Human lung: Difference between revisions
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{{Infobox Anatomy | |
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===Left lung=== |
===Left lung=== |
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[[File:illu_quiz_lung04.jpg |thumb| |
[[File:illu_quiz_lung04.jpg |thumb|240px| Diagram showing the left lung, showing (1) [[Oblique fissure]], (2) Vertebral part (3) [[Hilum of lung]], (4) [[Cardiac impression on lung|Cardiac impression]], and (5) [[Diaphragmatic surface of lung|Diaphragmatic surface]] ]] |
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[[File:Illu quiz lung03.jpg|thumb|right|240px|Lingula at #4]] |
[[File:Illu quiz lung03.jpg|thumb|right|240px|Lingula at #4]] |
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The '''left lung''' is divided into two lobes, an upper and a lower, by the [[oblique fissure]], which extends from the [[rib|costal]] to the [[mediastinal surface of the lung]] both above and below the [[Hilum of lung|hilum]]. The left lung, unlike the right does not have a middle lobe. However the term ''lingula'' is used to denote a projection of the lower lobe of the left lung that serves as the [[homologue]].This area of the left lobe - the lingula, means ''little tongue'' (in Latin) and is often referred to as the ''tongue in the lung''. There are two bronchopulmonary segments of the lingula: superior and inferior. It is thought that the lingula of the left lung is the remnant of the middle lobe, which has been lost through evolution. |
The '''left lung''' is divided into two lobes, an upper and a lower, by the [[oblique fissure]], which extends from the [[rib|costal]] to the [[mediastinal surface of the lung]] both above and below the [[Hilum of lung|hilum]]. The left lung, unlike the right does not have a middle lobe. However the term ''lingula'' is used to denote a projection of the lower lobe of the left lung that serves as the [[homologue]].This area of the left lobe - the lingula, means ''little tongue'' (in Latin) and is often referred to as the ''tongue in the lung''. There are two bronchopulmonary segments of the lingula: superior and inferior. It is thought that the lingula of the left lung is the remnant of the middle lobe, which has been lost through evolution. |
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===Development=== |
===Development=== |
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[[File:Gray949.png|left|thumb|Lung during development]] |
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{{Main|Development of human lung}} |
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The '''development of human lung''' arises from the [[laryngotracheal groove]]. The [[larynx]], [[trachea]], [[bronchus|bronchi]] and lungs begin to form during the fourth week of [[human embryogenesis|embryogenesis]].<ref name=Moore_2002>{{cite book | author = Moore KL, Persaud TVN | title = The Developing Human: Clinically Oriented Embryology | edition = 7th ed.| publisher = Saunders | year = 2002 | isbn = 0-7216-9412-8 }}</ref> At this time, the [[respiratory diverticulum]] ([[lung bud]]) appears ventrally to the caudal portion of the [[foregut]]. The location of the diverticulum along the gut tube is directed by various signals from the surrounding [[mesenchyme]], including [[fibroblast growth factors]]. As the lung bud grows, its distal end enlarges to form the [[tracheal bud]]. At the same time the future trachea separates from the foregut through the formation of [[tracheoesophageal ridge]]s, which fuse to form the [[tracheoesophageal septum]]. |
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The tracheal bud divides into two primary [[bronchial bud]]s. During the fifth week of development, the bronchial buds enlarge to form right and left main bronchi. These continue to develop into [[secondary bronchus|secondary]] and [[tertiary bronchus|tertiary bronchi]]. |
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==Phases== |
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The maturation of the lungs occurs in several phases:<ref name=Sadler_2003>{{cite book | author = Sadler T | title = Langman's Medical Embryology | edition = 9th ed.| publisher = Lippincott Williams & Wilkins | year = 2003 | isbn = 0-7817-4310-9 }}</ref> |
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{| class="wikitable" |
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| '''Period''' || '''Time''' || '''Description''' |
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| Pseudoglandular period (also known as "glandular period"<ref name="isbn0-7817-5309-0">{{cite book |author=Kyung Won, PhD. Chung |title=Gross Anatomy (Board Review) |publisher=Lippincott Williams & Wilkins |location=Hagerstown, MD |year=2005 |pages=156 |isbn=0-7817-5309-0 |oclc= |doi=}}</ref>) || weeks 6 to 16 || The developing lung resembles an [[endocrine gland]] at this time. By the end of this period, all of the major lung elements, except those required for gas exchange (e.g. [[alveolus|alveoli]]), have appeared. Respiration is not possible during this phase, and fetuses born during this period are unable to survive. |
