The pulmonary pleurae (''sing.'' pleura) are the two opposing layers of
serous membrane overlying the
lung
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of ...
s and the inside of the surrounding
chest wall
The thoracic wall or chest wall is the boundary of the thoracic cavity.
Structure
The bony skeletal part of the thoracic wall is the rib cage, and the rest is made up of muscle, skin, and fasciae.
The chest wall has 10 layers, namely (from sup ...
s.
The inner pleura, called the visceral pleura, covers the surface of each lung and dips between the
lobes of the lung as ''fissures'', and is formed by the
invagination of
lung buds into each
thoracic sac during
embryonic development
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...
. The outer layer, called the parietal pleura, lines the inner surfaces of the
thoracic cavity on each side of the
mediastinum
The mediastinum (from ) is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is an undelineated region that contains a group of structures within the thorax, namely the heart and its vessels, the esopha ...
, and can be subdivided into ''mediastinal'' (covering the side surfaces of the
fibrous pericardium,
oesophagus
The esophagus ( American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to ...
and
thoracic aorta), ''diaphragmatic'' (covering the upper surface of the
diaphragm
Diaphragm may refer to:
Anatomy
* Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen
* Pelvic diaphragm or pelvic floor, a pelvic structure
* Urogenital diaphragm or triangular ligament, a pelvic structure
Other
* Diap ...
), ''costal'' (covering the inside of
rib cage) and cervical (covering the underside of the
suprapleural membrane) pleurae. The visceral and the mediastinal parietal pleurae are connected at the
root of the lung ("hilum") through a smooth fold known as ''pleural reflections'', and a
bell sleeve
A bell sleeve can be either long or short and is usually set smoothly into the armscye (no pleating or shirring) and flares toward the bottom. Bell sleeves end anywhere from the elbow to the wrist. Flared sleeves ending at the upper bicep are s ...
-like extension of visceral pleura hanging under to the hilum is known as the
pulmonary ligament.
Between two pleurae is a
potential space called the
pleural cavity (also pleural space), which is normally collapsed and filled with only a tiny amount of
serous fluid (''pleural fluid'')
secreted by the pleurae, and is clinically considered
vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...
ous under healthy conditions. The two lungs bounded by parietal pleura, almost fill the
thoracic cavity.
Anatomy
Each pleura comprises a superficial
serosa made of a simple
monolayer of flat (squamous) or cuboidal
mesothelial cells with
microvilli
Microvilli (singular: microvillus) are microscopic cellular membrane protrusions that increase the surface area for diffusion and minimize any increase in volume, and are involved in a wide variety of functions, including absorption, secretion, ...
up to long. The mesothelium is without
basement membrane
The basement membrane is a thin, pliable sheet-like type of extracellular matrix that provides cell and tissue support and acts as a platform for complex signalling. The basement membrane sits between epithelial tissues including mesothelium an ...
, and supported by a well-vascularized underlying
loose connective tissue containing two poorly defined layers of
elastin
Elastin is a protein that in humans is encoded by the ''ELN'' gene. Elastin is a key component of the extracellular matrix in gnathostomes (jawed vertebrates). It is highly elastic and present in connective tissue allowing many tissues in the bo ...
-rich laminae. The costal parietal pleurae also have
adipocyte
Adipocytes, also known as lipocytes and fat cells, are the cells that primarily compose adipose tissue, specialized in storing energy as fat. Adipocytes are derived from mesenchymal stem cells which give rise to adipocytes through adipogenesis. I ...
s in the
subserosa
The subserosa or tela subserosa, is a thin layer of tissue in the walls of various organs. It is a layer of connective tissue (usually of the areolar type) between the muscular layer (muscularis externa) and the serosa ( serous membrane).
The ...
, which present as ''subpleural/extrapleural fats'' and are
histologically considered belonging to the
endothoracic fascia that separates the subserosa from the inner
periosteum of the
rib
In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ches ...
s. Both pleurae are quite firmly attached to their underlying structures, and are usually covered by surface
glycocalyces that limit fluid loss and reduce friction.
The enclosed space between the parietal and visceral pleurae, known as the
pleural space, is normally filled only by a tiny amount (less than ) of
serous fluid secreted from the apical region of the parietal pleura. The combination of
surface tension
Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) t ...
,
oncotic pressure, and the
fluid pressure drop caused by the inward
elastic recoil of the
lung parenchyma and the rigidity of the
chest wall
The thoracic wall or chest wall is the boundary of the thoracic cavity.
Structure
The bony skeletal part of the thoracic wall is the rib cage, and the rest is made up of muscle, skin, and fasciae.
The chest wall has 10 layers, namely (from sup ...
