Pulmonary pleurae

The pulmonary pleurae (sing. pleura)[1] are the two pleurae of the invaginated sac surrounding each lung and attaching to the thoracic cavity. The visceral pleura is the delicate serous membrane that covers the surface of each lung (the lung parenchyma) and dips into the fissures between the lobes.[2] The parietal pleura is the outer membrane which is attached to the inner surface of the thoracic cavity. It also separates the pleural cavity from the mediastinum. The parietal pleura is innervated by the intercostal nerves and the phrenic nerve.

Between the membranes is a fluid-filled space called the pleural cavity.[2]

Pulmonary pleurae
A transverse section of the thorax, showing the contents of the middle and the posterior mediastinum. The pleural and pericardial cavities are exaggerated since normally there is no space between the pulmonary pleurae and between the pericardium and heart.
SystemRespiratory system
Nerveintercostal nerves, phrenic nerves
Latinpleurae pulmonarius
Anatomical terminology


2313 The Lung Pleurea
Detail of lung showing the pleurae

The visceral pleura is a delicate serous membrane that closely covers the surfaces of the lungs and dips into the fissures that separate the lobes.

The parietal pleura is the outer membrane that attaches to and lines the inner surface of the thoracic cavity, covers the upper surface of the diaphragm and is reflected over structures within the middle of the thorax. It separates the pleural cavity from the mediastinum.

The parietal pleura is differentiated into regions in line with the location in the thorax. The "cervical pleura" (or "cupula of pleura") is in the region of the cervical vertebrae extending beyond the apex of the lung and into the neck. The "costal pleura" lines the inner surfaces of the ribs and the intercostal muscles and are separated from them by endothoracic fascia. An extension of the endothoracic fascia known as the suprapleural membrane covers the apex of each lung in a thickened layer of connective tissue. The "diaphragmatic pleura" lines the convex surface of the diaphragm. The "mediastinal pleura" attaches to the other organs in the mediastinum and forms the separating lateral wall.

Between the two membranes is a space called the pleural cavity or interpleural space, which contains a lubricating fluid. as it reaches the 4th rib – atria 8th rib – mid clavicular 10th rib – axillary area 12th rib – back side

Nerve supply

The parietal pleura is supplied by the intercostal nerves and the phrenic nerve. The costal pleura is innervated by the intercostal nerves. The diaphragmatic portion of the parietal pleura overlies the diaphragm and is innervated by the phrenic nerve in its central portion and by the intercostal nerves in its peripheral portion. The mediastinal portion of the parietal pleura forms the lateral wall of the mediastinum and is innervated by the phrenic nerve.


The visceral and parietal pleurae both derive from the lateral plate mesoderm which splits into two layers the somatopleuric mesoderm forming the parietal membrane and the splanchnopleuric mesoderm of the visceral membrane.[3]


The contraction of the diaphragm creates a negative pressure within the pleural cavity which forces the lungs to expand resulting in passive exhalation and active inhalation. This breathing process can be made forceful through the contraction of the external intercostal muscles which forces the rib cage to expand and add to the negative pressure in the pleural cavity causing the lungs to fill with air. The fluid in the cavity provides lubrication and cushioning.

Clinical significance

Pleurisy is a condition of inflamed pleurae.

Pleurisy can lead to a build-up of fluid known as pleural effusion in the pleural cavity. Pleural effusion can also occur from other causes.


  1. ^ "pleura Meaning in the Cambridge English Dictionary". dictionary.cambridge.org.
  2. ^ a b Light 2007, p. 1.
  3. ^ Larsen, William J. (2001). Human embryology (3. ed.). Philadelphia, Pa.: Churchill Livingstone. p. 138. ISBN 0-443-06583-7.


