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The diaphragm is a thin, dome-shaped musculotendinous partition separating the thoracic and abdominal cavities.
It is the chief muscle of respiration — contraction increases thoracic volume, causing inspiration.
It is convex upward (right dome higher due to liver).
At rest, its highest point (right dome) reaches the level of the 5th rib.
It descends up to one intercostal space during deep inspiration.
The diaphragm consists of:
Peripheral Muscular Part
Central Tendinous Part
Arises from three main parts:
a. Sternal Part
From posterior surface of xiphoid process (two small slips).
Separated by small gap — for superior epigastric vessels.
b. Costal Part
From inner surfaces of lower six ribs and their costal cartilages (interdigitating with transversus abdominis).
Forms largest portion.
c. Vertebral Part
Arises by crura and arcuate ligaments:
Right crus: from bodies of L1–L3 and intervertebral discs.
Left crus: from bodies of L1–L2.
The right crus is longer.
The two crura are connected by median arcuate ligament (in front of aorta).
Arcuate Ligaments:
Median arcuate ligament → over aortic opening.
Medial arcuate ligament → thickened fascia over psoas major.
Lateral arcuate ligament → thickened fascia over quadratus lumborum.
Strong, trifoliate (three-leafed) aponeurotic sheet.
Lies opposite xiphoid process (T8–T9 level).
The pericardium is fused to its central portion.
There are three large openings and several small ones.
Lies in central tendon (right leaf).
Structures passing:
Inferior vena cava.
Terminal branches of right phrenic nerve.
Mnemonic: “V8” — Vena cava at T8.
Function: enlarges during inspiration → facilitates venous return.
Lies in muscular part (right crus).
Structures passing:
Oesophagus.
Vagal trunks (anterior and posterior).
Oesophageal branches of left gastric vessels.
Mnemonic: “Oesophagus Ten (10)”.
Function: acts as a sphincter — diaphragm assists in preventing reflux.
Lies behind the median arcuate ligament.
Structures passing:
Aorta.
Thoracic duct.
Azygos vein.
Mnemonic: “Aortic Twelve (12)”.
Function: not affected by diaphragmatic contraction (lies posterior).
Right crus: greater and lesser splanchnic nerves.
Left crus: hemiazygos vein.
Between crura: sympathetic trunk.
Sternocostal triangle: superior epigastric vessels.
Behind lateral arcuate ligament: subcostal vessels and nerve.
Covered by pleura and pericardium.
Right dome: related to liver and right lung base.
Left dome: related to stomach, spleen, and left lung base.
Covered by peritoneum, related to:
Right dome → right lobe of liver, right kidney, suprarenal gland.
Left dome → left lobe of liver, fundus of stomach, spleen, left kidney, suprarenal gland.
Central tendon → pericardium (via fibrous layer).
T8 → Vena Cava (V8)
T10 → Oesophagus (OesophaTen)
T12 → Aorta (Aortwelve)
Phrenic nerve (C3, C4, C5) — “C3, 4, 5 keep the diaphragm alive.”
Right phrenic nerve supplies the right half, and the left phrenic nerve supplies the left half.
The central tendon region of the diaphragm is entirely phrenic-supplied.
Central part: Phrenic nerve (pain referred to shoulder – C4 dermatome).
Peripheral part: Lower six intercostal nerves and subcostal nerve (T12).
Pain from these peripheral parts is referred to the costal margins or abdominal wall.
Chief Muscle of Inspiration
On contraction, domes descend → thoracic cavity enlarges → pressure drops → air enters lungs.
Expiration (Relaxation Phase)
When the diaphragm relaxes, domes rise → thoracic volume decreases → air expelled.
Assists in Circulation
Contraction decreases intrathoracic pressure and increases intra-abdominal pressure, aiding venous return via IVC and lymph flow via thoracic duct.
Acts as a Partition and Sphincter
Through its openings, the diaphragm controls passage of oesophagus, aorta, IVC, etc.
