Lecture 37 - Mechanics of Ventilation Flashcards
What is the primary function of the respiratory system?
o Supply tissues with oxygen
o Remove CO2 from tissues
What is the oxygen cascade?
o Getting O2 from the environment
o To the blood
o To the tissue
o To the mitochondria
What is the difference between conductive zones and respiratory zones?
Conductive zones include the larger airways responsible for guiding air into lungs and conditioning it, whereas the respiratory zone consists of the smaller airways and alveoli where gas exchange takes place.
What is the conductive zone?
Also known as the anatomical dead space, air in this space does not undergo gas exchange but does undergo conditioning
Key structures found in conductive zone
Nasal cavity, pharynx, larynx, trachea, bronchi
What is the respiratory zone?
Where gas exchange occurs, oxygen is taken up by the blood and CO2 is released into the air.
Key structures of the respiratory zone
Bronchioles, alveolar ducts, alveoli, respiratory membrane.
Architecture of human lung (big to small)
o Conducting zone: Trachea – bronchi – bronchioles – terminal bronchioles
o Respiratory zone: respiratory bronchioles – alveolar ducts – alveolar sacs
Cell types found in alveolus
o Type I alveolar cells – squamous pulmonary epithelial
o Type II alveolar cells – septal
o Macrophages
Volumes of respiratory
o Tidal volume = 500mL
o Total ventilation = 6000mL
o Respiratory frequency = 12/min
o Anatomical dead space = 150mL
o Alveolar gas = 3000mL
o Alveolar ventilation = 4200mL
o Pulmonary capillary blood (in) = 70mL
o Pulmonary blood flow (out) = 4200mL/min
What are the muscles of inspiration?
o Diaphragm
2 hemi-diaphragms
Innervated by phrenic nerve
Origins C3-5
o External intercostal
Innervated by intercostal nerves
Origins T1-T11
o Accessory muscles
Sternocleidomastoid
Scalenes
Ventilation at rest
Inspiration = active
Expiration = passive
Ventilation under stress
o Inspiration = active
o Expiration = active
Active expiration muscles:
o Abdominal muscles
o Internal intercostals
Rest expiration muscles
o Expiration passive
o Relaxation of diaphragm
o Passive recoil of lungs
What is the role of upper airway muscles in ventilation and airway resistance?
o Help maintain airway patency (openness)
o Influence volume and speed of airflow
o Speech and phonation
o Swallowing and protection
o Exercise and breathing patterns
Describe and explain the pressure changes during the different phases of breathing
o Inhalation involves a decrease in intra-thoracic pressure as the volume inceases, allowing air to flow into lungs
o Exhalation involves an increase in intra-thoracic pressure as the volume decreases, facilitating air movements out of the lungs.
Site of airway resistance
Bronchial smooth muscles
Velocity of flow is inversely proportional to?
Cross sectional area
Control of airway resistance
o Contraction of bronchial smooth muscles
o Reduce diameter of airway
o Increase resistance
How are bronchial smooth muscles controlled?
o Contraction - cholinergic acting on muscarinic nicotinic receptors) + noncholinergic parasympathetic nerves
o Relaxation – circulating catecholamines acting of B2-adrenergic receptors
What is conductance
o Reciprocal of airway resistance
o Lung volume is inversely proportional to airway resistance
How is compliance measured?
Change in volume/change in pressure
What happens when compliance is decreased?
o Increase fibrosis
o Increase surface tension
o Alveolar oedema
o Ageing
o Emphysema
o Elastin and collagen aids elastic recoil
Effect of surfactants
o Increase compliance
o Increase stability
Type II alveolar cells extrude surfactants
o Rapid turnover
o Phospholipid DPPC
o Synthesised in lungs
What is the equation involving pressure, surface tension and radius?
P = 4T/r
Interdependence of alveoli and lung parenchyma
o Adjacent alveoli – lung parenchyma provide radial traction
o Elastic properties of the lung
