Diaphragm

The diaphragm is a large, dome-shaped muscle that separates the thoracic cavity from the abdominal cavity. The diaphragm consists of muscle fibers and a large central tendon, which is divided into right and left parts. As the primary muscle of inspiration, the diaphragm contributes 75% of the total inspiratory muscle force, and its contraction leads to flattening of the dome of the diaphragm. This flattening increases the volume of the thoracic cavity and allows the lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs to expand during inspiration.

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

Table of Contents

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Embryology

  • Develops between the 4th and 7th weeks of gestation
  • Develops from fusion of the following parts:
    • Septum transversum: located in the central portion; becomes the central tendon
    • Pleuroperitoneal membranes: becomes the muscular portion
    • Mesentery of the esophagus Esophagus The esophagus is a muscular tube-shaped organ of around 25 centimeters in length that connects the pharynx to the stomach. The organ extends from approximately the 6th cervical vertebra to the 11th thoracic vertebra and can be divided grossly into 3 parts: the cervical part, the thoracic part, and the abdominal part. Esophagus
    • Mesoderm of the body wall
  • Septum transversum originates in the cervical region → picks up myoblasts, which are innervated by C3, C4, and C5
  • As the diaphragm moves caudally → drags innervation → becomes phrenic nerve
  • Myoblasts invade other components of the diaphragm after fusion → form diaphragm muscle
Developing diaphragm

Developing diaphragm:
Embryonic development of the diaphragm from the pleuroperitoneal membranes and the septum transversum.

Image by Lecturio.

Anatomy

Parts

The diaphragm consists of 3 parts, all of which insert into the central tendon.

  1. Sternal: originates from the back of the xiphoid process
  2. Costal: originates from cartilage Cartilage Cartilage is a type of connective tissue derived from embryonic mesenchyme that is responsible for structural support, resilience, and the smoothness of physical actions. Perichondrium (connective tissue membrane surrounding cartilage) compensates for the absence of vasculature in cartilage by providing nutrition and support. Cartilage and adjacent inner surfaces of the lower 6 ribs
  3. Lumbar: connects to the spine through:
    • Medial lumbocostal arch: connects diaphragm to L1
    • Lateral lumbocostal arch: connects diaphragm to L1 and 12th rib
    • Right crus: attaches to the L1, L2, and L3 vertebrae
    • Left crus: attaches to the L1 and L2 vertebrae

Domes

  • Right dome: positioned higher than the left because of the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver underneath it
  • Left dome: positioned above the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach

Surfaces

  • Thoracic surface: in contact with the pleura Pleura The pleura is a serous membrane that lines the walls of the thoracic cavity and the surface of the lungs. This structure of mesodermal origin covers both lungs, the mediastinum, the thoracic surface of the diaphragm, and the inner part of the thoracic cage. The pleura is divided into a visceral pleura and parietal pleura. Pleura and the pericardium
  • Abdominal surface: in contact with the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver on the right and the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach and spleen Spleen The spleen is the largest lymphoid organ in the body, located in the LUQ of the abdomen, superior to the left kidney and posterior to the stomach at the level of the 9th-11th ribs just below the diaphragm. The spleen is highly vascular and acts as an important blood filter, cleansing the blood of pathogens and damaged erythrocytes. Spleen on the left

Openings

Table: Openings in the diaphragm through which the chest communicates with the abdomen
Opening Location Passage for
Vena caval foramen At level of T8–T9
  • Inferior vena cava
  • Right phrenic nerve
Esophageal hiatus At level of T10
  • Esophagus
  • Vagus nerve
  • Sympathetic nerves
  • Esophageal branches of the left gastric arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries and veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins
Aortic hiatus At level of T12
  • Descending aorta
  • Thoracic duct
  • Azygos vein
  • Hemiazygos vein

Minor diaphragmatic foramina (openings): 

  • Lesser aperture of left crus: opening for the hemiazygos vein and lesser and greater splanchnic nerves 
  • Lesser aperture of right crus: opening for lesser and greater splanchnic nerves
  • Foramen of Morgagni 
    • Between sternal and costal aspects of the diaphragm 
    • Contains lymphatics of the abdominal wall and the superior epigastric artery
  • Medial and lateral lumbocostal arches
    • Separate the pleura Pleura The pleura is a serous membrane that lines the walls of the thoracic cavity and the surface of the lungs. This structure of mesodermal origin covers both lungs, the mediastinum, the thoracic surface of the diaphragm, and the inner part of the thoracic cage. The pleura is divided into a visceral pleura and parietal pleura. Pleura from the superior and posterior surface of the kidneys Kidneys The kidneys are a pair of bean-shaped organs located retroperitoneally against the posterior wall of the abdomen on either side of the spine. As part of the urinary tract, the kidneys are responsible for blood filtration and excretion of water-soluble waste in the urine. Kidneys
    • Sympathetic trunk: runs posteriorly below the medial lumbocostal arches

Function

Respiration

Inspiration:

  • During inspiration, contraction of the diaphragm leads to:
    • Downward (toward the abdomen) movement of the central tendon
    • Increase in the vertical diameter of the thoracic cavity
    • Increase in the negative pressure inside the thoracic cavity (becomes more negative)
    • Expansion of the lung to allow inspiration
  • The diaphragm works in conjunction with the external intercostal muscles.
  • Contraction of the external intercostals increases the anteroposterior diameter of the thorax.
  • Responsible for 75% of the inspiratory muscle force
  • Main muscle of inspiration

Expiration:

  • During expiration, the diaphragm returns passively to its domed configuration.
  • Thoracic cavity becomes smaller.
  • Negative pressure inside the thoracic cavity decreases.
  • Air is passively expelled from the lung. 
Respiration

Respiration:
Image displays the changes of the thorax with the contracting and relaxing of the diaphragm muscle.

