Download The pleura

The pleura
The pleura
General arrangement of thoracic cavity
Development of the lung
Parts of parietal pleura
Pulmonary ligament
Surface projection of the pleura
Pleural recesses
Nerve supply
Blood supply
Pneumothorax
Pleural effusion
General arrangement of the
thoracic cavity
In a cross section
through the chest you
will find that the
thoracic cavity
contains principally
two pleural cavities
with, between them,
the mediastinum
General arrangement of the
thoracic cavity
the aorta lies in
contact with the
vertebral bodies
slightly to the left of
the midline producing
slight flattening of the
left side of the
thoracic vertebral
bodies of the middle
of the series
General arrangement of the
thoracic cavity
The esophagus lies
anterior to the aorta
General arrangement of the
thoracic cavity
the trachea is not
shown since the
section passes at a
level below the level
of the sternal angle
where the trachea
bifurcates
General arrangement of the
thoracic cavity
 The posterior border of
the lung is rounded
because it is shaped by
the ribs. The anterior
border is sharp because it
fits in between the heart
and the chest.
 From the front, therefore,
part of the heart is in
contact with the chest
wall but part of it is
overlaid by lung tissue
General arrangement of the
thoracic cavity
The mediastinum
forms a complete
septum across the
chest from front to
back so that change
in pressure in one
pleural cavity may
deflect the
mediastinum to one
side
The clinician can
recognize mediastinal
deviation by feeling
the position of the
trachea at the root of
the neck where the
trachea can normally
be felt most anteriorly
in the midline at the
jugular notch
Hilum and root of the lung
 The hilum of the lung is
the site where structures
like bronchi, pulmonary
vessels, and others enter
or leave the lung.
 These structures together
contribute what is called
the root of the lung,
which connects the lung
to the mediastinum
Pleural cavity
 The pleural cavity on
each side is almost
completely filled by a
lung, leaving a the cavity
as a potential space
containing a thin film of
fluid (pleural fluid).
 The pleura is a thin
membrane of fibrous
tissue surfaced by a
single layer of flat cells to
make it slippery
Layers of pleura
 The pleura is in two
layers, the visceral
pleura which covers the
outer surface of the lung
and is continuous at the
hilum with the parietal
pleura that lines the
thoracic cavity on each
side of the mediastinum
Visceral pleura
Unlike the parietal
pleura, the visceral
pleura dips into the
lung fissures;
therefore, in the
fissures, the visceral
pleura of adjacent
lobes lie in contact
with each other.
Development of the lung
each lung develops
from a lung bud from
what is called the
laryngotracheal tube
Development of the lung
Each lung bud
invaginates the wall
of the celomic cavity
Development of the lung
Each lung then grows
to fill the greater part
of the cavity so that
the original celomic
cavity is reduced to a
slit-like space called
the pleural cavity
Development of the lung
 The lung will be covered
with splanchnic
mesoderm that forms the
visceral pleura, while the
thoracic wall will be lined
by parietal pleura. This
also demonstrates how
the two layers of pleura
are continuous with each
other at the root of the
lung
Parts of parietal pleura
The parietal pleura,
though a continuous
sheet, is given
different names
according to the parts
it covers. It is
therefore divided into
costal, mediastinal,
diaphragmatic, and
cervical pleura
Costal pleura
 The costal pleura covers
the internal surfaces of
the sternum, costal
cartilages, ribs,
intercostal muscles and
the sides of thoracic
vertebrae, separated
from all these structures
by a thin layer of loose
connective tissue called
the endothoracic fascia
Mediastinal pleura
The mediastinal
pleura covers the
mediastinum, it is
continuous anteriorly
and posteriorly with
the costal pleura
Diaphragmatic pleura
Inferiorly, the
mediastinal pleura is
continues with the
diaphragmatic pleura
that covers the
superior surface of
the diaphragm while
superiorly it is
continuous with the
cervical pleura
Pulmonary ligament
At the root of the
lung, the mediastinal
pleura passes laterally
forming a sleeve that
encloses the
structures at the lung
root
Pulmonary ligament
Inferior to the lung
root the sleeve of the
mediastinal pleura is
too big for the
contained structures
forming a double
layer called the
pulmonary ligament
Pulmonary ligament
If you pinch together
the cuffs of a jacket
below your wrist, you
will understand how
the lower part of the
sleeve at the hilum
forms a double layer
i.e. the pulmonary
ligament
Pulmonary ligament
 The pulmonary ligament
is an ill-chosen name (a
misnomer), it has nothing
to do with the lung since
it is pleura; in addition,
the pulmonary ligament
is not a ligament in the
correct sense of the
meaning, it is a double
fold of pleura that hangs
down below the lung root
as an empty fold
Function of the pulmonary
ligament
The function of the
pulmonary ligament is
to provide a dead
space into which the
lung root descends
with descent of the
diaphragm.