The right crus acts as a physiological sphincter for the lower oesophagus.
Abdominal Pressurization
With other muscles, helps in micturition, defecation, parturition, and vomiting by raising intra-abdominal pressure.
The diaphragm is seen from the abdominal cavity after removing abdominal viscera.
Identify:
Central tendon – shiny and aponeurotic.
Crura – muscular slips attached to lumbar vertebrae.
Arcuate ligaments – median, medial, and lateral.
Openings – IVC at T8 (in tendon), oesophagus at T10 (in muscle), aorta at T12 (behind ligament).
Observe the phrenic nerves descending anteriorly and sympathetic trunks posteriorly.
Due to phrenic nerve injury (e.g., neck trauma, mediastinal tumor).
On X-ray → paradoxical movement (dome moves upward during inspiration).
Congenital thinning or absence of muscle → one dome balloons upward.
Commonly on left side; may compress lung.
Herniation of stomach into thorax through the oesophageal opening.
Sliding type: gastroesophageal junction moves upward.
Paraesophageal type: fundus herniates beside oesophagus.
Due to failure of closure of pleuroperitoneal canal (posterolateral defect).
Abdominal viscera herniate into thorax → pulmonary hypoplasia in newborn.
Herniation through sternocostal triangle (foramen of Morgagni) – rare, anterior type.
Central diaphragmatic pain → referred to shoulder (C4) via phrenic nerve.
Peripheral pain → referred to costal margins (intercostal nerves).
Pus collects below diaphragm (usually right side) following peritonitis or liver abscess.
Causes elevation of diaphragm and referred shoulder pain.
May arise from nerve to subclavius (C5) → joins phrenic nerve in thorax.
Damage to both may cause partial paralysis.
The diaphragm develops from four embryonic components:
Septum Transversum
Forms central tendon.
Lies opposite cervical somites (C3–C5) → hence phrenic nerve origin.
Pleuroperitoneal Membranes
Close the pleuroperitoneal canals on each side posteriorly.
Dorsal Mesentery of Oesophagus
Forms crura and median portion around oesophageal opening.
Body Wall (Peripheral Muscular Part)
Contributes to costal portion of diaphragm.
Timeline:
Fusion complete by the 8th week of development.
Initially cervical in position, descends to thoracic level by 8th week, dragging phrenic nerve downward — explaining its long course.
Clinical Correlation:
Failure of fusion → congenital diaphragmatic hernia (Bochdalek type).
Defect in septum transversum → eventration or Morgagni hernia.
Mnemonic: 🧠 “I 8 10 Eggs At 12”
I 8 → IVC at T8 → Inferior Vena Cava + Right Phrenic Nerve.
10 Eggs → Oesophagus at T10 → Oesophagus + Vagal Trunks + Left Gastric Vessels.
At 12 → Aorta at T12 → Aorta + Thoracic Duct + Azygos Vein.
Mnemonic: “Silly Great Lads Hide Behind Crura”
S – Sympathetic trunks.
G – Greater splanchnic nerves.
L – Lesser splanchnic nerves.
H – Hemiazygos vein.
B – Both crura connect via Median Arcuate Ligament.
Mnemonic: “L-M-M: Laterally Quadratus, Medially Psoas, Middle Aorta.”
Lateral arcuate ligament → over Quadratus lumborum.
Medial arcuate ligament → over Psoas major.
Median arcuate ligament → arches over aorta.
Mnemonic: “AIR PRESS”
A – Aids in Abdominal pressure (urination, defecation, parturition).
I – Inspiration (main function).
R – Returns venous blood to heart.
P – Partition between thorax and abdomen.
R – Reflex control of breathing via phrenic.
E – Expulsion (vomiting, cough).
S – Sphincter action at oesophageal opening.
S – Support to abdominal viscera.
Mnemonic: “Several Parts Develop Diaphragm.”
