Diaphram & lungs

Diaphragm function

• Contraction: diaphragm flattens → thoracic cavity volume increases → air enters lungs (inspiration).

• Relaxation: diaphragm returns to dome shape → thoracic volume decreases → air leaves lungs (expiration).

Attachment (origins)

Sternal part	Posterior surface of the xiphoid process
Costal part	Internal surfaces of ribs 7–12 and their costal cartilages
Lumbar part	Lumbar vertebrae via the right and left crura and arcuate ligaments

Openings in the diaphragm

Caval opening: inferior vena cava, branches of right phrenic nerve (T8)

Esophageal hiatus: Esophagus, vagus nerves (T10)

Aortic hiatus: aorta, thoracic duct, azygos vein (T12)

Blood supply

Superior phrenic arteries
inferior phrenic arteries

Musculophrenic artery

pericardiophrenic artery

Nerve supply

Phrenic nerve (C3,C4,C5)

Thoracic wall blood supply

1. subclavian artery

2. Axillary artery

3. Thoracic artery

Aortic arch brances

Right brachiocephalic trunk: common carotid a., right subclavian artery a.
Left subclavian a.
Left common carotid a.

Blood supply to thorax

Internal thoracic a.

superior thoracic a.

thoracoacrominal a.

lateral thoracic a.

thoracic dorsal a.

Intercostal vessels and nerves

• vein, artery, nerve – VAN

- Near angle of rib, they travel along costal
grooves

Thoracic wall drainage

Azygos, Hemiazygos and accessory hemiazygos veins

thoracic duct (lymph)

Intercostal nerve distrubution

1st intercostal –          supplies arm 

2nd intercostal -         supplies floor of axilla and part of arm

3-6 intercostal -          typical distribution   

7-11 intercostal -        supply anterior abdominal wall as well as thoracic

(12) subcostal -           lower anterior abdominal wall

Pleura

•        double-layered membrane that wraps around each lung

Parietal pleura (outer layer)

Visceral pleura (the inner layer)

Function of pleura

•        Reduce friction: serous fluid allows smooth lung movement during respiration

•        Pressure gradient: negative intrapleural pressure keeps lungs expanded

•        Compartmentalisation: separates lungs from surrounding structures

Pulmonary pressure

1.      Atmospheric pressure (760 mmHg)

2.      Inter-alveolar  pressure (760 mmHg)

3.      Intrapleural pressure (756 mmHg)

Lungs lobes

Lobes:
Right: 3 - superior, middle, inferior

Left: 2 - superior, inferior

Fissures

Horizontal fissure: separates inferior & middle lobe (only right lobe)
oblique fissure: separates inferior & superior lobe (both lobes)

Structures at hilum (root)

•        Main bronchi & branches

•        Pulmonary artery (deoxygenated) & branches

•        Pulmonary veins (oxygenated)

•        Bronchial arteries (oxygenated, from aorta)

•        Bronchial veins (deoxygenated, to SVC)

•        Sympathetic & parasympathetic nerves

•        Lymph nodes & channels

Mediastinum

central compartment of the thorax – medial to both lungs

Superior mediastinum

• Thymus

• Trachea

• esophagus

Inferior mediastinum

Anterior: Thymus
Middle: Heart, pericardium, azygos vein
Posterior: esophagus, hemiazygos vein, descending aorta