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
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 ____!
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