肺的结构和功能（The structure and function of the lungs）

Introduction引言

肺部属于人体的器官之一，这对于整个人类生物体的正常功能来说是至关重要的。但不幸的是，一般的人类的肺都是不完美的，它们常常会受到某些疾病的困扰。其中链接到肺部问题最严重的疾病是肺气肿。说到肺部，就有必要了解到作为人体的机体器官之一，肺的正常结构和功能是什么，肺气肿的症状是什么，这是什么类的疾病，以及最后的重要性，有什么办法可以防止这种疾病的发展等等。

The lungs belong to the organs, which are vitally important for normal functioning of the whole human organism. Unfortunately, as the human being in general, the lungs are not perfect and often they may be affected by some disease. Among the most serious diseases linked to the lungs problems is emphysema. Taking into consideration the importance of the lungs and their significance for the human organism it is necessary to clearly realize what the normal structure and functioning of the lungs is, what the symptoms of emphysema are, what the entity of this disease is and, finally, what measures can be undertaken to prevent the development of this disease. In fact all these questions will be answered in terms of this paper.

 

The structure and function of the lungs肺的结构和功能
肺部有相当复杂的结构。它们存在于胸腔和肋骨的骨性结构的保护之中。它们是由称为胸膜的双壁囊包围起来的。囊，这就是所谓的内脏胸膜，内层紧密地粘附到肺和外层组织，这被称为壁层胸膜，附着在胸腔的内壁上。

The lungs have quite a complicated structure. They are located in the thoracic cavity and protected by the bony structure of the rib cage. They are enclosed by a double-walled sac called pleura. The inner layer of the sac, which is called visceral pleura, adheres tightly to the lungs and the outer layer, which is called parietal pleura, is attached to the wall of the chest cavity. The two layers are separated by a thin space called the pleural cavity that is filled with the pleural fluid. Due to this the inner and outer layers slide over each other and they cannot be separated easily. It is worthy of noting that the left lung is smaller than the right one to give way to the heart.
 

The lungs attach to the heart and trachea through the structures that are called the ‘roots of the lungs’. The roots of the lungs include the bronchi, pulmonary vessels, bronchial vessels, lymphatic vessels and nerves. The lungs are divided into lobes by horizontal and oblique fissures. The right lung has three lobes and the left one has two. A unique feature of the left lung is the cardiac notch to create the lingula of the left lung.
 

The lungs are connected to the upper airway by trachea and bronchi. The trachea runs down the neck and divides into left and right bronchi behind the sternal angle. The right main bronchus is shorter than left and runs more runs more vertically. As a result, it is more common to aspirate foreign objects into the right lung. The bronchi enter the lung and branch out to form the bronchial tree. The bronchi divide into smaller bronchioles and the latter terminate in the alveoli. An alveolus is composed of respiratory tissue and is the site of the gas exchange in the lung.#p#分页标题#e#

The blood is supplied to the lungs from two sources: the pulmonary vessels and the bronchial vessels. The bronchial vessels support the nonrespiratory tissue while the pulmonary vessels provide support to the respiratory tissue.
 

The pulmonary arteries carry deoxygenated blood that has returned to the heart from the venous system to the lungs to be reoxygenated. The pulmonary veins carry oxygenated blood back to the heart to go to the arterial system. The right and left pulmonary arteries arise from the pulmonary trunk and carry ‘venous’ blood to their respective lungs while the pulmonary veins, two on each side, carry ‘arterial’ blood to the left atrium of the heart. The bronchial arteries that supply nonrespiratory tissue of the lungs arise from different sources. The left bronchial artery comes off thoracic aorta, while the right bronchial artery a variable source.
 

As for the normal functioning of the lungs, it should be pointed out that the main function is to transport oxygen from the atmosphere into the bloodstream and excrete carbon dioxide from the bloodstream into the atmosphere. Air enters and leaves the lungs through the bronchi and bronchioles and than it is redistributed to all tissues through the circulatory system. Air is brought in the organism through the airways, i.e. the nose, the pharynx, the larynx, the trachea, the bronchi and bronchioles, and the terminal branches of the respiratory tree. Than within the alveoli the gas exchange occurs, as it has been just described above. It should be pointed out that the drawing and expulsion of air is driven by a large muscle, known as the diaphragm, which drive ventilation by periodically altering the intra-thoracic volume and pressure. By increasing volume and decreasing pressure, air is sucked into airways, and by reducing volume and increasing pressure, the reverse occurs. During normal breathing, expiration is passive and no muscles are contracted.

