1. Respiratory System Anatomy
Breathing:
air movement in & out of lungs
nasal passages
Inspiration:
pharynx
air in
glottis
epiglottis
larynx
Expiration:
trachea
air out
bronchi
bronchioles
pleural membrane
*outer lines chest walls/inner lines lung
*fluid between makes air-tight seal
thoracic cavity = area within chest
lungs
alveoli
diaphragm
*thick, dome-shaped muscle on floor of thoracic cavity

2. Breathing – Path of Air
1. air enters nasal passages - hairs/cilia (projections from
cells in tissue) trap dust/debris – air warmed/moistened
2. air passes through pharynx (common passage for
food/air)
3. glottis = opening to larynx (triangular box where air
passes over vocal cords to produce sound) opens
*swallowing: epiglottis covers glottis
4. air enters trachea (vessel for air passage)
*trachea held open by cartilaginous rings, lined
with ciliated mucous membranes
*mucus traps dust/particulates, cilia sweep mucus up/
out of respiratory tract

3. Breathing – Path of Air
5. trachea divides into bronchi (passages supplying
air for each lung) then into bronchioles (smaller
passages that extend into lungs
6. bronchiole walls get thinner/ vessels get smaller as they
branch out
*bronchioles end in alveoli (sacs surrounded by capillary
beds - site of gas exchange)
*alveoli secrete a
lipoprotein so that
they do not collapse
alveoli
*alveoli have ↑ surface
area for optimal gas
exchange
capillaries

4. Breathing - Power 1. diaphragm contraction:
*moves down, becomes less dome shaped
*↑ volume within thoracic cavity/lungs
2. intercostal muscles:
*muscles attached to ribs contract during inspiration
*ribs pull up/out, ↑ volume within thoracic cavity
3. negative pressure:
*air pressure in lungs becomes < atmospheric pressure
*air rushes into lungs to fill natural vacuum
4. diaphragm relaxation:
*diaphragm up, intercostal muscles
relax, ribs move down/inward
*volume ↓ in thoracic cavity means air
forced out of lungs - expiration

5. Breathing - Control
*breathing rate subject to partial conscious control
*CO2 & H+ ions in blood control breathing rate
1. as cells continue to produce CO2 - ↑ [CO2] until it
reaches threshold level
2. *chemoreceptors in arteries detect ↑ CO2/H+ levels
*chemoreceptors in carotid artery/aorta
(carotid /aortic bodies) respond primarily to [H+],
also to CO2/O2 level in blood
3. chemoreceptors send signal to breathing center in
medulla oblongata of brain
*center not affected by ↓ oxygen levels

6. Breathing - Control
4. medulla oblongata sends nerve impulse to diaphragm
& intercostal muscles
5. diaphragm contracts/lowers, rib cage moves up
6. air flows into alveoli, alveolar walls expand/stretch
7. stretch receptors in alveoli walls detect stretching
8. Nerves in alveoli send signal to brain to inhibit
medulla oblongata from sending message to diaphragm
or intercostal muscles – contraction stops
9. diaphragm relaxes/moves upward, resuming original
shape - rib cage relaxes/moves downward/inward,
forcing air out of lungs

7. Breathing - Control tidal volume: air taken in per breath (~500 ml)
vital capacity:
difference between max inspiration & max expiration (~ 4800 ml)
residual volume:
air in lungs after expiration (~1200 ml)