S – Septum transversum → central tendon.
P – Pleuroperitoneal membranes.
D – Dorsal mesentery of oesophagus.
D – Derived muscle from body wall (peripheral part).
Mnemonic: “C3, 4, 5 keep the diaphragm alive.”
– Phrenic nerve origin from C3–C5 cervical segments.
The diaphragm is the principal muscle of inspiration.
It separates the thoracic and abdominal cavities.
Formed of peripheral muscle fibers and a central tendon.
The right dome lies higher (due to liver) than the left.
Central tendon lies at the level of xiphoid process (T8–T9).
Three major openings:
IVC – T8 (in tendon).
Oesophagus – T10 (in right crus).
Aorta – T12 (behind median arcuate ligament).
Arcuate ligaments: median (over aorta), medial (over psoas), lateral (over quadratus lumborum).
Right crus is longer and wider than the left.
Nerve supply:
Motor → Phrenic nerve (C3–C5).
Sensory → Phrenic (central part) and lower 6 intercostal + subcostal (peripheral part).
Blood supply: Musculophrenic, pericardiophrenic, superior and inferior phrenic arteries.
Action: Contraction → inspiration by lowering domes; relaxation → expiration.
During inspiration, the central tendon descends about 1–2 cm in quiet breathing, up to 5 cm in deep breathing.
Paralysis of one half → elevated dome on that side with paradoxical movement.
Eventration: Congenital deficiency causing ballooning of diaphragm.
Hiatus hernia: Protrusion of stomach through oesophageal opening.
Congenital diaphragmatic hernia: Failure of pleuroperitoneal membrane closure (Bochdalek type).
Phrenic pain is referred to the shoulder (C4); peripheral pain to costal margins.
The diaphragm develops from four embryological sources: septum transversum, pleuroperitoneal membranes, dorsal mesentery of oesophagus, and body wall.
Central tendon derived from septum transversum.
Clinical importance: Vital in respiration and venous return to heart.
A 42-year-old man presents with breathlessness. X-ray shows the right dome of diaphragm elevated and moving paradoxically on inspiration.
→ Diagnosis: Paralysis of diaphragm due to right phrenic nerve injury (C3–C5).
A patient with right subphrenic abscess complains of pain over right shoulder tip.
→ Explanation: Referred pain from diaphragm via phrenic nerve (C4 dermatome).
A child has abnormally high position of the left dome of diaphragm on X-ray, but no rupture.
→ Diagnosis: Eventration — congenital thinning or partial absence of muscle fibers, causing ballooning.
A newborn has severe respiratory distress immediately after birth. X-ray shows bowel loops in the thorax.
→ Diagnosis: Posterolateral diaphragmatic hernia due to failure of pleuroperitoneal canal closure.
An elderly woman with chronic cough presents with epigastric bulge near xiphoid process.
→ Cause: Herniation through sternocostal triangle (foramen of Morgagni).
Middle-aged patient with heartburn and regurgitation. Barium swallow shows stomach and gastroesophageal junction above diaphragm.
→ Diagnosis: Sliding hiatus hernia through oesophageal opening (T10).
A patient’s stomach fundus is seen herniating beside oesophagus without displacement of gastroesophageal junction.
→ Diagnosis: Paraesophageal hernia – dangerous due to possible strangulation.
Pain perceived in epigastrium when diaphragmatic pleura irritated (e.g. subphrenic abscess).
→ Reason: Central diaphragmatic part supplied by phrenic nerve, referred to epigastrium.
After cervical spinal cord injury at C4 level, patient develops respiratory failure.
→ Reason: Phrenic nerve roots (C3–C5) are affected, diaphragm paralyzed → ventilatory failure.
After open heart surgery, patient has raised left dome on X-ray.
→ Cause: Iatrogenic injury to left phrenic nerve (lies on pericardium).
Patient develops dyspnea after thyroidectomy.
