The structure of the human gas exchange system
The lungs are supported and protected by a boney box called the rib cage.
The lungs are a pair of lobed structures made up of a series of highly branched tubules,called bronchioles which end in tiny sacs called alveoli.
The trachea is a flexible pathway that is supported by rings of cartilage.The cartilage prevents the trachea collapsing as the air pressure falls when breathing in.
The bronchi are two divisions in the trachea each leading to one lung.
The bronchioles are a series of branching subdivisions of the bronchi.
The alveoli are minute sacs at the end of the bronchioles.They contain collagen and elastic fibres this allows the alveoli to strech as they fill with air when breathing in.They then spring back during breathing out in order to expel carbon dioxide rich air.
The mechanism of breathing
To mintain duffusion of gases across alveolar epithelium air must be constantly moved in and out.This is called ventillation.
Inspiration is when the air pressure of the atmosphere is greater than the pressure inside the lungs,air is forced into alveoli.
Expiration is when the air pressure is greater in lungs than atmosphere so air is forced out of alveoli.
Pulmonary ventillation: Tidal volume X ventilation rate
(dm3 min-1) (dm3) (min-1)
Exchange of gases in the lungs
Exchange surfaces have the fololowing charctersitics:
they have a large surface to volume ratio
they are very thin
they are partially permeable
there is a movement of the environmental medium
there is a movement of the internal medium.
Diffusion is proportional to:surface area X difference in concentration
/ Length of diffusion path
Diseases of the lung
Is caused by the bacterium Mycobacterium tubercolosis
The bacterium is sprad from person to person in droplets produced by sneezing and coughing.
When the droplets are inhaled the disease can progress in different ways depending on the health of the individual
Symptoms of TB:chest pain and coughing up blood,a cough that lasts for more than three weeks,chills and fever,night sweats,losss of apetite and loss of weight,fatigue.
People most at risk:
Those in regular contact with larger number of people,have an inadequate diet,inject drugs,drink excess alcohol,infected by HIV