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| Canalicular period || weeks 16 to 26 || The lumina of the bronchi enlarge and lung tissue becomes highly vascularized during the canalicular period. By week 24, respiratory bronchioles and alveolar ducts have developed from the terminal bronchioles. Respiration is possible towards the end of this period, but few fetuses born during this time will survive. |
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| Terminal saccular period || week 26 to birth || The important [[blood-air barrier]] is established during the terminal saccular period. Specialized cells of the [[respiratory epithelium]] appear at this time, including type I alveolar cells across which gas exchange occurs, and type II alveolar cells which secrete pulmonary [[surfactant]]. This surfactant is important in reducing the surface tension at the air-alveolar surface, allowing expansion of the terminal saccules. During this time, the lungs are rock-like and will sink if placed in water but will expand after the first breath, a trait which is used to determine if babies were born alive.<ref name="titleU.S. v. Nelson">{{cite web |url=http://www.armfor.uscourts.gov/opinions/2000Term/00-0010.htm |title=U.S. v. Nelson |accessdate=2007-11-22 |work=}}</ref> |
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| Alveolar period || birth to 2 years of age || During this stage the terminal saccules, alveolar ducts, and alveoli increase in number. True alveoli appear as indentations in the saccular wall and septae form to produce divisions in the wall.<ref>Hislop, A. (2002). Airway and blood vessel interaction during lung development. Retrieved 21 March 2012, from www.ncbi.nlm.nih.gov/pmc/articles/PMC1570917/</ref> |
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==First breath== |
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At birth, the baby's lungs are filled with fluid secreted by the lungs and are not inflated. When the newborn is expelled from the birth canal, its central nervous system reacts to the sudden change in temperature and environment. This triggers it to take the first breath, within about 10 seconds after delivery.<ref>[http://adam.about.com/encyclopedia/Changes-in-the-newborn-at-birth.htm About.com > Changes in the newborn at birth] Review Date: 27 November 2007. Reviewed By: Deirdre OReilly, MD</ref> The newborn lung is far from being a miniaturized version of the adult lung. It has only about 20,000,000 to 50,000,000 alveoli or 6 to 15 percent of the full adult compliment. Although it was previously thought that alveolar formation could continue to the age of eight years and beyond, it is now accepted that the bulk of alveolar formation is concluded much earlier, probably before that age of two years. The newly formed inter alveolar septa still contain a double capillary network instead of the single one of the adult lungs. This means that the pulmonary capillary bed must be completely reorganized during and after alveolar formation, it has to mature. Only after full microvascular maturation, which is terminated sometime between that ages of two and five years, is the lung development completed and the lung can enter a phase of normal growth.<ref>Burri, P (n.d). lungdevelopment. Retrieved March 21, 2012, from www.briticannica.com/EBchecked/topic/499530/human-respiration/66137/lung-development</ref> |
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==Function== |
==Function== |
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===Respiration=== |
===Respiration=== |
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Revision as of 15:57, 16 April 2014
| Lungs | |
|---|---|
 Detailed diagram of the lungs | |
| Details | |
| System | Respiratory system |
| Identifiers | |
| Latin | pulmo |
| TA98 | A06.5.01.001 |
| TA2 | 3265 |
| FMA | 7195 |
| Anatomical terminology | |
The human lungs are the organs of respiration. Humans have two lungs, a right lung and a left lung. The right lung consists of three lobes while the left lung is slightly smaller consisting of only two lobes (the left lung has a "cardiac notch" allowing space for the heart within the chest).[1] Together, the lungs contain approximately 2,400 kilometres (1,500 mi) of airways and 300 to 500 million alveoli, having a total surface area of about 70 square metres (750 sq ft) to 100 square metres (1076.39 sq ft) (8,4 x 8,4 m) in adults — roughly the same area as one side of a tennis court.[2] Furthermore, if all of the capillaries that surround the alveoli were unwound and laid end to end, they would extend for about 992 kilometres (616 mi). The lungs together weigh approximately 1.3 kilograms (2.9 lb), with the right lung weighing more than the left.
