L15 Respiratory Physiology Flashcards
What are the physical; factors that influence pulmonary ventilation?
1) airway resistance - anything that impedes air flow through the respiratory tract
2)alveolar surface tension - alveoli are covered with a thin film of liquid composed mainly of water creating a gas-water boundary
3)lung compliance - the ability of the lungs and chest walls to stretch
What is airway resistance?
- the opposition of flow caused by the forces of friction
- the ratio of driving pressure to the rate of air flow
What is airway resistance determined by?
- length of system (constant)
- airway diameter -> wider airways have less resistance
- flow : laminar (low R) or turbulent (high R)
- viscosity of gas (usually constant)
What is the equation for flow rate?
Driving pressure / r to the power of 4
What factors affect gas exchange in the alveoli?
1) oxygen reaching the alveoli
2) gas diffusion between alveoli and the blood
3) adequate perfusion of alveoli
Why do bronchi have the highest resistance?
Under what conditions does resistance increase?
- Inflammation of airways
- Increased mucus secretion
- Presence of a tumour
What is bronchodilation?
Airway resistance decreases as smooth muscle relaxes
-> increase in diameter of airway
What is bronchoconstriction?
Airway resistance increases as smooth muscle contracts
-> decrease in diameter of airway
What is central control in the bronchioles?
The parasympathetic innervation of airways
- bronchoconstriction increases resistance
There is NO sympathetic innervation of airways
What is non-neural control in bronchioles?
Sympathetic beta2 receptors present on smooth muscled activated by circulating adrenergic agonists (adrenaline)
- bronchodilation decreases resistance
How is surface tension formed in alveoli?
Alveoli are covered with a thin film of liquid (mainly water) which creates a gas-boundary
- Water molecules form hydrogen bonds
- Gases are nonpolar molecules and therefore do not form hydrogen bonds
This creates surface tension at the boundary
When is the surface tension in alveoli the greatest?
When the alveoli are at their smallest diameter - during expiration
When are alveoli hard to inflate?
When the surface tension is high therefore when alveoli are small
What is the role of a surfactant?
Reduces surface tension
How is the pressure equalized between small and large alveoli?
Small alveoli have more surfactant than large alveoli
- the more surfactant decreases the surface tension
What happens to alveoli with surfactant?
The hydrogen bonds are disrupted and the alveolus remains inflated
What happens to alveoli without surfactant?
Hydrogen bonds pull the water molecules together and the alveolus collapses
Why can alveoli collapse during expiration?
There is a high amount of unopposed surface tension = atelectasis
Why does the surfactant decrease the work of breathing?
- produced by type II alveolar cells
- mixture containing proteins and phospholipids
- similar chemical structure to detergent, with both polar and nonpolar end
- distrusts cohesive force of hydrogen bonding of water
- allows alveolus to remain partially open even during expiration
- more concentration in smaller alveoli therefore increased stability
Why does infant respiratory distress syndrome occur?
Surfactant is not produced significantly until the last 10-12 weeks of gestation so premature newborns may suffer
What is lung compliance?
The ability of lungs and the chest wall to stretch/distend
The ability of tissue to return to its original state when stretched
What is compliance defined as?
The change in volume produced by a change in pressure
What is lung compliance affected by?
- Alveolar surface tension : surfactant increases compliance
- Distensibility of elastic tissue of lung : during inflation
- Ability of the chest wall to move or stretch during inspiration
