Respiratory System - Ventilation and Gas Exchange Flashcards
key processes in respiratory phys
- pulmonary ventilation: air is added or removed from airways
- gas exchange: O2 and Co2 are exchanged between airways/blood and blood/tissue
- blood gas transport: o2 and CO2 transported between tissues and lungs
- control of breathing: bodily needs are met by ventilation adjustments
trachea seperation
splits into three lobes on the right and two lobes on the left (left room cause the heart)
- right: upper lobe, middle lobe, and inferior lobe of right lung
- left: upper lobe and lower lobe of left lung
role of upper airway mucosal lining in conditioning of inhaled gas
inspiration: loss of heat and moisture from the airway lining to warm and humidify the air
expiration: partial recovery of heat and moisture from expired air, and remaining recovery from blood supplying upper airway
**look at diagram for photo
movement of air through tracheobronchial tree
conducting zone (bulk flow, requires energy to contract respiratory muscles to create a pressure difference between airway and atmosphere resulting in air flow)
- trachea
- main bronchus
- bronchus
- bronchiole
- terminal bronchiole
respiratory zone (by diffusion, no need for energy input, depends on pressure gradient of gases)
- respiratory bronchiole
- alveolar duct
- alveolar sac
of alveolar sacs
2^23!
structural changes in airway wall
trachea/bronchus –> bronchiolus –> alveolus
1. decrease in epithelial height
2. loss of cartilage, smooth muscle, mucous glands
3. capillaries remain
alveolar gas exchange
how many alveoli?
~ 500 million alveoli in your lungs
- each is in contact with hundreds of pulmonary capillaries
alveolar cell types
cell type I: type I pneumocyte
- flat (squamous epithelium) like a fried egg with nucleus in middle
- covers 95% of alveolar surface area
- very thin 0.1-0.3 microns in width
- total alveolar surface area = 80-200 m^2
cell type II: type II / granular pneumocyte
- cuboidal shape
- contain lamellar inclusion bodies that store pulmonary surfactant
- pulmonary surfactant is a mixture of lipids and proteins that reduces alveolar surface tension
alveolar macrophage: dust cell
- migratory and phagocytic defend against foreign invaders
- on stains, these cells look angry! black dot with lighter coloured brush around them
blood air barrier
thickness
very thin!
airway clearance
different molecule size
particles > 10 micrometers in diameter
- filtered and trapped by nasal hairs
- irritant receptors that line nasal passage initiate sneeze reflex
particles 2-10 micrometers
- mucociliary clearance (MCC) system lining the airways proximal to terminal bronchioles
- irritant receptors in airway lining initiate cough
particles < 2 micrometers
- reach alveoli
- migrating and phagocytic macrophages engulf and degrade foreign particles
- non degradable particles (silica dust and asbestos fibers) injure alveolar epithelium resulting in inflammation, deposition of collagen to scar, and pulmonary fibrosis –> can lead to lung cancer
MCC transport system
mucociliary clearance transport system
- two layered mucous blanket
1. viscous and sticky gel layer
2. aqueous periciliary layer that is low viscosity and facilitates cilia beating stroke
- human lung processes 10,000 L of air daily for gas exchange
- MCC 1 trillion motile cilia beating @ 12-15 Hz
- propels mucus through vocal chords and into pharynx
- 30 ml mucus expectorated daily
impairment of MCC
- cigarette smoking: ciliary length goes down, and increased mucus production
- pathogenic microbes: release substances that paralyze and slow ciliary motion
- primary ciliary dyskinesia: inherited genetic mutation that reduces ciliary motility - airway particle clearance takes 1 week in PCD vs 12 hours in healthy ppl
- cystic fibrosis: inherited genetic mutation of cystic fibrosis transmembrane conductance regulator (CFTR) that is involved in water and sodium transport to maintain mucus osmolarity –> increased mucus viscosity
pleural space and compartments
outer parietal pleura
inner visceral pleura
middle pleural sac
cohesive forces of the pleural fluid
1. attach chest wall and lungs allowing lungs to inflate/deflate with chest wall movement
2. reduce friction when lungs glide past chest wall
pressures of lung compartments
pressures described relative to atmosphere in cm H2O
- pressure inside lungs/airways - alveolar pressure Pa = 0 cmH2O
- pressure inside pleural cavity Ppl = -5 cmH2O
respiratory system as a mechanical structure
- lungs want to collapse
- chest wall wants to extend
- outward recoil of chest is equal in magnitude to inward recoil of lungs –> opposite forces maintain lung shape
- constant balance of pressures that change during expiration and inspiration
pneumothorax
traumatic vs spontaneous
- collection of air outside lung but inside pleural cavity
1. traumatic pneumothorax: hole in chest wall
2. spontaneous pneumo: hole in lung
