The lungs – organ of gas exchange
Picture: “The major respiratory structures span the nasal cavity to the diaphragm.” By Phil Schatz. License: CC BY 4.0
Where is the lung??
The paired lungs fill the also paired pleural cavities (Cavitas pleural) completely on both sides. The two pleural cavities are located to the right and left of the mediastinum. The extension to the dorsal is up to the thoracic spine, ventral are the two pleural cavities in front of the pericardium. Due to the asymmetrical position of the heart and pericardium, the left pleural cavity, and thus the left lung, are slightly smaller than the right one.
Due to the close contact of the lungs and the heart, the so-called Impressio cardiaca, which in turn leads to an incision on the front of the left lung (Incisura cardiaca). At the caudal end of the incisura cardiaca is the lingula. This is a removal of the upper lobe and exists only on the left lung. The unpaired mediastinum and the two pleural cavities are again located in the thoracic cavity (Cavitas thoracis), which in addition to the abdominal and pelvic cavities (Cavitas abdominalis, Cavitas pelvis) belong to the three large body cavities. The extent of the lung is respiratory dependent, with the lung tip (Apex pulmonalis) always reaches into the upper thoraxaperatur. The lung base (Base pulmonis) is closely connected to the diaphragm.
Shape and structure of the lung
Image: by Phil Schatz License: CC BY 4.0
Basically, a distinction is made between right and left lung. The left lung consists of two cloth (Lobi superior and inferior pulmonis sinistri), which are separated from each other by the fissura obliqua. The right lung, in turn, consists of three lobes (lobi superior, medius and inferior pulmonis dextri). The subdivision is done by the Fissura obliqua and the Fisura horizontalis pulmonis dextri. These fissures extend deep into the lung tissue and are, like the surface of the lung, lined with the visceral pleura.
The further structure is identical in both lungs. One distinguishes between the lung tip (Apex pulmonis), the lung base (Base pulmonis), the lung surfaces and the lung margins. The lung surface is covered by a serous skin, the visceral pleura, and appears pale pink in the healthy to gray. Depending on the position and the relationship to the thorax one differentiates with the lung surfaces (Facies pulmonis) between the facies costalis, mediastinalis, diaphragmatica and the facies interlobar.
In the area of the mediastinal facets, the visceral pleura turns into the parietal pleura. This envelope creates a crease, which in the prepared lung as Pulmonary ligament becomes visible. Between the two pleural leaves is the fluid-filled pleural space (Cavitas pleuralis), which ensures shifts between the two Pleurablättern. In addition, the negative pressure (-5cm H2O) in the pleural space ensures that the lungs remain fixed and unfolded within the pleural cavities. If this pressure were removed, the lung would collapse following its elastic restoring force (see Pneumothorax).
In the middle of the facies mediastinalis is the hilum pulmonis, often referred to as “Hilus”. This represents the point of entry and exit for the bronchi and pathways of the lung. At the transitions of the lung surfaces, the lung margins (Margins pulmonis). The Margo anterior forms the boundary between the costal and mediastinal facies. At the junction of the Facies diaphragmatica to the Facies costalis or mediastinalis is the Margo inferior.
Pulmonary segments (Segmenta bronchopulmonalia)
In addition to the division of the lungs into lobes, this can be further subdivided into individual segments. The classification results directly from the course of the bronchial tree (explanation s.u.). In each segment runs central of the segmental and a segment branch of Pulmonary artery. Both the left and right lungs consist of ten segments. Due to the existing only on the left lung Incisura cardiaca the segment VII is often so small that it is attributed to the segment VIII.
|Right lung||Left lung|
- Segmentum apicale (I)
- Segmentum posterius (II)
- Segmentum anterius (III)
- Segmentum apicoposterius (I + II)
- Segmentum anterius (III)
- Segmentum lingulare superius (IV)
- Segmental lingular inferius (V)
- Segment lateral (IV)
- Segmentum medial (V)
- Segmentum superius (VI)
- Segmentum basal medial (VII)
- Segmentum basal anterius (VIII)
- Segmentum basal lateral (IX)
- Segmentum basal posterius (X)
- Segmentum superius (VI)
- [Segmentum basal medium (VII)]
- Sementum basal anterius (VIII)
- Segmentum basal lateral (IX)
- Segmentum basal posterius (X)
The bronchial tree begins with the splitting of the trachea into the two main bronchi (Bronchi principales) and serves to guide the humidified air all the way to the alveoli. The bronchial tree is composed of an air-conducting and a respiratory component.