, results in a normally negative pressure of -5 cm (approximately ) within the pleural space, causing it to mostly stay collapsed as a
potential space that acts as a functionally
vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...
ous
interface between the parietal and visceral pleurae. Contracting the
respiratory muscles expands the
chest cavity
The thoracic cavity (or chest cavity) is the chamber of the body of vertebrates that is protected by the thoracic wall (rib cage and associated skin, muscle, and fascia). The central compartment of the thoracic cavity is the mediastinum. There ...
, causing the attached parietal pleura to also expand outwards. If the pleural functional vacuum stays intact, the pleural space will remain as collapsed as possible and cause the visceral pleura to be pulled along outwards, which in turn draws the underlying lung also into expansion. This transmits the pressure negativity into the
alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit.
Uses in anatomy and zoology
* Pulmonary alveolus, an air sac in the lungs
** Alveolar cell or pneumocyte
** Alveolar duct
** Alveolar macrophage
* M ...
and
bronchioli, thus facilitating
inhalation
Inhalation (or Inspiration) happens when air or other gases enter the lungs.
Inhalation of air
Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...
.
Visceral pleura
The visceral pleura (from la, viscera, lit=organ) covers the
lung
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of ...
surfaces and the
hilar structures and extends
caudally from the hilum as a
mesentery
The mesentery is an organ that attaches the intestines to the posterior abdominal wall in humans and is formed by the double fold of peritoneum. It helps in storing fat and allowing blood vessels, lymphatics, and nerves to supply the intesti ...
-like band called the
pulmonary ligament. Each lung is divided into
lobes by the infoldings of the pleura as fissures. The fissures are double folds of pleura that section the lungs and help in their expansion,
allowing the lung to
ventilate more effectively even if parts of it (usually the basal
segments) fail to expand properly due to
congestion or
consolidation.The function of the visceral pleura is to produce and reabsorb fluid. It is an area that is insensitive to pain due to its association with the lung and innervation by visceral sensory neurons.
Visceral pleura also forms interlobular septa (that separates secondary pulmonary lobules). Interlobular septa contains connective tissue, pulmonary veins, and lymphatics.
Parietal pleura
The parietal pleura (from la, paries, lit=wall) lines the inside of the
thoracic cavity which is set apart from the
thoracic wall by the endothoracic fascia. The Parietal includes the inner surface of the
rib cage and the upper surface of the
diaphragm
Diaphragm may refer to:
Anatomy
* Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen
* Pelvic diaphragm or pelvic floor, a pelvic structure
* Urogenital diaphragm or triangular ligament, a pelvic structure
Other
* Diap ...
, as well as the side surfaces of the
mediastinum
The mediastinum (from ) is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is an undelineated region that contains a group of structures within the thorax, namely the heart and its vessels, the esopha ...
, from which it separates the pleural cavity. It joins the visceral pleura at the
pericardial base of the
pulmonary hilum and pulmonary ligament as a smooth but
acutely angled circumferential junction known as the ''hilar reflection''.
The parietal pleura is subdivided according to the surface it covers.
* The ''costal pleura'' is the pleural portion covering the inner surfaces of the
rib cage, and is separated from the
rib
In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ches ...
s/
cartilage
Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck ...
s and
intercostal muscles by the
endothoracic fascia.
** The apical part of the costal pleura, sometimes referred to as the ''cervical pleura'' or ''cupula of pleura'', bulges beyond the
thoracic inlet into the
posterior triangle of the
neck
The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...
, where it is covered by an extension of the endothoracic fascia known as the
suprapleural membrane. This is the most superficial (and thus most vulnerable) part of the pleura and can be
punctured by
subclavian catheterization or a
penetrating neck injury.
* The ''diaphragmatic pleura'' is the portion covering the convex upper surface of the
diaphragm
Diaphragm may refer to:
Anatomy
* Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen
* Pelvic diaphragm or pelvic floor, a pelvic structure
* Urogenital diaphragm or triangular ligament, a pelvic structure
Other
* Diap ...
. Its junction with the costal pleura at the diaphragmatic margin is a sharp gutter known as the ''
costodiaphragmatic recess
The costodiaphragmatic recess, also called the costophrenic recess or phrenicocostal sinus, costodiaphragmatic-recess Retrieved May 2011
Imaging
In anatomy, the costophrenic angles are the places where the diaphragm (''-phrenic'') meets the ribs ...
'', which has diagnostic significance on
plain radiography.
* The ''mediastinal pleura'' is the portion covering the lateral surfaces of the
mediastinum
The mediastinum (from ) is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is an undelineated region that contains a group of structures within the thorax, namely the heart and its vessels, the esopha ...
, predominantly the
fibrous pericardium,
thoracic aorta,
superior vena cava/
azygos vein,
esophagus
The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to t ...
and (very rarely) an enlarged
thymus
The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or '' T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders ...
