The diaphragm is one of the most important yet often overlooked muscles in the human body. As the primary driver of breathing, it plays a central role in every breath we take, working tirelessly to draw air into the lungs and expel it back out.
Beyond its mechanical role, the diaphragm also serves as a key point of focus in respiratory care, influencing how patients are assessed, treated, and managed across a wide range of conditions.
For respiratory therapists, a deep understanding of the diaphragm’s structure and function is essential, as it directly impacts patient outcomes in both routine care and critical settings.
What Is the Diaphragm?
The diaphragm is a dome-shaped sheet of skeletal muscle located beneath the lungs, separating the thoracic cavity from the abdominal cavity. Despite its simple appearance, this muscle is one of the most vital structures in the human body. It is the primary driver of breathing, responsible for generating the pressure changes that allow air to move in and out of the lungs.
The diaphragm attaches to the lower ribs, sternum, and lumbar spine, creating a strong and flexible partition that contracts and relaxes with each breath. Because of its central location, the diaphragm also plays a role in other bodily functions, including digestion, circulation, and even postural support.
The Diaphragm’s Role in Breathing
Breathing is largely an automatic process, and the diaphragm sits at the center of this mechanism. When it contracts, the dome flattens downward, expanding the thoracic cavity. This creates negative pressure inside the chest, drawing air into the lungs—a process known as inspiration.
During expiration, the diaphragm relaxes and returns to its dome shape, reducing the volume of the thoracic cavity and pushing air out of the lungs. While expiration is often passive, requiring little effort during quiet breathing, the diaphragm works continuously throughout life, contracting approximately 12–20 times per minute in adults.
Note: In situations that demand greater airflow, such as exercise, illness, or respiratory distress, the diaphragm works harder and recruits accessory muscles to meet the body’s oxygen needs.
Clinical Relevance of the Diaphragm
The diaphragm is not only essential for normal breathing—it also becomes a focal point in many medical conditions and treatments. Disorders affecting its function can lead to significant respiratory compromise. Examples include:
- Diaphragmatic paralysis or weakness due to nerve injury or neuromuscular disease
- Chronic obstructive pulmonary disease (COPD), which increases the diaphragm’s workload
- Obesity and abdominal distension, which can reduce diaphragmatic movement
- Trauma or surgery, which may impair its efficiency
Note: Understanding these conditions is crucial in respiratory care because they directly influence ventilation, oxygenation, and overall patient outcomes.
Why the Diaphragm Matters to Respiratory Therapists
For respiratory therapists, the diaphragm is at the heart of nearly every aspect of patient care. A thorough understanding of its anatomy and function helps guide assessment, treatment, and decision-making.
Here are a few reasons why it’s especially relevant:
- Ventilator Management: In patients who require mechanical ventilation, the diaphragm may become weak from disuse, a condition known as ventilator-induced diaphragmatic dysfunction. Therapists must carefully balance ventilator support to ensure adequate oxygenation while encouraging the diaphragm to remain active.
- Weaning from Ventilation: The diaphragm’s strength is a key factor in determining whether a patient can be successfully weaned off a ventilator. Respiratory therapists assess diaphragmatic function to predict readiness and reduce the risk of weaning failure.
- Breathing Exercises and Rehabilitation: Techniques such as diaphragmatic breathing are often taught to patients with chronic lung disease. These exercises help strengthen the diaphragm, improve lung expansion, and promote more efficient breathing patterns.
- Assessment of Respiratory Distress: Signs like paradoxical abdominal movement can indicate diaphragmatic fatigue or failure. Recognizing these patterns allows therapists to intervene promptly with the appropriate support.
- Diagnostic and Therapeutic Procedures: Therapists may encounter cases where diaphragmatic ultrasound or fluoroscopy is used to assess function. In addition, positioning and therapeutic maneuvers often take the diaphragm into account to optimize patient outcomes.
Mastering the role of the diaphragm allows respiratory therapists to deliver more precise and effective care across a wide range of clinical situations.
Whether managing mechanical ventilation, teaching breathing techniques, or assessing signs of distress, the diaphragm remains central to decision-making. By focusing on this vital muscle, therapists can enhance patient safety, improve outcomes, and support long-term respiratory health.
Broader Importance Beyond Breathing
While breathing is the diaphragm’s primary role, its function extends further. By contracting and relaxing, it also helps with:
- Coughing and airway clearance, essential for protecting the lungs
- Venous return, aiding circulation back to the heart
- Abdominal pressure regulation, supporting bowel movements, urination, and childbirth
Note: This interconnected role underscores why the diaphragm is so essential not just in respiratory care, but in overall human physiology.
