Respiratory System Flashcards
What is Boyle’s law?
The pressure of gas is inversely proportional to volume at a constant temperature in a closed system, so if a given amount of gas is compressed into a smaller volume pressure will increase.
What is Charles’s law?
Increasing temperature increases the kinetic energy so pressure increases
Why is the partial pressure of oxygen in the alveolus less than the atmosphere?
Air becomes saturated as it passes through the nose and water molecules exert a gas vapour pressure, thus reducing the partial pressure of oxygen.
What is meant by tension?
Dissolved gases exert tension on liquid, at equilibrium the partial pressure is equal to the tension.
Amount of gas dissolved = solubility X tension
Why might a diver get ‘the bends’?
Pressure below the sea level is 1atm + the weight of the water so air inspired is at a higher level than on the ground.
N2 moves from high pressure in the lungs into the blood, when returning to the surface quickly N2 does not have time to completely leave the blood and forms gas bubbles.
Name the paranasal sinuses:
Frontal sinus, ethmoid sinus, maxillary sinus, sphenoid sinus
What are the functions of the nasal cavity?
Filters air, humidifies and warms air, contribute to sense of smell, receives local secretions.
What is the larynx?
Vocal cords act as a ‘valve’ guarding the entrance to the trachea.
Open in respiration, closed when swallowing, partially closed in speech.
What is the glottis?
2 vocal cords and the aperture between them, moved by the intrinsic muscles of the larynx.
Adduction closes, abduction opens glottis.
What can cause hoarseness of voice?
Damage to the left recurrent laryngeal nerve that supplies the intrinsic muscles of the larynx.
Describe the histology throughout the respiratory tract:
Nasal cavity to bronchioles- pseudostratified columnar ciliated epithelium with goblet cells
Terminal bronchioles- simple columnar with cilia and Clara cells
Respiratory bronchioles and alveolar ducts- simple cuboidal with Clara cells
Alveoli- simple squamous, type I and II cells
Describe the histology if the olfactory region:
Tall pseudostratified epithelium with microvilli and olfactory cells (bipolar neurones associated with non-motile cilia to increase surface area and respond to odours).
What is the function of Clara cells?
Secrete surfactant lipoproteins that prevent walls sticking on expiration and Clara cell protein which is a maker is bronchoalveolar lavage fluid and serum.
What is the structure of alveoli?
Have capillaries supported by basket work of elastic and reticular fibres, type I pneumocytes and type II cells that secrete surfactant.
What is a partial pressure?
Molecules of gas behave independently and each gas exerts a fraction of the total pressure in a mixture
What makes up the bony thorax?
12 thoracic vertebrae, 12 ribs and costal cartilages, sternum
Describe the differences between ribs:
Ribs 1-7 connected by costal cartilages
8-10 connected to costal cartilage above
11+12 ‘floating ribs’ end free in abdominal muscles
List the features of a typical rib and the differences in atypical ones:
Typical- 2 articulate facets, head, neck, tubercle, shaft, costal groove and transverse process.
Atypical ribs- first rib is the shortest with only a single head facet, second rib has a poorly marked costal groove, 11/12 have a single facet and a no tubercle
How do the intercostal muscles move the ribs?
External, internal and innermost muscles in the intercostal spaces.
External muscles elevate upper ribs to increase AP diameter and elevate lower ribs to increase lateral diameter.
Internal and innermost muscles depress ribs in forced expiration.
Why should a chest drain be inserted at the bottom of an intercostal space above the next rib?
The neurovascular bundle (VAN) runs in the costal groove on the inferior surface of each rib between the internal and innermost intercostal muscles.
What is the neurovascular supply to the intercostal muscles?
Nerves from anterior rami of T1-12 supply muscles skin and parietal pleura.
Anterior intercostal artery from internal thoracic and posterior from the thoracic aorta.
Venous drainage into the azygous system.
At what vertebral levels do various structures cross the diaphragm?
IVC T8, oesophagus T10, aorta T12
What is the nervous supply to the diaphragm?
C3,4,5 phrenic nerve
Also is sensory to the pericardium and mediastinal pleura.
What is the ‘pleural seal’?
Pleural fluid resists the parietal and visceral pleura from pulling apart.
What passes through the hilum of the lung?
Pulmonary vessels, bronchus, nerves and lymphatics
What is meant by a bronchopulmonary segment?
An area of lung supplied by its own segmental bronchus and segmental branches of the pulmonary artery and vein.