The pleural cavity is the potential space between the two serous membranes, (pleurae) of the lungs; the parietal pleura, lining the inner wall of the thoracic cage, and the visceral pleura, lining the organs themselves–the lungs. The respiratory system includes the conducting zone, which consists of all parts of the airway that conducts air into the lungs.
The parenchyma of the lung, only relates to the functional alveolar tissue, but the term is often used to refer to all lung tissue, including the respiratory bronchioles, alveolar ducts, terminal bronchioles, and all connecting tissues.[3]
Structure
The lungs are located within the thoracic cavity, on either side of the heart and close to the backbone. They are enclosed and protected by the ribcage. The left lung has a lateral indentation which is shaped to accommodate the position of the heart. The right lobe is a little shorter than the left lung and this is to accommodate the positioning of the liver. Both lungs have broad bases enabling them to rest on the diaphragm without causing displacement.
Right lung
The right lung is divided into three lobes (as opposed to two lobes on the left), superior, middle, and inferior, by two interlobular fissures:
The right lung has a higher volume, total capacity and weight, than that of the left lung. Although it is 5cm shorter due to the diaphragm rising higher on the right side to accommodate the liver, it is broader than the left lung due to the cardiac notch of the left lung.
- Fissures
- The lower, oblique fissure, separates the inferior from the middle and superior lobes, and is closely aligned with the fissure in the left lung. Its direction is, however, more vertical, and it cuts the lower border about 7.5 cm. behind its anterior extremity.
- The upper horizontal fissure, separates the superior from the middle lobe. It begins in the lower fissure near the posterior border of the lung, and, running horizontally forward, cuts the anterior border on a level with the sternal end of the fourth costal cartilage; on the mediastinal surface it may be traced backward to the hilum.
- Lobes
The middle lobe is the smallest lobe of the right lung. It is wedge-shaped, and includes the part of the anterior border, and the anterior part of the base of the lung. The superior and inferior lobes are similar to those of the left lung (which lacks a middle lobe.)
- Impressions
On the mediastinal surface, immediately above the hilum, is an arched furrow which accommodates the azygos vein; while running superiorly, and then arching laterally some little distance below the apex, is a wide groove for the superior vena cava and right innominate vein; behind this, and proximal to the apex, is a furrow for the innominate artery.
Behind the hilum and the attachment of the pulmonary ligament is a vertical groove for the esophagus; this groove becomes less distinct below, owing to the inclination of the lower part of the esophagus to the left of the middle line.
In front and to the right of the lower part of the esophageal groove is a deep concavity for the extrapericardiac portion of the thoracic part of the inferior vena cava.
Left lung
The left lung is divided into two lobes, an upper and a lower, by the oblique fissure, which extends from the costal to the mediastinal surface of the lung both above and below the hilum. The left lung, unlike the right does not have a middle lobe. However the term lingula is used to denote a projection of the lower lobe of the left lung that serves as the homologue.This area of the left lobe - the lingula, means little tongue (in Latin) and is often referred to as the tongue in the lung. There are two bronchopulmonary segments of the lingula: superior and inferior. It is thought that the lingula of the left lung is the remnant of the middle lobe, which has been lost through evolution.
- Surfaces
As seen on the surface, this fissure begins on the mediastinal surface of the lung at the upper and posterior part of the hilum, and runs backward and upward to the posterior border, which it crosses at a point about 6 cm. below the apex.
It then extends downward and forward over the costal surface, and reaches the lower border a little behind its anterior extremity, and its further course can be followed upward and backward across the mediastinal surface as far as the lower part of the hilum.
