Lungs- Definition, Structure, Location, Functions, Diseases

Lungs are the respiratory organs in our body. All the gas exchange that occurs in our body takes place in the lungs. Normally humans have two lungs on either side of the lungs, left and right. They inspire oxygen and expire carbon dioxide (CO2). Lungs play a major role in the supply of oxygen to our body, without which we will be dead in a minute.


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Structure of Lungs

The respiratory system can be divided into two parts. Upper respiratory system and Lower respiratory system. The upper respiratory system begins from the nose, nostrils, larynx, and trachea, whereas the lower respiratory system completely comprises of lungs. The lung contains the following parts functioning in different functions. Trachea, alveoli and bronchi and pleura.

Structure of Lungs
Figure: Structure of Lungs.

Location of Lungs

  • Lungs are present on either side of the chest. They are situated in the thoracic cavity, one each on either side of the mediastinum above the diaphragm. They are covered by a pleural sac and protected by the rib cage. 
  • The lungs can be called left and right lungs concerning sides they are situated in our body.

Anatomically lung presents with four features

  • Apex- which is a conical end-directed upwards.
  • Base – it is the broader end and directed downwards
  • Three borders-
    • An anterior margin is a thin layer that faces forward,
    • The posterior margin is a rounded border that faces inwards, 
    • The inferior margin is a semilunar-shaped margin that separates the coastal surface and medial surface.
  • Two surfaces-
    • A coastal surface is a convex surface which directed outwards 
    • A medial surface is a flat surface directed outwards.


  • Apex- apex anteriorly is about subclavian artery, internal thoracic artery, and scalenus anterior.
  • Base- base is separated from the liver on the right side by the right dome of the diaphragm and separated from the spleen and fundus of the stomach on the left side by the left dome of the diaphragm.
  • The size of the lung varies from birth as we keep aging. At birth, the weight of the lung is around 40g, and in an adult, it is approximately 1kg. and the height of the lung at total capacity is 27cm, and at normal breathing, capacity is 24cm.
  • The left lung is smaller than the right lung. The right Lung has three lobes, and the left one has two lobes. Both the lungs are suspended by lung roots, and the membrane called mediastinum divides the lungs from each other.
  • Each lung contains a tube-like structure called Bronchi, they open from the trachea into the lungs. Further, bronchi are branched into smaller tubular structures called bronchioles. 
  • Bronchioles aid the flow of air into tiny organs called alveolars. It is estimated that each human lung contains 30 thousand bronchioles and 600 million alveoli combined.

Functions of Lungs

  1. The very important function of the lungs is to provide oxygen to the body. When we breathe in, the process is called inhaling, the air enters the lungs through the mouth, nose, and trachea. In the lungs, the air moves into bronchioles and fills up the alveoli. 
  2. And this is where the gas exchange occurs. Alveoli are connected to the blood vessels, which carry oxygen from the lungs to the heart and carbon dioxide from the heart to the lungs.
  3. Lungs also help in the immune system of the body. Alveolar macrophages are the most prolific innate immune cells present in the distal lung tissue.
  4. They are present in the luminal surface of the alveolar space
  5. They also indulge in homeostatic functions.

Mechanism of Breathing

  • When we inhale, the oxygen is taken in, and after the gas exchange in the lungs, carbon dioxide is exhaled out of the body. 
  • The inhaled oxygen then flows into the lungs through the trachea and then to the bronchus, bronchioles, and the alveoli. From alveoli, the oxygen is diffused into blood vessels.
  • The blood vessels which carry blood from the lungs to the heart are called Pulmonary veins, these carry oxygenated blood, in which oxygen molecules are bound to hemoglobin molecules.
  • And the ones which carry blood from the heart to the lungs are called pulmonary arteries, which carry deoxygenated blood from the heart, which contain carbon dioxide then released into the lungs.
Figure: Mechanism of Breathing. Image Source: FreePik.
  • During inhalation, the diaphragm moves down, and the intercoastal muscle is pulled upwards the low pressure created in the chest cavity draws in oxygen from the atmosphere.
  • During exhalation, the diaphragm relaxes and moves upwards, and the intercoastal muscle relaxes and moves downwards, which pushes the carbon dioxide out of the lungs into the trachea and then exhaled out of the body.

Disease and Disorder of the lungs

Chronic obstructive pulmonary disease (COPD)

  • It is a type of lung disease where the functioning ability of the lungs declines over the period. Globally 65 million people are affected, and 3 million deaths are reported every year due to Chronic obstructive pulmonary disease. 
  • It is a smoking-associated chronic disease. Smokers are 13 times more prone to COPD, and air pollution is also a potential reason.  
  • However, there is also a chance that disease can be transmitted genetically and found in people with immunocompromised hosts.
  • The complication of this may lead to pneumonia, lung cancer, COPD, heart failure, and various other lung complications.


  • It is one of the most common lung conditions found in the community. It caused due to the chronic inflammation of the lower respiratory tract.
  •  It is one of the underrated diseases despite the fact it requires excellent skill to diagnose the condition. 
  • Clinically, asthmatic patients exhibit common symptoms like recurrent episodes of wheezing, a cough, chest tightness, and shortened breathing.
  • Specific immunotherapy for asthma is not practically possible. However, there are some therapies that can help in optimizing the functions of the lung. 
  • Elimination of the allergens which trigger the asthmatic condition can be one of the most efficient ways to control the disease. Obesity also can be one of the reasons for the condition, hence weight reduction will help in the improved health of the lungs.