. Its anterosuperior part (especially of the left side) not infrequently can bulge into the
anterior mediastinum
The mediastinum (from ) is the central compartment of the thoracic cavity. Surrounded by loose connective tissue, it is an undelineated region that contains a group of structures within the thorax, namely the heart and its vessels, the esophagu ...
behind the
upper sternal body and even touch its contralateral counterpart in forced
inhalation
Inhalation (or Inspiration) happens when air or other gases enter the lungs.
Inhalation of air
Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...
, but the left and right pleurae ''do not'' communicate unless there is a significant
injury
An injury is any physiological damage to living tissue caused by immediate physical stress. An injury can occur intentionally or unintentionally and may be caused by blunt trauma, penetrating trauma, burning, toxic exposure, asphyxiation, o ...
(
traumatic or
iatrogenic) or
disease
A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...
process (e.g.
malignancy).
Neurovascular supply
As a
rule of thumb, the
blood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...
and
nerve supply of a pleura comes from the structures under it. The visceral pleura is supplied by the
capillaries that supply the lung surface (from both the
pulmonary circulation and the
bronchial vessels), and innervated by the
nerve ending
A free nerve ending (FNE) or bare nerve ending, is an unspecialized, afferent nerve fiber sending its signal to a sensory neuron. ''Afferent'' in this case means bringing information from the body's periphery toward the brain. They function as cut ...
s from the
pulmonary plexus.
The parietal pleura is supplied by blood from the cavity wall under it, which can come from the
aorta (
intercostal,
superior phrenic and
inferior phrenic arteries), the
internal thoracic arteries (
pericardiacophrenic
The pericardiacophrenic artery is a long slender branch of the internal thoracic artery. It anastomoses with the musculophrenic and superior phrenic arteries.
Location
The pericardiacophrenic artery branches from the internal thoracic artery. I ...
,
anterior intercostal and
musculophrenic branches), or their
anastomoses
An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be norm ...
. Similarly, its nerve supply is from its underlying structures — the costal pleura is innervated by the
intercostal nerves; the diaphragmatic pleura is innervated by the
phrenic nerve
The phrenic nerve is a mixed motor/sensory nerve which originates from the C3-C5 spinal nerves in the neck. The nerve is important for breathing because it provides exclusive motor control of the diaphragm, the primary muscle of respiration. ...
in its central portion around the
central tendon, and by the intercostal nerves in its periphery near the
costal margin; the mediastinal pleura is innervated by branches of the phrenic nerve over the
fibrous pericardium.
Development
The visceral and parietal pleurae, like all
mesothelia
The mesothelium is a membrane composed of simple squamous epithelial cells of mesodermal origin, which forms the lining of several body cavities: the pleura (pleural cavity around the lungs), peritoneum ( abdominopelvic cavity including the mesen ...
, both derive from the
lateral plate mesoderms. During the third week of
embryogenesis
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
, each lateral mesoderm splits into two layers. The dorsal layer joins overlying
somites and
ectoderm
The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from t ...
to form the
somatopleure; and the ventral layer joins the underlying
endoderm
Endoderm is the innermost of the three primary germ layers in the very early embryo. The other two layers are the ectoderm (outside layer) and mesoderm (middle layer). Cells migrating inward along the archenteron form the inner layer of the gast ...
to form the
splanchnopleure. The dehiscence of these two layers creates a fluid-filled cavity on each side, and with the ventral infolding and the subsequent midline fusion of the
trilaminar disc
A trilaminar embryonic disc (or trilaminary blastoderm, or trilaminar germ disk) is an early stage in the development of triploblastic organisms, which include humans and many other animals. It is the next stage from the earlier bilaminar embryoni ...
, forms a pair of
intraembryonic coeloms anterolaterally around the
gut tube during the fourth week, with the splanchnopleure on the inner cavity wall and the somatopleure on the outer cavity wall.
The
cranial
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
end of the intraembryonic coeloms fuse early to form a single cavity, which rotates anteriorly and apparently ''descends'' inverted in front of the thorax, and is later encroached by the growing
primordial heart as the
pericardial cavity. The
caudal portions of the coeloms fuse later below the
umbilical vein to become the larger
peritoneal cavity, separated from the pericardial cavity by the
transverse septum. The two cavities communicate via a slim pair of remnant coeloms adjacent to the upper
foregut called the ''pericardioperitoneal canal''. During the fifth week, the developing
lung bud
The lung bud sometimes referred to as the respiratory bud forms from the respiratory diverticulum, an embryological endodermal structure that develops into the respiratory tract organs such as the larynx, trachea, bronchi and lungs. It arises from ...
s begin to invaginate into these canals, creating a pair of enlarging cavities that encroach into the surrounding somites and further displace the transverse septum caudally — namely the pleural cavities. The mesothelia pushed out by the developing lungs arise from the splanchnopleure, and become the visceral pleurae; while the other mesothelial surfaces of the pleural cavities arise from the somatopleure, and become the parietal pleurae.