- Impressions
On the mediastinal surface, immediately above the hilum, is a well-marked curved furrow produced by the aortic arch, and running upward from this toward the apex is a groove accommodating the left subclavian artery; a slight impression in front of the latter and close to the margin of the lung lodges the left innominate vein.
Behind the hilum and pulmonary ligament is a vertical furrow produced by the descending aorta, and in front of this, near the base of the lung, the lower part of the esophagus causes a shallow impression.
Development
The development of human lung arises from the laryngotracheal groove. The larynx, trachea, bronchi and lungs begin to form during the fourth week of embryogenesis.[4] At this time, the respiratory diverticulum (lung bud) appears ventrally to the caudal portion of the foregut. The location of the diverticulum along the gut tube is directed by various signals from the surrounding mesenchyme, including fibroblast growth factors. As the lung bud grows, its distal end enlarges to form the tracheal bud. At the same time the future trachea separates from the foregut through the formation of tracheoesophageal ridges, which fuse to form the tracheoesophageal septum.
The tracheal bud divides into two primary bronchial buds. During the fifth week of development, the bronchial buds enlarge to form right and left main bronchi. These continue to develop into secondary and tertiary bronchi.
Phases
The maturation of the lungs occurs in several phases:[5]
| Period | Time | Description |
| Pseudoglandular period (also known as "glandular period"[6]) | weeks 6 to 16 | The developing lung resembles an endocrine gland at this time. By the end of this period, all of the major lung elements, except those required for gas exchange (e.g. alveoli), have appeared. Respiration is not possible during this phase, and fetuses born during this period are unable to survive. |
| Canalicular period | weeks 16 to 26 | The lumina of the bronchi enlarge and lung tissue becomes highly vascularized during the canalicular period. By week 24, respiratory bronchioles and alveolar ducts have developed from the terminal bronchioles. Respiration is possible towards the end of this period, but few fetuses born during this time will survive. |
| Terminal saccular period | week 26 to birth | The important blood-air barrier is established during the terminal saccular period. Specialized cells of the respiratory epithelium appear at this time, including type I alveolar cells across which gas exchange occurs, and type II alveolar cells which secrete pulmonary surfactant. This surfactant is important in reducing the surface tension at the air-alveolar surface, allowing expansion of the terminal saccules. During this time, the lungs are rock-like and will sink if placed in water but will expand after the first breath, a trait which is used to determine if babies were born alive.[7] |
| Alveolar period | birth to 2 years of age | During this stage the terminal saccules, alveolar ducts, and alveoli increase in number. True alveoli appear as indentations in the saccular wall and septae form to produce divisions in the wall.[8] |
First breath
At birth, the baby's lungs are filled with fluid secreted by the lungs and are not inflated. When the newborn is expelled from the birth canal, its central nervous system reacts to the sudden change in temperature and environment. This triggers it to take the first breath, within about 10 seconds after delivery.[9] The newborn lung is far from being a miniaturized version of the adult lung. It has only about 20,000,000 to 50,000,000 alveoli or 6 to 15 percent of the full adult compliment. Although it was previously thought that alveolar formation could continue to the age of eight years and beyond, it is now accepted that the bulk of alveolar formation is concluded much earlier, probably before that age of two years. The newly formed inter alveolar septa still contain a double capillary network instead of the single one of the adult lungs. This means that the pulmonary capillary bed must be completely reorganized during and after alveolar formation, it has to mature. Only after full microvascular maturation, which is terminated sometime between that ages of two and five years, is the lung development completed and the lung can enter a phase of normal growth.[10]
Function
Respiration
The respiratory system's alveoli are the sites of gas exchange with blood.
- The sympathetic nervous system via noradrenaline acting on the beta receptors causes bronchodilation.
- The parasympathetic nervous system via acetylcholine, which acts on the M-3 muscarinic receptors, maintains the resting tone of the bronchiolar smooth muscle. This action is related, although considered distinct from bronchoconstriction.
