Physiology 1 Flashcards
Internal mechanisms which consume O2 and produces CO2
Internal respiration
Exchange of O2 and CO2 between the external environment and body cells
External respiration
4 steps of external respiration?
- Ventilation between atmosphere and alveoli
- Exchange of gases between alveoli and blood
- Transport of gas from alveoli to tissues
- Exchange of gases between blood and tissues
Boyle’s law states?
At any constant temperature, the pressure exerted by a gas varies inversely with the volume of the gas
As the volume of a gas increases….
the pressure exerted by the gas decreases
Describe air flow.
Down a pressure gradient from a region of high pressure to a region of low pressure
What must happen for air to flow into the lungs during inspiration?
Intra-alevolar pressure must become less than alveolar pressure
When is intra-alveolar pressure the same as atmospheric pressure?
Before inspiration
During inspiration the thorax and lungs…
Expand
This increases volume, thus decreasing pressure
Allowing air to flow into the lungs down a pressure gradient
Name 2 forces that hold the thoracic wall and lungs together.
Intrapleural fluid cohesiveness
Negative intrapleural pressure
Define intrapleral fluid cohesiveness.
The water molecules in the intrapleural fluid are attracted to each other and resist being pulled apart, thus the pleural membranes stick together
Define negative intrapleural pressure.
The sub-atmospheric intrapleural pressure create a transmural pressure gradient across the lung wall and across the chest wall, thus the lungs expand out and the chest wall expands in
Transmural pressure gradient across lung wall =
Intra-alveolar pressure - intrapleural pressure
Transmural pressure gradient across throacic wall =
Atmospheric pressure - intrapleural pressure
Atmospheric pressure
760 mmHg
Intra-Alveolar pressure
760 mmHg
Intrapleural pressure
756 mmHg
Inspiration is an…..
Active process relying on muscle contraction
Describe the bucket handle mechanism.
Contraction of the external intercostal muscles LIFTS the ribs and moves the sternum out
What does contraction of the diaphragm do?
Increase the volume of the thorax vertically
What controls the diaphragm?
Phrenic nerves 3, 4 and 5
Expiration is a….
Passive process brought about by relaxation of the muscles
Across the lung wall, there is a ………. pressure gradient?
Transmural
What abolishes the transmural pressure gradient?
Pneumothorax
What 2 things allow the lungs to recoil during expiration?
Elastic connective tissues
Alveolar surface tension
What is alveolar surface tension?
Attraction of water molecules between liquid and air interface
What reduces alveolar surface tension?
Surfactant
LaPlance’s law
The smaller the alveoli (smaller radius), the more likely it is to collapse
Surfactant?
A mix of lipids and proteins secreted by type 2 alveoli
Surfactant prevents smaller alveoli collapsing and emptying contents into larger alveoli
TRUE
Surfactant lowers the surface tension of larger alveoli more than smaller alveoli
FALSE
smaller more than larger
How does surfactant work?
By spreading between water molecules lining the alveoli
When is surfactant made in pregnancy?
LATE
What does lack of surfactant cause?
RDS of the newborn
Define alveolar interdependance.
If an alveolus start to collapse the surrounding alveoli are
stretched and then recoil exerting expanding forces in the
collapsing alveolus to open it
Forces keeping alveoli open
Surfactant
Transmural pressure
Alveolar interdependance
Forces letting alveoli close
Elasticity
Alveolar surface tension