The Bronchi principales, Lobar, segmental, subsegmental and the Bronchioli terminales together make up the air-conducting share, whereas the Bronchioli respiratory, of the Ductus alveolaris and the Sacculi alveolar belong to the respiratory component. The structure shows a clear difference in the transition from the high-caliber bronchi to the smaller bronchioles.
The wall of the bronchi is stabilized by cartilage clips, which are missing in the bronchioles. In addition, the multi-row ciliated epithelium transforms into a single-layered prismatic ciliated epithelium. From the bronchioli terminal, i. with the beginning of the respiratory fraction, the goblet cells are missing. Instead, the alveoli can be found on the bronchial tree.
The alveoli represent small Aussackungen, with a diameter of 150 – 500 microns. The alveoli are lined by two types of pneumocytes (Alveolar epithelial cells). Type I pneumocytes make up most of the epithelial cells. They are closely connected via Zonulae occludentes and form together with the basal membrane of the endothelial cells of the surrounding capillaries Blood-air barrier.
The larger type II pneumocytes occur only occasionally (= niche cells) and form the surfactant. Surfactant reduces the surface tension of the alveoli and prevents it from collapsing. The total alveolar gas exchange surface is between 100 and 120 m 2 .
Vascular supply to the lungs
At the hilum The lung is the entry and exit point of the vessels of the lung. Depending on the function one differentiates between the Vasa publica, responsible for the gas exchange, and the Vasa privata for self-care of the lungs. The Vasa publica includes Aa. and Vv. pulmonales.
The Aa. pulmonales come from the pulmonary trunk and conduct the oxygenated blood from the right heart to the lungs. The oxygenated blood passes over the vv. pulmonales, which at the level of the hilum join on each side to two pulmonary veins, into the left atrium. It should be noted that the arteries branch always parallel with the bronchi, whereas the veins are intersegmental, independent of the bronchi.
The arteries for supplying the lungs themselves are called Rami bronchial and come from the thoracic aorta (more rarely also from the internal thoracic artery). Part of the outflow of the bronchial rami occurs via anastomization with the Aa. pulmonary and thus via the Vv. pulmonales. The remainder flows off via the associated Vv. Bronchiales. An exception are the hilumnahen Vv. Bronchiales which right into the V. azygos and left in the V. hemiazygos accessoria flow.
Lymphatic and nerve tracts of the lung
Similar to the vascular supply, both the lymph and the nerve tracts enter or leave the hilum of the lungs. The vegetative nerves form the here plexus pulmonary, which about the N. vagus parasympathetic and over the truncus sympathetic receives sympathetic efferents. The parasympathetic nervous system causes v.a. a bronchoconstriction, whereas the sympathetic provides for bronchodilation.
In addition, the pulmonary plexus contains afferent vegetative fibers, which are predominantly derived from bronchial wall extensor sensors. With a strong strain they inhibit by means of Hering-Breuer reflex the respiratory center. The sensory innervation of the parietal pleura is dependent on its location. The costal portion (Pleura costalis) is over the Nn. intercostales whereas the mediastinal pleura of the Phrenic nerve is innervated. In contrast to the parietal pleura, the pleura visceralis is not sensitively innervated.
The lymphatic drainage of the lungs is divided into a superficial and a deep system. The superficial system receives inflows from the subpleural networks and drains directly into the Nodi lymphoidei bronchopulmonales at Hilum. About the waypoint of the Nodi lymphoid intrapulmonary In the end, this also leads to the deep system. From the Nodi lymphoidei bronchopulmonales the lymph gets further to the Nodi lymphoidei tracheobronchial superiores and inferiores and finally over the Nodi lymphoidei paratracheal in the trunci bronchomediastinal.
