Anatomy of Thorax

Lung’s pleura

2 pleuras: continuous at hilum

  • Parietal pleura –  lines inner surface of the thoracic cavity
  • Visceral pleura – lines surface of lung

Pleural cavity: contains pleural fluid which lubricates lungs

4 parts of parietal pleura:

Parts of parietal pleura

parietal pleura and visceral pleura blood supply, innervation and lymphatic drainage

Pleural recesses:

Image result for pleural recesses


  • Drain fluid – insert needle superior to rib
  • Pleuritis
  • Pancoast tumor – on lung apex, erodes 1st rib
  • Pyothorax (pus), hemothorax (blood), pneumothorax (air), chylothorax (lymph) – collect in pleural cavity


Lung surfaces: Costal, mediastinal, diaphragmatic

Blood supply: Same as visceral pleura

Nerve: Same as visceral pleura

  • Sympathetic trunk: Relax bronchial smooth muscle, vasoconstrict vessels
  • Vagus: Contract smooth muscles, vasodilate

Bronchial tree: Trachea ⇒ Right and left bronchus ⇒ Lobar bronchus (3 right, 2 left) ⇒ Segmental bronchus ⇒ Interlobular bronchus ⇒ Terminal bronchiole ⇒ Respiratory bronchiole


lymphatic drainage of lungs

Bronchopulmonary segment:

Bronchopulmonary Segments

Right lung bronchopulmonary segments

Left lung bronchopulmonary segments

Clinicals: Lung resection – remove specific tumor on segment

Apex of lung – relations:

  • Anterior – subclavian artery, scalenus anterior, clavicle
  • Posterior – posterior intercostal arteries and veins
  • Lateral – 1st rib
  • Medial – phrenic nerve, vagus nerve, trachea, esophagus
  • Superior – brachial plexus

Right and left lung differences:

Difference between left and right lungs

Right – 10 segments, Left – 8 segments

Right and left bronchi:

  • Right: Shorter, vertical, 3 divisions, enters lung at T5 level
  • Left: Longer, horizontal, 2 divisions, enters lung at T6 level

Right and left hilum:

Image result for right and left hilum differences

Right and left lung impressions:

Image result for impression on lungs


  • Pulmonary embolism – dyspnea, chest pain, cough blood
  • Clavicle fractures – damage apex of lungs
  • Asthma
  • Chronic bronchitis
  • Cancer – smoking
  • Cystic fibrosis
  • Bronchoscopy
  • Aspiration of foreign object usually in right principal bronchus as it shorter, wider and more vertical than left



  • Anterior – sternopericardial ligament, sternum
  • Posterior – posterior mediastinum
  • Superior – tunica adventia of great vessels
  • Inferior – pericardiophrenic ligament
  • Laterally – pulmonary vein adventia


  • Anterior – sternum, 2-6 costal cartilage
  • Posterior – posterior mediastinum
  • Superior – thymus, great vessels
  • Inferior – pericardiophrenic ligament
  • Laterally -phrenic nerve, lungs and pleura pericardiophrenic vessels


  • Fibrous – prevents over distension of heart
  • Parietal – lines pericardium
  • Visceral – called epicardium

Sinuses between parietal and visceral layer:

Image result for pericardium sinuses

Blood supply:

  • Internal thoracic artery – pericardiophrenic and musculophrenic arteries
  • Thoracic aorta – bronchial, esophageal, superior phrenic
  • Coronary arteries (visceral layer)


  • Pericardiophrenic – drains into internal thoracic artery
  • Azygos venous system


  • Fibrous and parietal layer – phrenic nerve, intercostal nerve
  • Visceral layer – vagus and sympathetic trunk

Lymphatics: Parasternal, tracheobronchial

Functions of pericardium:

  • Fix heart with sternopericardial ligament and pericardiophrenic ligament
  • Prevent overfilling of heart
  • Lubrication
  • Protect from lung infection

Layers of heart wall:

  • Fibrous
  • Parietal
  • Serous fluid
  • Visceral/epicardium
  • Subepicardial layer
  • Myocardium – involuntary striated muscle (Clinicals: myocarditis, infarction)
  • Subendocardial layer – Purkinje fibers and vessels
  • Endocardium – lines heart cavities and valves (Clinicals: endocarditis)


  • Pericarditis
  • Cardiac tamponade – compressed heart and veins
  • Pericardial effusion – abnormal accumulation of fluid in the pericardial cavity
  • Pericardiocentesis – aspiration of fluid from 5th and 6th intercostal space


Divided into 1/3 right and 2/3 left by posterior interventricular sulcus, which contains posterior interventricular artery

Borders and surfaces of the heart:

Borders of the heart

Relations of the heart

Surface anatomy of the heart:

Image result for heart surfaces anatomy

Blood supply:

Image result for blood supply of heart

Aortic sinus gives off right coronary artery and left coronary artery

Right coronary artery branches:

  • Sino arterial nodal
  • Right marginal
  • AV nodal
  • Posterior interventricular

Left coronary artery branches:

  • Anterior interventricular
  • Circumflex
  • Left marginal (from circumflex)

As blood recoils during ventricular diastole, enters coronary arteries to supply heart

NB: Coronary dominance – The coronary artery that supplies SAN, can be right or left or both

Extracardiac anastomosis: Internal thoracic artery branches, bronchial, esophageal, superior and inferior phrenic arteries


Image result for venous drainage of heart

Coronary sinus:

  • Runs in posterior coronary groove
  • Opens in right atrium between AV orifice and IVC orifice
  • Tributaries:
  1. Great cardiac vein
  2. Small cardiac vein
  3. middle cardiac vein
  4. Left marginal vein
  5. Left posterior ventricular
  6. Oblique vein of left atrium

Anterior cardiac veins open directly in right atrium

Lymphatics: Tunica media ⇒ Efferent vessels ⇒ tracheobronchial nodes

Nerves: Sympathetic increases heart rate, parasympathetic decreases

Sympathetic: Right and left cardiac branches of sympathetic ganglia

  • Cervical: Superior, middle and inferior ganglia
  • Thorax: Ganglia 2,3,4


  • Vagus: Right and left upper cervical cardiac branches, right and left lower cervical cardiac branches
  • Left recurrent laryngeal – 1 branch

1. Superficial cardiac plexus – Below arch of aorta

  • Left superior cervical sympathetic nerve
  • Left lower cervical cardiac nerve (parasympathetic)

2. Deep cardiac plexus – infront of tracheal bifurcation

  • All the remaining nerves mentioned above

Image result for nerve supply of heart

Relations: Same as pericardium

Interior of heart:

Image result for interior of right ventricle

(I) Right atrium:

  • Crista terminalis (contains SAN)/ Sulcus terminalis – divides atrium into smooth and rough part
  • Sinus venarum – smooth – posterior part
  • Atrium proper – rough – anterior part
  • Pectinate muscles
  • SVC, IVC, coronary and AV orifice

(II) Interarterial septum: Fossa ovalis and limbus

Clinicals: Patent foramen ovale

(III) Left atrium:

  • Smooth  posterior part – absorbed pulmonary veins
  • Rough anterior part – Pectinate muscles

(IV) Right ventricle: Divided into 2 by supraventricular crest

  • Outflow part – Infundibulum, smooth walls
  • Inflow part – Trabeculae carneae which consists of:
  1. Ridges
  2. Bridges (eg. moderator band)
  3. Three Papillary muscles – attached to valves by chorda tendinea – prevents valve prolapse into atria during ventricular systole

(V) Interventricular septum: Superiorly membranous, inferiorly muscular

(VI) Left ventricle:

  • Outflow part – Aortic vestibule, smooth walls
  • Inflow part – Trabeculae carneae, 2 papillary muscles

Conducting system of the heart: 

Image result for conducting system of the heart

Triangle of koch: In right atrium, anatomical landmark of AV node

Boundaries: Tendon of Todaro, tricuspid valve and coronary sinus opening

Image result for Triangle of koch


  • Myocardial ischaemia
  • Angina pectoris
  • Coronary bypass graft – radial artery and long saphenous vein
  • Angiogram
  • Cardiac referred pain – pain felt in the neck, shoulders, and back
  • Heart block 1st, 2nd and 3rd degree

Superior thoracic inlet


  • Anterior – Manubrium
  • Posterior – T1 body
  • Lateral – 1st rib and costal cartilage


  • Trachea, esophagus, thoracic duct
  • Common carotid artery, subclavian artery and vein, IJV
  • Vagus, phrenic, recurrent laryngeal nerves and sympathetic chain
  • Apex of lung and pleura

Clinicals: Thoracic inlet syndrome – compression of structures, tumors, enlarged lymph nodes – leads to dysphagia, dyspnea

Inferior thoracic inlet


  • Anterior – 7-10 costal cartilage, xiphisternal joint
  • Posterior – T12 body
  • Lateral – 11th and 12th ribs


  • Abdominal aorta
  • Azygos vein
  • IVC
  • Esophagus
  • Vagus nerve
  • Thoracic duct


(I) Costotransverse and costovertebral joints:

Image result for Costotransverse and costovertebral joints

Costotransverse jointTubercle of rib articulates with transverse process of corresponding vertebrae

Costovertebral joint – Head of rib articulates with superior costal facet of corresponding vertebrae and inferior costal facet of the vertebra above, as well as the adjacent IVD

(II) Types of ribs:

Types of ribs

(III) Typical rib:

  • Anterior – Costal cartilage (hyaline)
  • Posterior – Tubercle and head (2 articular facets)
  • Superior – Thick and rounded
  • Inferior – Sharp, costal groove

Image result for typical rib

(IV) Atypical ribs:

Image result for atypical rib

1st and 2nd rib muscle origin and insertions

(V) 1st rib relations:

  • Superior – clavicle, subclavian vessels
  • Inferior – intercostal vessels
  • Medial – sympathetic trunk

(VI) Muscles:

1. Intercostal muscles:

Image result for Intercostal muscles

  • 11 pairs
  • Nerve supply – intercostal nerves (T1-T11)
  • Intercostal vein, artery and nerve between internal and innermost intercostal muscles
  1. External – in inspiration elevate ribcage
  2. Internal – forced expiration
  3. Innermost – inspiration

2. Transverse thoracic muscles:

  • From posterior inferior sternum to posterior surface of costal cartilage 2-6
  • Depress ribs

Transverse thoracic muscles

3. Subcostal muscles:

  • From posterior lateral rib to a 2nd or 3rd rib below
  • Depress ribs

Image result for subcostal muscles

(VII) Muscles of respiration:

Image result for muscles of respiration

(VIII) Thoracic wall/ Ribcage:

1. Blood supply:

  • Thoracic aorta – Posterior intercostals, subcostal artery
  • Internal thoracic – Anterior intercostals
  • Axillary – Superior and lateral thoracic arteries

2. Venous: Azygos system

3. Nerves:

  • Supraclavicular nerve – above 2nd rib
  • Anterior rami (T1-T11) intercostal nerves

4. Lymphatics: Intercostal, phrenic nodes


  • Age changes – costal cartilage ossify, xiphoid process ossify
  • Paralysis of diaphragm, phrenic nerve damaged – paradoxical movement
  • Extra ribs – transverse process of cervical or lumbar vertebrae
  • Decreased ribs – failure of 12th rib to form
  • Rib fracture – at angle or costal cartilage, most common in ribs 3-10 since they are immobile. 1st and 2nd are protected by clavicle, 11th and 12th are mobile.
  • Flail chest – anterolateral chest wall movable due to multiple rib fractures. Moves paradoxically (moves outwards during expiration)
  • Funnel chest 
  • Pigeon chest
  • Sternal puncture – to get bone marrow from manubrium, pierces skin, fascia and periosteum. May injure aorta, heart, or pericardium
  • Median sternotomy – vertical incision along sternum for heart and lung surgeries


Image result for Mediastinum

(I) Superior mediastinum:


  • Superior – Thoracic inlet
  • Inferior – Inferior mediastinum
  • Anterior – Manubrium
  • Posterior – T1-T4
  • Lateral – Lungs pleura


  • Nerves: phrenic, vagus, recurrent laryngeal
  • Vessels: SVC, thoracic duct, aorta, internal thoracic artery and vein
  • Trachea, esophagus
  • Thymus gland

(II) Anterior mediastinum:


  • Superior – Superior mediastinum
  • Inferior – Diaphragm
  • Anterior – Sternum
  • Posterior – Pericardium
  • Lateral – lungs pleura

Contents: Sternopericardial ligament, internal thoracic artery and branches, thymus gland

(III) Middle mediastinum:


  • Superior – Superior mediastinum
  • Inferior – Diaphragm
  • Anterior – Pericardium
  • Posterior – Pericardium
  • Lateral – lungs pleura

Contents: Heart, tracheal bifurcation, phrenic nerve, SVC, pulmonary artery, pulmonary vein, aorta

(IV) Posterior mediastinum:


  • Superior – Superior mediastinum
  • Inferior – Diaphragm
  • Anterior – Pericardium
  • Posterior – T5-T12
  • Lateral – lungs pleura

Contents: Thoracic aorta, thoracic duct, azygos system, esophagus

Vessels and nerves

(I) Internal thoracic artery:

  • Originates from 1st part subclavian artery
  • Anterior to lung apex
  • Enters thorax, posterior to clavicle
  • Runs downwards and lateral to sternum
  • At 6th intercostal space divides into: superior epigastric (rectus muscle) and musculophrenic (diaphragm)
  • Branches: Anterior intercostal arteries, perforators of breast, pericardiophrenic and mediastinal

(II) Aortic arch: (connected to pulmonary trunk by ligament arteriosum)

Location: Sternal angle to lower border T4


  • Superior – Brachiocepahlic trunk, left common carotid, left subclavian artery
  • Inferior – Pulmonary trunk
  • Left/anterior – Pleura, phrenic nerve and vagus nerve
  • Right posterior – trachea, esophagus

Branches: Brachiocepahlic trunk, left common carotid, left subclavian artery, right and left coronary arteries

(III) Thoracic aorta:

Location: Posterior mediastinum (T4-T12)