both lead to –> collapsed lung with expanded chest wall
boyle’s law
at constant temperature, pressure and volume are inversely related:
p1v1 = p2v2
inspiration
steps
- inspiratory muscles contract
- chest wall expands –> intra-thoracic pressures decrease (Ppl by 3 cm H2O and Pa by 1 cm H20)
- air flows into lungs
–> volume change precedes pressure change
expiration
- inspiratory muscles stop contracting
- lungs recoil inward (both Ppl and Pa increase)
- air flow out of lungs
–> Pa goes above atmospheric pressure which drives air out of lungs, so expiration is passive
lung compliance and elastance
- how easily can lungs be stretched
- elastance is the tendency of an object to oppose stretch, and is it able to return to its original form
- compliance = 1/elastance
static compliance of lungs (C sub L) and key factors that impact it
slope of the relaxation P-V curve during deflation
1. lung volume: smaller volume means smaller compliance
2. tissue elastic recoil:
- emphysema = disappearing lung disease (caused by cigarette smoke or genetically) destroys alveolar wall and increases compliance (floppy lungs) –> very vertical curve
- pulmonary fibrosis = collagen deposition in alveolar walls (in response to lung injury like asbestosis) and decreases compliance making stiff lungs –> very horizontal curve
3. alveolar surface tension: water molecules from humidified air cover alveolar surface and collapses the alveolus –> neonatal respiratory distress syndrome (NRDS) is stiff lungs that are hard to inflate because of inadequate production of pulmonary surfactant (which reduces surface tension)
restrictive vs obstructive ventilatory defect
res: problem with airflow into airways, inability to expand lungs or chest wall –> reduced compliance/enhanced elastance
obstructive: problem with airflow out of airways due to narrowed airways –> increased resistance
airway resistance
2 resistive forces
2 resistive forces
1. inertia of the respiratory system (negligible)
2. friction
- lung and chest wall surfaces gliding past each other (little)
- airways gliding past each other (little)
- air flowing through airways (80% of total airway resistance) –> 60% from upper airways and 40% from tracheobronchial tree
what decreases frictional resistance to airflow?
increasing total cross sectional area
airway branching in healthy vs smokers
healthy: major contributor to airway resistance are larger airways (upper airways)
smoker: smaller respiratory airways with reduced luminal size –> airflow is measured instead of resistance to quantify impact
relationship of flow, pressure (delta P), and resistance (R)
flow = delta P / R
R is proportional to 1/ radius ^4
if radius of airway is halved, how is flow changed?
factor of 1/16
airway and autonomic nervous system + asthma
parasympathetic: contraction of smooth muscle via acetylcholine release from vagus nerve –> dominant at rest
sympathetic: relaxation of smooth muscle via adrenaline release from adrenal medulla
–> in asthma, both mechanisms are exploited with medication
lung volumes and capacities
capacities:
- inspiratory capacity
- functional residual capacity
- vital capacity
- total lung capacity
volumes:
- inspiratory reserve volume
- resting tidal volume
- expiratory reserve volume
- residual volume
factors influencing static lung volumes
- height - taller has more lung vol
- gender - males have larger lung
- age - 20-25 is max lung volume
important volume ratio
FEV1 (forced expiratory volume in 1 second) / FVC (forced vital capacity) –> understand if there are problems
diagnosing respiratory disease
- slow vital capacity maneuver –> static lung volumes and capacities are reduced in restrictive diseases and FEV1/FVC is increased
- forced vital capacity maneuver –> FEV1/FVC will be < 75% in obstructive diseases
conditions that reduce chest wall compliance
- scoliosis
- obesity
- neuromuscular disorders
relaxation static pressure-volume curves
see slide (resp 1 page 74)
surface area of adult human lung
80-200 m^2
arterial blood –> partial pressure of alveolar gases
gas exchange = end capillary blood gases that are in equilibrium with the partial pressure of gases in the alveoli
driving pressure for gas exchange
across pulmonary capillaries:
- PO2 gradient alveoli to blood is 60 mm Hg
- PCO2 gradient blood to alveoli is 6 mm Hg
across tissue capillaries:
- PO2 gradient blood to tissue is 60 mm Hg
- PCO2 gradient tissue to blood is 6 mm Hg
ventilation and perfusion
high ventilation: air goes in
low perfusion: no blood to exchange with
–> dead space
the opposite system
–> “shunt like”
surface area and thickness of alveoli + gas exchanges
emphysema: destruction of walls –> increased compliance and reduced area for gas exchange
pulmonary fibrosis: collagen deposition –> reduced compliance and increased thickness
pneumonia: fluid and puss accumulation in and around alveoli
pulmonary transit time
- gas exchange between alveoli and blood
- at rest PTT is 3/4 sec