In the context of external breathing, there is a rhythmic change in thorax size. The negative pressure in the pleural space forces the lungs to follow these volume changes of the thorax. In inspiration two mechanisms increase the lung volume. First, the expansion of the thorax, by raising the ribs through the Intercostal muscles, and secondly the lowering of the diaphragm (diaphragm). Of the recessus costodiaphragmaticus The pleural cavity serves as a reserve space for the expansion of the lungs in the context of inspiration. It ensures a significant displacement of the lower lung margins to the caudal. Another reserve room is the recessus costomediastinal which is located at the border of the anterior chest wall to the mediastinum. Of the recessus phrenicomediastinalis between the diaphragm and pericardium is not a significant reserve space.
Picture: by Phil Schatz. License: CC BY 4.0
In contrast to inspiration, expiration is predominantly a passive process, which is caused by the elastic restoring forces of the lungs and thorax. Only in forced exhalation are expiratory muscles involved in reducing the size of the thorax more rapidly.
|Inspirationally effective respiratory muscles||Expiratory effective respiratory muscles|
|Mm. intercostalis externi||Mm. intercostal interni|
|Mm. intercartilaginei||M. transversus thoracis|
|Mm. serrate posterior superiores / inferiores|
Examination of the lungs
Examination of the lungs is part of the clinical part of medical studies. Nevertheless, an outlook should already be given here.
Following the anamnesis, the clinical examination is first carried out:
|inspection||Cyanosis? Use of respiratory aid muscles? Determination of the respiratory rate (standard value approx. 12-15 breaths / min)|
|palpation||Thorax stability check (pressure applied from cranial to the clavicle on both sides)|
|percussion||The lungs produce a sonorous knocking sound, whereas the liver and spleen produce a muted knocking sound. This is how the caudal lung boundaries can be determined.|
|auscultation||Auscultation is always performed in direct page comparison. The normal finding is a vesicular respiratory sound on both sides. A weakening of the breathing noise can e.g. Evidence of a pleural effusion, a pneumothorax or a chronic obstructive bronchitis. Whereas increased respiratory noise can occur in the context of pneumonia.|
|ejection||Depending on the color and consistency, different differential diagnoses are possible. In addition, direct germ detection is possible.|
During the course of the procedure, imaging to confirm suspected diagnosis, e.g. a pneumonia, be necessary.
|sonography||Proof of a pleural effusion|
|roentgen||Representation of the lung as radiolucent. Indications of pathologies would be lightening or shading. Assessment of the pulmonary vessels, the recess and the location of the trachea.|
|CT thorax||In the lung window differentiated statement about possible space requirements, lymph node swelling or pulmonary fibrosis possible.|
Invasive measures such as a biopsy bronchial lavage may be performed, e.g. be suspected of bronchial carcinoma. The pulmonary function parameters are examined in the context of spiroergometry.
In addition, some laboratory parameters provide important clues to lung function. Particularly noteworthy is the blood gas analysis with which the oxygen saturation of the blood from both arterial and venous blood can be determined.
By BruceBlaus. When using this image in external sources it can be cited as: Blausen.com staff. “Blue gallery 2014”. Wikiversity Journal of Medicine. DOI: 10.15347 / wjm / 2014,010. ISSN 20018762. (Own work) [CC BY 3.0], via Wikimedia Commons
Depending on the etiology is further differentiated into one spontaneous, one traumatic and one iatrogenic pneumothorax. Spontaneous pneumothorax occurs preferentially in young asthenic men and is often caused by the bursting of a subpleural emphysema blister. Clinically, pneumothorax is manifested by dyspnoea, sharp pains on the affected thoracic hemisphere, and asymmetric thoracic movement (retraction of the affected side). A possible complication is the tension pneumothorax, which leads to a mediastinal comes to the healthy side. As a result, it comes both to a compression of the healthy lung, as well as to a disability of the venous return.
