respiratory system part 2 Flashcards
Pulmonary ventilation consists of two phases
Inspiration: gases flow into the lungs
Expiration: gases exit the lungs
Atmospheric pressure (Patm)
Pressure exerted by the air surrounding the body
760 mm Hg at sea level
Respiratory pressures
Negative respiratory pressure is less than Patm (inhale)
Positive respiratory pressure is greater than Patm (exhale)
Zero respiratory pressure = Patm
Intrapulmonary (intra-alveolar) pressure (Ppul)
Pressure in the alveoli
Fluctuates with breathing
Intrapleural pressure (Pip)
Pressure in the pleural cavity
Fluctuates with breathing
Always a negative pressure
negative Intrapleural pressure is caused by
opposing forces
what inward forces promote lung collapse
Elastic recoil of lungs decreases lung size
Surface tension of alveolar fluid reduces alveolar size
what outward force tends to enlarge the lungs
Elasticity of the chest wall pulls the thorax outward
transpulmonary pressure
intrapulmonary pressure minus intrapleural pressure
Keeps the airways open
The greater the transpulmonary pressure, the larger the lungs
If Pip = Ppul
lungs collapse
Atelectasis
lung collapse
Atelectasis is die to
Plugged bronchioles leads to collapse of alveoli
Wound that admits air or excess fluid into pleural cavity
Pulmonary Ventilation
inspiration and expiration
volume changes result in pressure changes which result in gas flow to equalize the pressure
Boyle’s Law
The relationship between the pressure and volume of a gas - Pressure (P) varies inversely with volume (V): P1V1 = P2V2
Increased V = Decreased P
decreased V = increased P
Inspiration process
An active process
Inspiratory muscles contract (diaphragm & external intercostals)
Thoracic volume increases
Intrapulmonary pressure drops (to neg 1 mm Hg)
Lungs are stretched and intrapulmonary volume increases
Air flows into the lungs, down its pressure gradient, until Ppul = Patm
Expiration process
Quiet expiration is normally a passive process
Inspiratory muscles relax
Thoracic cavity volume decreases
Elastic lungs recoil
Ppul rises (to +1 mm Hg)
Air flows out of the lungs down its pressure gradient until Ppul = 0
and intrapulmonary volume decreases
forced expiration is an
active process, uses abdominal and internal intercostal muscles
positive pressure and negative pressure results in
positive presure exhale, negative pressure inhale
three factors that hinder air passage and pulmonary ventilation
Airway resistance
Alveolar surface tension
Lung compliance
change in pressure is the
change in P is the pressure gradient between the atmosphere and the alveoli (2 mm Hg or less during normal quiet breathing)
Increase the change in pressure = increase the rate of flow
The relationship between flow (F), pressure (P), and resistance (R) is:
force= change in pressure divided by resistance
what is the relationship between gas flow and resistance
Gas flow changes inversely with resistance (ie. less resistance produces more flow)
Resistance is usually insignificant because
Large airway diameters in the first part of the conducting zone
Progressive branching of airways as they get smaller, increasing the total cross-sectional area
Resistance disappears at the terminal bronchioles where diffusion drives gas movement
what bronchi size has least resistance
medium bronchi size due to fastest and largest drop in diameter
what does epinephrine due for resistance
Epinephrine dilates bronchioles and reduces air resistance
Surface tension
Attracts liquid molecules to one another at a gas-liquid interface
Resists any force that tends to increase the surface area of the liquid
Surfactant
produced by type II alveolar cells
Reduces surface tension of alveolar fluid and discourages alveolar collapse
Lung Compliance
A measure of the change in lung volume that occurs with a given change in transpulmonary pressure
Lung Compliance is normally high due to
Distensibility of the lung tissue
Alveolar surface tension
Lung Compliance diminished by
Nonelastic scar tissue (fibrosis)
Reduced production of surfactant
Decreased flexibility of the thoracic cage
homeostatic imbalances that reduce Lung Compliance
Deformities of thorax
Ossification of the costal cartilage
Paralysis of intercostal muscles
