Concept 42.5: Gas exchange occurs across specialized respiratory surfaces

page 915

• Gas exchange supplies O2 for cellular respiration and disposes of CO2

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Some comparisons we will be making

• Bacteria• Protists• Worms• Insects• Fish• Amphibians• Reptiles• Mammals

Partial Pressure Gradients in Gas Exchange

• A gas diffuses from a region of higher partial pressure to a region of lower partial pressure

• Partial pressure is the pressure exerted by a particular gas in a mixture of gases

• Gases diffuse down pressure gradients in the lungs and other organs as a result of differences in partial pressure

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Partial Pressure Gradients in Gas Exchange

• A gas diffuses from a region of higher partial pressure to a region of lower partial pressure

• Partial pressure is the pressure exerted by a particular gas in a mixture of gases

• Gases diffuse down pressure gradients in the lungs and other organs as a result of differences in partial pressure

• What gas is most prevalent in air?• What percent of air is oxygen?

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Composition of Air

• Air contains: 79.02% N;

20.95% O2;

0.03% CO2

• Air at sea level is at a pressure of 760 mmHg. What is the partial pressure of O2 at sea level?

• 760 mmHg X 20.95=159.2 mmHg

• How can organisms take in needed oxygen and expel CO2?

Respiratory Surfaces

• Animals require large, moist respiratory surfaces for exchange of gases between their cells and the respiratory medium, either air or water

• Gas exchange across respiratory surfaces takes place by diffusion

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

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6 mechanisms for gas exchange1. Diffusion through cell membrane

– Ex: Single Cell2. Diffusion through skin

– Ex: Earthworm3. Papillae- Increased folds in skin

– Ex: Echinoderms 4. Spiracles and tracheae

– Ex: Insects5. Gills

– Ex: Fish6. Alveoli of Lungs

– Ex: Mammals

Gills in Aquatic Animals

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

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Figure 42.22Gills are Shown In Pink

Parapodium(functions as gill)

(a) Marine worm (b) Crayfish

GillsGills

Tube foot

(c) Sea star

Coelom

• 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

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Figure 42.23

Gillarch

O2-poor blood

O2-rich blood

Bloodvessels

Gill arch

OperculumWaterflow

Water flowBlood flow

Countercurrent exchange

PO (mm Hg) in water2

150

PO (mm Hg)

in blood2

120 90 60 30

140 110 80 50 20Net diffu-sion of O2

Lamella

Gill filaments

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

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Tracheoles Mitochondria Muscle fiber

2.5

m

Tracheae

Air sacs

External opening

Trachea

Airsac Tracheole

Bodycell

Air

Figure 42.24

Amphibians and Reptiles

• Amphibians have lungs but also supplement their respiration through moist skin- cutaneous respiration.

• Reptiles have a partially divided ventricle that more efficiently separates oxygenated from deoxygenated blood, reducing the need for cutaneous respiration. Turtles supplement their respiration through skin on their ____!

What structures are involved in mammal gas exchange?

Mammalian Respiratory Systems: A Closer Look

• A system of branching ducts conveys air to the lungs

• Air inhaled through the nostrils is warmed, humidified, and sampled for odors

• The pharynx directs air to the lungs and food to the stomach

• Swallowing tips the epiglottis over the glottis in the pharynx to prevent food from entering the trachea

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Figure 42.25

Pharynx

Larynx(Esophagus)

Trachea

Right lung

Bronchus

Bronchiole

Diaphragm(Heart)

Capillaries

Leftlung

Dense capillary bedenveloping alveoli (SEM)

50 m

Alveoli

Branch ofpulmonary artery(oxygen-poorblood)

Branch ofpulmonary vein(oxygen-richblood)

Terminalbronchiole

Nasalcavity

• Air passes through the pharynx, larynx, trachea, bronchi, and bronchioles to the alveoli, where gas exchange occurs

• Exhaled air passes over the vocal cords in the larynx to create sounds

• Cilia and mucus line the epithelium of the air ducts and move particles up to the pharynx

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• Gas exchange takes place in alveoli, air sacs at the tips of bronchioles

• Oxygen diffuses through the moist film of the epithelium and into capillaries

• Carbon dioxide diffuses from the capillaries across the epithelium and into the air space

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• Let’s model how the blood gets oxygen to every body cell.

• Oxygen in the blood is affixed to _______• The more that the tissue needs oxygen, the

lower the affinity of hemoglobin for oxygen.

Modeling O2 Delivery

• 8 students are hemoglobin- cups with 4 O

• Each table is a body cell- 1 cup with 4 O• Body cells are digestive, brain, skeletal muscle

• Every hemoglobin has a route, one row.• Body Cells use O2

– Warm up- Every cell uses 1/ 20 sec– Raise hand when need an oxygen– Active tissue uses 1/10 sec, vary which tissue is active

Figure 42.31Oxyhemoglobin dissociation curve

2(a) PO and hemoglobin dissociation at pH 7.4

Tissues duringexercise

Tissuesat rest

Lungs

PO (mm Hg)2

(b) pH and hemoglobin dissociation

PO (mm Hg)2

0 20 40 60 80 1000

20

40

60

80

100

0 20 40 60 80 1000

20

40

60

80

100

Hemoglobinretains lessO2 at lower pH

(higher CO2

concentration)

pH 7.2pH 7.4

O2 unloaded

to tissuesduring exercise

O2 s

atu

rati

on

of

he

mo

glo

bin

(%

)

O2 unloaded

to tissuesat rest

O2 s

atu

rati

on

of

he

mo

glo

bin

(%

)

(b) pH and hemoglobin dissociation

PO (mm Hg)2

0 20 40 60 80 1000

20

40

60

80

100

Hemoglobinretains lessO2 at lower pH

(higher CO2

concentration)

pH 7.2pH 7.4

O2

sa

tura

tio

n o

f h

em

og

lob

in (

%)

Figure 42.31b

Oxyhemoglobin dissociation curve

• What effect does exercise have on the curve?• How do you think a fetus’ curve would look(shift left or shift right?).