Diaphragm Practice Questions
1. What is the diaphragm, and where is it located?
It is a double-domed sheet of skeletal muscle located at the base of the rib cage, separating the thoracic and abdominal cavities.
2. What is the primary function of the diaphragm in the respiratory system?
It contracts and relaxes to change thoracic cavity volume, facilitating inhalation and exhalation.
3. The diaphragm serves as the ____ of the thoracic cavity and the ____ of the abdominal cavity.
Floor; Roof
4. What are the two main types of attachments of the diaphragm?
Peripheral attachments and a central tendon attachment
5. Where are the diaphragm’s peripheral attachments located?
At the lumbar vertebrae, costal cartilages of ribs 7–12, and the xiphoid process of the sternum
6. What forms the central attachment of the diaphragm?
The muscle fibers merge into a central tendon that fuses with the fibrous pericardium of the heart
7. What are the three major openings in the diaphragm that allow structures to pass through it?
The caval hiatus (T8), esophageal hiatus (T10), and aortic hiatus (T12)
8. What structures pass through the caval hiatus of the diaphragm?
The inferior vena cava and branches of the right phrenic nerve
9. What structures pass through the esophageal hiatus of the diaphragm?
The esophagus, right and left vagus nerves, and vessels from the left gastric artery and vein
10. What structures pass through the aortic hiatus of the diaphragm?
The aorta, thoracic duct, and azygous vein
11. What role does the diaphragm play in breathing?
It acts as the primary muscle of respiration by generating pressure changes during inspiration and expiration
12. What occurs during inspiration involving the diaphragm?
It contracts and flattens, increasing thoracic cavity volume and drawing air into the lungs
13. What occurs during expiration involving the diaphragm?
It passively relaxes, returning to its dome shape and decreasing thoracic volume
14. Which nerve innervates the diaphragm?
The phrenic nerve, with right and left branches supplying their respective sides of the muscle
15. What causes the thoracic cavity to expand and contract?
The alternating contraction and relaxation of the diaphragm
16. How would you describe the diaphragm at rest?
Dome-shaped, forming a curved separation between the thoracic and abdominal cavities
17. Why is the superior surface of the diaphragm convex?
To form the elevated floor of the thoracic cavity
18. Why is the inferior surface of the diaphragm concave?
To form the curved roof of the abdominal cavity
19. What is the Valsalva maneuver, and how does it relate to the diaphragm?
It is the coordination between diaphragm and abdominal muscle contractions to increase intra-abdominal pressure
20. What are examples of the Valsalva maneuver in daily life?
Defecation, urination, and childbirth
21. How is breath-holding physiologically maintained?
Through sustained contraction of the diaphragm
22. What is the purpose of steady diaphragm contraction during strain?
It stabilizes pressure and volume within the abdominal cavity
23. What happens when the abdominal muscles contract during the Valsalva maneuver?
They increase intra-abdominal pressure while the diaphragm resists upward movement
24. What occurs when pressure cannot displace the diaphragm upward?
Increased pressure is directed onto the intestinal, urinary, or reproductive tract
25. How does increased intra-abdominal pressure affect the intestinal tract?
It facilitates defecation by pushing contents through the colon
26. What do the inferior surfaces of the pericardial sac and pleural membranes fuse with?
They fuse with the central tendon of the diaphragm.
27. What is another name for the outer pleural membrane that lines the thoracic cavity?
The parietal pleura.
28. What structures lie adjacent to the central tendon of the diaphragm?
The skeletal muscle portions of the diaphragm.
29. What do the skeletal portions of the diaphragm do in relation to the central tendon?
They insert into the central tendon and originate from various anatomical regions.
30. Why does the diaphragm have three major openings?
To allow essential structures to pass between the thoracic and abdominal cavities.
31. What structure passes through the diaphragm via the caval opening?
The inferior vena cava.
32. What passes through the esophageal hiatus of the diaphragm?
The esophagus along with the right and left vagus nerves.
33. Which structures pass through the aortic hiatus of the diaphragm?
The aorta, thoracic duct, and azygous vein.
34. What is the caval opening of the diaphragm?
An opening that allows passage of the inferior vena cava into the thoracic cavity.
35. Which two cavities are separated by the diaphragm?
The thoracic cavity and the abdominal cavity.
36. Why is the left dome of the diaphragm positioned lower than the right?
Because the liver on the right side elevates the right dome slightly.
37. During expiration, how high can the domes of the diaphragm reach?
The right dome can reach the level of the 5th rib; the left dome can reach the 5th intercostal space.
38. What factors influence the level of the diaphragmatic domes?
The phase of respiration, body posture, and the size and distension of abdominal viscera.
