Information about Human Lung
) | |
| Frontal view of lungs cut open Trachea branches into bronchi | |
| Latin | pulmo |
| subject #240 1093 | |
| MeSH | Lung |
Humans have two lungs, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately 1500 miles (2,400 km) of airways and 300 to 500 million alveoli, having a total surface area of about 75 m2 in adults — roughly the same area as a tennis court.[1] Furthermore, if all of the capillaries that surround the alveoli were unwound and laid end to end, they would extend for about 620 miles.
Organization
- The conducting zone contains the trachea, the bronchi, the bronchioles, and the terminal bronchioles
- The respiratory zone contains the respiratory bronchioles, the alveolar ducts, and the alveoli.
The conducting zone has no gas exchange with the blood, and is reinforced with cartilage and smooth muscle, which are very strong. Smooth muscle has variable resistance to air flow. The conducting zone warms the air to 37 degrees Celsius and humidifies the air. It also cleanses the air by removing particles.
The respiratory zone is the site of gas exchange with blood.
The smooth muscle tone in bronchioles, and therefore bronchiolar diameter, is controlled by:
- the sympathetic nervous system via noradrenaline acting on the beta receptors and causes bronchodilation
- the parasympathetic nervous system via acetylcholine which acts on the muscarinic receptors and causes bronchoconstriction
- many other non-autonomic nervous and biochemical stimuli including, for example, carbon dioxide.
Physiology
Total lung capacity (TLC) includes inspiratory reserve volume, tidal volume, expiratory reserve volume, and residual volume.[2] The total lung capacity depends on the person's age, height, weight, sex, and normally ranges between 4,000 and 6,000 cm3 (4 to 6 L). For example, females tend to have a 20–25% lower capacity than males. Tall people tend to have a larger total lung capacity than shorter people. Smokers have a lower capacity than nonsmokers. Lung capacity is also affected by altitude. People who are born and live at sea level will have a smaller lung capacity than people who spend their lives at a high altitude. In addition to the total lung capacity, one also measures the tidal volume, the volume breathed in with an average breath, about 500 cm3. For a detailed discussion of the various lung volumes, see the article on lung volumes.Typical resting adult respiratory rates are 10–20 breaths per minute with 1/3 of the breath time in inspiration.
Human lungs are to a certain extent 'overbuilt' and have a tremendous reserve volume as compared to the oxygen exchange requirements when at rest. This is the reason that individuals can smoke for years without having a noticeable decrease in lung function while still or moving slowly; in situations like these only a small portion of the lungs are actually perfused with blood for gas exchange. As oxygen requirements increase due to exercise, a greater volume of the lungs is perfused, allowing the body to reach its CO2/O2 exchange requirements.
Development
The larynx, trachea, bronchi and lungs begin to form during the fourth week of embryonic development.[3] 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.
The maturation of the lungs occurs in several phases:[4]
- Pseudoglandular period
- This stage occurs during weeks 6 to 16. The developing lung resembles an exocrine 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
- Lasting from weeks 16 to 26, the lumens 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
- The important blood-air barrier is established during the terminal saccular period. This period lasts from week 26 to birth. 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.
- Alveolar period
- This stage lasts from birth to 8 years of age. During this stage the terminal saccules, alveolar ducts, and alveoli increase in number.
Diseases
The following is a list of important medical conditions involving the lung. Many of these are caused or worsened by smoking.- Lung cancer
- Emphysema is an enlargement of the air spaces in the lung, making it hard to breathe.
- Asthma is an immunological disease which causes the bronchioles to narrow by inflammation and spasm of the lining of the airway wall.
- Cystic fibrosis is a hereditary disease which causes the lung to produce abnormally viscous mucus.
- A pulmonary embolism occurs when a blood clot obstructs an artery leading to the lung.
- Tuberculosis is a transmittable bacterial infection of the lung, the most common infectious disease today.
- Pneumonia is an infection of the lung, caused by bacteria, viruses or fungi.
- Bronchitis is an inflammation of the bronchi.
- A collapsed lung (pneumothorax) can occur when one or both walls of the pleural cavity are penetrated by injury, allowing air to enter.
- In pulmonary edema fluid from the capillaries enters the alveoli. This can be caused by weakness of the left side of the heart (resulting in a blood holdup in the lung), altitude sickness, or rarely inhaling toxic gases.
- Lung pinprick condition is a hereditary disease which results in decreased lung capacity and occasional shortness of breath.
References
1. ^ Rhoades RA, Tanner GA (editors) (2003). Medical Physiology, 2nd ed., Lippincott Williams & Wilkins. ISBN 0-7817-1936-4.