Function of the pulmonary
ligament
 More important is that
pulmonary veins
(contained in the lung
root) can expand during
periods of increased
venous return from the
lungs as in exercise
(remember that the
pulmonary veins carry
oxygenated blood from
the lungs to the heart)
Function of the pulmonary
ligament
It is interesting to
note that the two
pulmonary veins at
each root lie at the
lower part of the root
just above the
pulmonary ligament
At the lung hilum the
uppermost structure
is the pulmonary
artery (artery above)
while the main
bronchus is situated
more posteriorly
(bronchus behind). In
front and below are
the pulmonary veins
 You will notice that in
many regions of the
body, large veins always
have a dead space
nearby to allow for their
dilation during times of
increased venous return.
 Veins can dilate since
they consist of thin wall
unlike the arteries
The femoral vein is related medially to the femoral canal, a potential space
Cervical pleura
The cervical pleura or
the cupola of the
pleura extends
through the superior
thoracic aperture into
the root of the neck.
Cervical pleura
Its summit is 2-4 cm
superior to the medial
1/3rd of the clavicle
Cervical pleura
The cervical pleura
does not extend
superior to the neck
of the first rib
because the first rib
slopes inferiorly.
Cervical pleura
Extension of the lung
and pleura into the
root of the neck make
them liable to be
injured in wounds of
the neck
Surface projection of the
pleura
Think of even
numbers.
The cervical pleura
extends into the neck
2-4cm above the
medial third of the
clavicle
Surface projection of the
pleura
From this point, the
pleura passes behind
the sternoclavicular
joint reaching the
midline at the level of
the 2nd costal
cartilage.
Surface projection of the
pleura
From here, the two
pleural cavities are in
contact as far as the
4th cartilage, here the
right pleura continues
vertically down to the
level of the 6th costal
cartilage
Surface projection of the
pleura
Here the right pleura
continues vertically
down to the level of
the 6th costal cartilage
Surface projection of the
pleura
The left pleura arches
laterally at the level
of the 4th costal
cartilage and
descends lateral to
the border of the
sternum down to the
level of the 6th costal
cartilage
Surface projection of the
pleura
At the level of the 6th
costal cartilage the
pleura on both sides
pass around the chest
wall crossing the 8th
rib at the
mid-clavicular line
Surface projection of the
pleura
The pleura on both
sides pass around the
chest wall crossing
the 10th rib at the
mid-axillary line
Surface projection of the
pleura
The pleura on both
sides pass around the
chest wall crossing
the 12th rib at the
back
Pleural reflections
 The previously-mentioned
lines are called lines of
pleural reflection.
 The sternal pleural
reflection is where the
costal pleura is
continuous with the
mediastinal pleura
posterior to the sternum.
Pleural reflections
The costal pleural
reflection is where
the costal pleura is
continuous with the
diaphragmatic pleura
near the costal
margin
Pleural reflections
The vertebral
reflection lies
posteriorly along the
lateral side of the
bodies of thoracic
vertebrae.
Pleural reflections
The
mediastino-diaphragmatic
reflection connects the
inferior ends of the sternal
and vertebral reflections
The lung markings
correspond to those
of the pleura above
but are two ribs
higher in the lower
part of the thorax.
Thus the lung reaches
the level of the 6th
costal cartilage or rib
in the mid-clavicular
line, 8th rib in the
mid-axillary line
The lung reaches the
level of the 10th rib
posteriorly
Pleural recesses
During full inspiration,
the lung expands and
fill the pleural cavity;
but during quiet
inspiration there are
three sites where the
lung does not fully
occupy the pleural
cavities.
Pleural recesses
 At these sites the two
layers of parietal pleura
are in contact with each
other at their inner
surfaces. The sites where
parietal pleura comes into
contact with parietal
pleura are called pleural
recesses
Pleural recesses
The pleural recesses
are only occupied by
lung tissue during full
inspiration, they are
the right and left
costo-diaphragmatic
recesses and the
costo-mediastinal
recess
Costodiaphragmatic recess
Is located at the
inferior margin of the
pleura
Costodiaphragmatic recess
Radiologists call this
region the
costophrenic angle.