39. What is the sternal part of the diaphragm?
Two muscular slips that attach to the posterior side of the xiphoid process.
40. What is the costal part of the diaphragm?
Wide muscular slips attached to the inferior six costal cartilages and ribs, forming the domes of the diaphragm.
41. What forms the lumbar part of the diaphragm?
It originates from arcuate ligaments and lumbar vertebrae and forms the right and left crura.
42. What is the medial arcuate ligament of the diaphragm?
A thickened fascia over the psoas major muscle, spanning the lumbar vertebra to the 12th rib.
43. What structure is covered by the lateral arcuate ligament?
The quadratus lumborum muscle.
44. What are the crura of the diaphragm?
Musculotendinous bands arising from the lumbar vertebrae, anterior longitudinal ligament, and intervertebral discs.
45. From where does the right crus of the diaphragm arise?
From the bodies and discs of the first three or four lumbar vertebrae.
46. What forms the esophageal hiatus of the diaphragm?
Muscle fibers of the right crus.
47. From where does the left crus of the diaphragm arise?
From the bodies of the first two or three lumbar vertebrae.
48. What structures form the aortic hiatus of the diaphragm?
The right and left crura along with the median arcuate ligament arching over the aorta.
49. What does the superior surface of the central tendon fuse with?
It fuses with the inferior surface of the fibrous pericardium surrounding the heart.
50. Which arteries supply the superior surface of the diaphragm?
The pericardiacophrenic and musculophrenic arteries (from the internal thoracic artery), and superior phrenic arteries (from the thoracic aorta).
51. Which arteries supply the inferior surface of the diaphragm?
The inferior phrenic arteries, typically the first branches of the abdominal aorta or from the celiac trunk.
52. What veins drain the superior surface of the diaphragm?
The pericardiacophrenic and musculophrenic veins drain into the internal thoracic veins, and the right superior phrenic vein drains into the inferior vena cava. Some posterior veins also drain into the azygos and hemi-azygos veins.
53. What veins drain the inferior surface of the diaphragm?
The inferior phrenic veins; the right usually drains directly into the IVC, while the left is often doubled, with branches draining into the IVC and the left suprarenal vein. The right and left veins may anastomose.
54. Where do the lymphatic plexuses on the superior surface of the diaphragm drain?
Into the anterior and posterior diaphragmatic lymph nodes, which then drain into parasternal, posterior mediastinal, and phrenic lymph nodes.
55. Where do the lymphatic plexuses on the inferior surface of the diaphragm drain?
They drain into the anterior diaphragmatic, phrenic, and superior lumbar (caval/aortic) lymph nodes.
56. Why are lymphatic capillaries dense on the inferior surface of the diaphragm?
They play a key role in absorbing peritoneal fluid and substances introduced through intraperitoneal (I.P.) injections.
57. What provides the motor supply to the diaphragm?
The right and left phrenic nerves (C3–C5) provide the motor innervation.
58. What provides sensory innervation to the peripheral parts of the diaphragm?
The lower six or seven intercostal nerves and the subcostal nerves.
59. Where is the caval opening of the diaphragm located?
In the central tendon, to the right of the median plane at the junction of the right and middle leaflets.
60. What structures pass through the caval opening?
The inferior vena cava, right phrenic nerve, and a few lymphatic vessels traveling from the liver.
61. At what vertebral level is the caval opening located?
Approximately between the T8 and T9 vertebrae.
62. How does the diaphragm affect the inferior vena cava during inspiration?
Contraction of the diaphragm widens the caval opening and dilates the IVC, enhancing venous return to the heart.
63. Where is the esophageal hiatus of the diaphragm located?
In the muscle of the right crus at the level of the T10 vertebra, just left and superior to the aortic hiatus.
64. What structures pass through the esophageal hiatus?
The esophagus, anterior and posterior vagal trunks, esophageal branches of the left gastric vessels, and some lymphatic vessels.
65. How does the diaphragm contribute to the esophageal sphincter?
Fibers of the right crus cross beneath the hiatus, forming a muscular sphincter that tightens the esophagus during contraction.
66. Where is the aortic hiatus located in relation to the diaphragm?
Posterior to the diaphragm at the level of the T12 vertebra.
67. What structures pass through the aortic hiatus?
The aorta, thoracic duct, and sometimes the azygos and hemi-azygos veins.
68. Why doesn’t diaphragmatic movement affect blood flow through the aorta?
Because the aorta doesn’t pierce the diaphragm, it remains unaffected by diaphragmatic contraction.
69. What is another major opening in the diaphragm aside from the three main apertures?
The sternocostal triangle.
70. Where is the sternocostal triangle located?
Between the sternal and costal attachments of the diaphragm.
