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Phrenic Nerve
It arise from the neck from the anterior rami of the 3rd; 4th and 5th cervical nerves.
The right phrenic nerve:
It descends in the thorax along the right side of the right brachiocephalic vein and the
SVC. It passes in front of the root of the right lung and runs along the right side of the
pericardium, which separates the nerve from the right atrium.
Then, it descends on the right side of the IVC to the diaphragm.
Its terminal branches pass through the caval opening in the diaphragm to supply the
central part of the peritoneum on its underaspect.
Left phrenic nerve:
It descends in the thorax along the left side of the subcalvian artery. It crosses the left
side of the aortic arch and here crosses the left side of the left vagus.
It passes in front of the root of the left lung, then descends over the left surface of the
pericardium which separates the nerve from the left ventricle. The left lung and pleura
are lateral to it.
On reaching the diaphragm, the terminal branches pierce the muscle ( left copula ) and
supply the central part of the peritoneum on the under aspect.
Branches:
The efferent fibers are the sole
nerve to supply to the muscle of
the diaphragm.
The afferent fibers carry
sensation To the central nervous
system from:
1-The peritoneum covering
the central region of the
undersurface of the diaphragm.
2- Diaphragmatic parietal pleura,
covering the central region of
the upper surface of the
diaphragm and mediastinal
parietal pleura.
3- Fibrous and to the parietal
layer of the serous pericardium.
Vagus Nerve
Right Vagus:
It enters the thorax in front of the subclavian artery. It lies posterolateral to the
brachiocephalic artery, then lateral to the trachea and medial to the terminal part of the
azygos vein. It passes behind the root of the right lung and assists in the formation of
the pulmonary plexus.
On leaving the plexus, it passes onto the posterior surface of the esophagus and takes
part in the formation of the esophageal plexus.
It then passes through the esophageal opening of the diaphragm behind the
esophagus to reach the posterior surface of the stomach.
Left Vagus:
It descends in the thorax between the left common carotid and the left subcalvian
arteries. Then crosses the left side of the aortic arch. It is crossed by the left phrenic
nerve. It then turns backward behind the root of the left lung and assists in the
formation of the pulmonary plexus.
On leaving the plexus, it passes onto the anterior surface of the esophagus and
shares in the formation of the esophageal plexus.
It passes through the esophageal opening in the diaphragm in front of the esophagus
to reach the anterior surface of the stomach.
Branches: both vagi supply the lungs and esophagus.
A. The right vagus: it gives off 1- Cardiac branches.
2- The right recurrent laryngeal
nerve which arises from it in the neck and hooks around the
subclavian artery and ascends between the trachea and esophagus.
B. The left vagus: it gives the left recurrent laryngeal nerve which arises from it as it
crosses the arch of aorta. It hooks around the ligamentum
arteriosum & arch of aorta and ascends in the groove between the
trachea and the esophagus on the left side.
It supplies the muscles acting on the left vocal cord ( except the cricothyroid which
is supplied by the external laryngeal branch of the vagus in the neck ).
Pleurae
They with lungs lie on either side of the mediastinum within the chest cavity.
Each pleura has 2 parts:
The visceral layer which completely covers the outer surfaces of the lungs and
extends into the depths of the interlobar fissures ( pulmonary pleura ).
The 2 layers are separated from one another by a slitlike space ( pleural cavity or
space) which is filled with pleural fluid
The parietal layer which lines the thoracic
wall; covers the thoracic surface of the
diaphragm and the lateral aspect of the
mediastinum and extends into the root of
the neck to line the undersurface of the
suprapleural membrane at the thoracic
inlet ( outlet, clinically).
The parietal pleura is divided into:
1- Mediastinal pleura
It covers and forms the lateral boundary of
the mediastinum. At the hilum of the lung, it
is reflected as a cuff around the vessels
and bronchi and here becomes continuous
with the visceral pleura.
It is thus seen that each lung lies free
except at its hilum, where it is attached to
the blood vessels and bronchi that constitute
the lung root.
During full inspiration the lungs expands
and fill the pleural cavities.
However, during quiet inspiration the lungs do not fully occupy the pleural cavities
at 4 sites :
1 & 2 are the right & left costodiaphragmatic recesses which are slitlike spaces
between the costal & diaphragmatic parietal pleurae that are separated
only by a capillary layer of pleural fluid.
During inspiration, the lower margins of the lungs descend into the recesses.
During expiration, the lower margins of the lungs ascends so that the costal &
diaphragmatic pleurae come together again.
3 & 4 are the right & left costomediastinal recesses which are situated along the
anterior margins of the pleura. They are slitlike spaces between the costal &
the mediastinal parietal pleurae, which are separated by a capillary layer of
the pleural fluid.