Function
As a
serous membrane, the pleura secretes a
serous fluid (pleural fluid) that contains various lubricating
macromolecules such as
sialomucin,
hyaluronan
Hyaluronic acid (; abbreviated HA; conjugate base hyaluronate), also called hyaluronan, is an anionic, nonsulfated glycosaminoglycan distributed widely throughout connective, epithelial, and neural tissues. It is unique among glycosaminoglyca ...
and
phospholipid
Phospholipids, are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue (usually a glycerol molecule). Marine phospholipids typ ...
s. These, coupled with the smoothness of the glycocalyces and
hydrodynamic lubrication of the pleural fluid itself, reduces the
frictional coefficient when the opposing pleural surfaces have to
slide against each other during
ventilation, thus help improving the
pulmonary compliance
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of th ...
.
The
adhesive
Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that binds them together and resists their separation.
The use of adhesives offers certain advant ...
property of the pleural fluid to various cellular surfaces, coupled with its
oncotic pressure and the negative
fluid pressure, also holds the two opposing pleurae in close sliding contact and keeps the
pleural space collapsed, maximizing the
total lung capacity
Lung volumes and lung capacities refer to the volume of air in the lungs at different phases of the respiratory cycle.
The average total lung capacity of an adult human male is about 6 litres of air.
Tidal breathing is normal, resting breath ...
while maintaining a functional
vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...
. When
inhalation
Inhalation (or Inspiration) happens when air or other gases enter the lungs.
Inhalation of air
Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...
occurs, the contraction of the
diaphragm
Diaphragm may refer to:
Anatomy
* Thoracic diaphragm, a thin sheet of muscle between the thorax and the abdomen
* Pelvic diaphragm or pelvic floor, a pelvic structure
* Urogenital diaphragm or triangular ligament, a pelvic structure
Other
* Diap ...
and the
external intercostal muscles (along with the
bucket/
pump handle movements of the
rib
In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ches ...
s and
sternum) increases the
volume
Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). ...
of the pleural cavity, further increasing the negative
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...
within the pleural space. As long as the functional
vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...
remains intact, the lung will be drawn to expand along with the chest wall, relaying a negative
airway
The respiratory tract is the subdivision of the respiratory system involved with the process of respiration in mammals. The respiratory tract is lined with respiratory epithelium as respiratory mucosa.
Air is breathed in through the nose t ...
pressure that causes an
airflow into the lung, resulting in
inhalation
Inhalation (or Inspiration) happens when air or other gases enter the lungs.
Inhalation of air
Inhalation of air, as part of the cycle of breathing, is a vital process for all human life. The process is autonomic (though there are exceptions ...
.
Exhalation is however usually passive, caused by
elastic recoil of the
alveolar walls and relaxation of
respiratory muscles. In forced exhalation, the pleural fluid provides some hydrostatic cushioning for the lungs against the rapid change of pressure within the pleural cavity.
Clinical significance
Pleuritis or
pleurisy is a
inflammatory condition of pleurae. Due to the
somatic innervation of the parietal pleura, pleural irritations, especially if from acute causes, often produce a sharp
chest pain that is worse by breathing, known as ''pleuritic pain''.
Pleural disease or
lymphatic blockages can lead to a build-up of serous fluid within the pleural space, known as a
pleural effusion. Pleural effusion obliterates the pleural vacuum and can collapse the lung (due to
hydrostatic pressure
Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body " fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an i ...
), impairing ventilation and leading to
type 2 respiratory failure. The condition can be treated by mechanically removing the fluid via
thoracocentesis (also known as a "pleural tap") with a
pigtail catheter, a
chest tube
A chest tube (also chest drain, thoracic catheter, tube thoracostomy or intercostal drain) is a surgical drain that is inserted through the chest wall and into the pleural space or the mediastinum in order to remove clinically undesired substance ...
, or a
thoracoscopic procedure. Infected pleural effusion can lead to
pleural empyema, which can create significant
adhesion
Adhesion is the tendency of dissimilar particles or surfaces to cling to one another ( cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another).
The forces that cause adhesion and cohesion can ...
and
fibrosis that require division and
decortication. For recurrent pleural effusions,
pleurodesis can be performed to establish permanent obliteration of the pleural space.
See also
*
Pleural friction rub
References
Sources
*
External links
*
* - "X-ray, chest, posteroanterior view"
* - "Transverse section through lung"
*
Diagram at kent.edu
{{Authority control
Pleura