71. What passes through the sternocostal triangle?
Lymphatic vessels from the liver’s diaphragmatic surface and the superior epigastric vessels.
72. Where do the sympathetic trunks pass in relation to the diaphragm?
They pass deep to the medial arcuate ligament along with the least splanchnic nerves.
73. Through which openings do the greater and lesser splanchnic nerves pass through the diaphragm?
They pass through small apertures in each crus of the diaphragm—one for the greater splanchnic nerve and another for the lesser splanchnic nerve.
74. What happens to the diaphragm when it contracts?
It flattens downward.
75. What happens to the thoracic cavity volume when the diaphragm bulges upward?
The volume decreases.
76. What happens to intrathoracic pressure when the diaphragm moves upward and volume decreases?
The pressure inside the thoracic cavity increases.
77. What effect does increased thoracic cavity volume have on lung size?
The size of the lungs increases as they expand to fill the space.
78. Complete the sentence: The diaphragm is the ______-shaped sheet of muscle and tendon that serves as the main muscle of ________ and plays a vital role in the _______ process.
Dome-shaped; respiration; breathing.
79. What anatomical structure separates the thoracic cavity from the abdominal cavity?
The diaphragm.
80. What type of muscle is the diaphragm classified as?
Skeletal muscle.
81. The diaphragm is both ______ and ______ and is considered the most powerful and effective ______ muscle in the body.
Extrinsic and intrinsic; breathing.
82. Is the diaphragm under voluntary or involuntary control?
Mostly involuntary control, but it can also be moved voluntarily.
83. What are the three main structural parts of the diaphragm?
Peripheral muscle, central tendon, and openings (apertures).
84. What part of the diaphragm consists of radial muscle fibers that originate on the ribs, sternum, and spine?
The peripheral muscle.
85. What is the central tendon of the diaphragm composed of, and what is its function?
It is a flat aponeurosis of dense collagen fibers and serves as the insertion point for muscle fibers.
86. How many main openings and large gaps are there in the diaphragm?
Three main openings and one large gap.
87. What are the four general attachment sites of the diaphragm?
Sternum (xiphoid process), inferior six ribs, lumbar vertebrae (L1–L3), and fibrous pericardium.
88. Where is the sternal attachment of the diaphragm located?
On the posterior surface of the xiphoid process.
89. Where is the costal attachment of the diaphragm located?
On the internal surface of the lower six ribs and their costal cartilages.
90. Where is the lumbar attachment of the diaphragm located?
From the upper two or three lumbar vertebrae via the right and left crura.
91. The musculotendinous crura wrap around which structure and form which opening?
They wrap around the aorta and form the aortic hiatus; the right crus is longer than the left.
92. What structure forms the three arcuate ligaments of the diaphragm?
The thoracolumbar fascia.
93. What part of the diaphragm forms the median arcuate ligament?
The medial borders of both crura.
94. The medial and lateral arcuate ligaments pass over which muscles, respectively?
The psoas major and quadratus lumborum muscles.
95. What attaches the heart to the central tendon of the diaphragm?
The pericardiacophrenic ligament.
96. What nerve innervates the diaphragm?
The phrenic nerve, arising from spinal segments C3, C4, and C5.
97. From where does the phrenic nerve originate before reaching the diaphragm?
It originates from the cervical plexus and travels a long course to the diaphragm.
98. How does diaphragm contraction affect lung pressure and airflow?
Contraction lowers intrathoracic pressure, allowing air to flow into the lungs due to the created pressure gradient.
99. What is the primary role of the diaphragm in the respiratory cycle?
To initiate inspiration by contracting and expanding the thoracic cavity.
100. During quiet breathing, how much does the diaphragm descend on average?
Approximately 1.5 cm during quiet breathing, and up to 10 cm during deep inspiration.
Final Thoughts
The diaphragm is more than just a muscle; it is the engine of respiration and a cornerstone of human physiology. By creating the pressure changes that allow air to move in and out of the lungs, it makes every breath possible and sustains life around the clock.
For respiratory therapists, the diaphragm is not only central to understanding normal breathing but also critical in diagnosing and managing disorders, optimizing ventilator settings, and guiding patients toward recovery.
Recognizing its vital role ensures that the care provided is both effective and comprehensive, making the diaphragm an enduring focus in the field of respiratory care.
Written by:
John Landry is a registered respiratory therapist from Memphis, TN, and has a bachelor's degree in kinesiology. He enjoys using evidence-based research to help others breathe easier and live a healthier life.
References
- Bains KNS, Kashyap S, Lappin SL. Anatomy, Thorax: Diaphragm. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025.