During
inspiration & expiration, the anterior borders of the lungs slide in&out of recesses.
2- Cervical pleura: It extends up into the neck, lining the undersurface of the
dome
suprapleural membrane ( It is a part of the deep fascia of the neck
which is attached posteriorly to the transverse process of the C7
vertebra and anteriorly to the inner aspect of the 1st rib ). It reaches
a level 1-1.5 inch ( 2.5- 4 cm) above the medial third of the clavicle.
3- Costal pleura: lines the inner surface of the ribs, the costal cartilage; the intercostal
spaces; the sides of the vertebral bodies and the back of the sterum.
3- Diaphragmatic pleura: Covers the thoracic surface of the diaphragm. In quite
respiration, it & costal pleura are in apposition to each other below
the lower border of the lung. In deep inspiration, the margins of the
base of
the lung descends and the costal & diaphragmatic pleurae separate.
The original coelomic cavity is reduced to pleural cavity.
The 2 layers become continuous with one another by means of a Cuff of pleura that
surrounds structures entering and leaving the hila of the lungs.
To allow for movement of the pulmonary vessels and large bronchi during respiration,
the pleural cuff on the lower surface of the root hangs down as a loose fold called
the pulmonary ligament.
Nerve supply of the Pleura
The patietal pleura:
It is sensitive to pain, temperature, touch
and pressure.
The costal pleura is supplied by the
intercostal nerve segmentally.
The mediastinal pleura is supplied by
the phrenic nerve.
The diaphragmatic pleura is supplied is
supplied over the domes ( central ) by
the phrenic nerve and around the
periphery by the lower 6 intercostal
nerves.
The visceral pleura covering the lungs
is sensitive to stretch and receives an
autonomic supply from the pulmonary
plexus.
The costodiaphragmatic recess is 2in. ( 5cm) deep in the scapular line
posteriorly and 3- 3.5 in. ( 8- 9 cm ) in the midaxillary line and 1- 1.5 in.
( 2.5 – 4 cm ) in the midclavicular line.
Lungs
The lungs are situated so that one lies on
each side of the mediastinum. So, they
are separated by the heart and great
vessels and other structures in the
mediastinum.
Each lung is conical covered with
visceral pleura and suspended free in
its own pleural cavity, being attached to
the mediastinum only by its root.
Each lung has a blunt apex which
projects upward into the neck for about
1 in. ( 2.5 cm) above the clavicle.
It has a concave base that sits on the
diaphragm and a convex costal
surface which corresponds to the
concave chest
wall.
Its mediastinal surface is concave and
is molded to the pericardium and other
mediastinal structures. At about the
middle of this surface is the hilum, a
depression in which the bronchi; vessels
and nerves that form the root enter and
leave the lung.
Its anterior border is thin and overlaps
the heart . On the left lung the cardiac
notch is found.
The posterior border is thick and lies
Lobes and Fissures
Right Lung:
It is larger than the left and is divided by
the oblique and horizontal fissures into 3
lobes, the upper ;middle and lower
lobes.
The oblique fissure runs from the
inferior border upward and backward
across the medial and costal surfaces
until it cuts the posterior border about
2.5 in. ( 6.25 cm) below the apex.
The horizontal fissure runs
horizontally across the costal surface
at the level of the 4th costal cartilage
to meet the oblique fissure in the
midaxillary line.
The middle lobe is thus a small
triangular lobe bounded by the
horizontal and oblique fissures.
Left lung
It is divided by a similar oblique
fissure into 2 lobes. The upper and
lower . There are no horizontal
fissure in the left lung.
Root of the lung
It is formed of structures that are
entering or leaving the lung.
It is made up of the bronchi ;
pulmonary artery & veins; lymph
vessels ; bronchial vessels and
nerves.
It is surrounded by a tubular sheath of
pleura which joins the mediastinal
parietal pleura to the visceral pleura
covering the lungs.
Innervation of the lungs
The sympathetic postganglionic fibers
arise from the 2nd to 5th thoracic ganglia
of the sympathetic trunk.
The fibers pass through the pulmonary
plexuses and enter the lung where they
form networks around the bronchi and
blood vessels.
The efferent sympathetic fibers produce
bronchodilatation ( inhibitor to the
bronchial tree ) and vasoconstriction
( motor to pulmonary vessels ) and
inhibitor to the glands of the bronchial
tree.
Afferent sympathetic fibers ( impulses )
are also present ( derived ) in the
bronchial mucous membrane and from
stretch receptors in the alveolar walls
pass to the central nervous system but
their function is unknown.
The parasympathetic preganglionic fibers
arise from the dorsal nucleus of the vagus and
descend to the thorax within the vagus nerve.
The fibers terminate by synapsing with
postganglionic neurons in the pulmonary
plexuses and along the branches of the
bronchial tree. The postganglionic fibers
enter the lung where they form networks
around the bronchi and blood vessels.