What are the boundaries of the mediastinum?
Superior boundary- thoracic inlet and plane through sternal angle
Anterior- body of sternum and fibrous pericardium
Posterior- between pericardium and vertebral bodies
How do we bring about inspiration?
Contraction of diaphragm and external intercostals to increase volume and decrease intrathoracic pressure so air moves in
Explain expiration:
Passive elastic recoil decreases volume and increases the intrathoracic pressure so air flows out.
Explain what happens in forced expiration:
Requires force exerted by abdominal muscles (external and internal oblique, rectus abdominis) and rest of the intercostals
What are the accessory muscles required for forced inspiration?
Sternocleidomastoid, scalene, serratus anterior, pectoralis major
What is meant by lung compliance?
Stretchiness, volume change per unit pressure change. So compliance means easier to stretch. Elastic recoil is inversely proportional to compliance.
What is the purpose of surfactant?
Reduces surface tension and therefore compliance.
Why do smaller alveoli not collapse?
Alveoli get bigger surface tension increases and surfactant is not as effective so pressure is higher and therefore equalised to the smaller alveoli.
What causes infant respiratory distress syndrome?
Premature babies have too little surfactant so there are a few large alveoli and lungs are very stiff so breathing and gas exchange is compromised.
What is Poiselle’s Law?
Small tubes have high flow resistance but branching increases parallel airways thus reducing overall resistance. Therefore highest resistance is in the trachea and larger bronchii, and lowest in the small airways.
How would you calculate pressure?
Number of moles X gas constant X absolute temp / volume
What is Fick’s law?
Diffusion rate = pressure difference X cross-sectional area X solubility / distance X sqrt(molecular weight)
Does O2 or CO2 diffuse faster- explain why:
Oxygen is smaller so diffuses faster through gases.
Carbon dioxide is much more soluble than oxygen so diffuses faster through liquid e.g. in tissues.
How can you calculate permeability?
Diffusion coefficient X solubility / thickness of membrane
What makes up the diffusion barrier?
5 cell membranes, 3 layers of cytoplasm and 2 layers of tissue fluid
What factors can affect the rate of gas diffusion across a membrane?
Thickness (increased by oedema) Surface area (reduced by emphysema) - diffusion coefficients and pressure differences shouldn't change
Why is exercise not limiting on oxygen diffusion?
Equilibrium is reached a third of the way along the capillary so when the partial pressure of carbon dioxide goes up and blood spends less time in the capillary exchange of oxygen is not affected.
What is the advantage of several breaths being required to totally exchange alveolar air?
Guards against sudden changes in blood gas levels so of respiration is temporarily interrupted blood gas levels and pH are unaffected
How could you calculate the alveolar ventilation rate?
Pulmonary ventilation rate (TV X RR) - dead space ventilation rate (DSV X RR)
What is meant by physiological dead space?
Anatomical dead space (volume of airways measured by nitrogen washout) and distributive dead space (parts of lungs not functioning e.g. damaged alveoli)
What are the advantages of lung function tests?
Non-invasive, cheap, technically simple
Explain the principles of spirometry:
Subject breathes from a closed chamber over water attached to a pen which creates a Spirograph trace.
What affects vital capacity?
Compliance on inspiration, force of inspiration muscles, airway resistance on expiration
What is meant by FEV1.0?
Volume expired in the first second
How would you recognise an obstructive pattern on a flow volume plot?
Same volume expired, curve falls more rapidly.
FVC normal, FEV1 reduced
How would you recognise a restrictive pattern on a flow volume plot?
Less volume expired, curve narrowed. Decreased FVC, FVC:FEV1 ratio the same.
What are the features of myoglobin?
Binds one oxygen molecule. Stored in muscles.
What are the features of haemoglobin?
Binds four oxygen molecules in tetramer.
Has 2 alpha chains and 2 beta chains.
Low affinity T state, high affinity R state with cooperative binding.
What is the Bohr shift and what is its physiological significance?
pH is lower in metabolically active tissues so extra oxygen is given up (curve is shifted to the right).
Increased temperature also shifts curve to the right.
How does carbon monoxide affect blood?
Reacts to form CoHb and increases the affinity of subunits for oxygen but don’t give up to tissues.
What is pulse oximetry?
Detects level of haemoglobin saturation by differences in light absorption (only arterial).
What is the Henderson-Hasselbach equation?
pH=pK + Log10(HCO3/pCO2 x solubility factor 0.23)