The Respiratory System

Lungs, Functions and lung disease

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The Lungs


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Gaseous exchange


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Pulmonary Ventilation, Tidal Volume and Ventilatio

  • Pulmonary Ventilation is the amount of air taken into the lungs in one minute. This is measured in dm3 min -1. (cubic decimetres per minute)
  • Ventilation Rate is the number of breaths per minute/ min-1 (usually around 15 at rest)
  • Tidal Volume is the volume of air in each breath (usually around 0.4 dm3)

The equation for this is:

Pulmonary Ventiliation = Tidal Volume x Ventilation Rate

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Pumonary Tuberculosis (TB)

Pumonary Tuberculosis (TB) is caused by the bacterium Mycobacterium tuberculosis

TB is transmitted by droplet infection, which is when people cough or sneeze, the bacteria is inside the droplets of mucus or saliva that come from the mouth or nose. If an uninfected person breathes these in, the bacteria is passed on.

TB is more common in areas with poor hygene levels and/or people live in crowded conditions

It is prevented through the BCG vaccine and is treated with antibiotics

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TB Infection and Symptoms


  • When someone is infected by TB bacteria, the immune response is to build a wall around the bacteria in the lungs, forming small hard lumps called tubercles.
  • The infected tissue within the tubercles dies, damaging the gaseous exchange surface hence lowering the tidal volume.
  • Tuberculosis can also cause Fibrosis- which can also reduce the tidal volume.
  • The bacteria can spread to other parts of the body if they manage to enter the blood stream.

Symptoms can consist of a cough, coughing up blood and mucus, chest pains, shortness of breath, fatigue, fever and loss of appetite resulting in weight loss

Many people with TB are asymptomatic, where they don't show any symptoms as the infection is in an inactive form hence cannot pass the infection on. But if thye become weakened the infection can become active and be transmitted.

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Conditions Affecting Lung Function

Fibrosis is the formation on scar tissue in the lungs.

  • Scar tissue is thicker and less elastic that normal lung tissue, which means the lungs are less able to expand. Consequently the lungs can't hold as much air compared to normal, which means the tidal volume is reduced. It's also harder to push air out of the lungs.
  • Diffusion is slower across the thicker scarred membrane- reducing the rate of gaseous exchange. Sufferers generally have a faster breathing rate than normal so they can get enough air to oxygenate the blood.
  • Fibrosis is usually caused by infection or exposure to substances like dust or asbestos.

Symptoms include : Shortness of breath, a dry cough, chest pain fatigue and weakness.

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Asthma is where the airways become inflamed and irritated.

  • During an asthma attack, the smooth muscle lining of the brochioles contracts and a lot of mucus is produced.
  • This constricts the airways making it difficult to breathe, reducing the air flow in and out of the lungs, reducing the amount of oxygen that enters the blood and the alveoli.
  • Asthma is usually caused by an allergic reaction to substances such as dust and pollen.

Symptoms include: Wheezing, tight chest and shortness of breath. These symptoms can come on very suddenly and can be relieved by drugs (often in the form of inhalers) that relax the muscles in the bronchioles, opening up the airways.

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Emphysema is a lung disease caused by smoking or long-term exposure to air pollution.

  • Foreign particles become trapped in the alveoli, causing inflammation which attracts phagocytes to the area, which produce an enzyme that breaks down the elastin in the walls of the alveoli.
  • Loss of elastin means means that the alveoli can't recoil to expel the air, trapping it in the alveoli. The elastin also helps the alveoli to return to their original shape.
  • The enzyme can also destroy the alveoli walls, reducing the surface area and the level of gaseous exchange.       

( Symptoms include: shortness of breath and wheezing. They have an increased breathing rate to increase the amount oxygen reaching the lungs.

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