  • Anterior – Pericardium
  • Posterior – Vertebral column
  • Right – Thoracic duct, azygos vein
  • Left – Left lung and pleura

Branches: Posterior intercostals, bronchial, esophageal, pericardial, mediastinal, superior phrenic, subcostal

(IV) Brachiocephalic trunk:

Location: Posterior to manubrium


  • Anterior – Manubrium
  • Posterior – Trachea
  • Right – SVC
  • Left – Left common carotid

Branches: Right common carotid and right subclavian

(V) SVC:

Extent: 1st-3rd costal cartilage

Location: Anterior and right of superior mediastinum


  • Anterior – Ascending aorta, right lung
  • Posterior – Trachea
  • Lateral – Right lung and pleura

Tributaries: Right and left brachiocephalic veins, azygos vein, right and left supreme intercostal veins

(VI) Azygos venous system:

Azygos venous system

  • Azygos vein formed from right subcostal vein and right ascending lumbar vein
  • Hemiazygos and accessory hemiazygos drain into azygos vein
  • Azygos vein enters thorax via aortic hiatus
  • Ascends right of T12 – T4
  • Drains into SVC

(VII) Thoracic duct: Main lymphatic trunk

  • Continues as cisterna chyli in abdomen
  • Enters thorax via aortic hiatus
  • In posterior mediastinum, right to thoracic aorta snd posterior to esophagus
  • Crossed from right to left at T4
  • In superior mediastinum
  • Joins junction of left IJV and left subclavian to form left brachiocephalic vein

Territory of drainage: all except superior right quadrant

Clinicals: Laceration – thin wall tears, chyle accumulates in posterior mediastinum

(VIII) Phrenic nerve:

  • Origin: Anterior rami of C3,C4,C5
  • Begins at lateral border of anterior scalene muscle
  • Descends anterior to anterior scalene, deep to prevertebral layer

Right phrenic nerve:

  • Passes anterior to 2nd part of subclavian artery
  • Enters thorax via superior mediastinum
  • Right side of brachiocephalic vein, SVC and pericardium
  • Descends anterior to lung root
  • Pierce diaphragm near caval opening

Left phrenic nerve:

  • Passes anterior to 1st part of subclavian artery
  • Enters thorax via superior mediastinum
  • Crosses aortic arch and vagus nerve
  • Descends anterior to lung root
  • Pierce diaphragm

Phrenic nerve distribution:

  • Motor and sensory – Diaphragm
  • Sensory:
  1. Parietal pleura
  2. Parietal pericardium
  3. IVC
  4. Suprarenal glands
  5. Biliary apparatus

Clinicals: Referred pain

(IX) Thoracic sympathetic chain:

  • Runs over neck of ribs and transverse process of vertebrae
  • Pierce diaphragm to supply abdomen

Trachea, esophagus and thymus gland

Trachea, esophagus, thymus location, relation, blood supply, venous, nerves, lymph drainage


Constrictors: Cricopharyngeal sphincter, arch of aorta, left main bronchus, diaphragmatic constriction

Clinicals of esophagus: Cancer, compression due to right atrium hypertrophy – dysphagia



  • L1 and L2
  • 7-12 rib’s costal cartilage
  • Xiphoid process of sternum
  • Right (L1-L3) and left (L1-L2) crus – combine to form central tendon


Image result for diaphragm openingsImage result for diaphragm openings simple diagram

Blood supply:

  • Internal thoracic – Pericardiophrenic, musculophrenic
  • Thoracic aorta – Superior phrenic
  • Abdominal aorta – Inferior phrenic
  • Lower intercostal arteries

Nerves: Phrenic (motor), intercostal nerves and subcostal nerve (sensory)

Lymphatics: Parasternal, anterior and posterior diaphragmatic


  • Contract, flatten
  • Relax, dome shaped

Functions of diaphragm:

  • Muscle of inspiration – increase verticle diameter
  • Muscle of abdominal straining – helps anterior abdominal muscles to contract, therefore raise intraabdominal pressure for micturition, defecation or parturition
  • Weight lifting muscle
  • Thoracoabdominal pump – as diaphragm increases intraabdominal pressure and decreases intrathoracic pressure, it compresses blood in IVC and forces it upwards. Thoracic duct also aided.


  • Superior – Pericardium, lungs
  • Inferior – Liver, adrenals, kidney, stomach, spleen
  • Posterior – Aorta, azygos vein, esophagus


  • Paralysis (suffocation)
  • Hiccups  -involuntary contractions of diaphragm, irritation
  • Referred pain – shoulder region
  • Hiatal hernia – stomach enters thorax via th esophageal hiatus
  • Median arcuate ligament syndrome – abdominal pain due to compression of celiac artery

These are summarized notes from various sources, mainly TeachMeAnatomy and Wikipedia