Diaphragm

1. Overview

The diaphragm is a dome-shaped, musculotendinous structure that acts as the primary muscle of respiration. It separates the thoracic cavity from the abdominal cavity and contracts rhythmically and involuntarily to facilitate breathing. In addition to its respiratory role, the diaphragm is involved in several other physiological processes such as vomiting, defecation, and parturition due to its pressure-regulating abilities.

2. Location

The diaphragm is located at the inferior border of the thoracic cavity, marking the anatomical boundary between the thorax and abdomen. Key positional relationships include:

• Superiorly: Lungs and pleural cavities, heart (via the fibrous pericardium)

• Inferiorly: Liver (right), stomach and spleen (left), kidneys (posterior)

• Spanning: From the lower ribs (costal margin) to the lumbar vertebrae and central tendon

3. Structure

The diaphragm consists of muscular fibers converging onto a central tendon and has three major parts based on origin:

Muscular Parts

• Sternal part: Originates from the xiphoid process

• Costal part: From the internal surfaces of the lower six ribs and their costal cartilages

• Lumbar part: From the right and left crura attaching to lumbar vertebrae (L1–L3)

Central Tendon

• Thin, strong aponeurotic center into which all muscle fibers insert

• Fused with the fibrous pericardium above

Openings (Hiatuses)

The diaphragm contains three major openings allowing passage of structures between thorax and abdomen:

• Caval opening (T8): For the inferior vena cava

• Esophageal hiatus (T10): For the esophagus and vagus nerves

• Aortic hiatus (T12): For the aorta, thoracic duct, and azygos vein

4. Function

The diaphragm performs multiple key functions:

• Primary inspiration muscle: Contraction flattens the dome, increasing thoracic volume and creating negative pressure to draw air into the lungs

• Expiratory aid: During forceful expiration (e.g., coughing), the diaphragm relaxes and elevates, increasing intra-abdominal pressure

• Intra-abdominal pressure generation: Assists in defecation, urination, vomiting, and childbirth

• Mechanical support: Separates thoracic and abdominal organs and helps maintain position of viscera

5. Physiological Role(s)

Physiologically, the diaphragm supports:

• Ventilation: Accounts for ~75% of air movement during quiet breathing

• Abdominothoracic pressure gradient: Facilitates venous return to the heart via the “thoracoabdominal pump”

• Speech and vocalization: Regulates airflow pressure through the larynx

• Reflex control: Innervated by the phrenic nerve (C3–C5); automatic control from brainstem centers

6. Clinical Significance

Diaphragmatic Paralysis or Paresis

May occur unilaterally or bilaterally due to phrenic nerve damage. Causes include:

• Trauma (e.g., cervical spinal cord injury)

• Surgical injury (e.g., cardiac or neck surgery)

• Neuromuscular disorders (e.g., ALS, Guillain-Barré)

Symptoms: Orthopnea, dyspnea on exertion, elevated hemidiaphragm on imaging.

Hiatal Hernia

Occurs when part of the stomach herniates through the esophageal hiatus into the thorax. May lead to:

• GERD (gastroesophageal reflux)

• Chest discomfort or dysphagia

Diagnosis: Barium swallow, endoscopy; treatment may be conservative or surgical.

Congenital Diaphragmatic Hernia (CDH)

A birth defect where a portion of the diaphragm fails to develop, allowing abdominal organs to enter the thoracic cavity. Common types:

• Bochdalek hernia: Posterolateral defect (most common)

• Morgagni hernia: Anterior parasternal defect

Leads to pulmonary hypoplasia; often requires surgical correction in neonates.

Hiccups (Singultus)

Result from involuntary spasms of the diaphragm, often due to:

• Gastric distension

• Phrenic nerve irritation

• Central nervous system disorders

Referred Pain

Diaphragmatic irritation (e.g., subphrenic abscess) can cause referred pain to the shoulder (C3–C5 dermatomes), due to phrenic nerve sensory pathways.

Diaphragmatic Rupture

Can occur due to blunt trauma (e.g., motor vehicle accidents), typically on the left side. May lead to herniation of abdominal organs into the chest and require emergency surgical repair.