Respiratory Systems: Ventilation & Gas Exchange
Ventilation of Respiratory Surfaces
Non-directional ventilation:
◦ Medium flows past gas exchange surface in an unpredictable pattern.
Tidal Ventilation
◦ External medium moves in and out of respiratory system in a back and forth movement.
Unidirectional ventilation:
◦ Respiratory medium flows in at one point, and exits via another.
Perfusion of Respiratory Surfaces
The circulatory system allows oxygen
from the respiratory surface to be
transported long distances by bulk flow.
The movement of blood through the
respiratory surface can effect the
efficiency of gas exchange.
Ventilation & Perfusion of
Respiratory Surfaces
Non Directional Ventilation:
(1) skin breathers
(2) tidal ventilators
Unidirectional Ventilators
(1) Concurrent
(2) Countercurrent
(3) Crosscurrent
Non-Directional Ventilation
Partial pressure of oxygen (PO2) in the
blood leaving the gas exchanger can
approach the PO2 in the medium.
Anything that increases diffusion distance,
will decrease oxygen exchange efficiency
and reduce the PO2 in the blood leaving
the gas exchanger.
Non-Directional Ventilation
If ventilation is inefficient, an oxygen
depleted boundary layer will form at
the respiratory surface.
In animals that tidally ventilate, PO2 in the
respiratory cavity is lower than the
outside medium.
Respiratory cavities do not
fully empty.
Fresh air mixes with
oxygen-depleted residual air
PO2 of blood equilibrates
with the PO2 of the
respiratory cavity.
Tidal Ventilation
Tidal Ventilation
Unidirectional Ventilation
Blood can flow in one of 3 ways relative
to the flow of the medium:
(1) Same Direction = Concurrent
(2) Opposite Direction = Countercurrent
(3) At an angle = Crosscurrent
Concurrent Flow
PO2 of the blood to
equilibrate with the PO2
of the respiratory
medium.
Countercurrent Flow
PO2 of blood leaving the
gas exchange surface can
approach that of the
incoming medium.
Crosscurrent Flow
PO2 is usually higher than
what would be seen for
concurrent, but lower
than countercurrent.
Concurrent Flow
Countercurrent Flow
Ventilation of Respiratory Surfaces
Animals respond to changes in
environmental O2 or metabolic demands
by altering the rate or pattern of
ventilation rather than its direction.
Ventilation in Air & Water
Water:
◦ Unidirectionally ventilated gills
Air:
◦ Tidally ventillated lungs
◦ Unidirectionally ventillated lungs
Ventilation in Water
Oxygen content of air nearly 30x water
Water is more dense and viscous than air
Unidirectional ventilation is less energetically costly than tidal ventilation
Countercurrent arrangement of blood flow improves oxygen extraction efficiency.
Elasmobranchs
Use buccal pump for ventilation:
◦ Expand buccal (mouth) cavity volume
◦ Water rushes into the buccal cavity via the
mouth and spiracles.
◦ Muscular contraction forces water past the
gills and out via external gill slits.
Buccal cavity acts as both a suction pump
and a force pump.
Buccal Pump
http://www.youtube.com/watch?v=HeI
UySBQJUQ&feature=related
Teleost (Bony) Fish
Gills are located in opercular cavities
and protected by the operculum.
Buccal-Opercular Pump
Ram Ventilation
Fish swims forward with mouth open:
◦ water flows across gills without active pumping.
Ram Ventilation
Obligate ram ventilators = lost ability
to actively pump ater over their gills and
must rely soly on ram ventilation
Must swim to maintain oxygen levels in
blood
Fish Gills
Fish Gills
4 gill arches in each opercular cavity.
◦ Provided structural support
2 rows of gill filaments project from
each gill arch.
Each filament is covered with rows of
secondary lamellae.
◦ Perpendicular to filament
Fish Gills
Each gill arch contains an afferent & efferent
blood vessel.
◦ Afferent blood vessels carry deoxygenated
blood to the capillaries in the secondary lamellae.
◦ Efferent blood vessels carry oxygenated blood
from the capillaries back to the gill arch.
Secondary lamellae:
◦ Thin-walled & highly vascularized
◦ Primary respiratory surface
Fish Gills
Fish Gills
Counter current exchange.
Blood flow through capillaries in
secondary lamellae is opposite the flow of
water through the gills.
Oxygen extraction from water can be as
high as 70 - 80%.
Fish Gills
Ventilation in Air
Oxygen availability high
Density of medium is low
Face evaporation across respiratory
surface, therefore internally located.
Amphibians
Use cutaneous respiration, external gills,
lungs, or some combination of these 3.
◦ Depends if they are extracting oxygen from
water or from air.
Ventilate lungs using a buccal force pump.
Amphibians
Reptiles
Most have two lungs – tidal ventilation
Air comes into the organism via the
mouth and trachea, and each lung has a
bronchus that allows airflow into the
chambers of the lungs.
Reptiles
Rely on suction pumps to ventilate lungs.
Ventilatory cycle is triphasic –
divided into 3 phases:
1. Inspiration (suction pump)
2. Breath-hold
3. Expiration (passive)
Reptiles Changing volume of chest cavity:
Snakes and Lizards:
◦ Intercostal muscles
Turtle and tortises:
◦ Pair of sheet-like abdomen muscles & movement of forelimbs.
Crocodilians:
◦ Hepatic septum, liver, & diaphragmaticus muscles.
Reptiles
Reptiles
Birds
Unidirectionally ventilate their lungs.
Lung is stiff and undergoes little change in
volume during ventilatory cycle.
Series of air sacs associated with lungs:
◦ Posterior airs sacs
◦ Anterior air sacs
Birds
Birds
Bird ventilation requires two cycles of
inhalation and exhalation.
Airflow across the respiratory
surfaces of the lungs is unidirectional
and almost continuous.
Birds
Birds
At syrinx the trachea divides into 2 primary bronchi.
Primary bronchi split into secondary bronchi, termed dorsobronchi.
Dorsobronchi further divide into parabronchi.
Parabronchi lead into secondary bronchi, termed ventrobronchi, and back to primary bronchi.
Birds
Birds
Parabronchi
◦ smallest airways of a bird lung.
◦ are folded, forming hundreds of blind-ended
structures called air capillaries.
Air capillaries
◦ Primary site of gas exchange
◦ Thin walls = minimal barrier for gas exchange
Birds
Nares &
Mouth Trachea Syrinx
Primary Bronchi
(2)
Posterior
Air Sacs
Dorsobronchi Parabronchi
“air capillaries” Ventrobronchi
Anterior Air
Sacs
Trachea
Birds: Inspiration
Birds: Expiration
Birds: Parabronchi
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