2. ^ Weinberger SE (2004). Principles of Pulmonary Medicine, 4th ed., Saunders. ISBN 0-7216-9548-5.
3. ^ Moore KL, Persaud TVN (2002). The Developing Human: Clinically Oriented Embryology, 7th ed., Saunders. ISBN 0-7216-9412-8.
4. ^ Sadler T (2003). Langman's Medical Embryology, 9th ed., Lippincott Williams & Wilkins. ISBN 0-7817-4310-9.
2. ^ Weinberger SE (2004). Principles of Pulmonary Medicine, 4th ed., Saunders. ISBN 0-7216-9548-5.
3. ^ Moore KL, Persaud TVN (2002). The Developing Human: Clinically Oriented Embryology, 7th ed., Saunders. ISBN 0-7216-9412-8.
4. ^ Sadler T (2003). Langman's Medical Embryology, 9th ed., Lippincott Williams & Wilkins. ISBN 0-7817-4310-9.
Additional images
Detailed diagram of the lungs | ) |
Anatomy: respiratory system |
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| Nose • Nasal cavity • Pharynx • Larynx • Trachea • Lungs • Bronchi • Alveoli • Conducting zone • Respiratory zone |
Cardiovascular system |
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| Blood | Heart → Aorta → Arteries → Arterioles → Capillaries → Venules → Veins → Vena cava → Heart → Pulmonary arteries → Lungs → Pulmonary vein |
Anatomy of torso, respiratory system: Lungs and related structures | |
|---|---|
| lungs |
right
left
lingula
apex
base
root
cardiac notch
cardiac impression
hilum
borders (anterior, posterior, inferior)
surfaces (costal, mediastinal, diaphragmatic)
fissures (oblique, horizontal)
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| conducting zone | |
| respiratory zone | |
| pleurae | |
Latin}}}
Official status
Official language of: Vatican City
Used for official purposes, but not spoken in everyday speech
Regulated by: Opus Fundatum Latinitas
Roman Catholic Church
Language codes
ISO 639-1: la
ISO 639-2: lat
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Official status
Official language of: Vatican City
Used for official purposes, but not spoken in everyday speech
Regulated by: Opus Fundatum Latinitas
Roman Catholic Church
Language codes
ISO 639-1: la
ISO 639-2: lat
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Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. Created and updated by the United States National Library of Medicine (NLM), it is used by the MEDLINE/PubMed
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In animal physiology, respiration is the transport of oxygen from the ambient air to the tissue cells and the transport of carbon dioxide in the opposite direction. This is in contrast to the biochemical definition of respiration, which refers to cellular respiration
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alveolus (plural: alveoli, from Latin alveus, "little cavity"), is an anatomical structure that has the form of a hollow cavity. Mainly found in the lung, the pulmonary alveoli
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tennis court is where the game called tennis is played. It is a firm rectangular surface with a low net stretched across the center.
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Dimensions
Tennis is played on a rectangular flat surface, usually of grass, clay, concrete (hard court) or a synthetic suspended court...... Click the link for more information.
trachea, or windpipe, is a tube that has an inner diameter of about 20-25 mm and a length of about 10-16cm. It extends from the larynx to the primary (main) bronchi in mammals, and from the pharynx to the syrinx in birds, allowing the passage of air to the lungs.
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A bronchus (plural bronchi, adjective bronchial) is a caliber of airway in the respiratory tract that conducts air into the lungs. No gas exchange takes place in this part of the lungs.
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The bronchioles are the first airway branches that no longer contain cartilage. They are branches of the bronchi, and are smaller than one millimeter in diameter.
There are no glands or cartilage in any of the bronchioles, and the epithelial cells become more cuboidal in
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There are no glands or cartilage in any of the bronchioles, and the epithelial cells become more cuboidal in
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A terminal bronchiole is a bronchiole at the end of the conducting zone. At the transition into the respiratory zone, alveoli become present.
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External links
- Terminal+bronchiole at eMedicine Dictionary
- Diagram at davidson.edu
- Histology at umdnj.
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A respiratory bronchiole is a bronchiole at the beginning of the respiratory zone. It has cuboidal epithelia.
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Additional images
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Alveolar ducts are the tiny end tubules of the branching airways that fill the lungs. Each lung holds approximately 1.5 to 2 million of them. The tubules divide into alveolar sacs at the distal end.
