ONLINE ASSIGNMENT

ONLINE ASSIGNMENT

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                     THUSHARA.K

                      Natural Science

                       Reg No : 13367029

Topic

FUNCTION & STRUCTURE

OF LUNGS

INTRODUCTION

The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a fewsnails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart. Their principal function is to transport oxygen from the atmosphere into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere. A large surface area is needed for this exchange of gases which is accomplished by the mosaic of specialized cells that form millions of tiny, exceptionally thin-walled air sacs called alveoli.

To understand the anatomy of the lungs, the passage of air through the nose and mouth to the alveoli must be studied. The progression of air through either the mouth or the nose, travels through the nasopharynx, oropharynx, larynx, and thetrachea (windpipe). The air passes down the trachea, which divides into two main bronchi; these branch to the left and right lungs where they progressively subdivide into a system of bronchi and bronchioles until the alveoli are reached. These many alveoli are where the gas exchange of carbon dioxide and oxygen takes place.

Breathing is driven by muscular action; in early tetrapods, air was driven into the lungs by the pharyngeal muscles via buccal pumping, which is still found in amphibians. Reptiles, birds and mammals use their musculoskeletal system to support and foster breathing.

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). 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. Therespiratory system includes the conducting zone, which is part of the respiratory tract, 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.

STRUCTURE OF HUMAN LUNGS

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. Each lung near to the centre has a recessed region called the hilum which is the entry point for the root of the lung. (Root here means the anchoring part of a structure.) The bronchi and pulmonary vessels extend from the heart and the trachea to connect each lung by way of the root.

There are three surfaces to the lungs: the costal surface is the outer, thoracic surface which is smooth and convex. This surface area is large and corresponds to the form of the thoracic cavity, being deeper at the back than at the front. The costal surface is in contact with the costal pleura and in specimens that have been hardened in situ, slight grooves are visible which correspond to the overlying ribs.The mediastinal surface of the lung is in contact with the mediastinal pleura and presents the cardiac impression. The diaphragmatic surface of lung is the portion of the lung which borders on the thoracic diaphragm.

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 5 cm 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 fourthcostal 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

There is a deep concavity on the mediastinal surface called the cardiac impression, which accommodates the pericardium; this is not as pronounced as that on the left lung where the heart projects further. On the same 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 upper 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 twobronchopulmonary 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

There is a large and deep concavity called the cardiac impression, on the mediastinal surface to accommodate the pericardium. On the same 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.

FUNCTIONS OF LUNGS

 Respiration

v The sympathetic nervous system via noradrenaline acting on the beta receptors causes bronchodilation.

v The parasympathetic nervous system is through the vagus nerve, via acetylcholine, which acts on the M-3muscarinic receptors, maintains the resting tone of the bronchiolar smooth muscle. This action is related, although considered distinct from bronchoconstriction

v Many other non-autonomic nervous and biochemical stimuli, including carbon dioxide and oxygen, are also involved in the regulation process.

There is also a relationship noted between the pressures in the lung, in the alveoli, in the arteries and in the veins. This is conceptualised into the lung being divided into three vertical regions called the zones of the lung. 

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. Theconducting 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, comprise the air passageways, 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.^[14]

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.

LUNG DISEASES

Lung diseases are some of the most common medical conditions in the world. Tens of millions of people suffer from lung disease in the U.S.Smoking, infections, and genetics are responsible for most lung diseases.

The lungs are part of a complex apparatus, expanding and relaxing thousands of times each day to bring in oxygen and expel carbon dioxide. Lung disease can result from problems in any part of this system.