The parasympathetic fibers ( efferent fibers of
the vagus ) are motor to the smooth muscles of
the bronchial tree (bronchconstriction ) &
inhibitor to pulmonary vessels ( vasodilatation )
and increase glandular secretion
( secretomotor ).
Afferent fibers of the vagus nerve are sensory
to the respiratory epithelium ( touch & pain )
and to the branches of the bronchial tree
( stretch receptors in the alveolar walls ).
Blood supply of the Lungs
The bronchi; the connective tissue
of the lung and the visceral pleura
receive their blood supply from the
bronchial arteries which are
branches of the descending aorta.
The bronchial veins which
communicate with the pulmonary
veins drain into the azygos and
hemiazygos veins.
The alveoli receive deoxygenated
blood from the terminal branches of
the pulmonary arteries.
The oxygenated blood leaving the
alveolar capillaries drains into the
tributaries of the pulmonary veins
which follow the intersegmental
connective tissue septa to the lung
root.
2 pulmonary veins leave each
lung root to empty into the left
atrium of the heart.
Lymph drainage of the Lungs
The lymph vessels originate in superficial
and deep plexuses. They are not present in
the alveolar walls.
The superficial ( subpleural ) plexus lies
beneath the visceral pleura and drains
over the surface of the lung toward the
hilum, where the lymph vessels enter the
bronchopulmonary nodes.
The deep plexus travels along the bronchi
and pulmonary vessels toward the hilum of
the lung, passing through pulmonary
nodes located within the lung substance;
the lymph then enters the
bronchopulmonary nodes in the hilum of
the lung.
All the lymph from the lung leaves the hilum
and drains into the tracheobronchial
nodes and into the bronchomediastinal
lymph trunks.
Surface anatomy of theLungs
1- Apex of the lung:
it lies 2.5 cm above the medial third of the clavicle.
2- Anterior border:
It begins at the apex of the lung and descends downward and medially behind the
sternoclavicular joint to reach a point on the median plane behind the sternal
angle where the right and left borders meet.
The anterior border of the right lung continues vertically downward in the median
plane till it reaches the xiphisternal junction.
The anterior border of the left lung passes vertically downwards in the median
plane till it reaches the 4th costal cartilage then it turns to the left side to descend
behind the 5th and 6th costal cartilages 0.5 inch lateral to the left border of the
sternum and ends at the xiphisternal junction. This leaves part of the pericardium
uncovered by lung tissue but covered by pleura only and it is called the bare area of
the pericardium.
3- Inferior border of the Lung:
It is similar on the 2 sides
It is represented by a line convex
downward
It begins at the xiphisternal junction
and passes downward and backward to
cross the 6th rib in the midclavicular
line and the 8th rib in the midaxillary
line.
It ends at the level of 10th thoracic
vertebra 2.5 cm lateral to the median
plane.
4- Posterior border of the Lung:
It similar on the 2 sides
It begins 2.5 cm lateral to the 10th
thoracic spine and passes upward
along the vertebral column to meet the
apex of the lung 2.5 cm above the medial
third of the clavicle ( at the level of C7
spine 2.5 cm lateral to the median
plane ).
5- Oblique fissure of the lung:
it is similar on the 2sides
It begins at the posterior wall of the
thorax opposite the 3rd thoracic
spine, 2.5 cm. from the median plane.
Then it passes downward and forward
around the chest wall until it meets
the inferior border of the lung at the
6th chostochondral junction ( 7.5
cm. from the median plane ).
6- Root (hilum ) of the Lung:
Draw a vertical line parallel to the
medial border of the scapula, opposite
the 5th ; 6th and 7th thoracic V.
7- transverse fissure of the right Lung:
It begins on the anterior wall of the
thorax opposite the 4th right costal
cartilage.
Then, it passes transversely backward
along the 4th right rib until it meets
the oblique fissure near the
midaxillary line.
Surface anatomy of the Pleurae
1- Apex of the pleura
It is similar to the apex of the lung.
2- Anterior border of the pleura
- of the right is similar to the right lung
- of the left is similar to the left lung
except that when it reaches the 4th
costal cartilage it turns to the left side
and then descends along the left
border of the sternum until it reaches the
xiphisternal junction.
3- Inferior border of the pleura
it is similar on the 2 sides and is
represented by a line convex downward.
It begins at the xiphisternal junction and
passes downward and backward to cross
the 8th rib in the midclavicular line and
the10thrib in the midaxillary line. It ends at
the level of the 12th thoracic spine 2.5 cm.
lateral to the median plane.
4- Posterior border of the pleura
It is similar on the 2 sides.
It begins at the level of the 12th thoracic
spine and then is similar to that of the lung.