intra-abdominal pressure during actions such as vomiting, defecation, childbirth, and aids coughing and sneezing.

Clinical notes: Diaphragmatic weakness or paralysis can impair breathing, typically due to phrenic nerve injury or neuromuscular disease. Congenital diaphragmatic hernia is a serious condition where abdominal contents herniate into the thorax during development, reducing lung growth. Hiatal hernia involves protrusion of the stomach through the esophageal hiatus. Treatment ranges from observation to surgical repair in selected cases.

Etymology and terminology: The term diaphragm derives from Greek dia- meaning through and phragma, fence or barrier. In many languages diafragm is used for the same structure, while English uses diaphragm as the standard term.

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