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Notes on the Lungs

The Lungs

The lungs are elastic and recoil to approx. 1/3 of their sizewhen the thoracic cavity is opened.

Sectioning of root of lung before branching of the main

bronchus:

o Superior-most on left: Pulmonary Artery

o Superior-most on right: May be the superior lobar

bronchus

o Anterior-most: Superior Pulmonary vein

o Inferior-most: Inferior Pulmonary Vein

o Posterior wall & approx. at middle: Primary bronchus

Medial to hilum, root enclosed within area of continuity

between visceral and parietal layers: Pleural

sleeve/Mesopneumonium

Right lung: 3 lobes, larger & heavier that left butshorter &

wider because dome of diaphragm is higher (liver)

Left Lung: 2 lobes, greatly infringed upon by heart 2/3 of

heart is to the left of the mid-line

Percussion of lungs helps to establish whether underlying

tissues are air filled [resonant sound], fluid filled [dull sound]

or solid [flat sound]

Trachea & Bronchi

Walls of airways are supported by C-shaped rings of hyaline

cartilage.

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Sublaryngeal airway constitutes: Tracheobronchial tree

Bifurcation of trachea occurs @ Transverse thoracic plane(SAT4)

into main (primary) bronchus (Note: Carina)

Right main bronchus: wider, shorter & runs more vertically

than left

Left main bronchus: passes inferolaterally , inferior to arch of

aorta & anterior to esophagus & thoracic aorta

Each main bronchus divides into lobar bronchi: (1 per lobe)

o 3 on right

o 2 on left (Note: Lingular Bronchus)

Lobar bronchi divide into segmental bronchi:

o Right Upper Lobe: Usually 3 segments

o Middle Lobe: Usually 2 segments

o Right Lower Lobe: Usually 5 segments

o Left Upper Lobe: Usually 5 segments

o Left Lower Lobe: Usually 4 segments

Bronchopulmonary segments:

o Pyrimidal segments of the lung, with apices facing lung

root & bases @ pleural surface

o Largest subdivision of lobe separated from adjacent

segments by connective tissue septa

o Named according to segmental bronchi supplying them

Beyond segmental bronchi are 20-25 generations, ending in

terminal bronchioles

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Sequence of Tracheo-broncho-alveolar tree:

o Trachea

o Main (Primary) Bronchuso Lobar Bronchi

o Segmental Bronchi

o Large Intrasegmental Bronchi

o Small Intrasegmental Bronchi

o Bronchiole, consisting of:

Lobule, consisting of:

Terminal bronchiole

Acinus*, consisting of:

o Respiratory bronchiole

o Alveolar Sacs & Alveoli

*Acinus: part of lung supplied by terminal bronchiole

Vasculature of the Lungs & Pleurae

Each lung: Large pulmonary artery & 2 pulmonary veins

Right & Left pulmonary arteries arise from pulmonary trunk at

level of sternal angle

Arterial branch goes to each lobe and bronchopulmonary

segment of the lung, usually on anterior aspect of

corresponding bronchus.

Pulmonary veins run independantly of arteries and bronchi

course between different segments

Veins from visceral pleurae drain into pulmonary veins

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Bronchial arteries supply blood for nutrition of structures

making up root of lungs, supporting tissues of lungs, and

visceral pleurae:

o

2 left bronchial arteries: usually arise directly from aortao 1 right bronchial artery: may arise directly/indirectly

from aorta either via Intercostal arteries or common

trunk with left bronchial arteries

Pleurae are supplied by anterior & posterior intercostal

arteries

Majority of blood drained by pulmonary veins, except most

proximal part which is drained by bronchial veins (specifically

that part returning from the visceral pleura)

o Right bronchial vein drains into azygos vein

o Left bronchial vein drains into accessory hemiazygos or

superior intercostal vein

Nerves of the Lungs & Pleurae

Parasympathetic fibres from the Vagus Nerve (CNX):

Are motor to the smooth muscle of the bronchial tree

Inhibitory to the pulmonary vessels

Secretory to the glands of the bronchial tree

Parasympathetic ganglion cells are in the pulmonary plexi and

along the branches of the bronchial trees

Pulmonary plexi also contain sympathetic fibres from the

sympathetic trunks; sympathetic ganglion cells are in the

paravertebral sympathetic ganglia of the sympathetic trunks

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The sympathetic fibres are:

o Inhibitory to the bronchial muscle

o Motor to the pulmonary vessels

o Inhibitory to the alveolar glands of the bronchial tree T2 secretory epithelial cells of the alveoli

Nerves of the parietal pleurae derive from the intercostal and

phrenic nerves costal pleura and peripheral part of the

diaphragmatic pleura are supplied by the intercostal nerves,

mediating touch/pain central part of diaphragmatic pleura

and the mediastinal pleura supplied by phrenic nerves