Image by Lecturio.

Other functions

  • Abdominal straining:
    • Contraction of the diaphragm increases intraabdominal pressure
    • The diaphragm works in conjunction with the anterior abdominal muscles to raise abdominal pressure.
    • This is helpful for:
      • Functions such as defecation, micturition, parturition, and emesis (vomiting)
      • Compression of the inferior vena cava and upward movement of blood into the right atrium
      • Compression of the abdominal lymph vessels and drainage of lymph into the thoracic duct
  • Natural barrier between the thoracic and abdominal cavities: prevents herniation of abdominal organs into the chest

Neurovasculature

Vasculature

  • Arterial supply:
    • Superior phrenic artery: branch of the aorta
    • Inferior phrenic artery
    • Musculophrenic artery: branch of the internal thoracic artery
    • Lower 5 intercostal arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries
  • Venous drainage:
    • Left suprarenal vein
    • Azygos system

Innervation

  • Motor nerve supply: right and left phrenic nerves (originate from cervical spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord: C3–C5)
  • Sensory nerve supply:
    • Phrenic nerve: for central part of diaphragm
    • 6th–11th intercostal nerves for periphery of diaphragm
      • Activation of sensory phrenic nerves occurs throughout the respiratory cycle.
      • Input from sensory nerves to the CNS is important for regulation of the breathing cycle.

Clinical Relevance

  • Congenital diaphragmatic hernias Congenital diaphragmatic hernias Congenital diaphragmatic hernias are embryologically derived defects in the diaphragm through which abdominal structures can pass into the chest cavity. The presence of intestines and intra-abdominal organs in the chest interferes with embryonic development of the lungs, which is the major cause of pathology postnatally. Congenital Diaphragmatic Hernias: embryologically derived defects in the diaphragm through which abdominal structures can pass into the chest cavity. Hernias most often occur on the left posterolateral portion of the diaphragm. Prenatal diagnosis is commonly made by ultrasonography during pregnancy Pregnancy Pregnancy is the time period between fertilization of an oocyte and delivery of a fetus approximately 9 months later. The 1st sign of pregnancy is typically a missed menstrual period, after which, pregnancy should be confirmed clinically based on a positive β-hCG test (typically a qualitative urine test) and pelvic ultrasound. Pregnancy: Diagnosis, Maternal Physiology, and Routine Care, followed by confirmation by chest x-ray after birth. Immediate respiratory resuscitation at birth with endotracheal intubation and mechanical ventilation are required. Surgical repair is the only curative option. 
  • Diaphragmatic paralysis: can be unilateral or bilateral. Diaphragmatic paralysis is due to disruption of the integrity or function of 1 or both phrenic nerves or, in more rare cases, paralysis of the diaphragmatic muscle. Paralysis can be due to mass effect from a tumor, trauma, infection, or autoimmune inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation. Presentation is with dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea and orthopnea (shortness of breath when lying flat). Hypoxemia and hypercapnia may be noted. Treatment depends on the underlying cause. Occasionally, invasive or noninvasive mechanical ventilatory support is needed.
  • Hiccups: very common condition that occurs because of involuntary intermittent contractions of the diaphragm. A usual episode of hiccups lasts no more than a few minutes and only 1 hemidiaphragm is affected—the left in most cases. Treatment is often unnecessary because of the self-limited nature of hiccups. Pharyngeal stimulation (directly through a catheter, via drinking iced water, etc.) is a very effective nonpharmacologic intervention, as is Valsalva maneuver.

References

  1. Bains, K. N. S, Kashyap, S., & Lappin, S. L. (2021). Anatomy, thorax, diaphragm. StatPearls. Retrieved August 17, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK519558/
  2. Gamache, J. (2018). Diaphragmatic paralysis. Medscape. Retrieved August 17, 2021, from https://reference.medscape.com/article/298200-overview
  3. McCool, F. D., Manzoor, K., & Minami, T. (2018). Disorders of the diaphragm. Clin Chest Med 39, pp. 345–360.
  4. Sefton E. M., Gallardo M., & Kardon, G. (2018). Developmental origin and morphogenesis of the diaphragm, an essential mammalian muscle. Dev Biol 440, pp. 64–73.
  5. Wilkes, G. (2017). Hiccups. Medscape. Retrieved August 17, 2021, from https://reference.medscape.com/article/775746-overview

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