Lung Diseases Affecting the Airways

The trachea (windpipe) branches into tubes called bronchi, which in turn branch to become progressively smaller tubes throughout the lungs. Diseases that affect the airways include:

v Asthma: The airways are persistently inflamed, and may occasionally spasm, causing wheezing and shortness of breath. Allergies, infections, or pollution can trigger asthma's symptoms.

v Chronic obstructive pulmonary disease (COPD): Lung conditions defined by an inability to exhale normally, which causes difficulty breathing.

v Chronic bronchitis: A form of COPD characterized by a chronic productive cough.

v Emphysema: Lung damage allows air to be trapped in the lungs in this form of COPD. Difficulty blowing air out is its hallmark.

v Acute bronchitis: A sudden infection of the airways, usually by a virus.

v Cystic fibrosis: A genetic condition causing poor clearance of mucus from the bronchi. The accumulated mucus results in repeated lung infections.

  

Lung Diseases Affecting the Air Sacs (Alveoli)

The airways eventually branch into tiny tubes (bronchioles) that dead-end into clusters of air sacs called alveoli. These air sacs make up most of the lung tissue. Lung diseases affecting the alveoli include:

v Pneumonia: An infection of the alveoli, usually by bacteria.

v Tuberculosis: A slowly progressive pneumonia caused by the bacteriaMycobacterium tuberculosis.

v Emphysema results from damage to the fragile connections between alveoli. Smoking is the usual cause. (Emphysema also limits airflow, affecting the airways as well.)

v Pulmonary edema: Fluid leaks out of the small blood vessels of the lung into the air sacs and the surrounding area. One form is caused byheart failure and back pressure in the lungs' blood vessels; in another form, direct injury to the lung causes the leak of fluid.

v Lung cancer has many forms, and may develop in any part of the lungs. Most often this is in the main part of the lung, in or near the air sacs. The type, location, and spread of lung cancer determines the treatment options.

v Acute respiratory distress syndrome (ARDS): Severe, sudden injury to the lungs caused by a serious illness. Life support with mechanical ventilation is usually needed to survive until the lungs recover.

v Pneumoconiosis: A category of conditions caused by the inhalation of a substance that injures the lungs. Examples include black lung disease from inhaled coal dust and asbestosis from inhaled asbestos dust.

 Lung Diseases Affecting the Interstitium

The interstitium is the microscopically thin, delicate lining between the lungs' air sacs (alveoli). Tiny blood vessels run through the interstitium and allow gas exchange between the alveoli and the blood. Various lung diseases affect the interstitium:

v Interstitial lung disease (ILD): A broad collection of lung conditions affecting the interstitium. Sarcoidosis, idiopathic pulmonary fibrosis, and autoimmune disease are among the many types of ILD.

v Pneumonias and pulmonary edemas can also affect the interstitium.

CONCLUSION

The lungs are organs of the respiratory system that allow us to take in and expel air. In the breathing process, the lungs take in oxygen from the air through inhalation. Carbon dioxide produced by cellular respiration is in turn released through exhalation. The lungs are also closely associated with the cardiovascular system as they are the sites for gas exchange between the air and the blood.

In human beings Lungs are the main respiratory organs. Lungs are a pair of conical or­gans enveloped by a serious membrane - the pleura. The lungs oc­cupy a greater part of the thoracic cavity. The two lungs are separated from each other by the medi­astinum. Each lung is divided by deep fissures into lobes. The right lung has three lobes - the up­per, middle and lower while the left lung has two lobes the upper and the lower. The lung is also described as having a mediastinal and a cos­tal surface, an apex and a base.

The outer (costal) surface is in contact with the wall of the pleural cavity while the medial surface of the lung is applied to the mediastinum. The main feature here is the pres­ence of hilum where the main bronchus and pulmonary artery enter and the pulmonary veins leave the lung. Lymph nodes are present at the hilum which may get enlarged by diseases.

Tobacco smoke is a powerful trigger for people with asthma, and one that all children should avoid. Smoking should be avoided anywhere around infants and children - like family rooms, kitchens, cars etc. Young people and adults with

asthma should not smoke, as this further damages lungs. Where possible, they should try and avoid places where other people smoke too. Exposure to cigarette smoke during pregnancy and early childhood significantly increases the risk

of children developing asthma, and has also been shown to make asthma attacks more severe. It has been estimated that 8% of all childhood asthma (46,500 children) in Australia is due to parental smoking.