L20: Respiratory System I Flashcards
Fick’s law of diffusion
rate of diffusion = k * A * (P2-P1)/D
rate of diffusion depends on
solubility of gas, temperature, surface area, difference in partial pressures, thickness of the barrier
pulmonary ventilation
movement of air into and out of the lungs
movement into lungs
inspiration
movement out of lungs
expiration
pulmonary ventilation is done by
bulk flow
respiratory functions
pulmonary ventilation, exchange between lung air and blood by diffusion, transportation of O2 and CO2, exchange between body tissues and blood
upper airways include
nasal cavity, oral cavity, pharynx
pharynx
muscular tube that serves as a common passageway for both air and food
esophagus
muscular tube leading to the stomach
larynx
part of respiratory tract, a tube held open by cartilage in its walls
what structure contains vocal cords?
larynx
respiratory tract is divided into
conducting and respiratory zone
conducting zone
conducts air from the larynx to the lungs
respiratory zone
contains the sites of gas exchange within the lungs
the primary difference between conducting and respiratory zones
thickness of the walls of the airspaces
what air spaces can participate in gas exchange
only air spaces with sufficiently thin walls
larynx opens into
trachea
trachea opens into
two bronchi
right bronchus divides into
three secondary bronchi
left bronchus divides into
two secondary bronchi
within the lungs, there are more than ___ generations of branchings
20
major sites of gas exchange
alveoli
branching sequence
trachea – bronchi – bronchioles – terminal bronchioles –respiratory bronchioles – alveolar ducts – alveolar sacs
where do alveoli start to appear?
respiratory bronchioles
what structure entirely consists of alveoli?
alveolar sacs
alveolar sac is surrounded by
elastic fibers and network of capillaries
how many bronchioles are there?
80 million
air-facing surface of alveolar wall is lined by
type I alveolar cells
type I alveolar cells
flat epithelial cells
type I alveolar cells function
gas exchange
type II alveolar cells function
synthesis of the surfactant
each lung is surrounded by
pleural sac and chest wall
pleural sac
double membrane surrounding each lung, one membrane lines lungs, the other lines chest wall
pleural sac is similar to
fluid-filled balloon around air-filled balloon
ventilation occurs because of
the presence of pressure gradients between the alveoli and the outside air
air moves ___ a pressure gradient
down
inspiration occurs when the pressure in the alveoli is ___ than the pressure in the atmosphere
lower
expiration occurs when the pressure in the alveoli is ____ than the pressure in the atmosphere
higher
four primary pressures associated with ventilation
atmospheric pressure, intra-alveolar pressure, intra-plural pressure, transpulmonary pressure
atmospheric pressure value
760 mm Hg at sea level
atmospheric pressure ___ as altitude increases
decreases
atmospheric pressure ___ under the water
increases
for our purposes we treat atmospheric pressure
as constant and equal to zero
atmospheric pressure
pressure of outside air
intra-alveolar pressure
pressure of air in alveoli
intra-alveolar pressure value
varies with phase of respiration
intra-alveolar pressure during inspiration
negative/less than atmospheric
intra-alveolar pressure during expiration
positive/more than atmospheric
intra-alveolar pressure at rest
zero/equal to atmospheric
what drives ventilation?
difference between atmospheric and intra-alveolar pressure
intra-pleural pressure
pressure inside the pleural sac
intrapleural pressure value
always negative, always less than Palv, varies with phase of respiration
intrapleural pressure at rest
around 4 mm Hg
why is intrapleural pressure negative?
due to elasticity in lungs and chest wall
in what direction do lungs and chest wall pull
opposing, lungs recoil inward, while chest recoils outward
what holds lungs and chest wall together?
surface tension
to maintain negative intrapleural pressure ___
the pleural sac must be airtight
if the pleural sac is broken ___
the negative intrapleural pressure is lost as it equilibrates with atmospheric pressure
without negative P(ip) ___
the lungs recoil and collapse, while the chest wall recoils and expands
how does the condition when P(ip) is lost called?