→ Reason: Accidental ligation of phrenic nerve crossing anterior to scalenus anterior muscle.
Neonate with respiratory distress has no separation between thoracic and abdominal cavities.
→ Diagnosis: Agenesis of diaphragm – failure of all four embryonic components to fuse.
Partial diaphragmatic paralysis occurs though main phrenic nerve preserved.
→ Explanation: Injury to accessory phrenic nerve (from nerve to subclavius, C5).
Persistent involuntary contraction of diaphragm causing sudden inspiration with glottis closure.
→ Reason: Reflex irritation of phrenic nerve or medullary centers.
Post-appendectomy patient develops fever and shoulder pain.
→ Diagnosis: Subphrenic abscess beneath diaphragm due to pus collection.
→ Feature: Elevation of diaphragm and referred shoulder pain (C4).
During inspiration, one dome moves downward but the other moves upward.
→ Diagnosis: Paradoxical movement – sign of unilateral diaphragmatic paralysis.
A man sustains blunt abdominal trauma; stomach loops visible in left thoracic cavity.
→ Diagnosis: Traumatic rupture of diaphragm – more common on left side (liver protects right).
Infant’s X-ray shows high dome with gut shadow beneath intact pleura.
→ Differentiation: Eventration (no rupture) vs hernia (defect present).
An adult with chronic cough develops herniation of omentum through foramen of Bochdalek (posterolateral).
→ Significance: Late presentation of congenital defect.
Patient with pericardial irritation develops pain radiating to shoulder tip.
→ Reason: Common sensory pathway via phrenic nerve (C4).
Describe the origin, insertion, nerve supply, and actions of the thoracoabdominal diaphragm.
Write short notes on:
Major openings of diaphragm and the structures passing through them.
Minor openings and their contents.
Diaphragmatic hernia — congenital and acquired types.
Course and distribution of the phrenic nerve.
Explain why the cardiac end of the stomach is prone to sliding hernia.
Due to weakness of the phrenico-oesophageal membrane, allowing the cardiac end to slide through the oesophageal hiatus, disturbing the valvular mechanism at the gastroesophageal junction and causing reflux.
List the vertebral levels of major openings of the diaphragm and structures transmitted through each.
T8 → Inferior vena cava, right phrenic nerve.
T10 → Oesophagus, vagal trunks, left gastric vessels.
T12 → Aorta, thoracic duct, azygos vein.
Discuss congenital anomalies of diaphragm development.
Posterolateral (Bochdalek) hernia, Retrosternal (Morgagni) hernia, Eventration, and Complete absence of diaphragm.
What is the nerve supply of the diaphragm?
Motor: Phrenic nerve (C3–C5).
Sensory: Central part by phrenic nerve; peripheral part by lower six intercostal nerves.
Which of the following structures does not pass through the diaphragm?
