Lungs + TB

Structure + Function

Alveoli are the gas exchange surface with the body and atmosphere in humans.

Respiration/Ventilation used to uptake oxygen into the blood and to remove carbon dioxide

Passage of air:

  • As you breathe in, air enters the trachea which splits into the bronchi
  • Each bronchus leads to a lung, having branched into small tubes called bronchioles
  • Bronchioles end in small air sacks - alveoli

The lungs are surrounded by the ribcage with intercostal muscles inbetween and the diaphragm at the bottom

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Inspiration (breathing in) - active process

Intercostal muscles and diaphragm contract (flatten)

Rib cage moves upwards and outwards

This increases the volume of the thorax so pressure decreases below atmospheric pressure

This causes air to flow into lungs

Expiration (breathing out) - passive process

Intercostal muscles and diaphragm relax (domes)

Rib cage moves downwards and inwards

This decreases the volume of thorax so pressure increases above atmospheric pressure

Air is forced out of the lungs

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Gas Exchange in Alveoli

Gas exchange surface is the alveoli - millions of them so provide large surface area for diffusion

Surrounded by capillaries. O2 diffuses from alveoli across the alveolar epithelium and capilary endothelium into bloodstream were is combines with hameoglobin to form oxy-haemoglobin

CO2 diffuses across to alveoli and is breathe out

Adaptation for Gas Exchange

  • Large surface area - many alveoli form large surface to increase rate of diffusion
  • Thin exchange surface - epithelium and endothelium of alveoli and capillary are only one cell thick. Short diffusion pathway
  • Steep concentration gradient - ventilation maintains a constant in-flow of O2 and removal of CO2 so concentration gradient is maintained. Also maintained by flow of blood in capillaries bringing blood with low concentration of O2
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Pulmonary Ventilation

Measured in dm^3 min^-1

Pulmonary Ventilation = Tidal Volume x Ventilation Rate

PV = the volume of air taken into lungs in one minute

TD = the volume of air in each breath

VR = the number of breaths per minute

Often graphed with results from spirometer

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Pulmonary Tuberculosis

Cause and Infection

  • Caused by bacteria
  • White blood cells ingest bacterium and form hard lumps called tubercles - primary infection
  • Re-emerge years later as secondary infection

The bacteria damage the walls of alveoli which causes scar tissue to form - fibrosis. The damage to the walls and fibrosis reduce tidal volume and thicken the diffusion pathway


  • Persistent cough including coughing up blood and mucus
  • Chest pain, fatigue and shortness of breath
  • A fever and weight loss


  • Transmitted on droplets of moisture or mucus from infected person being breathed in. Makes people living in unhygenic and crowded places vulnerable
  • Can be spread from cows through milk
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