- Many other non-autonomic nervous and biochemical stimuli, including carbon dioxide and oxygen, are also involved in the regulation process.
Respiratory system
The trachea divides at a junction–the carina of trachea, to give a right bronchus and a left bronchus, and this is usually at the level of the fifth thoracic vertebra. The conducting zone contains the trachea, the bronchi, the bronchioles, and the terminal bronchioles.
The respiratory system contains the respiratory bronchioles, the alveolar ducts, and the alveoli.
The conducting zone and the respiratory components, except the alveoli, are made up of airways with gas exchange only taking place in the alveoli of the respiratory system. The conducting zone is reinforced with cartilage in order to hold open the airways. Air is warmed to 37 °C (99 °F), humidified and cleansed by the conduction zone; particles from the air being removed by the cilia which are located on the walls of all the passageways. The lungs are surrounded and protected by the rib cage.
Modification of substances
The lungs convert angiotensin I to angiotensin II. In addition, they remove several blood-borne substances, such as a few types of prostaglandins, leukotrienes, serotonin and bradykinin.[11]
Taste
In 2010, researchers found bitter taste receptors in lung tissue, which cause airways to relax when a bitter substance is encountered. They believe this mechanism is evolutionarily adaptive because it helps clear lung infections, but could also be exploited to treat asthma and chronic obstructive pulmonary disease.[12]
See also
Additional images
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Human lungs -
Left lung -
Diagram of the respiratory system -
Anatomy of lungs -
Front view of heart and lungs -
Transverse section of thorax, showing relations of pulmonary artery -
The position and relation of the esophagus in the cervical region and in the posterior mediastinum, seen from behind -
The thymus of a full-time fetus, exposed in situ -
Mediastinal surface of left lung. -
right lung -
Human right lung -
Lungs -
Right Lung -
Right and Left Lung -
Left Lung -
Right and Left Lung -
Human embryo, 38 mm, 8–9 weeks.
References
This article incorporates text in the public domain from page 1093 of the 20th edition of Gray's Anatomy (1918)
- ^ Tomco, Rachel. "Lungs and Mechanics of Breathing". AnatomyOne. Amirsys, Inc. Retrieved 2012-09-28.
- ^ Notter, Robert H. (2000). Lung surfactants: basic science and clinical applications. New York, N.Y: Marcel Dekker. p. 120. ISBN 0-8247-0401-0. Retrieved 2008-10-11.
- ^ medilexicon.com > Medical Dictionary - 'Parenchyma Of Lung' In turn citing: Stedman's Medical Dictionary. 2006
- ^ Moore KL, Persaud TVN (2002). The Developing Human: Clinically Oriented Embryology (7th ed. ed.). Saunders. ISBN 0-7216-9412-8.
{{cite book}}:|edition=has extra text (help) - ^ Sadler T (2003). Langman's Medical Embryology (9th ed. ed.). Lippincott Williams & Wilkins. ISBN 0-7817-4310-9.
{{cite book}}:|edition=has extra text (help) - ^ Kyung Won, PhD. Chung (2005). Gross Anatomy (Board Review). Hagerstown, MD: Lippincott Williams & Wilkins. p. 156. ISBN 0-7817-5309-0.
- ^ "U.S. v. Nelson". Retrieved 2007-11-22.
- ^ Hislop, A. (2002). Airway and blood vessel interaction during lung development. Retrieved 21 March 2012, from www.ncbi.nlm.nih.gov/pmc/articles/PMC1570917/
- ^ About.com > Changes in the newborn at birth Review Date: 27 November 2007. Reviewed By: Deirdre OReilly, MD
- ^ Burri, P (n.d). lungdevelopment. Retrieved March 21, 2012, from www.briticannica.com/EBchecked/topic/499530/human-respiration/66137/lung-development
- ^ Walter F., PhD. Boron (2004). Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. ISBN 1-4160-2328-3. Page 605
- ^ http://umm.edu/news-and-events/news-releases/2010/when-bad-tastes-good-discovery-of-taste-receptors-in-the-lungs-could-help-people-with-asthma-breathe-easier