Respiratory System Part 1 Flashcards
Steps of Respiration
Air moves by bulk flow (like blood) from high to low pressure.
- Ventilation
* Bulk flow - Gas exchange @ lungs
* Diffusion - Gas transport
* Bulk flow - Gas exchange @ tissues
* Diffusion - Cellular respiration
* Oxidative phosphorylation
Lungs are located in
the pleural cavity
which is in the thoracic/chest cavity
Ventilation and Lung Mechanics
Ventilation– Exchange of air between the atmosphere and alveoli
F = ΔP/R
Flow (F) is proportional to the pressure difference (ΔP) between two points and inversely proportional to the resistance (R)
Boyle’s Law
Pressure of a gas varies inversely with its volume (at a constant temperature)
P1V1 = P2V2
Gases always fill their container
Subsequent change in volume leads to a pressure change. Pressure changes lead to the flow of gases along concentration gradient to equalize the pressure.
Pressure Measurements
Intrapulmonary Pressure
Respiratory pressures are always relative to atmospheric pressure
Measured in mmHg or atmospheres (atm)
Sea level = 760 mmHg or 1 atm
Different altitudes = different pressures
Intrapleural Pressure
Pip = intrapleural cavity pressure
Always 4 mmHg less than Palv
This negative pressure
helps keep the lungs inflated
Transpulmonary Pressure
Palv – Pip = Transpulmonary pressure (Ptp)
Pressure difference that keeps the lungs inflated, opposes inward elastic recoil of the lungs
Governs the static properties of the lungs
Transpulmonary is the Transmural pressure
Inflation of a balloon-like structure like the lungs requires an increase in the transmural pressure such that Pi increases relative to PO
Ptp= 4 mmHg Pressure difference holding lungs open
Pcw= -4 mmHg Pressure difference holding chest wall in
Pressure Changes During the Respiratory Cycle: Inspiration
The diaphragm and inspiratory intercostals contract
Thorax expands
Pip becomes more subatmospheric
Transpulmonary membrane increases
Lungs expand
Palv becomes subatmospheric
Air flows into alveoli
Intrapulmonary Pressure
Palv = alveoli pressure
When Palv < Patm
– air flows into the lung
– “negative pressure breathing”
- When Palv > Patm
– air flows out
Pressure Changes During the Respiratory Cycle: Expiration
The diaphragm and inspiratory intercostals stop contracting
Chest wall recoils inward
Pip moves back towards pre inspiration value
Transpulmonary pressure moves back toward preinspiration date
Lungs recoil toward pre inspiration size
Air in alveoli becomes compressed
Palv becomes greater than Patm
Air flows out of lungs
Lung Compliance
Compliance= How easily a structure stretches
Compliance– inverse of stiffness
The greater the lung compliance, the
easier it is to expand the lungs at any
given change in transpulmonary pressure.
Two major determinants of lung compliance:
1. The stretchability of the lung tissues
2. The surface tension at the air-water interfaces within the alveoli
Surfactant
Markedly reduces the cohesive forces between water molecules on the alveolar surface
Lowers the surface tension
Increases lung compliance
Makes it easier to expand the lungs
Tidal volume (TV)
air inhaled & exhaled in one breath
Inspiratory Reserve Volume (IRV)
air inhaled beyond TV with
max effort
Expiratory Reserve Volume (ERV)
air exhaled beyond TV with
max effort
Residual Volume (RV)
air remaining in lungs after ERV, keeps lungs inflated
Vital Capacity (VC)
max air movement possible
= (TV + IRV + ERV)= Assess pulmonary function
Inspiratory Capacity (IC)
max inspiration = (TV + IRV )
Functional Residual Capacity (FRC)
air remaining after TV = (ERV + RV)
Total Lung Capacity (TLC)
max air contained in lungs = (VC + RV)
Forced Expiratory Volume (FEV1)
forced VC in 1 second
