Lecture 24 Respiratory 1 Flashcards
Primary functions of respiratory system
supply O2 and eliminate CO2
maintain acid-base balance via regulation of CO2 in blood
ventilation and gas exchange
4 integrated processes
- Ventilation
- gas exchange
- transport of O2 and CO2 in the blood
- exchange of O2 and CO2 between blood and cells
Conducting zone
nasal cavity pharynx larynx trachea primary bronchi bulk flow region, no gas exchange = anatomic "dead space"
Upper respiratory
nasal cavity
pharynx
Lungs
secondary, tertiary, and smaller bronchi
bronchioles
terminal bronchioles
respiratory zone
respiratory bronchioles alveolar ducts alveolar sacs alveoli gas exchange region
Alveoli
primary sites of gas exchange
huge surface area
type 1 cells - simple squamous
type 2 cells - surfactant cells
alveolar macrophages ("dust cells")Pulmonary Capillaries
surround alveoli, exchange O2 and CO2 with air in the alveoli
Thoracic Cavity
chest wall, diaphragm, pleurae, intrapleural space, respiratory muscles
Chest wall
surrounds thoracic cavity (ribs, intercostal muscle, etc.)
Diaphragm
separates thoracic and abdominal cavities
primary muscle of inspiration
Pleurae
serous membranes surround each lung, form fluid-filled pleural sacs
parietal pleura lines chest wall and diaphragm
visceral pleura covers the lungs
Intrapleural space
thin, fluid filled space between parietal and visceral pleurae
fluid in the intrapleural space connects lungs to chest wall and diaphragm
Inspiration
muscles
primary: diaphragm
secondary: external intercostals, neck muscles
Expiration
muscles
passive: elastic recoil of lungs
active: internal intercostals, abdominal muscles
Mechanics of air breathing
Pressure
Air flow
Forces
Pressure
P of gas is inversely related to volume (V)
Boyle’s law P1V1=P2V2 (closed system)
during inspiration, resp. muscles contract -> lungs expand -> V increases -> P decreases
Air Flows
in and out of lungs because of pressure differences between lungs and atmosphere
air flows from higher pressure to lower pressure
during inspiration, P decreases -> air flows in
during expiration, P increases -> air flows out
Forces
are transmitted between chest wall and lungs through fluid in the intrapleural space
opposing recoil forces of the lungs (inward) and chest wall (outward) create a negative pressure in the intrapleural space
Pressures involved in breathing
atmospheric
alveolar
intrapleural space
atmospheric
(Patm) = 760 mm Hg at sea level (= “0 mm Hg” used as reference)
alveolar
intrapulmonary Palv - air pressure in the alveoli
P alv= P atm (=0) at end of expiration
Palv < Patm during inspiration, Palv>Patm during expiration
intrapleural
Pip
pressure inside the intrapleural space = -4 mm Hg (0 lung coppalses (atelectasis)
Inspiration pressure changes during breathing
resp. muscles contract -> Pip decreases (< -4 mm Hg) -> V increase -> Palv decreases -> air flows in
Expiration changes during breathing
resp. muscles relax -> Pip increases )back to -4 mmHg) -> V decreases -> Palv increases -> air flows out
Physical Properties of lungs
compliance
elasticity
airway resistance
compliance
ease of expansion
increase compliance -> easier to expand lungs -> decrease work of breathing
elasticity
stretching force; ability to return to normal length or volume
inward recoil force of lungs is due to elastic tissue and surface tension of fluid lining alveoli
airway resistance
mostly depends on diameter of small airways
smooth muscle of bronchioles -> bronchoconstriction/dilation
Surface tension
results from forces between water molecules at air-water interface
contributes to inward recoil force in lungs, tends to collapse alveoli inward
greater effect on small alveoli than large alveoli (Law of LaPlace: P=2T/r)
Pulmonary Surfactant
secreted by type II alveolar cells -> reduces surface tension
increase compliance, decreases work of breathing
stabilizes alveoli by reducing surface tension more in small alveoli
Respiratory distress syndrome (RDS)
in premature infants is due to insufficient surfactant
Lung Volumes
are non overlapping volumes that add up to total lung capacity
Lung capacities
are combinations of two or more lung volumes
Residual Volume
minimum lung volume = 1200 mL
Functional residual capacity (FRC)
volume in lungs at end of relaxed expiration = 2500 mL
Tidal volume
Vt
volume inspired and expired in each breath = 500 mL (quiet breathing)
a portion of tidal volume remains in anatomic dead space (DSV=150mL)
Vital Capacity
VC
maximum breathing volume =4000-5000 mL
total pulmonary ventilation
minute volume
Ve = ventilation rate (RR) x tidal volume
resting: VE = (12breaths/min) X (500mL/breath) = 6000 mL/min
how does minute volume increase
increases in proportion to gas exchange requirements (a to metabolic rate)
Alveolar ventilation
“effective” ventilation of fresh air to gas exchange surfaces
Va =RR X (Vt-DSV)
12 breaths/min X (500 - 150 mL/breath) = 4200 mL/min
Restrictive disorders
e.g. pulmonary fibrosis
reduced lung compliance -> difficult inspiration, reduced vital capacity
Obstructive disorders
e.g. asthma
increased airway resistance -> difficult expiration, lower rate of expiration
Obstructive Pulmonary disease
COPD
emphysema, asthma, chronic bronchitis
Emphysema
involves destruction of alveolar tissue
fewer, larger alveoli -> decreased surface area for gas exchange
reduced elastic recoil of lungs -> difficult expiration, small airways collapse -> air trapping
force expiratory volume (FEV) test
normal FEV1 = 80%
FEV1 < 70% indicated OPD