Costodiaphragmatic recess
Excess fluid in the
pleural cavity will
cause an opacity
which obliterates the
angle
Costo-mediatinal recess
 Lies along the anterior
margin of the pleura
where the costal angle
and mediastinal parts of
the left pleura come into
contact at the cardiac
notch in the anterior
border of the left lung
where it overlies the
heart.
Costo-mediatinal recess
Lies at the anterior
ends of the 4th and
5th intercostal spaces
and during full
inspiration it becomes
occupied by the
lingula of the left lung
4
5
The pleura descends
inferior to the costal
margin in three
regions
1- the right
infrasternal angle
2 & 3:The right and
left costovertebral
angles.
 These regions should be
remembered by the
surgeon when making
incisions through the
anterior abdominal wall
so that the incision
should not enter the
pleural sac since this
results in pneumothorax.
 This is especially
important for the costovertebral angles Which
are located behind the
upper pole of the kidney
and are liable to be
opened while incising for
nephrectomy (removal of
the kidney)
Nerve supply
The visceral pleura
should be regarded
as part of the lung,
the parietal pleura as
part of the chest wall.
Nerve supply
 The nerve supply of the
visceral pleura as in the
lung is autonomic
through nerves that
accompany the bronchial
arteries, these are
vasomotor.
 The visceral pleura is
thus insensitive to
ordinary stimuli as pain
and touch.
Nerve supply
The parietal pleura as
part of the chest wall
is supplied by somatic
nerves namely
intercostal and
phrenic nerves.
Nerve supply
The collateral
branches of
intercostal nerves
segmentally supply
the costal pleura and
the peripheral part of
the diaphragmatic
pleura
Nerve supply
The central part of
the diaphragmatic
pleura and the
mediastinal pleura are
supplied by the
phrenic nerves.
The parietal pleura is
thus sensitive to pain.
Refered pleural pain
 Irritation of the costal
and peripheral part of the
diaphragmatic pleura by
disease causes local pain
and referred pain i.e.
pain referred or seems to
be arising frown regions
supplied by the same
intercostal nerves that
supply the pleura. Thus
pain is referred to the
chest and abdominal
walls, both are supplied
by intercostal nerves
Refered pleural pain
 Irritation of the
mediastinal or central
part of the diaphragmatic
pleura supplied by the
phrenic nerve is referred
to the tip of the shoulder
where the dermatome
there is that of C4 since
the root value of the
phrenic nerve is C3, 4,
and 5 mainly C4
Irritation of the
parietal peritoneum
below the diaphragm
(which is also
supplied by the
phrenic nerve) is also
referred to the tip of
the shoulder
therefore pain is
referred to the
dermatome whose
root value is the same
as that of the phrenic
nerve.
A root value of a
nerve is the spinal
cord segment from
which it is derived
Blood supply
The visceral pleura
derives its arterial
supply froth bronchial
arteries that supply
lung tissue with
oxygenated blood
Blood supply
The bronchial arteries
are branches of the
thoracic aorta.
Blood supply
The blood supply of
the parietal pleura is
derived from that
supplying the chest
wall namely internal
thoracic, intercostal,
and musculophrenic
arteries
Intercostal vessels
The pleural cavity is a
potential space
containing a thin film
of pleural fluid
The pressure inside
the cavity is slightly
below atmospheric
The pressure inside
the lung is more or
less atmospheric.
Pneumothorax
 If the chest wall is
penetrated following for
example a stab wound or
the visceral pleura is
punctured usually as a
result of rupture of bullae
on the surface of the
lung, air enters the
pleural cavity so that its
pressure becoming the
same as that inside the
lung; since the lungs are
more elastic, the lungs
tend to collapse
Tension pneumothorax
Sometimes air enters
the pleural cavity
during inspiration
Tension pneumothorax
But air cannot leave
during expiration
causing an increased
accumulation of air
(positive pressure
pneumothorax).
Tension pneumothorax
 This is dangerous since
air accumulation will not
only compress the
ipsilateral lung but it will
push the mediastinum to
the other side
compressing the opposite
lung and killing the
patient
Pleural effusion (hydrothorax)
The presence of
excess fluid in the
pleural cavity
The fluid tends to
gravitate towards the
costomediastinal
recesses, thus, it
obliterates the
costophrenic angle.
Pleural effusion (hydrothorax)
Accumulation of more
fluid, like in
pneumothorax, tends
to collapse the lung
and displace the
mediastinum to the
other side