Respiratory System Flashcards
Give 2 reasons why gas exchange at the lungs is so efficient
- Very thin barrier between the alveoli and the adjacent capillaries so short distance for gases to travel (barrier ~0.3μm so offers little diffusion resistance)
- Partial pressure gradient between air and blood drives diffusion (high pO2 of lungs and low pO2 of venous blood allows O2 to travel down a gradient)
Explain how Boyle’s Law can be applied to ventilation in the lungs
- P α 1/V
- Expansion of chest during inspiration increases thoracic volume, therefore alveolar pressure decreases (below atmP causing air to move into the lungs down a partial pressure gradient)
- Compression of chest during expiration decreases thoracic volume, therefore increases alveolar pressure (above atmP causing air to flow out)
Define Boyle’s Law of gases
- PV = nRT
- Pressure is inversely proportional to volume in a closed system, provided no. of moles and temperature remain constant
With reference to the division of the lungs, explain where gas exchange takes place
- 23 divisions
- 1-16 conducting airways where no gas exchange takes place (anatomical “dead space”)
- 17-23 RESPIRATORY ZONE where gas exchange occurs
What is meant by the ‘partial pressure’ of a gas?
- Individual pressure exerted independently by a gas within a gas mixture
- Measure of the CONCENTRATION of a gas in kilopascals (kPa)
Define Dalton’s Law of partial pressures
- The partial pressure of a gas is the individual pressure exerted independently by that gas within a gas mixture
- Each gas exerts a partial pressure equal to the pressure it would exert if it was the only gas present
What is the normal composition of atmospheric air?
- Nitrogen 78.6%
- Oxygen 20.9%
- CO2 0.03%
- H2O 0.46% (variable)
How do you calculate the partial pressure of O2 in atmospheric air?
- Partial pressure of a gas is directly proportional to its percentage in a mixture
- Total atm pressure = 101kPa and air is 20.9% O2
- pO2 = 101 x 0.209 = 21.1(1) kPa
Define ‘saturated vapour pressure’ and explain its relevance in the lungs
- Pressure exerted by water vapour in the lungs ~ 6.28kPa
- Air comes into contact with water when it diffuses into the capillary and exerts a partial pressure on the liquid
- Water molecules will evaporate to enter gas phase and saturate air and air molecules will dissolve in liquid until an equilibrium is reached
Define Henry’s Law when applied to O2 in the lungs
- Amount of O2 dissolved in the plasma is proportional to the pO2 of the alveolar gas it is exposed to
- The higher the pO2, the more O2 dissolves in plasma
Explain how you would calculate the amount of O2 dissolved in the plasma using the pO2 of alveolar air
Amount dissolved = solubility coefficient of O2 x pO2 of alveoli
What determines how well a gas will dissolve in the plasma?
SOLUBILITY COEFFICIENT for that specific gas
Why are ribs I-VII known as ‘true ribs’?
They are attached to the body and head of the sternum
Where does the intercostal space lie to its corresponding rib?
Below
How are false ribs (XIII-X) attached?
Connected to the costal cartilage of the above ribs
What is the term used to describe ribs which aren’t attached to any other ribs?
Floating ribs
Where is the inferior thoracic aperture located and what is its significance?
- Inferior boundary of the bony thorax composed of T12 and the lower margins of the ribcage and sternum
- Level at which the base of diaphragm is connected (where the thoracic cavity becomes the abdominal cavity)
Describe the articulation between a rib and the vertebral column, stating the name of each joint involved (2)
- Head of the rib articulates with the superior articular process of the corresponding vertebrae and the inferior articular process of the above vertebrae (costovertebral joint)
- Tubercle of rib articulates with the transverse process of the corresponding vertebrae (costotranverse joint)
Describe the movements of the chest during inspiration to increase surface area in the thoracic cavity (2)
- Lateral movement of ribs (up and side) increases lateral diameter (bucket handle)
- Superior movement of sternum (up and out) increases anterior-posterior diameter (pump handle)
Why is the diaphragm positioned higher on the right than the left?
- Liver pushes diaphragm up on the right
- Heart pushes diaphragm down on the left
At rest, roughly which level is the diaphragm at?
4th ICS on the right and 5th ICS on the left
How far down can the diaphragm move when we breathe in?
~1.5 intercostal spaces
Which nerve innervates the diaphragm? State the nerve roots
- Phrenic nerve (right and left)
- C3, C4, C5
Describe the action of the external intercostal muscles (2)
- Muscle fibres run parallel to the external oblique muscles in the abdominal wall (inferiomedially)
- Contraction causes the ribs to move UP