pneumothorax
transpulmonary pressure
distending (expanding) pressure across the lung wall
transpulmonary pressure
P(alv) - P(ip)
an increase in transpulmonary pressure creates __
a larger distending pressure across lungs
a larger distending pressure across lungs causes ___
lungs expand and increase the volume
pressure gradients are created
by changing the volume of the lungs
Boyle’s law
pressure is inversely related to volume
intra-alveolar pressure is determined by
the quantity of air in alveoli and the volume of alveoli
inspiration 1: at the start of inspiration ___
the lungs expand as a result of contraction of the inspiratory muscles
inspiration 1: the expansion of alveolar volume ___
lowers P(alv); P(alv) < P(atm); air drawn into the lungs
inspiration 2: P(alv) rises as ____
the number of air molecules flow in
rest: when P(alv) = P(atm), ___
air stops flowing inward
expiration 1: as the lung volume decreases, __
P(alv) increases and air flows out
expiration 2: P(alv) lowers as ___
the number of air molecules flow out
inspiration is initiated by
neural stimulation of inspiratory muscles – ACh is released at the NMJ
what causes lungs to flatten and move downward?
contraction of the diaphragm
what causes the ribs to pivot upward and outward?
contraction of the external intercostal muscles
what does pivoting ribs do?
expand the chest wall
as chest wall expands, ____
its pulls outward on the intrapleural fluid, causing P(ip) to decrease
decrease of P(ip) causes transpulmonary pressure to ___
increase
increase in transpulmonary pressure leads to
larger distending pressure across the lungs and lungs start expanding
when alveoli expand,
P(alv) < P(atm), so air flows into the alveoli by bulk flow
during quiet breathing, ____
expiration is normally a passive process and does not require muscle contraction
when motor neurons to inspiratory muscles stop firing, ___
inspiratory muscles relax
when inspiratory muscles relax, ___
lungs and chest wall recoil to original positions
volume of cavity thoracic decreases, causing ___
P(alv) > P(atm)
air flows out until ___
P(alv) = P(atm)
what factors affect pulmonary ventilation?
lung compliance and airway resistance
compliance
measure of the ease with which lung can be stretched
what factors affect lung compliance?
elasticity and surface tension
lung lobes
superior, middle and inferior
airway resistance
resistance of the airways in the respiratory tract
lung compliance formula
lung compliance = delta(V)/delta(P)
having larger lung compliance is
advantageous
larger lung compliance is better because
a smaller change in transpulmonary pressure is needed, so less work or muscle contraction is required
lungs are elastic because of ___
the presence of elastic connective tissue fibers
forces by elastic fibers ___ lung expansion
oppose
emphysema
destruction of elastin fibers found in lung tissue
surface tension of a liquid
work required to increase its surface area by a certain amount
the greater the surface tension, ___ work needed to spread the fluid out
the more
surface tension of lungs is created by
the air liquid interface formed by the thin layer of fluid lining the alveoli
as lung expands, work is required to
stretch the elastic tissue and increase the surface area of the fluid layer
greater surface tension lead ____ compliance
lower
Laplace’s law
P = 2T / r
what decreases the surface tension in alveoli?
pulmonary surfactant
surfactant is secreted from
type II alveolar cells
how does surfactant decrease the surface tension?
by interfering with hydrogen bonding between water molecules
surfactant stabilizes alveoli of different size by
differentially altering surface tension
prematurely born babies can develop
newborn distress syndrome (NRDS)
too little surfactant causes
stiff, low compliance lungs, allows alveoli collapse and re-inflate
treatment for NRDS
administration of steroid hormones to increase surfactant production, aerosol administration of artificial surfactant, artificial ventilation
lung compliance is determined by
the elastic connective tissues of the lungs and the surface tension of the fluid lining the alveoli
surface tension is greatly reduced and compliance increased by
surfactant
airway resistance determines
how much air flows into the lungs at any given pressure different between atmosphere and alveoli
major determinant of airway resistance
the radii of the airways
four primary pressures associated with ventilation are
atmospheric pressure, intra-alveolar pressure, intra-plural pressure, transpulmonary pressure
inspiration and expiration are driven by
differences in atmospheric and intra-alveolar pressures
pressure gradients in lungs are created when
the volume of the lungs is changed
inspiration is caused by
the contraction of the diaphragm and the external intercostal muslces
active expiration involves
contraction of internal intercostals and abdominal muscles
