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
Describe the action of the internal and innermost intercostal muscles (2)
- Muscle fibres run perpendicular to the external intercostal muscle fibres (superiomedially) so act antagonistically
- Contraction causes the ribs to jive DOWN
At which vertebral level does the inferior vena cava pass through the diaphragm?
T8
At which vertebral level does the oesophagus pass through the diaphragm?
T10
At which vertebral level does the aorta pass through the aortic hiatus behind the diaphragm?
T12
What is meant by ‘accessory respiratory muscles’?
Use of neck, pectoral or abdominal muscles to aid in breathing if there is strain on normal ventilation e.g. following exercise, COPD and the intercostal muscles alone are insufficient
Where would you insert the needle for a chest drain? Explain your reasoning (3)
- Main neurovascular bundle supplying each ICS runs within the costal groove on the inferior border of the corresponding rib
- Collateral vessels run superior to the below rib and are less important
- Place needle ABOVE a rib in the retrospective ICS to avoid damage to main neurovascular bundle
Describe the venous drainage of the intercostal spaces (4)
- Azygous and hemiazygous venous system (longitudinal vein which collects blood from ICS)
- Posterior intercostal veins drain into the azygous (right) and hemiazygous (left) veins
- Hemiazygous veins drain into azygous vein at T8/T9
- Azygous vein drains into SVC at the level of the heart
Describe the action of the phrenic nerve (2)
- Provides motor (and sensory) innervation to the diaphragm muscle
- Provides sensory innervation to the cervical dermatomes C3-5, mediastinal pleura and pericardium
Describe the order of the neurovascular structures running in the costal groove from superior to inferior
Vein, Artery, Nerve
Between which muscular layers does the intercostal neurovascular bundle insert?
Between the internal and innermost intercostal muscles (inserts superiorly)
With reference to the phrenic nerve distribution, explain the concept of referred pain (2)
- Phrenic nerve provides both motor and sensory innervation to diaphragm and sensory innervation to mediastinal pleura, pericardium and cervical dermatomes C3-5
- Due to widespread distribution, brain cannot distinguish where pain is arising from e.g. Pain in the pericardium detected by the phrenic nerve may be referred to shoulder as nerve provides sensory innervation to both of these regions
Describe the lobar structure of the right and left lungs
- Left lung has 2 lobes separated by an oblique fissure
- Right lung has 3 lobes separated by a horizontal and oblique fissure
Describe the position of the horizontal fissure in the right lung (2)
- Runs horizontally from the sternum at the level of the 4th rib to separate the superior and middle lobes
- Joins the oblique fissure at the level of the hilum
Explain the course of the oblique fissure
Originates from the inferior border of the lung and ascends in a superoposteiror direction until it meets the posterior lung border
Which lobe are you listening to when auscultating the lungs from the back?
Inferior lobe
Explain why foreign bodies are more likely to get lodged in the right lung compared to the left
Right bronchus angle of entry is less acute compared to the left so foreign bodies enter the right bronchus more easily
What is contained between the visceral and parietal layers of the pleura?
Pleural cavity and small amount of serous fluid
What type of cells make up the pleura?
Simple squamous epithelia (mesothelium)
Explain why the pleura extends further down than the lungs
Allows lungs to expand down into the cavity and fill with air during inspiration
Describe the blood supply to the lungs (2)
- Pulmonary circulation carries deoxygenated blood from right heart to lungs to be oxygenated and sent back to the heart
- Bronchial circulation provides blood supply to the lung tissue itself (branch from the intercostal arteries)
Explain the significance of the lungs having a dual blood supply
Bronchial blood supply can help to maintain lung viability following a pulmonary embolism
Describe the orientation of the pulmonary vessels from the heart to the lungs (2)
- Pulmonary arteries carrying deoxygenated blood run anterosuperiorly
- Pulmonary veins carrying oxygenated blood run anteroinferiorly
Which muscles are involved during quiet inspiration?
- Diaphragm
- External intercostal muscles
Describe the 4 stages of the respiratory cycle
- Inhalation
- Rest
- Exhalation
- Pause
