Drive - physiology Flashcards
What is meant by the term minute volume?
The volume air inspired/expired in a minute
What is the approximate minute volume?
5L/ min
What is interpleural pressure?
The pressure in the pleural space
What is alveolar pressure
Air pressure in the pulmonary alveoli
Where does the phrenic nerve arise from?
C3, C4 and C5
What is inspiration initiated by?
Neurally induced contraction of the diaphragm and the external intercostal muscles located between the ribs
What is the most important inspiratory muscle that acts during normal quiet breathing?
Diaphragm
When stimulated to contract what is the movement of the diaphragm?
Downwards
When stimulated to contract what is the movement of the external intercostal muscles?
Upwards and outwards
What happens to the intrapleural pressure and transpulmonary pressure when the thoracic volume increase?
Intrapleural pressure = decreases
Transpulmonary pressure = increases
What happens (during inspiration) when transpulmonary pressure becomes more positive? (and why)
The lungs expand because transpulmonary pressure > elastic recoil.
What effect does lung expansion have on alveolar pressure?
Becomes more negative
What occurs when alveolar pressure becomes more negative?
Inwards airflow
What occurs to the muscles of the diaphragm and external intercostal muscles during (passive) expiration? and what does this cause?
They relax resulting in a decreasing thoracic volume
What allows the lungs and chest walls to passively collapse?
Elastic recoil
(as muscle relaxation causes increased intrapleural pressure which decreases transpulmonary pressure to below that of the elastic recoil force)
What causes alveolar pressure to increase?
Air temporarily compressed
What does increased alveolar pressure cause?
Outwards airflow
What additionally to the process of passive expiration occurs during forced expiration?
The internal intercostal muscles also contract (as do the abdominal muscles)
What does the contraction of the internal intercostal muscles cause?
The ribs to move downwards and inwards (actively decreasing thoracic volume)
What does contraction of the abdominal muscles result in?
Forcing the relaxed diaphragm moving further up - decreases thoracic volume
In what lung structure is the greatest resistance and why is this?
Trachea as it has a much smaller surface area than (combined) the bronchi do.
