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