Physiology Flashcards
what is internal respiration?
refers to the intracellular mechanisms which consume oxygen and produce carbon dioxide.
what is external respiration?
refers to the sequence of events that lead to the exchange of oxygen and carbon dioxide between the external environment and the cells of the body.
what are the four steps of external respiration?
1- ventilation (gas exchange between the atmosphere and alveoli)
2- exchange of 02 and C02 between air in alveoli and blood in pulmonary capillaries.
3-binding and transport of 02 and C02 in the circulating blood
4 - exchange of 02 and C02 between blood and tissues
what are the four systems involved in external respiration?
- respiratory
- cardiovascular
- haematology
- nervous
describe the anatomy of the respiratory system.
nasal passages and mouth > pharynx >larynx > trachea > right and left bronchus > bronchioles > terminal bronchiole > alveoli
what is boyle’s law?
At any constant temperature the pressure exerted by a gas varies inversely with the volume of the gas.
how does air move into the lungs during inspiration?
The intra-alveolar pressure must become less than atmospheric pressure for air to move into the lungs during inspiration. It does this by active contraction of inspiratory muscles. during inspiration the thorax and lungs expand reducing intra-alveolar pressure and allowing air to enter down its pressure gradient.
what two forces hold the thoracic wall and the lungs in close opposition?
1 - intrapleural fluid cohesiveness = the water molecules in the inrapleural fluid are attracted to each other and resist being pulled apart, hence the pleural membranes tend to stick together.
2 - The negative intrapleural pressure = the sub-atmospheric intrapleural pressure creates a transmural pressure gradient across the lung and chest walls. so the lungs are forced to expand outwards and the chest is forced to squeeze inwards.
what is atmospheric pressure?
the pressure caused by the weight of the gas in the atmosphere on the Earths surface - normally 760mm Hg at sea level.
what is intra-alveolar (intrapulmonary) pressure?
pressure within the lung alveoli. (760 mm Hg when equilibriated with atmospheric pressure)
what is intrapleural (intrathoracic) pressure?
pressure exerted outside the lungs within the pleural cavity, usually less than atmospheric pressure.
what is inspiration?
= an active process depending on muscle contraction
- the volume of the thorax is increased vertically by contraction of the diaphragm flattening out its dome shape.
- the external intercostal muscle contraction lifts the ribs and moves out the sternum (bucket handle mechanism).
what is expiration?
-normal expiration is a passive process brought on by the relaxation of inspiratory muscles. The chest wall and lungs resume their original size and the intra-alveolar pressure rises. The air then leaves down its pressure gradient until the intra-alveolar pressure equals the atmospheric pressure.
what is a pneumothorax?
= air in the pleural space
- can be spontaneous, traumatic or iatrogenic and air can have entered from outside of from the lungs.
- this can abolish transmembrane pressure leading to lung collapse.
- small pneumothorax can be asymptomatic. larger pneumothorax may have symptoms such as shortness of breath and chest pain
- physical signs = hyperressonant percussion note and decreased/ absent breath sounds.
what causes the lungs to recoil during expiration?
- elastic connective tissue in the lungs
- alveolar surface tension (most important)
what is alveolar surface tension?
- attraction between water molecules at liquid air interface
- in the alveoli this produces a force which resists the stretching of the lungs
- if the alveoli were lined with water alone the surface tension would be too strong so the alveoli would collapse.
what is LaPlace’s law?
the smaller the alveoli, the higher the tendency to collapse
what is pulmonary surfactant?
= a complex mixture of lipids and proteins secreted by type 2 alveoli
- it lowers alveolar surface tension by interspersing between the water molecules lining the alveoli.
- it lowers the surface tension of smaller alveoli more than larger alveoli, preventing collapse.
what can cause respiratory distress of a new born?
developing foetal lungs are unable top produce surfactant until late pregnancy so premature babies may not have enough surfactant. This may lead to the baby making very strenuous inspiratory efforts in an attempt to overcome the high surface tension and inflate the lungs.
what is alveolar interdependence?
if an alveolus starts to collapse the surrounding alveoli are stretched and then recoil exerting expanding forces in the collapsing alveolus to open it.
what are the major inspiratory muscles?
diaphragm and external intercostal muscles
what are the accessory muscles of inspiration?
(contracts only during forceful inspiration) sternocleidomastoid, scalenus and pectoral
what are the muscles of active expiration?
abdominal muscles and internal intercostal muscles.
what is tidal volume?
volume of air entering or leaving lungs during a single breath (average 0.5L)
what is inspiratory reserve volume?
Extra volume of air that can be maximally inspired over and above the typical resting tidal volume (3.0L average)
what is expiratory reserve volume?
Extra volume of air that can be actively expired by maximal contraction beyond the normal volume of air after a resting tidal volume. (average 1L)
what is residual volume?
minimal volume of air remaining in the lungs even after maximal expiration (1.2L)
what is inspiratory capacity?
= inspiratory reserve volume + tidal volume
maximum volume of air that can be inspired at the end of a normal quiet expiration = 3.5L average
what is functional residual capacity?
= Expiratory reserve volume + reserve volume
volume of air in lungs at the end of normal passive expiration - 2.2L average
what is vital capacity?
maximum volume of air that can be moved out during a single breath following maximal inspiration.
= inspiratory reserve volume + tidal volume + expiratory reserve volume. (4.5L average)
what is total lung capacity?
vital capacity + residual volume
-(5.7L average)
why might residual volume increase?
when elastic recoil of the lungs is lost e.g. in emphysema
what can volume time curves/ dynamic lung volumes tell you?
FVC = forced vital capacity (maximum volume that can be forcibly expelled from the lungs following a maximum inspiration)
FEV1 = Forced expiratory volume in one second. Volume of air that can be expired during the first second of expiration in an FVC determination.
FEV1/FVC ratio = the proportion of the FVC that can be expired in the first second (normally more than 70%)
what does a low/ normal FVC, a low FEV1 and a low FEV1/FVC ratio suggest?
airway obstruction
what does a low FVC, a low FEV1 and a normal FEV1/FVC ratio suggest?
lung restriction
what does a low FVC, a low FEV1 and a low FEV1/FVC ratio suggest?
a combination of obstruction and restriction.
what is the primary determinant of airway resistance?
the radius of the conducting airway.