Lungs and Disease

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  • Created by: claire
  • Created on: 14-12-13 13:13

Gas Exchange

Vol of o2 that has to be absorbed and the vol of CO2 that must be removed are large in mammals because:

  • relatively large organisms with large volume of living cells
  • maintain high body temp, high metabolic and respiratory rates

Lungs are inside the body because:

  • air isn't dense enough to support and protect delicate structures
  • would otherwise lose lots of water

Lungs - pair of lobed structures made up of brioncholes which end in alveoli                             Trachea - flexible airway supported by rings of cartilage, prevents tracheo collapsing as air pressure inside falls in inspiration. Lines with ciliated epithelium and goblet cells. Goblet cells produce mucus that traps dirt particles and bacteria. Ciliar move mucus up to throat, down oesophagus into stomach                                                                                                       Bronchi - 2 divisions of trachea, produce mucus, larger bronchi supported by cartilage               Bronchioles - muscle lines with epithelial cells, allows them to constrict to control flow of air       Alveoli - collagen and elastic fibres, lines with epithelium. elastic fobres allow alveoli to stretch 

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Mechanism of Breathing


  • Active process
  • External intercostal muscles contract, internal intercostal muscles relax
  • Ribs pulled upwards and outwards, increasing vol of thorax
  • Diaphragm muscles contract, flatten, increases vol of thorax
  • Reduction of pressure in lungs
  • Atmospheric pressure greater than pulmonary pressure, air forced into lungs


  • Passive process
  • Internal intercostal muscles contract, external intercostal muscles relax
  • Ribs move down and inwards, decreasing vol of thorax
  • Diaphragm  muscles relax, doomed, decreasing vol of thorax
  • Increased pressure of lungs
  • Pulmonary pressure greater than atmospheric pressure, air forced out of lungs
  • recoil of elastic lungs

pulmonary ventilation = tidal vol (dm3)  x ventilation rate (min)

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Exchange of gases

  • Large s.a to vol ratio
  • Very thin - keep the diffusion pathway short
  • Partially permeable
  • Movement of environmetal medium - maintain diffusion gradient
  • Movement of internal medium - maintain diffusion gradient

Alveoli Role

  • R.b.c slowed as they pass through pulmonary capillaries, allowing more time for diffusion
  • Distance between alveolar air and and r.b.c reduced, r.b.c flattened against capillary walls
  • Walls of alveoli and capillaries very thin, distance over which diffusion occurs is very short
  • Alveoli and pulmonary capillaries have very large total s.a
  • Breathing movements constantly ventilate lungs. Action of heart constantly circulates blood around alveoli. Steep concentration gradient of gases to be exchanged is maintained
  • Blood flow through pulmonary capillaries maintains concentration gradient
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Pulmonary Tuberculosis

Caused by mycobacterium tuberculosis. Spread through the air by droplets released when infected cough. Some are at greater risk of contracting TB, eg people who:

  • are in close contact with infected over long periods
  • work in long term care facilities where large numbers of people live together
  • are from countries where TB is common
  • have reduced immunity - very young/old, AIDS, immunosuppressant drugs


  • Bacteria grow in lungs where there is lots of O2
  • Immune system responds, w.b.c accumulate at site of infection to ingest bacteria
  • Inflammation of lymph nodes - primary infection
  • Bacteria may re-emerge - post primary tuberculosis
  • Bacteria destroy tissue of lungs, results in cavities and scar tissue
  • Damaged lung tissue and bacteria and blood coughed up
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Lung Disease

Pulmonary Fibrosis

Occurs when scars form on epithelium of lungs, thicker epithelium. Alveoli need to be thin for diffusion. Elasticity of lungs reduced, breathing out more difficult. Oxygen can't diffuse into blood as efficiently.

  • Shortness of breath - air space within lungs occupied by fibrous tissue, less oxygen taken into lungs at each breath, thickened epitehlium of alveoli means diffusion pathway is increased, diffusion of oxygen into blood is slower, loss of elasticity means ventilating lungs is difficult. Hard to maintain diffusion gradient across exxhange surface
  • Chronic dry cough - fibrous tissue creates obstruction in airways. Reflex reaction is to remove obstruction but tissue is immovable
  • Pain in chest - higher pressure and damage from mass of fibrous tissue in lungs and coughing
  • Weakness - reduced intake of oxygen into blood, release of energy by cellular respiration reduced
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Lung Disease


  • Allergens cause w.b.c on linings of bronchi to release histamine
  • Lining becomes inflamed
  • Cells of epitehlial lining secrete more mucus
  • Fluid leaves capillaries and enters airways
  • Muscles surrounding bronchioles contracts and constricts airways
  • Greater resistance to flow of air through alveoli. Difficult to ventilate lungs and maintain diffusion gradient across exchange surface
  • Difficulty in breathing - constriction of bronchi, inflamed linings, additional mucus
  • Wheezing - air passing though constricted bronchi
  • Coughing - reflex to obstructed bronchi
  • Tight chest - Inadequately ventilated lungs, constricted bronchi

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Lung Disease


Elastin is permanently stretched, lungs can't force out all the air from alveoli, little exxchange of gases.

  • Short breath - difficulty in exhlaing air due to loss of elasticity in lungs. Difficult to inhale fresh air containing oxygen. Smaller alveolar surface area, reduced levels of oxygen in blood, more rapid breathing
  • Chronic cough - body's effort to remove damaged tissue and mucus that can't be removed naturally, cilia on bronchi destroyed
  • Bluish skin coloration - low levels of oxygen in blood, poor gas diffusion in lungs


  • Smoking
  • Air pollution
  • Genes
  • Occupation
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