Pneumonia represents an acute or chronic inflammation of the alveolar and / or the interstitial lung tissue It is one of the most common fatal infectious diseases in industrialized countries. There are several ways in which pneumonia can be classified:
- Pathological-anatomical: localization and extent
- Etiology: infectious, physical / chemical noxae, circulatory disorders
- Clinical: primary / secondary pneumonia, acute / chronic pneumonia
- Place of origin: outpatient (purchased at home), nosocomially (at least 48 – 72 hours after hospitalization)
Bronchial asthma belongs to the Formenkreis of the obstructive Lung diseases and provides one chronic–inflammatory Disease of the respiratory tract. The inflammation leads to a seizure-like dyspnea as a result of a bronchial obstruction. This bronchial obstruction can be achieved by means of a methacholine–test provoked and is classically associated with bronchial asthma reversible.
COPD (chronic obstructive pulmonary disease)
Similar to bronchial asthma, COPD belongs to the group of forms of the obstructive Lung diseases. The obstruction is in contrast to the bronchial asthma (s.o.) not reversible. The respiratory arrest usually progresses over the years and is associated with a pathological inflammatory reaction of the lung, e.g. on chemical noxae like nicotine (in 90% the cause of COPD).
According to the WHO, chronic bronchitis occurs when in one patient for two consecutive years, for at least three consecutive months per year to cough + ejection (= productive cough) passed.
Pulmonary fibrosis is one of the interstitial Pulmonary diseases caused by an increase in the connective tissue of the lungs. Possible causes that can lead to such connective tissue proliferation are e.g. Inhalative noxae such as inorganic or organic dusts but also systemic diseases such as sarcoidosis or collagenosis.
Bronchial carcinoma is the most common cause of cancer death in men and the third most common cause in women (after breast and colon cancer). The main risk factor is the nicotine consumption (85% of lung cancers), with duration and extent of cigarette consumption determining lung cancer risk. A measure of this risk are the so-called pack years (engl. pack years), which is made up of the number of daily smoked packs and smoker years.
Another risk factor is occupational carcinogens, where asbestos With > 90% makes up the majority. In addition to the carcinogens, there is also a genetic disposition or other risk factors such as e.g. Lung scarring. Histologically, between the small cell Lung carcinoma (SCLC = “Small cell lung cancer”) and the Not–small cell Lung carcinoma (NSCLC = “Non-small cell lung cancer”). Non-small cell lung cancer is the most common of both, accounting for 85% of cases, and can be further subdivided into squamous, adenocarcinoma, large cell lung carcinoma, adenosquamous carcinoma, sarcomatoid carcinoma, carcinoid tumor and salivary gland tumor.
Adenocarcinoma is usually located peripherally and is the most common type of lung cancer in non-smokers. Squamous cell carcinoma and small cell lung carcinoma are predominantly located centrally.
Possible carcinomas that can form metastases in the lungs are v.a. Tumors the hematogen over the Vena cava sprinkle such as Renal cell carcinomas, bone tumors, liver carcinomas or carcinomas in the head and neck area. The lung carcinoma itself preferentially metastasizes in the brain, liver, adrenals and bones.
Popular exam questions to the lungs
The solutions are below the sources.
1. Which statement about the structure of the lung is correct?
- The horizontalis pulmonis fissure is on the left
- The left lung consists of three lobes
- The left lung is composed of 9 segments
- The hilum pulmonis is located at the Facies diaphragmatica
- The incisura cardiaca is on the right
2. How many segments has the middle lobe of the right lung??
- there is no middle lobe on the right lung
3. Which of the following muscles is not an inspiratory respiratory muscle??
- Mm. scaleni
- Mm. intercostalis externi
- Mm. intercartilaginei
- M. subcostalis
Pocket Textbook Anatomy, Cherry, J. and MA. – Thieme Verlag
Herold, G. and MA. Internal Medicine (2015) – Gerd Herold Verlag
Prometheus, Internal Organs, 2nd edition – Thieme Verlag
Welsch: Textbook Histology, 3rd Edition – Urban & fisherman
MEDI-LEARN Scripts series Anatomy, 3rd edition – MEDI-LEARN
Solutions to the questions: 1C, 2C, 3E
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