Gas Exchange
Ventilation
The Respiratory System
the continuous flow of air into and out of the lungs
maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood in the adjacent capillaries
mechanism:
lungs can't actively inflate or deflate
muscles around the thoracic cavity control its volume
internal and external intercostal muscles (antaonistic)
abdominal muscles
diaphragm
increase in volume (of T.C.)
decrease in pressure (inside T.C)
air flows into lungs
Inspiration
Expiration
- diaphragm and external intercostal muscles contract
- internal intercostal muscles and abdominal muscles relax
- rib cage moves up and out
- volume of the thoraic cavity and lungs increase
- pressure inside the cavity and lungs decrease
- air flows in through an open mouth or nasal passages filling alveoli with air
- diaphragm relaxes, moving up
- at the same time, external intercostal muscles relax and the internal intercostal muscles contract
(moving the rib cage down and in)
- abdominal muscles contract
(pushing the diaphragm up)
- volume of the thoraic cavity and of the lungs decrease
- pressure inside the cavity and inside the lungs increase
this forces air to flow out through an open mouth or nasal passages
emptying alveoli
Alveoli
Type I pneumocytes
extremely thin (similar to endothelial cells of capillaries)
adapted to carry out gas exchange
Constitute the wall of each alveoli
Type II pneumocytes
rounded cells that occupy only about 5% of surface area of alveoli
secrete a solution with surfactant
(reduces the surface tension of a liquid)
the surfactant helps the diffusion of oxygen into the cell and prevents the internal walls of each alveoli from adhering to each other
Epidemiology
the study of the incidence and causes of disease
usually uses data gathered from observations
occuring in populations
since one cannot carry out experiments with humans
it provides important information about correlations between different factors and disease
when the analysis of data is done correctly, it allows us to differentiate a causal correlation from an incidental one
Causes of Lung Cancer
the most common cancer in the world
smoking: about 87% of the cases of lung cancer are caused by tobacco smoking
passive smoking: about 3% of the cases of lung cancer are caused by tobacco smoke exhaled by smokers
air pollution: about 5% of the cases of lung cancer are caused by chemicals found in air
nitrogen oxides from vehicle exhaust fumes
smoke from burning coal
etc.
Asbestos, silica and other solid particles found usually on construction sites or in quarries, mines or factories.
Emphysema
type of COPD
(chronic obstructive pulmonary diseased)
caused by damage to the alveoli
(there are fewer alveoli, with thicker walls)
mainly caused by cigarette smoking
theories that try to explain the molecular mechanisms involved in emphysema:
phagocytes inside alveoli normaly engulf bacteria and produce elastaase
alpha-1-antitrypsin (AAT) prevents elastase from digesting lung tissue
but in smokers there are more phagocytes, which then produce more elastase, damaging alveoli
genetic factors afect the quantity and effectiveness of AAT