Pulmonary fibrosis

  • Pulmonary fibrosis is caused due to alveoli injury, which may lead to chronic inflammation and deposition of extracellular components in the lungs, mainly containing collagen, which will result in scarring of the lung tissue.
  • It is mainly found in genetically susceptible individuals. Sometimes it may also be due to microbial agents, chemotherapeutic agents, and occupational inhalants.
  • The treatment of pulmonary fibrosis is complicated, but conventional treatment options include corticosteroids, immunosuppressive agents, and antifibrotic agents.
  • If the condition is due to microbial agents, it can be treated using antimicrobial agents such as antibiotic, antiviral and antifungal drugs depending upon the causative agent.6

Lung Cancer

Lung Cancer Stages
Figure: Lung Cancer Stages.
  • The leading cause of cancer death in the world. 
  • Smoking is one of the major reasons for lung cancer, along with other risk factors such as genetic reasons, radiation exposure, exposure to radon gas, and other carcinogens. 
  • Developed due to the repeated damaging of the cell line of the lungs, which causes normal cells to act abnormal and eventually cause cancer. 
  • Symptoms include short breath, coughing blood, pleural effusion, and chest pain. 
  • Treatments are only good if detected in the early stages. Multiple surgical techniques are available such as including wedge resection, segmentectomy, lobectomy, and pneumonectomy.

Lung conditions due to Microbial Agents


  • Severe Acute Respiratory Syndrome Coronavirus 2 is a global pandemic that the world is dealing with currently. It is the third-highest infective virus that the world has ever seen. 
  • They are primarily transmitted to respiratory droplets. 
  • Transmission through direct contact with contaminated surfaces, aerosols, and fecal-oral routes is also reported. 
  • They infect the lungs and colonize them, causing difficulty in respiration and failure of respiration in complicated cases. Common symptoms include fever, cough, and dyspnea.
Figure: SARS-CoV-2_ What We Know About Its Effects on Respiration.


  • It is one of the most common infections of the lungs seen in individuals, especially in elderly patients. It is the acute inflammation of the lower respiratory tract and lung parenchyma. 
  • Pneumonia can be caused either by bacterial agents or viral agents. The most common bacterial agent that causes pneumonia is Streptococcus pneumoniae
  • Apart from this, Klebsiella pneumonia, Hemophilus influenzae, and Staphylococcus sp. can also cause pneumonia. 
  • Influenza virus, respiratory syncytial virus (RSV), and SARS-CoV-2 commonly cause viral pneumonia. These pathogens colonize the lung tissue and cause inflammation of the lung tissue. This will lead to the complications such as fever, cough, malaise, and shortness of breath. 
  • If untreated, the death of the patient may occur.
  • The treatment of pneumonia mainly depends upon the causative agent, and therefore the diagnosis of the disease should be carried out very carefully. 
  • Bacterial pneumonia can be treated with an appropriate antibacterial agent, and viral pneumonia can be treated with antiviral drugs.


  • Pulmonary tuberculosis is the chronic infection of the lungs caused by the bacteria called Mycobacterium tuberculosis. The transmission of the disease occurs through droplet infection. 
  • They enter the lungs by inhalation of aerosols containing the bacteria and infect the lung and colonize the upper parts of the lungs. Children and immunosuppressed individuals are more prone to the disease. 
  • The most common symptoms of TB include fever, night sweats, abnormal fatigue, cough, and hemoptysis.
  • Tuberculosis should be diagnosed very carefully to distinguish between latent tuberculosis infections. The treatment includes 2 months of antibiotic therapy.


  • Influenza, commonly called flu, is an acute viral infection that affects the respiratory system caused by influenza viruses.
  • There are three types of Influenza virus that cause infection in humans, among which Influenza A is responsible for most of the cases.
  • It can be transmitted through airborne, direct contact, saliva, and by touching contaminated surfaces. 
  •  It causes the impairment in the air sac of the lungs and creates difficulty in breathing, leading to pneumonia. 
  • Symptoms are like that of the severe common cold, including high fever, fatigue, headache, muscle pain, diarrhea, and vomiting. 

Acute bronchitis

  • Bronchitis is the inflammation of the bronchial tubes by pathogens commonly, virus and bacteria.
  • Smoking is one of the major etiological factors.
  • Symptoms of bronchitis include coughing, which lasts about weeks, chest pain, fever, and fatigue. 
  • Treatment depends on the causative agents of the infection. Bacterial infection can be treated with antibiotics. While the viral infection is mild and self-limiting.


  • Also called whooping cough, it is an inflammatory condition of the respiratory tract caused by Bordetella pertussis
  • It is highly contagious and spreads from person to person. Symptoms include extreme coughing with a whooping sound, coughing fits, and breathing difficulty.
  •  It can be treated with antibiotics. 
  • Vaccines are available to prevent infection in infants and adults.

Common tests to be carried out to determine the cause of breathing difficulty


 It is one of the pulmonary functioning tests which is used to evaluate how quickly air can flow in and out of the lungs. 

It is a very useful tool in the management of individuals with chest restriction and mixed disease.

Lung plethysmography test

Optoelectronic plethysmography is a procedure where we measure chest wall movements and lung volumes.

It is an accurate method to measure lung volume. It helps to monitor the respiratory patterns in children, adults, and patients with breathing difficulties.

Diffusing capacity of the lungs test

In this test, the amount of oxygen and carbon dioxide that is diffused in the bloodstream is measured. Based on these results functioning of one’s lungs can be determined.


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