External links


Hypereosinophilia is an elevation in an individual's circulating blood eosinophil count above 15.0 x 109/L (i.e. 1,500/μL). This disorder is distinguished from 1) eosinophilia, which is an elevation in this count above normal levels of 5.0 x 109/L (i.e. 500/μl) but below the hypereosinophilia cutoff level and 2) the hypereosinophilic syndrome, which is a sustained elevation in this count above 15.0 x 109/L (i.e. 1,500/μl) that is also associated with evidence of eosinophil-based tissue injury. Informally, blood eosinophil levels are often regarded as mildly elevated at counts of 500–1,500/μL, moderately elevated between 1,500–5,000/μL, and severely elevated when greater than 5,000/μL. Elevations in blood eosinophil counts can be transient, sustained, recurrent, or cyclical.Eosinophil counts in human blood normally range between 100–500 per/μL. Maintenance of these levels results from a balance between production of eosinophils by bone marrow eosinophil precursor cells termed CFU-Eos and the emigration of circulating eosinophils out of the blood through post-capillary venules into tissues. Eosinophils represent a small percentage of peripheral blood leucocytes (usually less than 8%), have a half-life in the circulation of only 8–18 hours, but persist in tissues for at least several weeks.Eosinophils are one form of terminally differentiated granulocytes; they function to neutralize invading microbes, primarily parasites and helminthes but also certain types of fungi and viruses. They also participate in transplant rejection, Graft-versus-host disease, and the killing of tumor cells. In conducting these functions, eosinophils produce and release on demand a range of toxic reactive oxygen species (e.g. hypobromite, hypobromous acid, superoxide, and peroxide) and they also release on demand a preformed armamentarium of cytokines, chemokines, growth factors, lipid mediators (e.g. leukotrienes, prostaglandins, platelet activating factor), and toxic proteins (e.g. metalloproteinases, major basic protein, eosinophil cationic protein, eosinophil peroxidase, and eosinophil-derived neurotoxin). These agents serve to orchestrate robust immune and inflammatory responses that destroy invading microbes, foreign tissue, and malignant cells. When overproduced and over-activated, which occurs in certain cases of hypereosinophilia and to a lesser extent eosinophilia, eosinophils' may misdirect their reactive oxygen species and armamentarium of preformed molecules toward normal tissues. This can result in serious damage to such organs as the lung, heart, kidneys, and brain.


The lungs are the primary organs of the respiratory system in humans and many other animals including a few fish and some snails. In mammals and most other vertebrates, two lungs are located near the backbone on either side of the heart. Their function in the respiratory system is to extract oxygen from the atmosphere and transfer it into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere, in a process of gas exchange. Respiration is driven by different muscular systems in different species. Mammals, reptiles and birds use their different muscles to support and foster breathing. In early tetrapods, air was driven into the lungs by the pharyngeal muscles via buccal pumping, a mechanism still seen in amphibians. In humans, the main muscle of respiration that drives breathing is the diaphragm. The lungs also provide airflow that makes vocal sounds including human speech possible.

Humans have two lungs, a right lung and a left lung. They are situated within the thoracic cavity of the chest. The right lung is bigger than the left, which shares space in the chest with the heart. The lungs together weigh approximately 1.3 kilograms (2.9 lb), and the right is heavier. The lungs are part of the lower respiratory tract that begins at the trachea and branches into the bronchi and bronchioles, and which receive air breathed in via the conducting zone. The conducting zone ends at the terminal bronchioles. These divide into the respiratory bronchioles of the respiratory zone which divide into alveolar ducts that give rise to the microscopic alveoli, where gas exchange takes place. Together, the lungs contain approximately 2,400 kilometres (1,500 mi) of airways and 300 to 500 million alveoli. Each lung is enclosed within a pleural sac which allows the inner and outer walls to slide over each other whilst breathing takes place, without much friction. This sac also divides each lung into sections called lobes. The right lung has three lobes and the left has two. The lobes are further divided into bronchopulmonary segments and lobules. The lungs have a unique blood supply, receiving deoxygenated blood from the heart in the pulmonary circulation for the purposes of receiving oxygen and releasing carbon dioxide, and a separate supply of oxygenated blood to the tissue of the lungs, in the bronchial circulation.

The tissue of the lungs can be affected by a number of diseases, including pneumonia and lung cancer. Chronic obstructive pulmonary disease includes chronic bronchitis and previously termed emphysema, can be related to smoking or exposure to harmful substances such as coal dust, asbestos fibres and crystalline silica dust. Diseases such as bronchitis can also affect the respiratory tract. Medical terms related to the lung often begin with pulmo-, from the Latin pulmonarius (of the lungs) as in pulmonology, or with pneumo- (from Greek πνεύμων "lung") as in pneumonia.

In embryonic development, the lungs begin to develop as an outpouching of the foregut, a tube which goes on to form the upper part of the digestive system. When the lungs are formed the fetus is held in the fluid-filled amniotic sac and so they do not function to breathe. Blood is also diverted from the lungs through the ductus arteriosus. At birth however, air begins to pass through the lungs, and the diversionary duct closes, so that the lungs can begin to respire. The lungs only fully develop in early childhood.

Pleural cavity

The pleural cavity is the thin fluid-filled space between the two pulmonary pleurae (known as visceral and parietal) of each lung. A pleura is a serous membrane which folds back onto itself to form a two-layered membranous pleural sac. The outer pleura (parietal pleura) is attached to the chest wall, but is separated from it by the endothoracic fascia. The inner pleura (visceral pleura) covers the lungs and adjoining structures, including blood vessels, bronchi and nerves. The pleural cavity can be viewed as a potential space because the two pleurae adhere to each other (through the thin film of serous liquid) under all normal conditions. Parietal pleura projects up to 2.5 cm above the junction of the middle and medial third of the clavicle

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