Circulation and Gas Exchange

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Respiratory surfaces vary by animal and can include the outer surface, skin, gills, tracheae, and lungs.

Slide 68

Gills are outfoldings of the body that create a large surface area for gas exchange

Parapodium (functions as gill)

(a) Marine worm

Gills

(b) Crayfish

(c) Sea star

Tube foot

Coelom

Gills

Slide 69

Ventilation moves the respiratory medium over the respiratory surface.

Aquatic animals move through water or move water over their gills for ventilation.

Fish gills use a countercurrent exchange system, where blood flows in the opposite direction to water passing over the gills; blood is always less saturated with O2 than the water it meets… maximizes diffusion.

Slide 70

Structure and function of fish gills

Anatomy of gills

Gill

arch

Water

flow

Operculum

Gill

arch

Gill filament

organization

Blood

vessels

Oxygen-poor blood

Oxygen-rich blood

Fluid flow

through

gill filament

Lamella

Blood flow through

capillaries in lamella

Water flow

between

lamellae

Countercurrent exchange

PO2 (mm Hg) in water

PO2 (mm Hg) in blood

Net diffusion

of O2from

water to

blood

150

120

90

60

30

110

80

20

Gill filaments

50

140

Slide 71

Tracheal Systems in Insects

The tracheal system of insects consists of tiny branching tubes that penetrate the body.

The tracheal tubes supply O2 directly to body cells.

The respiratory and circulatory systems are separate.

Larger insects must ventilate their tracheal system to meet O2 demands.

Slide 72

Tracheal systems

Air sacs

Tracheae = air tubes

External opening:

spiracles

Body

cell

Air

sac

Tracheole

Tracheoles

Mitochondria

Muscle fiber

2.5 µm

Body wall

Trachea

Air external openings

spiracles

Slide 73

Lungs = Infoldings of the body surface

The circulatory system (open or closed) transports gases between the lungs and the rest of the body.

The size and complexity of lungs correlate with an animal’s metabolic rate.

Slide 74

Mammalian Respiratory Systems: A Closer Look

A system of branching ducts / air tubes conveys air to the lungs.

Air inhaled through the nostrils --> pharynx --> larynx --> trachea --> bronchi --> bronchioles --> alveoli = site of gas exchange.