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alveolus (plural: alveoli, from Latin alveus, "little cavity"), is an anatomical structure that has the form of a hollow cavity. Mainly found in the lung, the pulmonary alveoli
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airways are those parts of the respiratory system through which air flows, to get from the external environment to the alveoli.
The airway begins at the mouth or nose, and accesses the trachea via the pharynx.
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The airway begins at the mouth or nose, and accesses the trachea via the pharynx.
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Gas exchange or respiration takes place at a respiratory surface - a boundary between the external environment and the interior of the body. For unicellular organisms the respiratory surface is simply the cell membrane, but for large organisms it usually is carried out in
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The Sympathetic Nervous System (SNS) is a branch of the autonomic nervous system. It is always active at a basal level (called sympathetic tone) and becomes more active during times of stress.
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Norepinephrine (INN)(abbr. norepi or NE) or noradrenaline (BAN) is a catecholamine and a phenethylamine with chemical formula C8H11NO3. The natural stereoisomer is L -(−)-(R)-norepinephrine.
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adrenergic receptors (or adrenoceptors) are a class of G protein-coupled receptors that are targets of the catecholamines. Adrenergic receptors specifically bind their endogenous ligands, the catecholamines adrenaline and noradrenaline (called epinephrine and norepinephrine
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A bronchodilator is a substance that dilates the bronchi and bronchioles, increasing airflow. Bronchodilators may be endogenous (originating naturally within the body), or they may be medications administered for the treatment of breathing difficulties.
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parasympathetic nervous system (PSNS) is one of three divisions of the autonomic nervous system (ANS). The ANS -a subdivision of the peripheral nervous system (PNS)- is subdivided into the sympathetic (SNS), parasympathetic (PSNS) and enteric (bowels) nervous system (ENS).
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The chemical compound acetylcholine, often abbreviated as ACh, was the first neurotransmitter to be identified. It is a chemical transmitter in both the peripheral nervous system (PNS) and central nervous system (CNS) in many organisms including humans.
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Muscarinic receptors are those membrane-bound acetylcholine receptors that are more sensitive to muscarine than to nicotine. Those for which the contrary is true are known as nicotinic acetylcholine receptors. Muscarine and nicotine are both alkaloids.
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Bronchoconstriction is the constriction of the airways in the lungs due to the tighting of surrounding smooth muscle, with consequent coughing, wheezing, and shortness of breath. Bronchoconstriction can also be due to an accumulation of thick mucus.
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Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. It is a gas at standard temperature and pressure and exists in Earth's atmosphere in this state.
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pleurae. The outer pleura is attached to the chest wall and is known as the parietal pleura; the inner one is attached to the lung and other visceral tissues and is known as the visceral pleura.
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pleurae. The outer pleura is attached to the chest wall and is known as the parietal pleura; the inner one is attached to the lung and other visceral tissues and is known as the visceral pleura.
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Larger volumes Smaller volumes
males females
taller people shorter people
non-smokers heavy smokers
professional athletes[1] non-athletes
people living at high altitudes people living at low altitudes
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males females
taller people shorter people
non-smokers heavy smokers
professional athletes[1] non-athletes
people living at high altitudes people living at low altitudes
..... Click the link for more information.
Larger volumes Smaller volumes
males females
taller people shorter people
non-smokers heavy smokers
professional athletes[1] non-athletes
people living at high altitudes people living at low altitudes
..... Click the link for more information.
males females
taller people shorter people
non-smokers heavy smokers
professional athletes[1] non-athletes
people living at high altitudes people living at low altitudes
..... Click the link for more information.
Larger volumes Smaller volumes
males females
taller people shorter people
non-smokers heavy smokers
professional athletes[1] non-athletes
people living at high altitudes people living at low altitudes
..... Click the link for more information.
males females
taller people shorter people
non-smokers heavy smokers
professional athletes[1] non-athletes
people living at high altitudes people living at low altitudes
..... Click the link for more information.
Larger volumes Smaller volumes
males females
taller people shorter people
non-smokers heavy smokers
professional athletes[1] non-athletes
people living at high altitudes people living at low altitudes
..... Click the link for more information.
males females
taller people shorter people
non-smokers heavy smokers
professional athletes[1] non-athletes
people living at high altitudes people living at low altitudes
..... Click the link for more information.
Larger volumes Smaller volumes
males females
taller people shorter people
non-smokers heavy smokers
professional athletes[1] non-athletes
people living at high altitudes people living at low altitudes
..... Click the link for more information.
males females
taller people shorter people
non-smokers heavy smokers
professional athletes[1] non-athletes
people living at high altitudes people living at low altitudes
..... Click the link for more information.
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