a. Oesophagus
b. Aorta
c. Cisterna chyli ✅
d. Inferior vena cava
To build a complete exam-ready MCQ section, here are additional standard questions (patterned on BD Chaurasia and AIIMS/NEET PG level):
a. Intercostal nerve
b. Vagus nerve
c. Phrenic nerve ✅
d. Sympathetic nerve
a. T8
b. T10 ✅
c. T12
d. L1
a. T8 ✅
b. T10
c. T12
d. T6
a. T10
b. T12 ✅
c. L1
d. T9
a. C2–C3
b. C4–C6
c. C3–C5 ✅
d. T1–T3
a. Oesophagus
b. Vagus nerve
c. Left gastric artery
d. Azygos vein ✅
a. Septum transversum ✅
b. Pleuroperitoneal membrane
c. Dorsal mesentery of oesophagus
d. Lateral body wall
a. Right ✅
b. Left
c. Equal
d. Variable
a. Costal arch
b. Central tendon ✅
c. Vertebral column
d. Linea alba
a. Aorta
b. Thoracic duct ✅
c. Inferior vena cava
d. Oesophagus
a. Trauma
b. Inflammation
c. Congenital muscle defect ✅
d. Hernia
a. Pericardiophrenic
b. Musculophrenic
c. Inferior mesenteric ✅
d. Inferior phrenic
a. External intercostals
b. Internal intercostals
c. Diaphragm ✅
d. Scalene
a. L1–L2
b. L1–L3 ✅
c. L2–L4
d. T12–L2
a. L1–L3
b. L1–L2 ✅
c. L2–L3
d. T12–L2
a. Epigastrium
b. Shoulder (C4 dermatome) ✅
c. Lower chest
d. Back
a. Morgagni hernia
b. Bochdalek hernia ✅
c. Hiatus hernia
d. Paraesophageal hernia
a. Inferior vena cava
b. Oesophagus
c. Aorta ✅
d. Vagus nerve
a. Caval opening
b. Oesophageal hiatus
c. Aortic hiatus
d. Renal opening ✅
A dome-shaped musculotendinous partition separating the thoracic and abdominal cavities; the chief muscle of inspiration.
Muscular part – sternal, costal, and vertebral.
Central tendinous part – aponeurotic and trifoliate in shape.
The right dome, because it rests on the liver.
Motor: Phrenic nerve (C3, C4, C5).
Sensory: Phrenic (central part) and lower six intercostal + subcostal nerves (peripheral part).
“I 8 10 Eggs At 12”
IVC → T8
Oesophagus → T10
Aorta → T12
Caval opening (T8) for inferior vena cava and right phrenic nerve.
Oesophagus
Anterior and posterior vagal trunks
Oesophageal branches of left gastric vessels.
Aorta
Thoracic duct
Azygos vein.
The right crus (arises from L1–L3) is longer than the left (L1–L2).
They form a sling around the oesophagus and act as a physiological sphincter preventing gastric reflux.
Median arcuate ligament – arches over aorta.
Medial arcuate ligament – over psoas major.
Lateral arcuate ligament – over quadratus lumborum.
Inspiration: Increases thoracic volume by descending.
Expiration: Relaxes and ascends.
Abdominal compression: Assists in defecation, micturition, parturition.
Venous return: Aids blood flow via IVC.
From four embryonic sources:
Septum transversum
Pleuroperitoneal membranes
Dorsal mesentery of oesophagus
Muscular ingrowths from body wall.
Septum transversum.
Bochdalek hernia (posterolateral)
Morgagni hernia (sternocostal)
Eventration (muscle defect)
Complete absence (rare).
Approximately T8–T9.
A congenital condition where one dome is elevated due to defective muscular development, replaced by thin membrane.
Herniation of the stomach through the oesophageal hiatus into thorax; may be sliding or paraesophageal.
Pain from the diaphragm is felt at the shoulder tip (C4) because both phrenic and supraclavicular nerves share the same spinal root value.
Bochdalek: Posterolateral defect (common).
Morgagni: Anterior retrosternal defect (rare).
In unilateral diaphragmatic paralysis, the paralyzed dome moves upward during inspiration instead of descending.
It’s short and runs over the inferior vena cava, hence easily damaged during hepatic or pericardial surgery.
Arteries: Musculophrenic, pericardiophrenic, superior & inferior phrenic arteries.
Veins: Drain into azygos, inferior phrenic, and internal thoracic veins.
Aids in vomiting, micturition, defecation, parturition, and cough reflex.
Not an organ — refers to Bochdalek’s foramen, the site of posterolateral congenital diaphragmatic hernia.
Diaphragm.
Paralysis of diaphragm on that side → elevation of dome and loss of respiratory function.
Because of phrenic nerve stimulation → contraction → increase in vertical thoracic diameter.
The right crus forms a sling around the oesophagus acting as an external sphincter.
It causes compression of developing lungs, leading to pulmonary hypoplasia and respiratory distress.
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