INERVATION
Lung innervations are automatic, both Para sympathetic and sympathetic and produce bronco constriction and bronco dilation due to the straight muscle presence. Para sympathetic innervations mainly reach through the pneumo-gastric nerve. However, the sympathetic fiber amount is low. Fortunately, the bronchial arbola is very much exposed to noradrenalin and adrenalin which come from blood and produce bronchial dilation (simile sympathetic effect).
PLEURA
It is serous membrane which covers the lungs. There are two leaves: parietal and visceral and both reflect each other in the lung hilio. A pleural space lies between them. It is considered a virtual space since it possesses very few liquid and some free cells. It could transform into real during pathological conditions such as pneumo thorax, hemo thorax and hydro thorax.
LUNG PHYSIOLOGY
The main function of the lungs is to provide tissues with O2 and eliminate CO2. Its physiology could be divided into four main functional facts.
1. Lung ventilation: air flow, entrance and exit between atmosphere and alveoli.
2. Gas diffusion between alveoli and blood.
3. Gas transportation from and to the cells.
4. Regulation.
VENTILATION
Lungs might expand and contract and that is how they are filled and emptied of air. The organs which cause inspiration and expiration are:
The diaphragm muscle pulls the lung inferior surfaces in order to inspire. During expiration it simply relaxes, lungs elastically draw back. During energetic respiration the abdominal muscles also participate.
Ribs: its aperture expands the thoracic cavity. Anterior-posterior diameter rises a 20%. Muscles which produce this expansion are intercostals, esternocleidomastoid, serratum, escalenum and abdominal rectum.
Lung is an elastic structure; if nothing keeps it inflated it expels the air.
Alveolar Pressure
Air pressure in the interior of the alveoli: In order to originate an inside air flow (inspiration), the alveolar pressure must be inferior as compared with atmospheric pressure., this is why it reaches to minus 1 cm of water. This is enough to displace 500 ml of air to the interior of the lungs during the two seconds that a normal inspiration lasts. During expiration ( 2 to 3 seconds) pressure amounts to plus 1 cm of water.
Lung Volumes
Current volume: inspired and expired air during every normal respiration (500 ml).
Inspiratory reserve volume: maximum additional volume which might be inspired over the current volume (3,000 ml)
Reserve Expiratory volume: maximum additional air volume which might be expired through forced expiration after a normal current expiration (1,100 ml).
Residual Volume: Air volume which remains in the lungs after a forced expiration (1,200 ml)
Lung Capacities
Inspiratory capacity: CV plus IRV. It is the total amount of air that a person might breathe starting at a normal expiratory level and expanding his lung to reach a maximum capacity (3,500 ml).
Functional residual Capacity: ERV plus RV. It is the air remaining inside the lungs after normal expiration, 2,300 ml.
Vital Capacity: IRV plus CV plus ERV. It is the maximum amount of air that can be expelled by a person after he accomplishes his maximum inspiration effort and after he makes a maximum expiration effort, 4,600 ml.
Total Lung capacity: Vital capacity plus RV which is the maximum volume that lungs can reach, 5,800 ml.
In women, these volumes are 20-25% inferior and athletic or tall persons might increase it.
Respiratory Volume Minute
It is the amount of new air that penetrates the respiratory conducts each minute. It is current volume x respiratory frequency. Normal respiratory frequency reaches 12 per minute.
RMV equals 6,000 ml per minute.
Alveolar Ventilation
During current respiration, the air volume only gathers to fill the respiratory conducts up to the terminal bronchioles and only a small portion reaches the alveoli. Thus, alveolar ventilation is mainly produced through diffusion.
The space in the respiratory conducts where there is no gaseous exchange is usually called dead space. A young man shows some 150 ml, but this figure rises with age.
Alveolar ventilation rate (usually called alveolar ventilation) is the total volume of new air that penetrates the alveoli and close areas in which gaseous exchange takes place.
That is, AV equals Respiratory frequency x (CV minus Dead Space V) which yields 4,200ml per minute.