 

Emphysema as a lung disease肺气肿是一种肺部疾病

Unfortunately, there are many diseases that affect lungs normal functioning. One of such diseases is emphysema. In scientific terms, emphysema is defined as permanent destructive enlargement of the airspaces distal to the terminal bronchioles without obvious fibrosis. Basically this disease is characterized by elasticity of the lung tissue, destruction of structures supporting the alveoli, and destruction of capillaries feeding the alveoli. As a result the process of breathing, and gas exchange in particular becomes quite problematic for the small airways collapse during expiration, leading to an obstructive form of lung disease, when air is trapped in the lungs. The main features of the disease are the shortness of breath on exertion, particularly when climbing stairs or incline and later at rest, hyperventilation and expanded chest. As emphysema progresses, clubbing of the fingers may be observed, that is a feature of longstanding hypoxia.#p#分页标题#e#

 

Sometimes emphysema patients are referred to as ‘pink puffers’ because emphysema sufferers may hyperventilate to maintain adequate blood oxygen levels. Hyperventilation explains why emphysema patients do not appear to be cyanotic like chronic bronchitis sufferers often do. This is why they are ‘pink’ puffers, due to adequate oxygen levels in the blood.

Consequently it is obvious that it is necessary to help he patients suffering from emphysema as soon as possible but what is even more important is to provide a proper diagnosis in time in order to start treatment at the beginning stage of the disease when patients have more opportunities to recover from it.
 

Traditionally diagnosis is made by spirometry, lung function testing, including diffusion testing. In addition other investigations might be used, for instance, X-ray, high resolution spiral chest CT-scan, bronchoscopy (especially when other lung disease is suspected, including malignancy), blood test, pulse oxymetry and arterial blood gas sampling.
 

In fact emphysema is irreversible degenerative condition that needs proper and thorough treatment. Speaking about the treatment it is necessary to say that the most effective measure that can be taken to slow the progression of emphysema is for the patient to stop smoking and avoid all exposure to cigarette smoke and lung irritants. Pulmonary rehabilitation may be very helpful to optimise the patient’s quality of life and teach the patient how to actively manage his or her care. It is treated by supporting the breathing with anticholinergics, bronchodilators and inhale or oral steroid medication, and supplemental oxygen as required. Treating patient’s other conditions including gastric reflux and allergies may also help the patient’s lung function. Supplement oxygen used as prescribed, i.e. 20+ hours/day, is the only non-surgical treatment which has been shown to prolong life in emphysema patients. Nonetheless, other medications are currently being researched and probably in the future there would be found some plausible and effective treatment. Also there are lightweight portable oxygen systems which allow patients increasing mobility and patients can fly, cruise and work while using supplemental oxygen.
 

However, surgical methods seem to be the most effective treatment of emphysema patients. For instance, lung volume reduction surgery (LVRS) can improve the quality of life for carefully selected patients. It can be done by several different methods, some of which are minimally invasive. The only ‘cure’ for emphysema is a lung transplant, although not many patients are strong enough physically to survive the surgery. The combination of the patient’s age, oxygen deprivation and the side effects of the medications used to treat emphysema cause damage to the kidneys, heart and other bodily organs. Transplants also require the patient to take an anti-rejection drug regimen which suppresses immunities and creates new medical issues.#p#分页标题#e#

 

Conclusion结论

Thus, taking into account all above mentioned, it is possible to conclude that emphysema is a serious chronic disease which affects the lungs and influences the proper functioning the whole organism and needs an emergent treatment. Unfortunately, non-surgical treatments are ineffective as a rule and supplemental oxygen is the only effective non-surgical treatment. In fact the most effective is the surgical treatment but in the same time it is the most dangerous one since not all patients can survive it. Consequently, it may be said that it is necessary to find alternative ways of treatment, desirably non-surgical ones that could really improve the emphysema patient’s state and cure them effectively but it is only a future perspective while nowadays the problem still remains unsolved and the patients has either to undergone the surgical treatment or hopefully wait, if they physically can, for better and safer treatment.

 

Bibliography:文献参考

1. Johnson, D.R. Respiratory System. New York: Touchstone, 2001.

2. Livingston, G. L. Emphysema: Diagnosis and Treatment. LA: McGraw Hill, 2002.

3. Thompson, K. Introductory Anatomy. New York: Routledge, 2000.

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